SYNTHESIS AND CHARACTERIZATION OF CONDUCTING POLYMER COMPOSITES

_..:<«* ' .-..

biSSERTATION \ 'N,

//^^'\ fly 'V\L.!.N/ ;"\"{i-''^^?^.

SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS

FC R THE AWARD OF THE DEGREE OF THE If f "/ \

IN

\} APPLIED CHEMISTRY

AMIR-AL-AHMED

Under the Supervision of

Dr. FAIZ MOHAMMAD

DEPARTMENT OF APPLIED CHEMISTRY ALIGARH MUSLIM UNIVERSITY,

ALIGARH (INDIA)

2001

DS3253

^\«rt^"t^*^

f . ^^'32 S3 /Ij

3 0 JU 2003

DEPARTMENT OF APPLIED CHEA XSTRY ALI^ARH IWSU^ UNIVERSITY

CERTIFICATE

This is to certify that the dissertation entitled "SYNTHESIS

AND CHARACTERIZATION OF CONDUCTING POLYMER

COA^POSITES" submitted in partial fulfillment for the award of

M.Phil. Degree in Applied Chemistry is a bonafide research work

carried out by Mr. Amir-AI-Ahmed under my guidance and

supervision. This is his original work and has not been submitted for

any other degree.

FAIZ MOHAMMAD, D.PhiL(Sussex)

Senior Lecturer

Dated: April 9. 2002

ACKNOWLEDGEMENTS

I am most indebted to the grace of "One Universal Being" who inspires entire

humanity towards knowledge, truth and eternal joys.

I would like to avail this opportunity to express my deep sense of gratitude to

my supervisor. Dr. Faiz Mohammad who extended his invalu-able guidance and

encouragement during the course of this study and presentation of this work.

I am thankful to the chairman, teaching and non-teaching staff of the

Department of Applied Chemistry for their valuable assistance, suggestions and

encouragement in their respective capacities. I am especially thankful to Dr.Zaki

Abdur Rahman, Head, Polymer Research Group, Department of Chemistry, University

Putra Malaysia, Selangor, Malaysia for his timely assistance in carrying out the FTIR

of the samples.

My sincere thanks to all my colleagues, specially, Ms. A.Abidi, M.Mezbaul

Alam, Z.Alam, Ms. S. Singh, Ms.S.Rafique and M.F.Ansari for the help rendered by

them. The financial assistance given by AMU is also thankfully acknowledged.

Last but not the least, I feel deeply obliged to my parents and my sister, Ms. Afia

Arafat, for the constant inspiration and support.

(AMIR-AL-AHMEb)

CONTENTS

1. Introduction

1.1. Polymers 1

1.2. Polymenzation 1

1.3. Classification of polymers 2

1.4.Properties of polymers 3

1.5.Composites materials 8

1.6.Electrically conducting polymers 9

1.7.Polymer composites 9

1.8. Charge transfer complex and radical ion/compounds 12

1.9. Organic molecular solid and polymers 13

1.10. Doping of conducting polymers and composites 14

1.11. Electrical conduction in polymers 17

1.12. Degradation of electrically conducting polymers & composites 32

1.13. Stabilization 33

1.14. Application of conducting polymers 34

2. Review of literature and objectives

2.1 Composites based on polyaniline 39

2.2 Composites based on polyaniline 46

3. Experimental

3.1. Chemicals 55

3.2. Preparation of materials 55

3.3. Doping 59

3.4. Pellet preparation 59

3.5. Electrical conductivity measurements 59

3.6. FTIR studies 60

3.7. Stability of poly aniline :nylon-6 composites 60

4. Result and discussion

4.1. Preparation of materials 61

4.2. Doping and electrical properties 62

4.3. FTIR studies 66

5. Conclusion 117

Appendix-1 118

Bibliography 122

CHAPTER-1

IIMMI

1.1. Polymers

The Swedish chemist, Jacob Berzelius, first used the word

'polymeric' in 1832. He understood that some chemicals could have the

same molecular formula and, therefore, the same empirical formula.

These molecules were recognized as isomers. However, chemists also

knew that some molecules had the same empirical formulae but different

molecular formulae. An example that we are familiar with is of ethylene

(C2H2) and benzene (C6H6). Both have the same empirical formula, CH,

but different molecular formula, hi the time of Berzelius the knowledge of

the structures of molecules was markedly different. He thought that such

molecules belonged to a special class of isomers and said "To describe

this equality of composition coupled with a difference of properties, I

suggest that such substances be called polymeric" [1].

hi the years following this definition, chemists began to refer

benzene as polymer of ethyne. hi modem notion a polymer must have a

high relative molecular mass. Such as poly(ethene), better known as

polythene. It is a giant, linear and high molecular weight molecule, made

up of thousands of ethane molecules joined together [1]. So polymers are

long chain and high molecular weight compounds in which many small

molecules combine together. These small molecules are called

monomers. If a monomer combines with itself, it forms a homo-polymer,

if two, then copolymer and if three, then terpolymer is formed.

1.2. Polymerization

Polymerization is the process of producing polymers by joining of

monomers. A monomer must have at least two reactive sites to form

polymer by repeatedly by joining with it self or with other similar

molecules [2,3,4].

Low molecular heat and/or pressure High molecular weight molecules weight material 1 (monomers) and/or catalyst (polymer)

1.2.1. Chain (addition) polymerization

This polymerization involves joining of monomers by chain

reaction. The reaction is very fast and high molecular weight polymers

are formed in the early stage of polymerization. The steps in the process

of polymerization include initiation, propagation and termination

catalyzed by free radicals, cations, anions or coordination complex.

1.2.2. Step (condensation) polymerization

Step polymerization proceeds through the reaction between the

functional groups of the monomers. As the reaction takes place stepwise,

the chain length increases slowly and high molecular weight polymers are

formed only towards the end of the reaction. Polyesters, polyamides,

polyethers, polyurethanes etc. are synthesized by condensation

polymerization.

1.2.3. Co-polymerization

In co-polymerization two monomers are polymerized

simultaneously involving free radicals, ions or co-polycondensation

process.

1.3. Classification of polymers

Large number of chemical compounds undergoes polymerization in

different reaction conditions and the resulting polymers exhibit wide

range of physical, chemical, mechanical, thermal and electrical properties.

So the polymers are classified on the basis of origin (natural and

synthetic), physico-mechanical properties (glasses, elastomers, fibers,

foams, liquid resins), thermal behavior (thermoplastics, thermosetting),

chemical structure (homopolymers, copolymers, linear, branched, network

and cross linked, random comb, regular comb, cruciform, ladder, star,

semi-ladder) (Figure-1.1), backbone (organic and inorganic) and

apphcation (commodity, engineering and specialty) [2,3,4].

1.4. Properties of polymers

Polymers show a wide range of physical, mechanical, thermal,

electrical characteristics due to their chemical structure, geometrical

structure, molecular weight, molecular weight distribution, crystallinity,

crystallizabihty etc [2,3,4].

1.4.1. Chemical Structure

Here the fme structure of polymers is considered like the type of

monomer consisting the chain, the number of monomers, i.e. (I) Organic

and hiorganic polymers, (11) Homo chain polymers and Hetero chain

polymers, copolymers. As these are the parameters which relate

ultimately to the three dimensional aggregated structure and influence the

extent of polymer's crystallinity, flexibility and symmetry.

1.4.2. Geometrical structure

This feature depends on the spatial arrangement of the monomeric

units with respect to each other. Polymers having same chemical

structure can have different geometrical structures. On this basis

polymers are (i) Linear, (ii) Branched, (iii) Cross-linked, (iv) Random,

(v) Alternating, (vi) Block and Graft, (vii) Stereo-regular etc.

Branched Network

Cioiciform

Regular Comb

Ladder Semiladder

SVw-rt.

Figure 1.1. Possible model structure of some branched polymers.

The effects of the above parameters are reflected in such properties of

polymers like modulus and crystallinity, solubility etc.

1.4.3. Molecular weight

' rhe mechanical properties of the polymers are generally increases

with the increase in molecular weight in a non-linear fashion. Increase in

molecular weight gives the polymer increased mechanical strength

however some undesirable characteristic arise like increase in the melt

viscosity leading to difficulty in the melt processing, solubility of a

polymer in its solvent decrease with increase in molecular weight (Figure-

1.2 & 1.3). If the polymer possesses broad molecular weight distribution

the presence of high and low molecular weight fractions will further

control the polymer properties. For example if a polymer sample has

average molecular weight 40,000, it means that molecule in the sample

may have molecular weight ranging from 20,000 to 80,000 or 500 to

10,0,000 or some other range but the figures are uncertain. The presence

of molecular weight fraction enhances melt flow whereas high molecular

weight fraction may lead to incomplete dissolution.

1.4.4. Crystallinity

Crystallinity of a polymer sample is defined as the fraction of the

sample, which is crystalline. The highest crystallinity is generally

associated with polymers, which have a simple unit structure and exhibit a

relatively high degree of long-range molecular order. Polymers

possessing high crystallinity do not pass from solid to soft and rubbery

state upon heating rather they pass directly to the melt state from solid

state. The temperature at which this transition takes place is called the

200 Degree of Polymerization 2000

Figure-1.2. Dependence of mechanical properties on molecular weight.

S

ii

commercial polymers

200 Degree of Polymerization 2000

Figure-1.3. Dependence of melt viscosity on molecular weight.

crystalline melting point, Tm. On the other hand polymers possessing low

degree of crystallinity, pass from hard and glassy state in to soft, flexible

and rubbery state on heating. The temperature at which this change

occurs is called glass -rubbery state transition or glass transition

temperature, Tg. On fiirther heating, these polymers become highly

viscous hquid and start flowing. This state is termed as visco-fluid state

and the temperature at which this transition occurs is called as flow

temperature, Tf. Thus it is clear that crystallinity direcfly affect the

rheological properties of the polymers.

Besides these points various agencies such as heat, chemicals, UV

and other radiation may affect the polymer properties by changing the

physical and chemical nature of the polymer. If the effect is undesirable

the term "degradation" is commonly used which may cause addition,

cross-linking, substitution, hydrolysis, chain-scission etc. leading to a

different type of polymer. The capability of a polymer to withstand

chemical attack depends on its chemical constitution. For example

polymers having C-C, C-H, C-Cl, C-F, aromatic moieties etc. are more

resistant to chemical attack than those containing 0-0 (Eg. polyesters

undergo hydrolysis), C=C (dine rubber undergoes hardening due to attack

of atmospheric oxygen leading to cross linking).

Thermal as well as light energy alone or in presence of oxygen or

moisture can cause bond scission if the energy required for bond

dissociation is low and hence the low band dissociation energy and light

sensitive bonds are the most susceptible to attack. Polymers containing

-CN, -CO, -C=C-, -OH, -C-Cl may easily be degraded by light or heat.

especially in presence of atmospheric oxygen. Whereas polymers with

aromatic backbone show excellent thermal and photorstability owing to

the relative inertness of the phenylene rings [2,3,4].

1.5. Composite materials

Two or more materials are combined together to produce a new

material, which may posses much better properties than any one of the

constituent materials. The new material is called as composite material.

For example, wool is a natural composite, which consists of long cellulose

fibers held together by amorphous lignin. Some artificial or synthetic

composite materials are cement, glass reinforced plastic, plywood etc.

Mainly there are three types of composite materials [9].

1.5.1. Agglomerated materials

In this process the particles are condensed together to form an

integrd mass and are known as agglomerated composite materials (e.g.

cement concrete).

1.5.2. Laminated materials or laminates

The materials, which are produced by bounding two or more layers

of different materials completely to each other, are known as laminated

materials or laminates (e.g. plywood, tufiiol).

1.5.3. Reinforced materials

The materials, which are produced by combining some suitable

material to provide additional strength, which does not exist in a single

material known as reinforced materials (e.g. nylon reinforced rubbers,

fiber reinforced plastics etc.).

8

1.6. Electrically conducting polymers

Due to the insulating properties, polymers remained unsuccessful in

replacing active components in metal and semiconductor devices. It was

observed that polymers with conjugated backbone showed enhanced

electrical conductivity on reacting with oxidizing or reducing agents.

Conjugated polymers such as polyacetylene, polyphenylene,

polythiophene, polypyrrole, polyaniline etc. possess a backbone that can

produce, sustain and assist the motion of charge carriers in the form of

electrons or holes (Figure-1.4). This process of reacting a conjugated

polymer with some oxidizing or reducing agent leading to the increase in

electrical conductivity to many orders of magnitude (Figure-1.5) is called

"doping" in analogy to the semiconductor technology. The perceived

advantages of such materials include lightweight, simple preparation,

cheap raw materials and tailorable electrical properties [5,10,11,12].

1.7. Polymer composites

To meet the demand of materials of improved performance,

commercial polymers are always mixed together with various additives of

monomeric or polymeric in nature. It is aimed that the additives will act

synergistically with the polymer and will meet the combined requirements

of a particular apphcation.

The word composite is used in the technical sense to describe a

product that arises from the incorporation of some basic structural

material in to a second substance, the matrix, which is incorporated either

in the form of particles, whiskers, fibers or a mesh. The main

characteristics sought in an additive that in turn gets conferred on the

POLYACETYLENE

^=r\=/ ^=w^ POLYANILINE

POLYPYRROLE

V V V V

f( M H H H

Q+-POLYTHIOPHENE

#

Figure-1.4. Structure of some conjugated polymers

10

I

s

O U

10 ,M Pb at 4k

(Superconduction)

X 10"

10

10

1

10

10^

•10^

10 10

10 -n

i-t 10

,0-16

10'*

10 20

Pt

Au, Ag, Cu

Hg-Fe, Al

Si, Ge (Intrinsic) C (Graphite)

Glass, Cotton

Nylon

Polystyrene

Polyethylene Quartz

T /f\

PA

^

^

. ^

PPP

JJ

f^O>^r PAni

^

_ ^

Figure-1.5. Electrical conductivity of various elements, compounds and polymers.

11

composite, are elastic rigidity, tensile and fatigue strength, hardness and

appropriate electrical and magnetic properties. Thus, a polymer composite

may be defined as combination of one or more other material with a

polymer matrix to produce a material with certain desirable properties.

Conducting composites are also prepared by mixing conducting polymer

in an insulating polymer matrix.

The simplest conducting composite consists of a fine metal powder

dispersed uniformly throughout an insulating plastic matrix. Composite

based on silver powder can be made with conductivity as high as

10 S m' at a loading of 85 % by weight, where the insulating matrix

serves essentially as a glue to hold the metal powder in position without

disrupting the metal-metal contact. The metal powder composites are

unsatisfactory for many applications because of poor mechanical strength

and high level of conductivity. The art of making a good conducting

composite is to use the minimum quantity of conductive component to

achieve the required degree of electrical performance. There are two

main factor related to it- (i) quality of inter-particle contacts and (ii) shape

and size of conductive particles [5].

1.8. Charge transfer complex and radical ion/compounds

There is a special class of organic compounds, which show high

electronic conductivity. The most notable are charge transfer complexes

and radical ionic system.

Charge-transfer complex packed closely in their crystalline phase

through formation of rigid multi-sandwich stacks. Charge-transfer

complexes are formed by partial transfer of an electron, from a donar

12

molecule of low ionization potential to an acceptor molecule of high

electron affinity.

D + A -> D^^ +A^- 8

Complete charge transfer would imply the formation of radical

ions. Such as pyrene has conductivity 10' ^ S m' and iodine has

conductivity 10" Sm'^ But reaction between them, give a complex with

conductivity 1.3 Sm" Polymeric version of the charge transfer system

with donor species attached to the backbone, have been synthesized. The

conductivity is generally lower then that of the corresponding monomeric

complex. Polymeric charge transfer complexes are quite brittle materials

and so they can only be used where mechanical properties are not so

important. Developing of highly conductive material based on radical ion

system has been the discovery of 7,7,8,8-tetracyanoquinodimathane

(TCNQ) by Du Pont workers [6].

This molecule is a very strong electron acceptor, forming first the

radical anion and then the dianion. The polymeric version of this

complex has much less conductivity.

There are also a few radical cation systems, which exhibit similar

conduction phenomena. Particularly, stable radical cations are based on a

category of heterocyclic compounds called violenes, which contain even

polyene structures. Polymers based on a netural violene doped with a

radical-cation salt are lightly colored and very stable [5].

1.9. Organic molecular solid and polymers

Here the groups of atoms are chemically bonded together in

discrete molecules, which in turn are held together by relatively weak van

13

der Waals forces. Therefore, we must distinguish between intra- and

inter- molecular electronic motion. In a long polymeric molecule, the

inter-molecular conduction is much less important because few

intermolecular transfers are required. Hence, the possibility of

intermolecular transport may be investigated. If each polymer molecule is

regarded a miniature lattice, the following points seem to be worth

considering- (i) a definitely spaced series of atoms with rigidly fixed

distances between nearest neighbors, (ii) small separation of atoms giving

good overlap of atomic orbitals, (iii) a full valence shell analogous to a

full valance band, and (iv) a very large excitation energy to the lowest

excited electronic state, due to strong chemical bonding i.e. a wide band

gap.

Me Cubbin and Gumey [7] studied long polyethylene molecule and

predicted a very wide band gap i.e. > 5 eV. They estimated carrier -> O i l

mobility to be about, 5x10' m v' s' for holes, which is comparable to that

in metals. Because of very wide band gap, the process of conduction

requires very high energy for electrons to overcome band gap and,

therefore, it may be anticipated that in long polymeric molecule, which

are fully saturated, there would be no significant conductivity under

normal circumstances [5].

1.10. Doping of conducting polymers and composites

Doping of conducting polymers and composites involves random

dispersion of dopants in molar concentrations in the disorder structure of

entang;led chain and fibrils. When a conjugated polymer is doped defects

are foimed like solutions, poltroons or bipolar in the polymer chain. The

14

reaction between oxidant (p-type doping by an acceptor) or reductant (n-

type doping by a donor) with conjugated polymers have been observed to

cause a dramatic increase in electrical conductivity. A general equation

for doping of a conjugated polymer may be given by the following

chemical reactions-

(-P-) + 2FeCl3 ^ (-p-)' + FeCU" + FeClj 9

(-p-)"^+ 2FeCl3-> (-p-) "" + FeCV + FeCli 10

Doping agents or dopants may be strong reducing agents, oxidizing

agents, neutral molecules, polymers, inorganic salts etc [10,16].

1.10.1. Doping techniques

Doping of conducting polymers and composites may be carried out

by the following methods [10]-

1.10.1.1. Gaseous doping

In this process polymers are exposed to the vapors of the dopants in

absence of air and moisture. The level of dopant concentration in

polymers may be controlled, by controlling the temperature, pressure and

time of exposure.

1.10.1.2. Solution doping

Solution doping involves the use of a liquid dopant or solution of a

dopant in an appropriate solvent. The doping of polymer is controlled, by

controlling the concentration and time of exposure.

1.10.1.3. Electrochemical doping

In electrochemical doping, polymerization and doping occurs

simultaneously. This technique is used for doping of polymers obtained

by ottier methods as well as for redoping or further doping. In this

15

process, only ionic types of dopants are used as electrolyte dissolved in

polar solvents.

1.10.1.4. Self-doping

Self-doping does not require any external doping agent. The

ionizable groups attached in the polymer chain act as dopant for the

polymer.

1.10.1.5. Radiation induced doping

High-energy radiations such as gamma rays, electron beam and

neutron radiation are used for doping of polymers by neutral dopants. For

example gamma-ray irradiation in the presence of SFe gas or neutron

radiation in the presence of I2 has been used to dope polythiophene.

1.10.2. Mechanism of doping

Since dopants are strong oxidizing or reducing agents, positive or

negative charge carriers are developed in the polymers on doping with

such dopants.

Polymer + p-Type Dopant -> p-Type Doped Polymer 11 (Oxidant)

Polymer + n-Type Dopant •> n-Type Doped Polymer 12 (Reductant)

But doping is not merely an oxidation or reduction reaction. It was

found that doping results in rearrangement of polymer chains and thereby

new ordered structures are formed. In the doped polymers charged

solitons are formed. These are charged defects with no spin. A reducing

(donor type) dopant, introduces an electron to the polymer chain which

couples with a neutral defect resulting in a negative soliton with zero spin.

16

Similarly an oxidizing (acceptor type) dopant abstracts an electron from

the polymer chain and a positive spin less soliton is formed. This is

illustrated by the doping of poly thiophene (Figure-1.6). The above

sequence of electronic event occurs in the polymer chain at a very low

doping level. But as the doping level is increased, formation of a polaron

takes place (Figure-1.7). With increase in the doping level more and more

polarons interact to form bipolaron, which is a dication. Electrical

conductivity of polymers, though, primarily depends on extent of doping

and the strength of doping agent it is also influenced by many other

factors such as- method of synthesis resulting in different structures,

processing of polymers, degree of crystallinity, temperature etc [10,13].

1.11. Electrical conduction in polymers

Polymers are normally used as insulators in electrical and electronic

devices because their electrical conductivity lies in the range of 10' ^ to

lO'^^Scm-'.

Material show electrical conduction due to the movement of

electron, holes or ions on application of voltage as given by the following

equation-

a = qn|Li 13

where a is electrical conductivity of the material, n is the number of

charge, q is the charge and \x is drift mobihty of charge carriers [5,11].

1.11.1. Conjugated chain

In this case, each carbon atom along the chain has only one other

atom, i.e. hydrogen, attached to it. The electrons in p orbitals of the

carbon atoms overlap with those of carbon atoms on both sides, forming a

17

(i) An unstable diradical with spin and without charge.

OV-^_>-<_>=<_^KO (ii) A stable polaron 'p-type' with spin and charge.

Electron Acceptor

(iii) A stable bipolaron 'p-type with charge and without spin.

C Electron Acceptor

(iv) A Stable polaron 'n-type' with spin and charge.

Electron Donor

(v) A stable bipolaron 'n-type' with charge and without spin.

ez-\__/-v^/-\e d C Electron Donor

Figure- 1.6. Formation of polarons and bipolarons in polyparaphenylene on reaction with oxidizing and reducing agents.

18

e p

3

B O

2

Dopant Concentration, x (arb. units)

Figure- 1,7. Schematic representation of formation of polarons and bipolarons with increasing dopant concentration (x) and its impact on electrical conductivity and spin concentration of the polymer.

19

de-localized molecular orbital of n- symmetry. This is conjugated system,

represented by alternating single and double bonds along the chain, hi a

very long conjugated system, the discrete set of molecular electronic

states merge into a half-full valance band, giving metal-like condition

within the chain.

In a finite conjugated chain, the electrons in the ground state will be

paired in the lowest energy set of molecular orbitals. Conduction will

required the excitation of an electron fi"om the highest occupied orbital to

the lowest unoccupied one. For example, in a conjugated system where

N=100, the energy required for excitation of electrons is comparable with

average thermal energy at room temperature i.e. 0.025 eV.

In most conjugated polymers, the conductivity is little better than

that in ordinary polymers. There are two major reasons (i) in the long

chain conjugated polymers instead of equal bond lengths along the chain,

long and short bonds occur alternately, which limit the delocalization of

electrons. As the TI:- electrons do not delocalize over a correspondingly

greater length with increase in chain length, the activation energy Eg for

the generation of carriers no longer falls linearly with increase in chain

length, (ii) the molecules must remain planer for the retention of

conjugation, while rotation about any bond will disturb the conjugation

[5].

1.11.2. Ionic conduction

Ionic conduction is evident from the detection of electrolysis

products formed on discharge of the ions as they arrive at the electrodes.

20

But very low level of conductivity in polymers generally precludes such

detection.

The absorption of water, which has a high dielectric constant,

generally enhances the conductivity of a polymer greatly [5].

1.11.3. Electronic conduction

Electrical properties of materials may be discussed in the light of

band theory as follows-

1.11.3.1. Band theory

To understand the behavior of other atoms, we can take the

example of the hydrogen atom, which has the simplest electronic

arrangement. When two hydrogen atoms come close, their Is- orbital

overlap and two new u electronic orbital (bonding and antibonding) are

formed around the atoms (symmetrical with respect to the interatomic

axis) (Figure-1.8). In bonding orbitals, electrons have lower energy than

in the isolated atomic orbitals and in the anti-bonding orbital electrons

have higher energy. The two electrons from hydrogen atoms if they are of

opposite spin may pair in the bonding orbital to give a stable molecule

with total energy less than the sum of the energies of the two isolated

hydrogen atoms.

In solids, where many atoms strongly interact, similar splitting of

energ)' levels occurs. The sets of energy levels form two continuous

energy bands called the valence band and the conduction band analogous

to the bonding and anti-bonding levels of the diatomic molecules (Figure-

1.9 & 1.10). The energy gap between them represents a forbidden zone

21

Anti-bonding

Is orbitHl /

> v

< / ^-v

Bonding

Is orbital

Figure- 1.8. Splitting of energy levels of hydrogen atom.

22

Antibonding Orbital

H Bonding Orbital H

e

G

2 '•O u 3

T3 B O

H = l n^ 2 ta: nrcC

Figure-1.9. Molecular orbitals and bands in conjugated polymers.

23

Metal Semiconductor Insulator

Figure-1.10. Band structure of (i) Metal, (ii) Semiconductor and (iii) Insulator

24

for the electrons (Figuire-1.11). The energy difference between these two

bands (valence band and conduction band) is called band gap "Eg".

.!\n important feature of band system is that the electrons are

delocalized or spread over the lattice. Some delocalization is naturally

expected when an atomic orbital of any atom overlaps appreciably with

those of more than one of its neighbors. Suppose, a free electron

propagates through space as a wave, characterized by a wave vector, K,

whose magnitude is related to the momentum, p, of the electron by the

fundamental relation-

K-27rp/h 14

where h is Plank's constant. In a lattice of strongly interacting atoms

where the orbitals of the valence electrons overlap well, the valence

electrons are nearly free to roam any where within the confines of the

lattice. For a simple linear lattice with a spacing, a, the Bragg's condition

is-

K = ±n7i/a 15

where n is an integer and for a simple linear lattice of length, L -

L = Na 16

where N is total number of atoms.

It may be shown that the total number of electron wave states in the

lowest energy band is exactly N. This means that each cell of the lattice

contributes one independent K-value to the energy band. This result

applies to every energy band of the system and also carries over to

3-dimentional lattice.

25

Conduction Band

4\ optical band gap

Y

Vacuum

i c o I .

A

Nk

« c a. o a. G o

••B

V

4 Band

^

width

Figure- 1.11. Relationship of polymer's 7t-electron band structure to vacuum and other energetic parameters.

26

In a full band there can be no flow of electronic charge under an

external electric field. The reason is that for every wave state in which an

electron is traveling in one direction, there is another wave state in which

the electron is traveling in the opposite direction and there is no spare

space (i.e. equal number of+K and -K values). Therefore, intrinsic

conduction can only occur when electrons are promoted across the band

gap in to the conduction band by photonic or thermal means. Then, both

the electrons in the conduction band and holes in the valence band can

contribute to net charge flow.

As electron obey Fermi-Dirac statistic, the distribution function

giving the occupation probability /(E) of a state of energy E at

equilibrium is-

/(E)=l/[l+e^^-V^'^] 17

where Ep is Fermi energy.

Detailed statistical analysis shows that for intrinsic conduction in a

semiconducting material, where the concentration of conduction

electrons, n, always equals the concentration of holes, p, and the energy

band gap. Eg, is wide (Eg»KT), then-

n = p = 2[(27mi*KT)/h ] ^^^^e- ' 18

where m* is the effective mass of the electron or hole. Thus, as the

temperature is increased the charge carrier concentration increases. This

dominates the temperature dependence of the conductivity, giving it an

Arrhenius- like character with an effective activation energy VsEg.

Another feature, which is important in semiconducting materials, is

the occurrence of energy levels in the forbidden energy zone due to the

27

presence of impurities. Deliberate doping which give donor states near

the conduction-band edge and electron acceptor states near the valance-

band edge, can produce enormous increase in the population of

conduction electrons or holes at a given temperature. This is an example

of extrinsic conduction [5].

1.11.3.2. Hopping and tunneling conduction

Both energetic and spatial distributions of electronic states are

affected by the presence of disorder in the lattice. If atoms are randomly

distributed, the density of electronic energy state tails into the forbidden

zone and the electron in these tails are localized. There is an intermediate

range of electronic energy state in which mobilities are very low (Figure-

1.12). Conduction is only possible if electrons are excited to higher

energy state with greater mobilities. Conduction via localized electrons

implies direct jumps across an energy barrier from one site to the next. An

electron may either hop over the top of the barrier or tunnel through the

barrier (Figure-1.13). The relative importance of these two mechanisms

depends upon the shape of the barrier and availability of the thermal

energ> [5].

1.11.3.3. Photoconduction

Exposure of a semiconducting material to light or other

electromagnetic radiations may produce a temporary increase in the

population of free charge carriers and the resulting extra flow of current

under the influence of applied field is called photoconduction.

The photon of the radiation can interact with the semiconducting

material in a variety of ways to generate carrier, hi ordinary polymers,

28

CI

a

Mobility

Figure-1.12. Mobility gap.

/^

C

Hopping

Site-I

Figure- 1.13. Hopping and Tunneling conduction.

29

like polyethene and PET it is very difficult to observe any

photoconduction, even with UV radiations, where the photon energy is

more than the energy gaps of these polymers. This is a consequence of the

very short lifetime (lO' s) of carriers, leading to rapid recombination or

deep trapping.

One class of organic polymer stands out above all other in its

photoconductive efficiency. It is based on vinyl derivatives of certain

polynuclear aromatic compounds such as poly (2- vinyl carbazole) [5].

1.11.3.4. Percolation theory

In a carbon black composite the increase in electrical conductivity

is not linear; instead a moderate increase is followed at a certain carbon

black concentration by a sudden jump, which is again followed by

moderate increase. This sequence of events was called percolation. The

carbon black concentration at which the conductivity jumps is known as

critical concentration (Oc).

Percolation theory is a statistical and geometrical approach to

explain the shape of the conductivity curve in composite materials.

Percolation theory proceeds from a statistical distribution of the

conducting particles, which corresponds to a maximum of entropy. It thus

denies any interaction between matrix and conducting particles. As the

concentration of conducting particles increases, they become closer to

each other and at the critical concentration (Oc), they are fmally

sufficiently close together or even touching leading to the conduction of

charge-carriers [14] as evident from schematic diagram given in figure-

1.14.

30

I c o

u

Concentration of conducting material

Figure 1.14. Schimatic diagram of a percolation conducting composite. curve m

31

1.12. Degradation of electrically conducting polymers & composites

The process of deterioration of useful polymer properties involving

chemical reactions is defined as degradation. There are many external

causes of degradation of polymeric materials such as heat, light,

mechanical stress, oxygen, ozone, moisture, atmospheric pollutants etc.

along with the factors effective at the time of processing. Also the

presence of reactive sites in the polymer (e.g. superoxides, defects,

chemically reactive groups etc.) may degrade the polymer properties with

or without combination of external factors [15-18].

The pristine conjugated polymers have been reported to contain

electronic spins leading to the inter- and intra- chain reactions between

these reactive sites which can alter the chemical structure even when they

are pure, affecting their dopability and, hence, the electro-activity. There

are two main factors, which affect the intrinsic degradation of conjugated

polymers viz. reactivity of polymer backbone and the reactivity of dopant.

Whereas the oxidative degradation of most polymers proceeds via

chemical reaction of peroxy radicals.

Sunlight consists of IR and visible radiations, apart from the high

energy UV radiations of the range, 200-380 rmi, of the electromagnetic

spectixim. The conjugated bonds, present in conducting polymers,

undergo n-7i*, %-%* and (y-a* transitions very easily, leading to formation

of free radicals on exposure to sunlight. The UV radiations contain

enough energy to cause C-C, C-N and C-O hemolytic bond fission.

Thus produced free radicals can react with atmospheric oxygen leading to

32

oxidation accompanied by depletion of chain length of the polymer [19-

21].

Of late, conductive polymers are being used for electrical storage in

non-rechargeable (primary) and rechargeable (secondary) batteries. In

spite of their high electrical conductivity, they have high selectivity to

electrode reactions low catalytic activity towards side reactions, sufficient

mechanical strength, fabricability, cost etc. The electrode materials must

also possess high stability towards degradation reactions during the

passage of current or storage. The degradation of electrode materials

leads to instability in electrode potential with time that takes place due to

diffusional processes occurring at the electrode and other side reactions

such as cross-linking, chemical reactions of dopant ions with polymer etc.

For a commercial battery, a good shelf life (capability to retain its charged

state) as well as ability to repeated charging and discharging many

hundred times is a pre-qualification. It has been observed that electro-

active polymers are distinct from traditional inorganic electrode materials

as they neither deteriorate nor re-deposit during charging and discharging

process and, hence, they may be expected to give long life storage

systems. The durabihty studies of polymeric electrodes may be done

galvanostatically or potentiostatically to evaluate their life in battery

application [22-24].

1.13. Stabilization

The long conjugated backbone of conductive polymers could

sustain defects such as free radicals. Such states can readily be oxidized.

The preventive measures undertaken to inhibit the degradation process,

33

are collectively known as " polymer stabilization". There are a variety of

methods of stabilizing such systems some of them are as follows [25-26]-

(i) by incorporating anti-oxidants such as benzoquinone and hindered

phenols or by using radical traps such as azo-bis-isobutyronitrile in the

systems, (ii) by ion implantation or by predoping the material with a

strong electron acceptor prior to oxygen exposure, (iii) by encasing the

polymer in a system with reduced oxygen and moisture permeability, (iv)

by synthesizing new polymers with less susceptibility to intrinsic

degradation to oxygen and to moisture, even at elevated temperature and

(v) by forming composites of conducting polymers with environmentally

stable polymers.

1.14. Application of conducting polymers

Besides electrical conductivity like metals, conducting polymers

have emerged as fascinating materials due to a wide range of other

desirable properties such as architectural flexibility, environmental

stability, ease of fabrication, light weight, mechanical properties and so

on. Therefore, these materials are finding apphcations from coating to

lubricants to solid-state technology to biotechnology. One of the major

areas of application includes solid-state rechargeable polymer battery [27]

as electrochemical studies have suggested their better rechargeability than

inorganic batteries.

Polyheterocyclics show wide variations in their colors with the

applied voltage when switched between oxidized and reduced states

[28,29]. Similarly they also exhibit photoelectronic phenomenon as a

result of optical density change [30,31]. Therefore employing these

34

physical effects, display devices may be developed by coupling a

conducting polymer with a semiconductor. Solid- state electrochromic

device based on polyaniline has been fabricated [32]. Thin films of

electrically conducting polymers coated on silicon, cadmium sulfide,

gallium arsenide and other surfaces showed reduced photodecomposition.

So they have already found applications in the electrochemical

photovoltaic and photo-electrolysis cells [33,34]. The conductivity of

conjugated polymers can be maintained in the semiconducting region by

controlling the dopant concentration and thus Schottkey barrier type diode

and field-effect transistor from conducting polymers have been developed

[35-38]. A condenser based on polypyrrole and aluminium solid

electrolyte has been developed by Marcon Company. This condenser

exhibits good stability at higher temperatures and shows application in

multilayer printed circuits, audiovisual instruments etc. [39-43]

Conducting polymers could be used as fillers in place of carbon black,

graphite or metals. They can also be used as conductive component in

conductive adhesives [44]. Conducting polymers can be used as

precoating before metal plating on plastic components [45]. Indicators

have been developed to detect moisture, radiation, electrochemical and

mechanical abuse [46]. Gas sensors and biosensors have also been

developed. In biotechnology [47-49], the use of conducting polymer has

also been suggested. Some possible appUcation of electrically conducting

polymers and composites are given in the table-1.1 and some schemetic

diagrams (Figure-1.15, 1.16 &1.17) of the devices.

35

DtSCHARGINQ

CHARGING

ELECTROLYTE

Li*

LITHIUM

METAL

Figure- 1.15. A schematic diagram of polyaniline-lithium battery.

36

sr

-A,

\m\\\\\\\ ^ ^ A,

i i l i V i vl i -^

Figure-1.16. A schematic diagram of a single-layer conducting polymer based light emitting diode (LED). 1. Al/Mg/Ca metal film, 2. conducting polymer layer, 3. Indium-tin-oxide coated 4. Glass substrate and 5. Electrical contacts.

(4 M- 3

1 m^N^

/ ^ \ i _ i i _

s

- -

Figure-1.17. A schematic diagram of a conducting polymer based conductimetric sensor device. 1. Catalytic layer, 2. Conducting polymer layer, 3. Reference electrode, 4. Working electrode and 5. EPSIS.

37

Table-1.1 Possible application of some important electrically conducting polymers.

Polymers

Polyacetylene

Polyaniline

Polypyrrole

Polythiophene

Polyphenylene

Possible Application

Rechargeable batteries, Photovoltaics, Gas sensors. Solar cells. Optoelectronics, Chemical indicators, Radiation detectors, Schottky diodes.

Rechargeable batteries, Electrochromic devices. Bio-sensors, Conducting textiles, Solar cells. Indicators.

Rechargeable batteries. Conducting textiles, Photovoltaics, Field effect transistors. Electroplating, Printed circuit board, Electromagnetic shielding, Adhesives, Fillers, Transparent coatings, Gas sensors. Solar cells. Optoelectronics, Chemical indicators. Radiation detectors, Schottky diodes.

Rechargeable batteries. Display devices, Field effect transistors. Gas sensors. Optoelectronics, Schottky diodes. Fillers, Photocatalysis,

Rechargeable batteries, Solid lubricants. Fillers, Photocatalysis.

38

« >

'S

CHAPTER-2

. - ' < ' * «

l . . _ , •• •a •«<•

«« J * & •

- - | - -

It

$r • -•*

A .. | . . . > S K « -)•..„

• ' \

- , ' • % . .

^-—\% - '•< t i

"J

1 ^ ?!!,. „ "

' >

2.1. Composites based on polyaniline

Siftillina et al [1] reported the electrochemical synthesis of

polyaniline composites in porous polyethyleneterepthalate (PET) and

polyethylene (PE) matrixes prepared by solvent crazing. Electro chemical

polymerization of aniline in porous matrices produced highly dispersed

polyaniline of morphology, different from that of polyaniline prepared in

absence of matrices. Distribution of polyaniline in the porous matrices

was observed to be dependent on the mode of solvent crazing and the

extent of drawing of the solvent crazed polymer.

Kalhori et al [2] reported the surface grafting of polyaniline on

silica by chemical polymerization. Whereas the change in electrical

conductivity composite of polyaniline and poly(ethylene-co-vinyl acetate)

was investigated by Tsanov et al [3]. It was observed that the fraction of

polyaniline at which a conductivity jump occurs is not constant during

aging as well as during storage. The electrical conductivity of the films of

low polyaniline content (up to 2.5 wt.%) increased by several orders of

magnitude over a period of eight months. It was proposed that the

polyaniline phase undergoes flocculation, which subsequently forms a

continuous conductive network. The conductivity jump was attributed to

dynamic interfacial interactions between the constituents of the

polyaniline-EVA composites.

Conductive blends prepared from plasticized cellulose acetate and

polyaniline protonated with sulfonic acids, phosphonic acids and

phosphoric acid, diesters were observed to be highly transparent. Fihns

39

casted from m-cresol solution showed a percolation threshold below 0.5

wt.% and excellent mechanical properties [4].

A green colored Porous Vycor glass polyaniline composite was

prepared by oxidative polymerization of aniline, on aniline impregnated

porous vycor glass. Exposure of composite to NH4OH solution leads to a

reversible color change from dark green to dark blue (emeraldine) [5].

Jan et al [6] prepared composites of polyaniline and polypyrrole with

vinylidenechloridemethylacrylate and butylacrylate copolymer by

chemical method. Appropriate polymerization conditions made it possible

to obtain composites containing ~5 to 50 % of polynaUine whereas < 15%

of polypyrrole in the respective composites and the electrical conductivity

was observed to be 1.5 and 1 Scm" respectively.

Charge transport studies were reported on camphorsulfonic-

acid:polyaniline with nylon-12 and toluenesulfomcacid:polyaniline with

carbon black. The CSA-PANI/Nylonl2 showed a temperature dependent

insulator-metal transition and anomalous high microwave adsorption

whereas the TSA:PANI/CB showed an unusual insulator to metal

transition from the individual materials to the composites. A common

mechanism was suggested for the inhomogeneous charge transport due to

formation of ordered regions during the polymerization of conducting

polyaniline in both the composites [7].

Electrical conductivity of polyaniline:polycarbonate composites

could be increased more than 15 orders of magnitude by a small variation

in amount of polyaniline in composite as explained by percolation model.

The percolation threshold and critical exponent of electrical conductivity

40

suggests the anisotropy in electrical conductivity while highly conducting

composite is found to be stable up to 160°C in terms of electrical

conductivity [8].

Percolation threshold of electrical conductivity of emulsion

polymerized polyanilinexhlorosulfonated polyethylene and

polyaniline.styrene-butadiene triblock copolymer composites were

observed to be 21% and 70% respectively. However, it increased two

orders of magnitude and exhibited a new percolation threshold 3.0% for

both the composites after secondary doping by m-cresol. The secondary

doping noticeably increased permanent set change with polyaniline

content as well as changed the ductile fracture into the brittle fracture.

Secondary doping did not show any marked effect on tensile strength and

elongation [9].

Young et al [10] reported the preparation of electrically conductive

polyaniline:polystyrene composites by in situ polymerization and

blending. The electrical conductivity of polyaniline:polystyrene

composites was improved with increasing amount of polyaniline and

reached to a high value of 0.1 Scm' at a content of 12 wf/o was calculated

by elemental analysis. The composites were found very soluble in organic

solvents such as chloroform, xylene and N-methylpyrrolidone (NMP)

while electrical conductivity of composites, doped with dodecylbenzene-

sulfonic acid and thermally treated at 180°C for 3 hours showed good

stability.

41

A conductive nylon-6:polyaiiiline composite for rechargeable

battery electrode and for liquid crystal display with improved mechanical

strength and electrical stability was reported [11].

Phase separation and conductive pathways formation was observed

in polyaniline:poly(ethylene-co-vinylacetate) composite films resulting in

the formation of poly aniline enriched lower side layers during storage. A

distinct difference in the conductivity of the two sides of the fikns was

detected. A mathematical interpretation of the evolution in percolation

behavior of polyaniline:ethylene-co-vinylacetate composites versus time

is presented. The unstable conducting properties (both conductivity Jump

and phase separation phenomena) of polyaniline:ethylene-co-vinylacetate

composites over time revealed their dissipative nature supporting the

dynamic interfacial model of conductive polymer composites [12].

Zheng et al [13] used electro chemical technique to synthesize

highly conducting polyaniline:polyvinylacetate composite film using

perchloric acid as a dopant as well as oxidant. Electrical conductivity

measured 0.173 Scm"\

Synthesis and characterization of highly conducting

polyanilinexlay nanocomposite with extended chain conformation was

reported by Qiuju et al [14]. The conductive emeraldine salt form of

polyaniltne was inserted into the galleries of montmorillonite to produce

the hybrid with highly conducting polyaniline. The product obtained was

a nano-composite and over 90% polyaniline chain was inserted between

the layers. Where polyaniline existed in single chains with extended-chain

conformation owing to the confined environment in the nanocomposite

42

size gallery. It was also found that the polymerization is a diffusion-

limited process.

A composite of polyaniline (PANI) encapsulating titanium oxide

(TiOa) with nanometer size has been synthesized by in situ emulsion

polymerization. Particle dimensions have been measured and the nature of

the association between the components have been observed using SEM

and TEM techniques. The interaction between PANI and Ti02 and the

nature of chain growth have been investigated and explained according to

the results of FTIR. The improvement of thermal stability and crystallinity

of nanocomposites of polyaniline and TiOihave been evaluated by using

TGA and XRD by Wei et al [15]. The mechanism of charge transport and

photo induced charge transfer in composites has also been reported.

Polyaniline thermally blended with butadiene-styrene triblock

rubber at different weight composition and then were capillary extruded to

fibers. Microscopic analysis on the extrudates revealed that polyaniline

was deformed during the process to produce elongated structures i.e.

ellipsoids or even short fibers in the blends. Electrical measurements were

performed and it was found that blends with more than 20 weight %

polyaniline could produce an electrical conductive composite with a good

level of conduction. The relationship between the volume conductivity

and content of polyaniline in the blends showed characteristics of a

percolation system, with a threshold as low as 5 weiglit % of polyaniline

[16].

Oyama et al [17] reported a composite of 2,5-dimercapto-1,2,4-

thiodia> ole and polyaniline on a copper current collector that provides

43

high charge density exceeding 225 Ah/Kg cathode with average discharge

voltage at 3.4V. The composite cathode showed excellent rate capability

and cyclability of >500 cycles. While large increase in the charge density

to 550 Ah/Kg cathode is achieved by adding elemental sulfor (Sg) to the

composite cathode.

A conducting elastomeric foam composite from an elastomer foam

and a conducting polymer (polypyrrole, polythiophene or polyaniline and

derivatives there of) was reported by Bessette et al [18]. Only -5% of

conductive polymer is required for insulator to conductor transition and

the electrical conductivity of the composite foam could be effectively

controlled between 10" and lO.i Scm' by varying the amount of oxidant

used and/or by variation in the copolymer composition.

Several protonated poly(o-anisidine):polyvinylalcohol composites

were prepared with different types of acids (sulfuric, p-toluenesulfonic,

camphorsulfonic, and p-dodecylbenzenesulfonic). The linear dependence

of the logarithmic electrical conductivity on the variation of humidity was

observed for all the composites, which was caused by the salt-base

transition of the conducting polymer i.e. by the movement of free acid

between the active sites of the conducting polymer and the strongly bound

water existing in polyvinylalcohol, which in turn depended directly on the

environmental humidity. The response time of the composites to humidit}'

was shortened with a decrease in the size of the dopant anions [19].

A conducting composite of polyaniline and polycarbonate was

prepared by a blending using chloroform as a solvent by Lee et al [20].

Polycarbonate containing sulfo-group enhances the Coulombic interaction

44

between two phases of the composite. The effect of ionic groups in

sulfonated polycarbonate was monitored using measurements of both the

mechanical and thermal properties. The electrical conductivity was

increased to 7.5 Scm" on doping with camphorsulfonic acid or

dodecylbenznesulfonic acid.

Iroh and Rajagophlan [21] electrochemically co deposited

polyaniline and polypyrrole on carbon fibers under potentiostatic

conditions. Electro polymerization was carried out by varying the applied

potential and the feed ratio of monomers. Weight gain plots indicated that

polyaniline is preferentially formed when the monomer ratio is 90%

aniline: 10% pyrrole, however more polypyrrole was formed as pyrrole

concentration increased. The thermal stability of the composites was

observed to be between the stability of homopolymers. The morphology

of the composite was affected by the polymerization potential and

monomer feed ratio.

An improvement in the electrical conductivity of polyaniline:nylon-

6 composite fabrics was observed on surface modification of nylon-6

fabrics by various plasma treatments by Oh et al [22]. Electrical

conductivities of polyaniline:nylon-6 composite fabrics were highly

increased by ultrasonic treatment, which assisted the diffusion of aniline

in to the inside of nylon fabrics by cavitation and vibration. The fabric

conductivity was also observed to increase with increase in monomer

concentration and the polyaniline deposition cycles.

The composite of polyaniline and its derivatives with polyvinyl-

alcohol were observed to be useful materials as humidity sensors by

45

Shiigi et al [23] such as polyaniline. Certain composites like poly(o-

phenylenediamine), and poly(o-aminophenol) with polyvinylalcohol

exhibited linear dependence of electrical conductivity versus atmospheric

humidity whereas those of poly(m-phenylenediamine) and poly(o-

toluidine) with polyvinylalcohol showed non-linear dependence on

humidity without hysteresis.

2.2. Composites based on polypyrrole

Paoli et al [24] prepared composite films of polypyrrole:polyvinyl-

chloride by potentiostatic electro-oxidation using a platinum-working

electrode. The composite films were synthesized in a three-electrode

single compartment cell containing 0.006M pyrrole and 0. IM tetra-

ethylammoniumfluoroborate- acetonitrile. The results showed electrical

conductivity in the range of 5-50 Scm'\They recommended that the

composite could be used for a wide range of technological applications as

electrical properties are comparable with polypyrrole while mechanical

properties similar to polyvinylchloride.

Yosomiya et al [25] carried out an experimental investigation to

study the preparation of polypyrrole:polyvinylalcohol composite films

througli vapor phase polymerization using a polyvinylalcohol:cupric

chloride complex fihn as a base polymer and on their electrical properties.

They found that the composite fihns exhibited behavior similar to a p-type

semiconductor and that the highly transparent and conductive composite

films could be obtained.

Electrically conductive composite from polypyrrole and poly(p-

phenyleneterepthalamide) were formed by electropolymerization of

46

pyrrole on the electrode covered with poly(p-phenyleneterepthalainide)

fihn. The morphologies of the composites varied, depending on the

supporting electrolytes. The electrical conductivity of the composite was

observed in the range of 5-50 Scm'\ The conductivities of the composites

doped with p-toluenesulfonate and perchlorate were retained at all times

up to 150°C, whereas that of the pure polypyrrole film decreased to 80%

of the original value after annealing at 150°C, betug independent of the

dopant. Fihn was dimensionally stable and heat resistant and these

properties provided a stable conductive composite fihn [26].

Trivedi and Dhawan [27] developed a process for polymerizing

aniline or pyrrole on the surface of textile fibers, where each single fiber

of the textile assembly has a smooth, adherent and coherent layer of the

electrically conductive polymer. The co-axial test revealed that these

conductive textiles were ideally suitable for shielding of electromagnetic

interference as well as electrostatic charge dissipation.

Kang et al [28] studied the chemical process of preparing

polypyrrole :polyvinylchloride composite films with high electrical

conductivity and transparency. The diffused pyrrole in the polyvinyl-

chloride matrix in the swelling medium of n-hexane and acetone mixture.

The oxidative polymerization of the diffiised pyrrole in the binary solvent

system of acetonitrile and methanol was done and it gave high

conductivity of the polypyrrole as well as good penetration of the oxidant

in to the polyvinylchloride matrix.

Mohammadi et al [29] prepared electrically conducting polymer

composite fihns by a template polymerization process. The fihns were

47

produced by polymerization of pyrrole in to matrix polymer of poly(4-

vinylpyiidine) complex with cupric ions. These fihns showed high

electrical conductivity and good mechanical and chemical stability.

Electrically conductive polypyrrole:poly(p-phenyleneterepthalamide)

composites shaped as fibers were prepared by continuous vapor phase

polymerization of pyrrole on fibers as they rolled through the reactor at a

rate of 0.5-1.5 mm.min' using FeCls. 6H2O, as an oxidizing agent. The

fibers showed electrical conductivity of 0.68 Scm"', tensile strength of

2731 Nmm' and elongation at break of 4.8%, wide angle x-ray diffraction

analysis and SEM showed that amorphous polypyrrole coated on the

surface of fibers and the diffused in to the bulk of fiber. The use of these

conducting polymer fibers in a variety of electronic device applications

was suggested [30].

Electrically conducting composite particles were prepared by using

a morphine-imprinted methacrylicacid-ethyleneglycoldimethacrylate

copolymer interpenetrated with polypyrrole network. The resulting

composite was found to have retained its molecular-recognition

properties. Potential applications of these composite polymers, especially

in sensor technology were suggested [31].

Kang et al [32] prepared conducting composites of polypyrrole and

poly(N-methylpyrrole) by electrochemical polymerization of the

corresponding monomers at a platinum electrode in 0.036M tetrabutyl-

amminiumdodecylsulphate/acetonitrile electrolyte system. They prepared

two types of composites of polypyrrole:poly(N-methylpyrrole) bi-layer

composite fihns and monomer mixture containing polymer composite and

48

N-methylpyrrole. The composites exhibited different electrical resistance

and thermal stabilities, depending on the preparation method. They also

investigated their electrochemistry and compared electrical conductivity

and thermal stability of the synthesized composites with polypyrrole

homopolymer films [33].

Electrically conducting polypyrrole :aramid composite fibers were

prepared by vapor phase polymerization of pyrrole using FeCl3.6H20 as

an oxidant. Conducting stability and mechanical properties were

investigated and the change of electrical resistance due to the applied

strain and its recovery were analyzed. Composite fibers showed a good

thermal stability in conductivity up to 170°C. The mechanical properties

of conducting composite fibers were affected slightly by polymerization

of pyrrole on the aramid fiber, while modulus increased slightly and

tenacity decreased only slightly. The electrical resistance of the composite

fibers initially increased slowly with increasing elongation but increased

sharply near breaking point, however, the residual electrical resistance

appeared on removal of the applied strain. Thus the possibility of the

application of conducting polypyrrole:aramid composite, were mentioned

[34].

Mohammad [35] carried out work on thin films of p-type doped

polythiophene. He showed that these films react rapidly but irreversibly

with ammonia and water, whereas the loss of conductivity in them was

largely reversible by evacuation in p-type doped polypyrrole. He

examined the interaction between compensating agents such as ammonia,

49

water and p-type doped polythiophene and polypyrrole, and proposed

chemical schemes with potential for use in sensing devices.

Suk-Hye et al [36] prepared conducting composites in porous

polymethylmethacrylate particles with different specific surface area by

seeded emulsion polymerization using divinylbenzene as a cross linker

followed by solvent extraction. The dried porous polymer particles were

dipped in a FeCls oxidant solution then immersed into pyrrole dissolved

in an organic solvent and pyrrole became polymerized in the porous. The

electrical conductivity was systematically investigated.

The effect of polyethyleneterephthalate blending on the electrical

conductivity of polypyrrole xopolyester composite film was investigated

by Baik et al [37]. The polypyrrole composite fihns were prepared by

polymerization of pyrrole through vapor phase absorption on to the

copolyester-polyethyleneterephthalate blend fikns containing FeCls.The

high electrical conductivity of the blend samples was thought to be due to

the phase separation between polyethyleneterephthalate and copolyesters

in amoi phous region.

Hernandez and Kamloth [38] carried out experiments to study the

optical and electrical properties of a conducting polypyrrole.polyoxy-

phenylene composite. The conducting polymer was prepared by in situ

electro polymerization process. The fihns obtained were characterized

optically by UVA IS and IR spectroscopy and electrically by

measurements of temperature dependence of the AC and DC electrical

conductivity.

50

Synthesis of block and graft copolymers containing polyether and

conducting polypyrrole moieties were incorporated at the chain ends of

polytetrahydrofliran and polysiloxane and at the side chains of poly-

ethylvinylether by ionic polymerization and appropriate chemical

reactions. Subsequent electro polymerization with pyrrole through these

moieties yielded freestanding fihns of the corresponding block and graft

copolymers. The two surfaces of copolymer films generally differ in

appearance, the surface at the solution side being cauliflower like or

wrinkled, whereas the surface at the electrode side was smooth.

Conductivity of the copolymers was comparable with that of the pure

polypyrrole [39].

Secondary ion mass spectrometry (SIMS) has been used to

characterized novel conducting polypyrrole:silicagel composite. The silica

gel particles act as a high surface inorganic substance for the in situ

chemical synthesis of polypyrrole in aqueous medium. However, the

conventional method using untreated silica gel as a host material for

pyrrole polymerization led to insulating polypyrrole:silicagel composite,

which exhibited a sihca rich surface. By pretreatment of the silica gel

particles by aminopropyltriethoxysilane prior to polymerization results in

conducting polypyrrole:aminopropyltriethoxysilane-silica composites, the

surface of which was found to be rich in polypyrrole [40].

Multi-layers consisting of polypyrrole.polystyrenesulfonate and

polyvioligen were electrochemically prepared on gold electrode up to 13

layer-pairs to enhance long-term and enviroimiental stability of poly­

violigen modified electrodes. The electrochemical and electro chromic

51

George et al [44] reported an electrochemical method to synthesis

carbonnanotube:polypyrrole composite, which has a high concentration of

well-dispersed nanotubes that are wetted by the continuous polymer

phase. Anionic carbon nanotube acts as a strong and conductive dopant in

pyrrole polymerization. A remarkable uniform polypyrrole coating is

prepared on individual carbon nanotube.

Pyrrole was polymerized in situ by using FeCls in ABS matrix

dissolved in acetone solution. The resulting polypyrrole was also

dissolved in ABS solution. A cast soft free-stand composite fihn was

prepared by the evaporation of matrix solvent. Conductivity was

measured about 3.8 Scm' by fore-probe method. It was found quite stable

in air [45].

Using the ion-exchange properties of conducting polymers

Weidlich et al [46] has developed a polypyrrole based electrochemical

switchable ion-exchanger for water purification, especially for softening

drinking water.

53

OBJECTIVES

Polymers have traditionally been utilized in electrical and electronic

applications as insulators and dielectrics. However, polymer remained

unsuccessfiil in replacing metal and semiconductors in electrical and elec­

tronic applications as conductors. To meet the demand of materials of

improved performance, commercial polymers are always mixed together

with various additive of monomeric or polymeric in nature. It is aimed

that the additives will act synergistically with the polymer and will meet

the combined requirement of a particular appUcation. Conducting poh-

mer composites possess the combination of traditional and conducting

polymer as has observed during literature survey. Thus, the problem

entitled "synthesis and characterization of conducting polymer

composites", m which the insulating polymer matiix acts as solid

adhesive keeping the conducting components together and providing

mechanical sti'ength without any contribution in electi'ical conduction,

have been selected after careful scrutiny of literature surveyed. The

conducting component selected is a conducting polymer. The work has

been carried out to-

> prepare conducting composites based on polyaniline and nylon-6

and nylon-6,6,

> study their doping and undoping behavior,

> study their electrical properties,

> characterize them by FTIR spectroscopy and

> study their stability in term of electrical conductivity^ retention.

54

CHAPTER-3

a.l.Chemicals V - ^ 5 ^ 5 2 S 3 Z- '

Aniline, 99% (Qualigens); Curcumtn (Al3h^i<QtieKi^^=^lon-6;

Nylon-6,6; Potassium persulphate, 98% (CDH); Hydrochloric acid, 35%

(E.Merck, India); Formic acid, 85% (Qualigens); Iodine (E.Merck, India);

Acetone (Qualigens); Ammonia, 25% (Qualigens); Poly(aniline-co-p-

toluenesulfonicacid) received as-prepared.

3.2. Preparation of materials

3.2.1. Synthesis of polyaniline

Polyaniline was synthesized by oxidative polymerization of doubly

distilled aniline solution in aqueous HCl at ice temperature using

potassium persulphate in aqueous HCl as an oxidant. Aniline (0.2 mol.)

dissolved in 500 ml of aqueous solution of HCl (IM) and potassium

persulphate (0.25 moles) was dissolved in 500 ml HCl (IM). Then the

oxidant solution was added slowly to the aniline solution with continuous

stirring at ice temperature. The reaction mixture was kept under

continuous stirring for an hour and then kept overnight in a refrigerator.

The reaction mixture was filtered and washed with HCl (IM) till the

filtrate became colorless and acid free. Thus synthesized polymer was

undoped by treatment with excess of aqueous ammonia (IM) and

repeatedly washed with distilled water until the filtrate became neutral.

Polyaniline was dried for 48 hours at 60°C in an air oven. This polymer

was ground to fine powder and low molecular weight oligomers were

removed by soxhalation with acetone [1,4].

3.2.2. Synthesis of polyaniline:nylon composites

.Aniline was added to nylon solution in formic acid and then kept

55

in an ice bath for an hour. Solid potassium persulphate was added as

polymerization catalyst under continuous stirring and left for 24 hours at

ice temperature. The contents were poured into distilled water, then

filtered and washed repeatedly with distilled water until the filtrate

become neutral. Materials were dried approximately for 48 hours at 60°C

in an air oven and stored in a desiccator. The compositions of reaction

mixture for the synthesis of polyaniline:nylon-6 and polyaniline:nylon-6,6

composites are given in (Table-3.1 and Table-3.2) respectively. This

method is slightly modified technique reported by Ahn and Park [5],

3.2.3. Preparation of polyaniline:curcumin composite

Composite of polyanilne with curcumin (20:1 w/w) was prepared

by mechanical mixing of the constituents.

3.2.4. Synthesis of copolymer of aniline and amino acid (L-argenine)

Aniline (0.2 mol) was dissolved in the 100 ml of aqueous solution

of L-argenine (O.OIM) and a solution of potassium persulphate (0.25 mol)

in 100 ml of L-argenine was prepared by shght warming on the water

bath. The copolymerization was carried out by slowly adding potassium

persulphate solution into the aniline solution at 60°C with continuous

stirring. The copolymer, so produced, was washed with distilled water till

the filtrate gave negative test for hydrogen ions. The material was then

dried at 60°C in an air oven and stored in a desiccator.

3.2.5. Synthesis of phthalic acid:curcumin copolymer

A copolymer of phthalic acid with curcumin (20:1 w/w) was

synthesized by refluxing the solution in acetone (100 ml) in presence of

cone. H2SO4. The copolymer obtained was washed with distilled water

56

Table-3.1. Synthesis of polyannine:nylon-6 composites.

Sample ID No

PANI:N6-1

PAN]:N6-2

PANI;N6-3

PAN[:N6-4

PANI:N6-5

PANr.N6-6

Nylon 6 (ing)

Formic Acid

(in ml)

35

35

35

35

35

35

Potassium persulphate

Ong)

0.35

0.71

1.05

1.40

1.75

2.10

1 1

Aniline !

(in ml)

0.1

0.2

0.3

0.4

0.5

0.6

(ing) i 1

0.1023 1 1

0.2046

0.3069 ^

0.4092

0.5115

0.6138

57

TabIe-3,2. Synthesis of polyaniline:nylon-6,6 composites.

Sample ID No

PANI:N66-1

PANI:N66-2

PANI:N66-3

PANI:N66-4

PANT:N66-5

PANl:N66-6

PANI:N66-7

PANI:N66-8

PANI:N66-9

PAN1:N66-10

NyIon66 (ing)

Formic Acid

(in ml)

35

35

35

35

35

35

35

35

35

35

Potassium persulphate

(ing)

0.35

0.71

1.05

1.40

1.75

2.10

2.45

2.80

3.15

3.50

Aniline

(in ml

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

(ing)

0.1023

0.2046

0.3069

0.4092

0.5115

0.6138

0.7161

0.8184

0.9207

1.023

58

and slightly hardened by reacting with fine sulftir powder at 70°C. The

solubility of copolymer was tested in most of the common solvents.

3.3. Doping

3.3.1. Poly aniline: nylon-6 composites

Doping of composites (0.2 g each) was done by treatment with 10

ml aqueous HCl (1 M) and 10 ml iodine (0.03 M) solution in acetone for

2 days whereas poly(aniline-co-p-toluenesulfonicacid) (0.03 g) doping of

the composites (0.2 g each) was done in acetone for 2 days. After doping,

the materials were washed with distilled water repeatedly till the filtrate

became neutral.

3.3.2. Polyaniline:curcumin composite

Composite in powdered form was exposed to the vapors of HCI and

I2 vapors under ambient conditions. The composite powder in a small

petri dish was kept for 4 days in another petri dish containing dopant,

covered with a big petri dish.

3.3.3. Phthalic acid:curcumin copolymer

Solid iodine (0.3g, 0.5g and 0.7g) was added to the solutions of

copolymer (1.4 g each) in acetone (30 ml) respectively.

3.4. Pellet preparation

Fine powder of the doped composites was pressed into pellets by

using a hydraulic press under 50KN pressure for 20 minutes in KBr die.

3.5.Electrical conductivity measurements

3.5.1. Polyaniline composites

Doped composite was pressed into pellets and electrical

conductivity was measured with increasing temperature by using a 4-in-

59

line probe DC electrical conductivity-measuring instrument (Scientific

Equipments). Electrical conductivity (a) was calculated using the

following equation-

cy = G7(W/S)/ao 19

G7(W/S) = (2SAV)ln2 20

ao=I/2V7iS 21

G7(W/S) is a correction divisor which is a function of thickness of the

sample as well as probe-spacing where I, V, W and S are current (A),

voltage (V), thickness of the film (cm) and probe spacing (cm)

respectively (See appendix-I).

3.5.2. Phthalic acid:curcuinin copolymer

Each solution was diluted to different concentrations and the

change in electrical conductivity with decreasing concentration of

copolymer in acetone was measured by using a Conductivity Meter

(Elico, CM-180). Electrical conductivity of iodine solution was also

measured for comparison.

3.6. FTIR studies

FTIR spectra of all the samples were recorded by using Perkin

Elmer FTIR (1710) spectrophotometer on KBr pellets.

3.7. Stability of polyani!ine:nylon-6 composites

The stability (30 days after doping) of the composites in terms of

electrical conductivity retention was studied by repeatedly measuring 4-

probe DC electrical conductivity on pressed pellets with increasing

temperature from 35°C to 130°C at an interval of 30 min for 7 times.

The data obtained for each sample were plotted as log a versus 1/T (K).

60

CHAPTER-4

D • • ^ ^ ^ ^ I ^ C ^ ^ v s ^ ^

4.1. Preparation of materials

4.1.1. Polyaniline

In 1835 Polyaniline was first introduced as "aniline black" [1].

However, a systematic and detailed study on its synthesis and character­

ization for possible appHcations as an electrically conductive material was

reported only in 1910 by Green and Wood head [2]. Diaz and Logan [3]

observed the reversibility of electrical conductivity and of color on doping

and undoping by a redox process in 1980. Polyaniline has become an

important conducting material because of its ease of synthesis from cheap

raw materials and its sensivity towards hydrogen ions, hence, due to its

electroactivity. When aniline is oxidized in aqueous acidic medium with

potassium persulphate, the protonated conducting form of poly-aniline

(Chemical structure.4.1) is produced as given in the following chemical

equation [4]-

4 Fh-NHj^ + 5 SzOs^ -^ 2 [Ph-NH-Ph-NH*-]- + 12 H^ + 10 S04^ 22

Thus, prepared dark green polyaniline was of high molecular

weight as very little (<0.5%) oligomers from its undoped counter-part

could be extracted by acetone soxhlation for 24 hours. The yield of

polymer was more than 50% after washing and drying.

4.1.2. Composites

ITie method of composite preparation by oxidative polymerization

of aniline in the soluble matrix of nylon is very well demonstrated. As

expected, a gradual change in color from light green to dark green with

increasing concentration of aniline in reaction mixture was observed. The

yield of composites was observed to be sufficiently high, ranging from

61

60% to 97% as given in table-4.1 and table-4.2. The yield of poly-

aniline:nylon-6,6 composite is comparatively better than that of poly-

aniUne:nylon-6 composites. It was found that the yield increases to a

maximum, then decreases with rise in the aniline concentration in the

reaction mixture in case of polyaniline:nylon-6 composites whereas

continuously increases in case of polyaniline:nylon-6,6 composites as

evident from figure-4.1 and figure-4.2. Very little systematic work has

been done on conducting nylon composites as I came across only one

paper on the poly aniline :nylon-6 fabric during my literature survey [5].

Polyanilne:curcumin (20:1 w/w) composite, prepared by mecha­

nical mixing of the constituents, was observed to be a black powder.

4.1.3. Copolymer

The copolymer of curcumin with phthalic acid (1:30 w/w) was

formed by condensation reaction between carboxylic group of phthalic

acid and hydroxyl of curcumin (Chemical structure.4.2) as evident from

the presence of ester linkages. The copolymer was tacky, hence, the

partial hardening by sulphur decresed the tackiness of material which was

insoluble in water. However, the copolymer was observed to be soluble

in most of the common organic solvents, polar as well as non-polar, such

as acetone, benzene, toluene, chloroform, methanol etc.

4.2. Doping and electrical properties

4.2.l.Polyaniline:nylon-6 composites

Controlling the doping process the electrical conductivity of these

materials could be varied from insulator, through semiconductor to metal

range and vice versa as mentioned earlier. Schollhom and Zagefka [6]

62

have suggested a redox reaction for ammonia or amine intercalation into

layered metal chalcogenides, which has further been supported by the

work of Foot and Shaker [7]. On the basis of the disproportionation

reaction of ammonia as suggested by above workers, Mohammad [8] also

has suggested an analogous reaction for the undoping of polythiophene by

water. The overall chemical reactions are given in the following

equations-

8NH3-> 6NH/+6e-+N2 23

PTH^-BF4" + NH4^ + e- ^ PTH + NH4BF4 24

6H2O -> 4H30^+ 4e" + O2 25

PTH^-BF4" +H30^ + e- ^ PTH + HBF4.H2O 26

HBF4^HF+BF3 27

As-prepared polyaniline was in doped state and was green in color.

The color change iiom dark green to sk>' blue is associated with the

neutralization of positive charges on protonated polyaniline chains. The

charge neutralization reaction depends on the rate of chemical reaction

between the polymer and dopant, which in turn will depend upon the

reactivity of polymer chain and the basic strength of dopant [8]. The

basic strength of water is very low, hence, it does not act as an undoping

agent in case of polyaniline. However, the undoping by water was

observed in case of polyaniline :nylon composites as washing with

distilled water was accompanied by a color change from green to black as

well as loss of electrical conductivity. Hence, analogous neutralization

reactions for undoping of polyaniline by ammonia and polyaniline:nylon

composites by water may be suggested as under-PANT^-a'+Ml4'^ + e ' ^ P A N I + NH4a .^8

63

PANI^-HCOO"(NYLON) + HjO^ + e -> PANI(NYLON) + HCOOH + H2O 29

Thus prepared nylon-6 composite were redoped with HCl, I2 and

poly(aniline-co-p-toiuenesulphomc acid) after thorough washing with

distilled water and drying. The enhancement in electrical conductivity on

exposure to HCl, I2 and poly(aniline-co-p-toluenesulphomcacid) suggests

the involvement of charge-transfer reaction leading to doping as described

above.

ITie temperature dependence of electrical conductivity of HCl

doped polyaniline:nylon-6 composites are given in table-4.3. The

electrical conductivity increases with increase in polyaniline concen­

tration in the composites from insulator (<10' Scm'') to semiconductor

(>10~* Scm'*) as evident from figure-4.3. All the plots of log a versus 1/T

(K) follow Arrhenius equation except two viz. PANI:N6-1 and PAN1:N6-

2 because they showed electrical conductivity in insulating region. The

energies of activation of electrical conduction (E,) for the composites

have been calculated from the slopes of the Arrhenius plots figure-4.4,

4.5, 4.6 and 4.7.

Temperature dependence of the electrical conductivity of h doped

polyaniline;nylon-6 composite is given in table-4.4 . Electrical conduc­

tivity of the composites is in the range of semiconductor (>10'* Scm'*) as

evident from figure-4.8, 4.9, 4.10 and 4.11. All the plots of log a versus

1/T (K) follow Arrhenius equation except two viz. PANI:N6-1 and

PANI:N6-2 because they showed electrical conductivity in the insulating

region. The energies of activation of electrical conduction (Ea) for the

composites have been calculated from the slopes of the Arrhenius plots.

64

The electrical conductivity increases with increase in polyaniline concen­

tration in the composites then falls as evident from figure-4.12.

hi case of poly(aniline-co-p-toluenesulphonicacid) doped

polyairiline:Tiiylon-6 composite, the temperature dependence of electrical

conductivity is given in table-45. The electric^ eonduetivity increases

with increase in polyaniline coneenteation up to PANI:N6-3 then it began

to decreasee as evident from figure-4.13. All the plots of log a versus 1/T

(K) given in figure-4.14, 4.15, 4.16, 4.17, 4.18 and 4.19 follow Arrhenius

equation- The energies of activation of electrical conduction (£«) for the

composites have been calculated from the slopes of the Arrhenius plots.

The activa-tion energies of conduction calculated from the slopes of the

Arrhenius plots are given in table-4.6 and in figure-4.20 which are

comparable with polypyrrole:polyvinylchloride composites [9].

4.2.2. Potyanitineicurcumin composite

The electrical conductivity of HCl doped polyanitinercurcumin

composite was measured from 45°C to 170°C. The variation of electrical

conductivity of the composite with increase in temperature is presented in

table-4.7. On comparison with the standard values of electrical conduc­

tivity for traditional semiconductors [10], it is observed that the initial

electrical conductivity of the HCl doped composite is within the semi­

conducting region. The initial electrical conductivity of HCl doped

composite was observed to be 1.57X10" Scm" at 45°C which decreases

with rise in temperature as evident from figure-4.21. It may be attributed

to the evaporation of HQ or due to oxidative degradation of curcumin by

atmospheric oxygen as polyaniline is sufficiently stable upto the

65

experimental temperature. It may also be possible that the addition

reaction of HCl on the carbon-carbon double bond of curcumin lead to the

puncturing of conjugated backbone.

The temperature dependence of electrical conductivity of I2 doped

composite was measured rpm 3G°C up to 180°C. Here initial electrical

coiKluctivity is found to be 1.79X10' Scm' I at 30°C, which increases

with the rise in temperature (table-4.7.) i.e. it follows Arrhenius equation

similar to other semiconductors [11] as shown figure-4.22.

4.2.3 Copolymer

The copolymer of phthalic acidxurcumin was observed to be tacky

and soluble in most common organic solvents such as benzene, acetone,

methanol, chloroform, toluene etc. Hence, the electrical conductivity was

studied in acetone solution of copolymer after partial hardening by

sulphur powder to reduce tackiness. The electrical conductivity of pure

acetone used as solvent was found to be 1 x lO" Scm' and that of I2

solution in acetone at experimental concentration to be 1.1 x 10"'* Scm'.

All the three solutions showed an increase in electrical conductivity with

increase in iodine concentration and decrease in electrical conductivit}'

with dilution as given in table-4.8 and shown in figure-4.23.

4.3. FTIR studies

4.3.1. PolyaniIine:nylon-6 composites

The FTIR spectral data of the composites are given in tabulated

form as well as v (cm' ) versus %T as detailed below-

Table-4.9: FTIR data of as-prepared poly aniline :nylon-6 composites.

Table-4.I0: FTIR data of HCl doped polyaniline:nylon-6 composites.

66

Table-4.11: FTIR data of I2 doped polyanilme:nylon-6 composites.

Table-4.12: FTIR data of poly(aniline-co-p-toluenesulphonicacid)

doped polyaniline:nylon-6 composites.

FTgiire-4.24; FTIR spectra of as-prepared polyanitine:iiylon-6 composites.

Figiif€-4.25: FTIR spectra of HCl doped polyafliline:nylon-6 composites.

Figure~4.26: FTIR spectra of I2 doped polyanilineinylon-^ composites.

Figure-4.27: FTIR spectra of poly(aniliiie-co-p-toliienesulphonicacid)

doped polyaniline:nylon-6 composites.

As evident from above table-4.9 and figure-4.24, as-prepared

polyaniline:nylon-6 composites showed a strong band at 1641 cm"'

corresponding to carbonyl group of nylon-6 while the bands at 1146,

1264, 1304, 1371, 1463, 1503, 1548 cm"' correspond to polyanilme m the

composites. The assignments from reference-12 for nylon-6 and from

reference-13 for polyaniiine have been used. The band corresponding to

out of plane bending vibration of C-H bond of p-disubstituted benzene

ring appears at 825 cm'^ The bands corresponding to sfretching vibra­

tions of N-B-N and N=Q=N structures appear at 1463 cm'' and 1564 cm"'

respectively (where -B- and =Q= stand for benzenoid and quinoid

moieties in the polymer). The band corresponding to vibration mode of

N=Q=N ring and sfretching mode of C-N bond appear at 1146 cm' and

1304 cm"'. The gradual increase in the intensities in the bands corres­

ponding to polyaniiine and decrease in the bands corresponding to nylon-

6 support the gradual change in the composition of the composite

formulations (table-4.10, 4.11 and 4.12 and figure-4.25, 4.26 and 4.27).

The bands of nylon-6, polyaniiine and due to doping of the composite,

67

beyond 2000 cm'\ could not be observed because the data was available

between 800 cm"' to 2000 cm"' only.

4.3.2. Polyanilineicurcuniin composite

The FTIR spectra of the composites are given in tabulated form as

well as V (cm"') versus %T as detailed below-

Table-4.13: FTIR data of as-prepared, HCl doped and I2 doped

poly aniline: curcumin composite.

Figure-4.28: FTIR spectra of as-prepared, HCl doped and h doped

polyamline:€urcumin ^xjmposite.

As evident from table-4.13 and figure-4.28 in case of cucumin

component of the composite, the asymmetric and symmetric C-O-C

stretching bands appear at 1262 cm"' and 1037 cm"' respectively whereas

a band for in plane bending of 0-H bond appears at 1382 cm"'. The band

corresponding to carbonyl group appears at 1716 cm"', at a lower wave

number due to conjugation. There is a band corresponding to olefin

substituted benzene ring appears at 1655 cm" ' [14, 15]. Whereas in case

of poly aniline component of the composite, the band corresponding to the

out of plane bending vibration of C-H bond of p-disubstituted benzene

ring appears at 896 cm"'. The bands coiresponding to stretching vibra­

tions of NTB-N and N=Q=N structures appear at 1466 cm"' and 1542 cm'

respectively (where -B- and =Q= stand for benzenoid and quinoid moie­

ties in the polymer). The band corresponding to vibration mode of

N=Q=N ring and stretching mode of C-N bond appear at 1180 cm"' and

1365 cm"'. After doping the composite with HCl and I2 the bands are

broaden and appears at higher frequency [13]. The bands of polyaniline.

68

curcuniin and due to doping of the composite, beyond 2000 cm', could not

be observed because the data was available between 800 cm' to 2000 cm"

4.3.3. Copolymer phthalic acid:curcumin

The FTIR spectra of the composites are given in tabulated form as

well as V (cm"') versus %T as detailed below-

Table-4.13: FTIR data of phthalic acidxurcumin composite.

Figure-4.29: FTIR spectra of phthalic acidxurcumin composite.

The copol Tner of phthalic acid with curcumin is formed by

condensation reaction between -COOH and -OH leading to tlie formation

of ester linkages linkages containing polymer corresponding the shaqi peak

at 1685cm-l. Band at 905cm-L I281cm-L 1453cm-l, 1403 cm-1 predicts

the presence of carbox}4ic group. The bands at 640 cm-1, 1403 cm-1, 2957

X^tll 1 11 I Vj-l^t.^LW>J L.11V^ i y i W L J W I IWV^ Vf 1. L>1 A W l l V ^ i l X / V ^ A 1 iL,l \J \^ yj 1-1 1 <,! i W V l l C i l H j £ I j t ^ ^

evident form, table-4.13 and tlgure-4.29.

4.4, Stability of nolyaniline:nylon-6 composites

Composite PANl:N6-6 from the three doped categor\' was taken to

test tlie stability of the electrical conductance. In HCl doped composite it

shows some irregularit>' in first tliree of its cycle and after that it become

constant, in iodine doped composite tlie conductivity appears in higher

tempercimre in the first cycle and alter that it gives a constant reading and

in case of poly(aniline-co-p-tolunesulfonicacid) doped composite there is

no such change in the conductivity as compared with the first electrical

conductivit}' as evident from. t3ble-4.14, 4.15 and 4.16. The plot of the

conductivity is given in the figure-4.30, 4.31 and 4.32 show that all of them

follow .^rrhenius eauation^

69

Table-4.1 Yield of PANI:nylon-6 composites.

Sample ID No

PANI:N6-1

PANI:N6-2

PANI:N6-3

PANl:N6-4

PANI:N6-5

PANI:N6-6

Yield

(ing)

0.67

0.72

1.02

1.04

1.1

1.18

(%)

60.78

59.77

78.04

73.80

72.77

73.11

Color

As-Prepared

Light green

Light green

Green

Green

Dark green

Dark green

Undoped

Light brown

Dark brown

Black

Black

Black

Black

70

iwTWi w I I n»i if'I f w w i i i t i r CD

Z

z < a.

wn i i i i i» i i iwi—in 'n—nr i'

f l l l» iWII I |« I I I I I I IWWWWW»WlTWWtWi| l t t l l fWII I I I« l i l l l»WWII IW>frr iWWWII l l l l l lMl l i»l>lWTItt t1l l l l l l 'HI I | | i l l l lHMll l lMI«l l»l

• . • . • • . • • . • • • . • • • • • • . . . • • ••• «., • • • • • • • • • • • • • I . . . . . . . • • . • • • • ••••1

in <D Z

?•

< a.

(0 7 Z <

CO CD Z

z < Q.

Q

(U a. E (0 (0

(0 0) <-> ' « o a E o u «? c o

o c IZZ

c (0 > o a O "O 0)

> •

CD

Z

z < a.

t3)

r-

riifwi»iwniiimwi

I

o 05 o (»

CD

-o CD o in o •<T

O CO o CM

P|9!A %

Table-4.2 Yield of PANI:nylon-6,6 composites.

Sample ID No

PANI:N66-1

PANI:N66-2

PAM:N66-3

PANI;N66-4

PANI:N66-5

PANI:N66-6

PANI:N66-7

PANI:N66-8

PANI:N66-9

PANI:N66-10

Yield

(»ng)

0.831

1.11

1.03

1.19

1.21

1.22

1.57

1.69

1.81

1.96

( % )

60.78

59.77

78.04

73.80

72.77

73.11

91.48

92.93

94.23

96.88

Color

As-prepared

Light green

Light green

Green

Green

Dark green

Dark green

Dark green

Dark green

Dark green

Dark green

Undoped

Light brown

Dark brown

Black

Black

Black

Black

Black

Black

Black

Black

72

i8 z <

«?

i 9 a

-? E ?; w z < CL

z

CD

z z < Q.

<o z z < 0.

.•2 (0 O a E o u

«? c

c

_c

'E (0 _>« o a

» t -o

0) 3

i l

z <

o o o o o CM

P|9!A %

Table-4.3. Temperature dependence of DC electrical conductivity of PoIyanillne:nyIon-6 composites (HCI doped).

Temp.

(°C)

35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155

Sample ID->

Temperature (1/K)

3.2467x10'

3.1948x10-

3.1446x10-

3.0959x10"

3.0487x10"

3.003x10- 2.9585x10- 2.9154x10- 2.8735x10- 2.8328x10- 2.7932x10- 2.7548x10- 2.7173xl0- 2.6808x10- 2.6455x10-

2.6109x10"

2.5773x10" 2.5445x10" 2.5125x10-

2.4813xW^

2.4509x10-

2.4213x10"

2.3923x10-

2.3640x10- 2.3364x10"

PANI:N6-3

axlO"*

(Scm*)

0.8262 0.7340 0.6219

0.5857 0.5739 0.5517 1.0558 1.0623 1.1142

1.1675 1.2305 1.3574 1.5203

1.8591 2.1928

2.2213

2.3430

2.4434 4.1718

PANI:N6-4

CTXlO-*

(Scm')

3.8065 4.3459

4.7928

5.1630

5.5463 5.6955 5.8846 6.0147 6.1856 6.6382 7.1622 7.9464 8.4392

8.7093 8.9235

9.2259 9.3048

PANI:N6-5

axlO^ (Scm')

2.3551

3.9285

6.2908 10.814 16.886 28.731 31.048 55.001 62.097 71.296 83.696 113.23

160.41

213.89

PANI:N6-6

CT XIO"-'* (Scm*)

1.4134

1.6698

2.3143 3.6643

4.8262

5.2072 6.1836 6.2818 6.5959 7.4670 8.9944 11.639 12.766 13.851

15.830

16.189 16.663

17.932 19.006

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TabIe-4.4. Temperature dependence of DC electrical conductivity of Polyaniline:nyIon-6 composites (Iodine doped).

Temp. ro 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180 185 190

Sample ID->

Temperature 1/K

3.2467x10"^

3.1948x10-^ 3.1446x10-^

3.0959x10-^

3.0487x10-^

3.003x10'^ 2.9585x10"^

2.9154x10-^ 2.8735x10"-'' 2.8328x10-^ 2.7932x10-' 2.7548x10"^ 2.7173x10'^ 2.6808x10-^

2.6455x10'^

2.6109x10'^

2.5773x10-^ 2.5445x10'^

2.5125x10"^ 2.4813x10-^

2.4509x10-^ 2.4213x10"^

2.3923x10"^ 2.3640x10"^ 2.3364x10-^ 2.3094x10"^ 2.2831x10-^ 2.2573x10-^ 2.2321x10"^ 2.2075x10"^ 2.1834x10-^ 2.1598x10-^

PANI:N6-3

(Scm*)

1.7747 1.4485 1.3493 1.2236 1.0884

2.0205

2.6742

3.7884

3.9204

4.2275

4.3778 4.6905 5.1036

5.5337 5.9697 6.6554 13.8733 18.0585 27.5802 41.3460 57.5851

PANI:N6-4

0x10-^ (Scm*)

0.4301 0.5116

0.5744

0.6014

0.6525

0.6926

0.8163 0.8414

0.9738

1.0541

1.1352 1.1770

1.2790 1.5106 1.8809 2.7407 12.3776 22,5707 29.5158

PANI:N6-5

0x10-* (Scm*)

0.3671

0.3676 0.3899

0.5962

0.6805

0.7905 0.9131 1.0930 1.2656

1.4951 1.7074 1.9764

2.2721 2.5764

2.8290 2.8856

3.1028

3.3949 3.6995

4.1821

PANI:N6-6

0x10-* (Scm')

0.4674

0.4746 0.4770

0.4778

0.4795

0.4949 0.5219 0.5465 0.5984 0.6062 0.8731 1.1641 1.3966

1.6626 1.9914 1.9954

2.0589

2.3731 2.4356

5.2388

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Temp (°C)

35

40

45

50

55

60 65

70

75

80

85

90

95

100

105 110

115 120

125

130

Sample ID-^

Temperature (1/K)

3.2467x10"^

3.1948x10-^

3.1446x10"^

3.0959x10"^

3.0487x10-^

3.003x10"^ 2.9585x10-^

2.9154x10"^

2.8735x10-^

2.8328x10"^

2.7932x10-^

2.7548x10-^

2.7173x10-^

2.6808x10"^

2.6455x10'^ 2.6109x10"^

2.5773x10-^

2.5445x10-^

2.5125x10'^

2.4813x10"^

PANI:N6 -1

(Scm-^)

0.42467

0.43411

0.46511

0.48234

0.55028

0.59197

0,61046 0.67362

0.75134

PANI:N6 -2

a x 10^ (Scm^)

3.0177

3.2727

3.5530

4.1792

4.5384

5.0078 5,3295

5.7802

6.2464

6.7157

7.6942

8.3584

9.1482 9.6819

10.2816 10.7576

11.3905

11.7356

11.8554

12.1024

PANI:N6 -3

axlO^ (Scm"')

1.4079

1.4613

1.5188

1.5941

1.6920

1.7070

1.7222

1.7535

1.8027

1.8911

1.9289

1.9350

1.9761

1.9974

PANI:N6 -4

a xlO"* (Scm*)

9.3877

9.7929

10.4709

10.9762

14.1059

15.0828

16.2534

17.3404

18.5832

19.8719

21.1863

22.4996

23.7768

25.0917

26.3038 27.4995

29.2736

29.7535

30.0823

30.2494

PANI:N6 -5

(Scm^)

0.2773

0.2898

0.3130

0.3252

0.3321

0.3618 0.3794

0.4032

0.4154

0.4441

0.4496

0.4730

0.5278

0.5518

0.6173 0.6390

0.7095

0.7333

PANI:N6 -6

a xlO * (Scm^)

1.4933

1.6800

1.7986

2.0677

2.2297

2.3834 2.5465

2.6731

2.7807

2.7968

2.8295

2.8800

2.9683

3.1418

3.3140

3.6934

3.9659

4.0320

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Sample ID

PAN:[:N6-1

PAN:[ :N6-2

PAN[:N6-3

PAN[:N6-4

PANl:N6-5

PAJ^I:N6-6

Activation energy (eV)

HCl doped composites

0.2050

0.1116

0.6218

0.2641

I2 doped composites

0.4097

0.5339

0.2525

0.2193

PoIy(anilineco-p-toluenesulfonicacid)

0.1457

0.1447

0.059

0,1235

0.1021

0.0930

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Temperature

CC)

30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180

(1/K)

3.3003x10'^ 3,2467x10-' 3.1948x10'^ 3.1446x10-' 3.0959x10-' 3.0487x10-' 3.003x10'

2.9585x10-' 2.9154x10'' 2.8735x10"' 2.8328x10-' 2.7932x10-' 2.7548x10-' 2.7173x10-' 2.6808x10-' 2.6455x10-' 2.6109x10-' 2.5773x10-' 2.5445x10"' 2.5125x10-' 2.4813x10"' 2.4509x10"' 2.4213x10"' 2.3923x10"' 2.3640x10"' 2.3364x10"' 2.3094x10"' 2.2831x10-' 2.2573x10-' 2.2321x10-' 2.2075x10-'

HCl doped

CT (Scm'*)

1572.53x10"' 314.49x10-' 116.80x10-' 74.88x10-' 26.65x10-' 14.90x10-' 11.23x10-' 9.19x10-' 8.23x10-' 5.49x10-' 3.91x10-' 2.92x10-' 2.87x10"' 2.76x10"' 2.69x10"' 2.57x10"' 2.34x10"' 2.13x10-' 1.94x10"' 1.81x10"' 1.73x10"' 1.69x10"' 1.62x10"' 1.47x10"' 1.34x10-' 1.23x10"'

Logo

-1.80 -2.50 -2.93 -3.12 -3.57 -3.82 -3.94 -4.03 -4.08 -4.25 -4.40 -4.53 -4.54 -4.55 -4.57 -4,59 -4.63 -4,67 -4,71 -4.74 -4.83 -4.91 -4.97 -5.15 -5.18 -5.21

I2 doped

a (Scm"')

1.79x10"' 1,84x10"' 1,90x10"' 1,97x10"' 2,32x10"' 2,42x10-' 2,77x10"' 3,06x10-' 3,23x10-' 3,63x10-' 4,31x10"' 5,06x10-' 5,54x10"' 5.81x10"' 6.12x10"' 6.84x10"' 7.27x10-' 7.76x10"' 9.05x10"' 12.24x10"' 18,43x10"' 19,39x10"' 21,10x10"' 22.21x10"' 26.43x10"' 29.58x10"' 31.37x10"' 33.02x10"' 35.66x10-' 38.64x10-' 40.21x10"'

Log a

-2.74 -2.73 -2.72 -2.70 -2.63 -2.61 -2.55 -2.51 -2,49 -2,43 -2,36 -2,29 -2.25 -2.23 -2.21 -2.16 -2.13 -2.11 -2.04 -1.91 -1.73 -1.71 -1.67 -1.65 -1.57 -1.52 -1.50 -1.48 -1.44 -1.41 -1.39

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Table-4.8. Concentration dependence of specific conductance (Scm"') of iodine doped phtiialicacidrcurcumin copolymer with different extent of doping in acetone.

Concentration

0.035 0.028

0.0233 0.02

0.0175 0.0155 0.014

0.0127 0.0116 0.0107

0.01 9.33x10-' 8.75x10'^ 8.23x10"^ 7.77x10-' 7.36x10-' 7.00x10-'

Specific conductance (Scm'*)

Sample-1

2.41x10"^ 2.16x10"' 1.69x10' 1.42x10' 1.24x10"' 1.09x10"' 0.96x10"' 0.89x10"' 0.81x10"' 0.72x10"' 0.67x10-' 0.59x10-' 0.52x10"' 0.46x10"' 0.39x10"' 0.33x10"' 0.28x10"'

Sample-2

3.25x10"' 2.78x10"' 2.36x10"' 1.98x10"' 1.76x10"' 1.60x10"' 1.41x10-' 1.27x10"' 1.18x10"' 1.06x10"' 0.97x10-' 0.91x10"' 0.85x10"' 0.79x10"' 0.74x10"' 0.68x10"' 0.61x10"'

Sample-3

3.67x10-' 3.06x10' 2.56x10"' 2.04x10-' 1.74x10"' 1.59x10-' 1.42x10-' 1.30x10-' 1.18x10-' 1.10x10' 10.1x10-' 0.94x10"' 0.87x10-' 0.81x10-' 0.77x10-' 0.72x10-' 0.68x10"'

Sample-1 copolymer (1.4g)+ iodine (0.3g) Sample-2 copolymer (1.4g)+ iodine (0.5g) Sample-3 copolymer (1.4g)+ iodine (0.7g)

99

o

Y OJ CO

^ A A Q. a a E e ~ CO (0

W CO CO

CO

o CO

CM

o CN

O o o

E

c « u c o o

_ o

CO

(V Q. o •o 0)

c

o

(1> 0) o c (0 ir ••-> o o -•-' | s o c o ~ u a> S E o >.

^1 (A ' ^

o "

^ I •o <J = 3 ^ 9. a> "o XJ o c «o I = (0 tc \z SI

•Ss •*-> c x: 0) Q. o c o o

CO CM

i 3

iZ

o o

(UJo/s) aoueisnpuoo ayjoads

Table-4.9. FTIR peak positions (cm"') in PANI:N6 composites (As prepared)

PANI:N6-1

1641

1546

1463

1419

137?

1264

1202

1170

1122

930

PANl:N6-2

1641

1546

1478

1463

1441

1419

1372

1308

1265

1237

1202

1170

112!

1076

977 930 833

PANI:N6-3

1641

1547

1503

1463

1307

1264

1169

821

PANI:N6-4

1641

1544

1503

1479

1463

1307

1264

1202

1168

1122

821

PANi:N6-5

1726

1641

1564

1548

1502

1463 1304

1124

PANI:N6-6

1641

'" 1564 i

1548

1513 j

1503

1463 1 137!

1304

1264

1146 825

i

1

rable-4.10. FTIR peak positions (cm"') in PANI:N6 composites (Dopedwith HCl)

PANI:N6-1

1641

1545

1463

1419

1373

1264

1202

1171

1120 977

PANl:N6-2

1641

1546

1463

1372

1264 1237

1203

1170

1121 976

PAIVI:N6-3

1641

1547

1463

1372

1305 1263

1169

826

PA]NI:N6-4

1641

1547

1463 1302

1264 1169

820

PANI:N6-5

1641

1564

1548 1502

1301 1143

PANl:N6-6

1 1641

1547

1513 1463

1372 1304 J

1263 i 1168

825

101

Table-4.11. FTIR peak positions (cm') in PANI:N6 composites (Doped with I2)

PANI:N6-1

1641 1545 1463 1440 1418 1372 1264 1202 1171 1120

PANl:N6-2

1641 1547 1463 144) 1371 1303 1264 1202 1170 1122

PANI:N6-3

1722 1641 1564 1548 1502 1479 1463 1371 1303 1264 1169

PANI:N6-4

1725 1641 1564 1547 1503 1479 1463 1371 1304 1265 1202 1170 1147 822

PAiM:i\6-5

1755 1726 1711 1641 1565 1548 1537 1502 1480 1462 1452 1371 1302 1265 1124

PANI:N6-6

1755 : 1739 i 1726 i 1711 1658 1641 1 1565 1548 1 1537 ; 1513 1502 : 1481 1463 1452 ; 1371 1303 ; 1145 1

Table-4.12. FTIR peak positions (cm') in PANI:N6 composites [Doped with poly(aniline-co-p-toluinesulfonicacid)j

PANI:N6-1

1723 1641 1548 1478 1463 1371 1302 1264 1202 1170 1122 1033 1012

PANl:N6-2

1725 1641 1548 1502 1463 1371 1303 1264 1203 1170 1122 1034 1011

PANI:N6-3

1722 1641 1565 1548 1503 1463 1306 1263 1167 1123 1010 819

PANl:N<>-4

1726 1641 1564 1548 1512 1502 1463 1305 1264 1147 1011 820

PANl:N6-5

1726 1711 1641 1565 1549 1537 1495 1304 1143

PANI:N6-6

1726 1711 164! 1 1565 1 1554 1 1537 I 1501 1371 1304 : 1144 1 816

102

cm >-i

7:r

1-000 i^ov i(,e>o lijoo 1X00 Soo " I C'V^ <I3VU IfUU IJ.O0 I DOT) i - —

ure-4.24.'JP'xiR spectra of polyaniIine:Nylon-6 composites (Undoped)

103

cm rl

%T

- i WW tgo* t(,co Jt/eo ixbo \ooo goo

FJgsire-4.25. FTIR spectra of poIyaniIine:NyIon-6 composites (Doped with HCl)

104

cm - 1

%T

J6e<> (gov iCoV _ I (i^eo ti-oo looo 2oo

Figure-4.26.,FTIR spectra of polyaninne:Nylon-6 composites (Doped with Iodine)

105

cm -1

%T

XOOD (9O0 I Coo lqe>o itae I t>eo iaa

Figure-4.27.FTIR spectra of polyaniline:Nylon-6 composites (Doped with pol(aniIine-co-p-toluenesuIfonic acid)

106

Table-4.13. FTIR peaks position (cm" ) of polyanilinercurcumin composite and Phthalicacidrcurcumin copolymer.

POLYANILEVErCURCUMIN COMPOSITE

As prepared

1716.00 1655.00

1542 1508 1466 1382 1365 1262 1180 1074 1037 896

HCl doped

1974 1953 1939 1918 1911 1878 1832 1820 1808 1786 1777 1765 1752 1739 1715 1699 189 1669 1658 1638 1583 1572 1560 1538 1530 1511

I2 doped

1978 1937 1919 1679 1574 1565 1554 1537 1512 1484 1451 1290 1238 n i l 1077 1065 1010 974 813

PHTHALICACn) : CUMCUMIN

COPOLYMER

As prepared

3427.04 2957.47 2922.56 2652.43 2524.69 2360.45 1685.74 1585.74 1453.58 1403.55 1281.63 1153,53 1071.65 974.48 905.42 829.91 797.11 739.96 694.01 674.24 604.09 556.77 464.60 424.12

107

cm , -1

I2 doped

7oT

HCl doped

As prepared

iooo goo

Fig ^2^00 tfOD lioo l^OD l>bD

ure-4.29.FTIR spectra of poly aniline: Curcumin composites

108

cm r l

%T

LfOoe '^Soo 2>ooi> 2^00 2000 iroo I oeo Soo

Figure-4 2.7.FTIR spectra of phthalic acidrCurcumin copolymer

109

rabIe-4.14. Stability of DC electrical conductivity of PANI:N6-6 composites (Doped with HCI).

Temperature

(°C)

35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130

(1/K)

3.24x10-^ 3.19x10'^ 3.14x10-^ 3.09x10"^ 3.04x10"^ 3.00x10-^ 2.95x10-^ 2.91x10'^ 2.87x10-^ 2.83x10-^ 2.79x10"^ 2.75x10-^ 2.71x10'^ 2.68x10"^ 2.64x10"^ 2.61x10-^ 2.57x10"^ 2.54x10-^ 2.51x10-^ 2.48x10-^

Cycle-1

0.5139 0.5241 0.6685 0.6870 0.8860 0.9731 1.2257 1.5563 2.2707 6.0223 9.2342 4.3285 2.5650 1.5740 1.3714 1.1141 1.1141 1.1141

Electrical conductivity

Cycle-2

0.9076 1.0095 1.2630 1.3967 1.5921 1.6489 1.6688 1.5740 1.4428 1.2257 0.7467 0.7283 0.8361 1.1992 1.6960 2.1986 2.8268 3.3921 3.4919 3.5977

Cyde-3

0.6427 0.6580 0.7709 0.8893 0.9556 1.0445 1.0793 1.1712 1.2011 1.2658 1.3290 1.4625 1.6044 1.7381 2.1456 2.8857 6.5959 19.7877 24.7346 24.7346

Cycle-4

0.3226 0.4397 0.4628 0.4826 0.5106 0.5421 0.5819 0.6183 0.8244 0.8603 0.8678 0.8755 0.8913 0.9160 0.9333 0.9422 0.9513 1.1095

5 (Scm*)

Cycle-5

0.2150 0.2283 0.2483 0.2710 0.2968 0.3059 0.4421 0.4739 0.6183 0.8022 1.0061 1.1307 6.5959 0,3735 0.3243 0.2082 0.1766

xlO-*

Cycle-6

0.1364 0.1491 0.1578 0.2217 0.2307 0.2545 0.2553 0.2569 0.2595 0.2683 0.3435 0.3584 0.3597 0.3610 0.3664 0.3691 0.4381 0.4397 0.4776 0.5173

Cycle-7

0,1007 0.1062 0.1082 0.1208 0.1595 0.1679 0.1754 0.1839 0.2337 0.2437 0,2547 0,2674 0.2780 0.2881 0.3021 0.3243 0.3946 0.2579 0.3617 0.3964

110

CO

^ i o >. O

1

CM (D O >, o

1

CO <D C) >» O

• *

(D O >.

1

»o (D (> >< o

1

9 (D O >% o

1

r>-1 OJ o >% O

1

CO

IS

CNJ

c '•B o

•o

a o Q

i (0 o a E o o (O

I

<

o

o 3 "O c o o "n o

u "S O Q

c\i

to

i 9

CM

in

i CM

in <9 <9

(ijuo/s) A)iA!)onpuo3 Boi

Tabel-4.16. Stability of DC electrical conductivity of PANI:N6-6 Composites [Doped with poIy(aniIine-co-p-toluenesulphonicacid)].

Temperature

(°C)

35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130

(1/K)

3.24x10-^

3.19x10-^ 3.14x10"^

3.09x10"'

3.04x10-^

3.00x10-^ 2.95x10-^ 2.91x10-^ 2.87x10-^ 2.83x10-'

2.79x10'^ 2.75x10-' 2.71x10"' 2.68x10"'

2.64x10' 2.61x10' 2.57x10"'

2.54x10"' 2.51x10"'

2.48x10-'

Cyclc-1

0.2926

0.3901 0.4005

0.5073

0.5142

0.6256 0.6300 0.7453 0.7506 0.8640 0.8702 0.9861 0.9932 1.1036 1.1630 1.1712 1.1880

1.2688 1.2600

1.2600

Electrical conductivity

Cycle-2

0.2043

0.3128 0.3240

0.3360

0.3516

0.3718

0.3718 0.5169 0.5305 0.6750 0.6935

0.7269 0.7560 0.8042 0.9969 1.0309

1.0673

1.1200 1.7819

1.2837

Cycle-3

0.2534

0.2562 0.3496

0.3621

0.3803

0.4909 0.5040 0.5178 0.6434 0.6574 0.6770

0.8079 0.8204 0.9524 0.9676 0.9754 0.9914

1.1340 1.1435

1.1532

CycIe-4

0.1689

0.2592 0.2668

0.2732

0.3643

0.3687

0.7565 0.4754 0.4846 0.4877 0.5968

0.6213 0.6388 0.7614 0.7669 0.7840 0.9233

0.9376

0.9524 1.0800

CT (Scm')

CycIe-5

0.1976

0.2002

0.2071 0.2144

0.3335

0.3436

0.3543 0.3658 0.4998

0.5082 0.5213 0.6690 0.6810 0.6935 0.8400 0.8558 0.8640

0.8723 1.0275

1.0376

xlO'

Cycle-6

0.2043

0.2085 0.3217 0.3287

0.3409

0.3779

0.5081 0.5258 0.6809 0.6998 0.7198

0.7267 0.8556 0.8556 0.9983 0,9983 0.9983

1.0078 1.1628

1.1741

CycIe-7

0.2399

0.2438

0.2505 0.2591

0.3578

0.3687

0.3803 0.4845 0.4972 0.5107 0.6170 0.6255 0.7400 0.7504 0.8763 0.8892 0.9025

1.0307

1.0465

1.1718

14

g

T —

(D O >.

1

CM 0) O >> o

CO

a> <) >. O

^ <D O >.

O

1

lO

(1> CI >, O

1

«? (D O > N

1

1 ^

(D

<) > o

1 o

CO

CO

oo Csi

CD CNJ

(A O a £ o u to

1

to

z — V

z < Q. «^ o ^ > ^ 3 o c o o "m o 'C • ^

u o o O a 1

^

^ • ^

5 'o (0 u •£ o »-3 tn 0) c 0) 3 o

• J 1

a 1 o o 1

c = u c <-> ( 0 ••-»

5 3 a £ «rf

5 •o ®

CN

^1 CO *—

0) 3

i l

i

i n

CM CM

m CO

id u> in in

en in

<tuo/s) AjiAjionpuoo 6oT

:o>-'» H

D>HO H

Protonated blue pemisranilint

.+2H ^Q=NxoyN Violet pemigraniline base

® +H

H ^ Protonated green cmeraldine

+H 5y?-<Q H

Blue emeraldine base

+H

H ^ LeucoemeraWine (Colouriess)

Chemical structure-4.1. Different forms of poiyaniline and their interconversions.

Chemical structure-4^. Phthalicacid:curcumin copolymer.

116

CHAPTER-5

INCIIISM

The technique employed in the synthesis of polyaniline:nylon-6 composites is a successful modification of that mentioned in the Hteratuie.

The yield of the composites was fairly good.

The electrical properties of the materials were of high quality as almost all the composites showed a great increase in their electrical conductivity from insulator to conductor after doping with hydrochloric acid, iodine and poly(aniline-co-p-toluenesulphonicacid).

Stability of composites in terms of retention of DC electrical conductivity was also fairly good in the severe experimental temperature range, checked for one sample from each doped category.

Polyanilinexurcumin composite also gave conductivity in the range 10"' Scm" but in case of HCl doped material the conductivity decreases with the increase in temperature due to degradation of curcumin or due to volatilization of HCl. Whereas iodine doped composite showed semiconductor properties.

The copolymer of phthalicacidxurcumin was found to be soluble in common organic solvents like acetone, methanol, chloroform etc. Electrical conductivity was measured by dissolving the copolymer and dopant (T) in acetone. The electrical conductivity was observed to be dependent on the concentration of copolymer as well as dopant in the solution.

The com.posites and copolymer so produced showed electrical conductivity in the semiconductor range and the temperature dependence followed Arrhenius equation. TTie activation energies are comparable with similar materials.

The composites and copolymer so produced were characterized by FTIR spectroscopy.

117

APPENDIX-I

Electrical conductivity measurement by 4-in line probe method

In two probe electrical conductivity measurement system we face some general

problems such as rectifying nature of metal-semiconductor contacts, the injection of

minority carriers by one of the current carrying contacts which affects the potential of

other contacts and modulate the conductance of the materials etc. But in case of 4-in

line probe method we overcome this problem and it become the most satisfactory

method to measure the electrical conductivity of semiconductors having variety of

shapes. To use the 4-in line probe method we need to make the following

assumptions-

(i) The electrical conductivity of the material is uniform within the area of

measurements, (ii) If there is minority carrier injection into the material to be tested by

the current carrying electrodes, most of the carriers recombine near the electrodes so

that their effect on the conductivity in negligible, (iii) The surface on which the probes

rest is flat with no surface leakage, (iv) The four probes used for conductivity

measurement must contact the surface at points that lie in a straight line, (v) The

diameter of the contact between the metallic probes and the material should be small

then the distance between the probes, (vi) The surfaces of the material may be either

conducting or non-conducting [(a.) a conducting boundary is one in which the bottom

surface of the material to be tested is of much higher conductivity than that of the

material itself This could be achieved by copper plating on the bottom surface of the

semiconductor slice, (b.) a non-conducting boundary is produced when the bottom

surface of the material to be tested is in contact with an insulator such as

polytetrafluroethyene. ]

The instrument consists of four devices-

1. Four-in line probes

It consists of four individually spring loaded probes, coated with zinc at their tips. The

probes are coUinear and equally spaced at a probe spacing of 2 mm. The zinc coating

and individual spring ensure good electrical contacts with the sample. The probes are

118

mounted in a teflon bush, which ensure good electrical insulation between the probes.

A teflon spacer near the tips is also provided to keep the probes at equal distance. The

whole arrangement is mounted on a suitable stand and leads are provided for current,

voltage and temperature measurement.

2. Voltmeter

A digital micro-voltmeter with the following specifications-

Range- 1 mV, 10 mV, 100 mV, 1 V, 10 V

Resolution- 1 | V

Accuracy- ± 0.25% of reading ± I digit

Impedance- > 10 MQ on 10 V range

Display- S'/z digits, 7 segment, LED (12.5 mm height) with auto polarity and decimal

indication.

Overload indicator- Sing of 1 on the left and blanking of other digits.

3. Low current source

A battery operated low current source with the following specifications-

Current range- 0-100 \x.K and 0-1 mA

Accuracy- ± 0.25% of reading ± 1 digit

Open circuit voltage- 15V minimum

Display- 3'/2 digit LCD display

Power- 3x 9 V battery

4. Oven

A small PID controlled oven for the variation of temperature of the material from

room temperature to about 200°C with the following specifications-

Temperature range- Ambient to 200°C

Resolution-OA°C

Short range stability- ± 0.2°C

Long range stability- ± 0.5°C

Measurement accuracy- ± 0.5°C

Sensor- RTD (A class)

19

Display- SVa digit, 7 segment, LED with auto polarity and decimal indication.

Power- 150 W

Conductivity measurement

The sample is placed on the base plate of the 4-probe arrangement and the

probes were allowed to rest in the middle of the sample. A very gentle pressure is

applied on the probes and then it was tighten in this position so as to avoid piercing of

the probes into the samples. The arrangement was placed in the oven. The current was

passed through the two outer probes and the floating potential across the inner pair of

probes was measured. The oven supply is then switched on, the temperature was

allowed to increase gradually while current, and voltage was recorded with rise in

temperature. The data so generated for the determination of electrical conductivity of

the samples was processed for calculation of electrical conductivity using the

following equation-

a = G7(W/S)/ao 22

where o is the electrical conductivity in Scm'', G7(W/S) is a correction divisor [it is a

function of thickness of the sample as well as probe-spacing and equals to (2SAV)ln2],

W is thickness of the film (cm) and ao= I/2V7tS where I, V and S are current (A),

voltage (V), and probe-spacing (cm) respectively.

120

SPRING LOADED PRODE

FOUR IN LINE DC ELECTRICAL CONDUCTIVITY MEASURING INSTRUMENT

121

CHAPTER!

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123

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