seminar report on electro active polymers done by manojkumar mahadevan , india

8/14/2019 Seminar Report on Electro active polymers Done by Manojkumar Mahadevan , India

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Chapter 1

INTRODUCTION

Electroactive polymers, or EAPs, are polymers that exhibit a change in size or shape when

stimulated by an electric field. The most common applications of this type of material are in

actuators and sensors. A typical characteristic property of an EAP is that they will undergo a

large amount of deformation while sustaining large forces.The majority of historic actuators are

made of ceramic piezoelectric materials. hile these materials are able to withstand large forces,

they commonly will only deform a fraction of a percent. !n the late "##$s, it has been

demonstrated that some EAPs can exhibit up to a %&$' strain, which is much more than anyceramic actuator.(") *ne of the most common applications for EAPs is in the field of robotics in

the development of artificial muscles+ thus, an electroactive polymer is often referred to as an

artificial muscle.

Electro active polymers EAP- are actuation materials that are used to drive mechanisms and are

fastly replacing conventional methods. everal investigations are in its way to utilize the

excellent properties of the polymer. These materials are now applied in various fields including

robotics, medicine, defense etc/0and are effective alternatives for conventional sensors and

actuators such as motors, gears, piezoelectric crystals, bearings, screws etc/ 0 These are uni1ue

materials capable of soft actuation under low applied voltages. They have been called by some

researchers 2artificial muscles3 due to their large strain characteristics and electro0mechanical0

chemical muscle0 li4e behavior. They have been shown to be 1uite capable of low temperature

actuation as well as being 1uite durable when compared to other actuators in their class. This

leads to the belief that there is great potential for use in space applications. EAP3s can change all

the paradigm of design and they show great potential as soft robotic actuators, artificial muscles

and dynamic sensors in macro0to0micro size range.

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1.1 History of Electro Active Polymers

The field of EAPs emerged bac4 in "&&$, when ilhelm 56ntgen designed an experiment in

which he tested the effect of an electrical current on the mechanical properties of a rubber band.

(7) The rubber band was fixed at one end and was attached to a mass at the other. !t was then

charged and discharged to study the change in length with electrical current. 8.P. acerdote

followed up on 5oentgen9s experiment by formulating a theory on strain response to an applied

electric field in "#.(7) !t wasn3t until "#7: that the first piezoelectric polymer was discovered

Electret-. Electret was formed by combining carnauba wax, rosin and beeswax, and then cooling

the solution while it is subject to an applied ;< electrical bias. The mixture would then solidify

into a polymeric material that exhibited a piezoelectric effect.

Polymers that respond to environmental conditions other than an applied electrical current have

also been a large part of this area of study. !n "#=#, >atchals4y et al. demonstrated that when

collagen filaments are dipped in acid or al4ali solutions they would respond with a change in

volume.(7) The collagen filaments were found to expand in an acidic solution and contract in an

al4ali solution. Although other stimuli such as p?- have been investigated, due to its ease and

practicality most research has been devoted to developing polymers that respond to electrical

stimuli in order to mimic biological systems.

The next major brea4through in EAPs too4 place in the late "#@$s. !n "#@#, >awai demonstrated

that polyvinylidene fluoride P;B- exhibits a large piezoelectric effect.(7) This spar4ed

research interest in developing other polymers systems that would show a similar effect. !n "#CC,

the first electrically conducting polymers were discovered by ?ide4i hira4awa et al.(%)

hira4awa along with Alan 8ac;iarmid and Alan ?eeger demonstrated that polyacetylene was

electrically conductive, and that by doping it with iodine vapor, they could enhance its

conductivity by & orders of magnitude. Thus the conductance was close to that of a metal. Dy the

late "#&$s a number of other polymers had been shown to exhibit a piezoelectric effect or were

demonstrated to be conductive.

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Chapter 2

ITREATURE RE!IE"

(") !onic polymer metal composites, a subclass of electro0active polymer actuators, offer a

promising approach to the problem of manipulating small objects, such as those found in micro0

electro0mechanical systems 8E8-. hile other technological alternatives exist, such as piezo0

electric devices, each has at least one characteristic impeding its widespread adoption. A new

class of ionic polymer metal composite !P8


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electrodes/ the direct use of aluminum foil and the gold sputtering techni1ue. !t was found that a

cellophane paper exhibits a remar4able bending performance. hen 7 8 m0" excitation

voltage was applied to the paper actuator, more than % mm tip displacement was observed from

the %$ mm long paper beam. This is 1uite a low excitation voltage compared with that of other

EAPs. ;etails of the experiments and results are addressed.

(%) ;ue to their inherited mechano0electric transduction capability, long0life, and effective

operation in both air and water, ionic polymerImetal composites !P8


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(:) hape0memory polymers 8Ps- have been one of the most popular subjects under intensive

investigation in recent years, due to their many novel properties and great potential. These so0

called 8Ps by far surpass shape0memory alloys and shape0memory ceramics in many

properties, e.g., easy manufacture, programming, high shape recovery ratio and low cost, and so

on. ?owever, they have not fully reached their technological potential, largely due to that the

actuation of shape recovery in thermal0responsive 8Ps is normally only driven by external

heat. Thus, electro0activate 8P has been figured out and its significance is increasing in years

to come. This review focuses on the progress of electro0activate 8P composites. pecial

emphases are given on the filler types that affect the conductive properties of these composites.

Then, the mechanisms of electric conduction are addressed.

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Chapter #

T$PE% O& EECTRO ACTI!E PO$'ER%

EAP can have several configurations, but are generally divided in two principal classes/

a- ;ielectric and !onic.

b- ;ielectric EAPs

;ielectric EAPs, are materials in which actuation is caused by electrostatic forces between two

electrodes which s1ueeze the polymer. ;ielectric elastomers are capable of very high strains and

are fundamentally a capacitor that changes its capacitance when a voltage is applied by allowing

the polymer to compress in thic4ness and expand in area due to the electric field. This type of

EAP typically re1uires a large actuation voltage to produce high electric fields hundreds to

thousands of volts-, but very low electrical power consumption. ;ielectric EAPs re1uire no

power to 4eep the actuator at a given position. Examples are electrostrictive polymers and

dielectric elastomers.

&erroelectric Polymers

Berroelectric polymers are a group of crystalline polar polymers that are also ferroelectric,

meaning that they maintain a permanent electric polarization that can be reversed, or switched, in

an external electric field. Berroelectric polymers, such as polyvinylidene fluorideP;B-, are

used in acoustic transducers and electromechanical actuators because of their inherent

piezoelectric response, and as heat sensors because of their inherent pyroelectric response.

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&i()re #.1* %tr)ct)re of Poly +vi,yli-e,e fl)ori-e

Electrostricive Graft Polymers

Figure 3.2: Cartoon of an Electrostricive graft polymer.

Electrostricive graft polymers consist of flexible bac4bone chains with branching side chains.

The side chains on neighboring bac4bone polymers cross lin4 and form crystal units. The

bac4bone and side chain crystal units can then form polarized monomers, which contain atomswith partial charges and generate dipole moments, shown in Bigure %.7. hen an electrical field

is applied, a force is applied to each partial charge and causes rotation of the whole polymer unit.

This rotation causes Electrostricive strain and deformation of the polymer

8
http://en.wikipedia.org/wiki/File:Electrostrictive_Graft_PolymerII.PNG


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Liquid Crystalline Polymers

8ain0chain li1uid crystalline polymers havemesogenicgroups lin4ed to each other by a flexiblespacer. The mesogens within a bac4bone form the mesophase structure causing the polymer

itself to adopt a conformation compatible with the structure of the mesophase. The direct

coupling of the li1uid crystalline order with the polymer conformation has given main0chainli1uid crystalline elastomers a large amount of interest. The synthesis of highly oriented

elastomers leads to have a large strain thermal actuation along the polymer chain direction with

temperature variation resulting in uni1ue mechanical properties and potential applications asmechanical actuators.

Io,ic EAPs

!onicEAPs, in which actuation is caused by the displacement of ions inside the polymer. *nly a

few volts are needed for actuation, but the ionic flow implies a higher electrical power needed foractuation, and energy is needed to 4eep the actuator at a given position. Examples of ionic EAP

are conductive polymers,ionic polymer0metal composites!P8


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application of a large electric field the viscosity of the suspension increases. Potential

applications of these fluids include shoc4 absorbers, engine mounts and acoustic dampers.

Ionic polymer-metal composite

!onic polymer0metal composites consist of a thin ionomeric membrane with noble metal

electrodes plated on its surface. !t also has cations to balance the charge of the anions

fixed to the polymer bac4bone. They are very active actuatorsthat show very high

deformation at low applied voltage and show low impedance. !onic polymer0metal

composites wor4 through electrostatic attraction between the cationic counter ions and

the cathode of the applied electric field, a schematic representation is shown in Bigure

%.%. These types of polymers show the greatest promise for bio0mimetic uses as

collagen fibers are essentially composed of natural charged ionic polymers. afion and

Blemion are commonly used ionic polymer metal composites.

Stimuli-responsive gels

timuli0responsive gels hydrogels, when the swelling agent is an a1ueous solution- are a special

4ind of swellable polymer networ4s with volume phase transition behavior. These materialschange reversibly their volume, optical, mechanical and other properties by very small

alterations of certain physical e.g. electric field, light, temperature- or chemical concentrations-

stimuli. The volume change of these materials occurs by swellingOshrin4ing and is diffusion0based. els provide the biggest change in volume of solid0state materials.


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Chapter

'ICRO%TRUCTURE AND CO'PO%ITION

The bending actuator is composed mainly of perflourinated ion exchange membrane metallic

composite bac4bone called ionic polymer metallic composite or !P8< $."&Qm-. !P8< have

commercial name afionR. The ionomer bac4ground or matrix is coated on both sides with

metallic electrodes made of noble metals such as Pt, Au or PtOAu :0"$Qm-. !t is then neutralized

with a certain amount of counter0ions such as monovalent cations of al4ali metals such as Si,

a, >and 5b. A finishing layer of gold is provided to increase surface conductivity. !t is then

fully solvated. The most common solvent used is water but we can also use organic solvents li4e

Ethylene glycol or lycerol. An !P8< has to be 4ept moist continuously for long wor4ing =months- and it is done by providing a polysilicon coating.

The preparation of ionic polymer metallic composites !P8


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the polymer by a chemical reduction means. The metallic platinum particles are not homogeneously

formed across the membrane but concentrate predominantly near the interface boundaries. !t has been

experimentally observed that the platinum particulate layer is buried microns deep typically "I7$ Qm-

within the !P8< surface and is highly dispersed.

The primary reaction for platinum composites is/

SiD?= =(Pt(?%)=)7 &*?0UUV =Pt "@?% SiD*7 @?7*

&i()re .1* I,itial Compositi,( Process

.2 %)rface Electro-i,( process

!n the subse1uent surface electroding process, multiple reducing agents are introduced under optimized

concentrations- to carry out the reducing reaction similar to previous e1uation in addition to the initial

platinum layer formed by the initial compositing process. The roughened surface disappears. Platinum

will deposit predominately on top of initial Pt layer. *ther metals which are also successfully used

include palladium, silver, gold, carbon, graphite etc/ 0 After the upper electrode material is deposited and

allowed to air dry, the glass slide is placed in an oven and annealed at C$$$

< for =:minutes. The siliconewell is filled with deionized water for %$ minutes to saturate the !P8


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&i()re .2* %)rface Electro-i,( Process

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Chapter 3

'ECHANI%' &OR EECTRICA ACTUATION

The electrical0chemical0mechanical response of the !P8


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:.1 &actors Affecti,( Act)atio,

hen a voltage is applied the !P8 and 5b. The properties of the bare

ionomer as well as that of !P8< change with the cation type for the same membrane. !t has

been shown that using Si as cationic base we can get greater displacement and force density per

volt.

Hy-ratio,

The speed and magnitude of the actuation towards the anode depends on the type of solvent. The

actuation towards the anode is relatively slow with ethylene glycol comparing to water, and it is

comparatively much slower with glycerol than with water or ethylene glycol as solvents.

&re4)e,cy

!ts fre1uency dependence shows that as fre1uency increases the beam displacement decreases.

?owever, it must be realized that, at low fre1uencies $."I" ?z-, the effective elastic modulus of

the !P8< cantilever strip under an imposed voltage is also rather small. *n the other hand, at

high fre1uencies :I7$ ?z- such moduli are larger and displacements are smaller. This is due to

the fact that at low fre1uencies water and hydrated ions have time to gush out of the surface

electrodes while at high fre1uencies they are rather contained inside the polymer.

Pote,tial

The deflection increases as voltage is increased and reaches saturation as the voltage rises. Hnder

an A< voltage, the film undergoes swinging movement and the displacement level depends not

only on the voltage magnitude but also on the fre1uency. enerally, activation at lower

fre1uencies down to $." or $.$" ?z- induces higher displacement and it reaches saturation as the

voltage increases.

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Temperat)re

5ecent tests of the performance of the ionomers at low temperatures showed that while the

response decreases with temperature, a sizeable displacement was still observed at the

temperature of 0"=$o


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Chapter 5

CHARACTERI6ATION

hile there are many different ways electro active polymers can be characterized, only three will

be addressed here/ stress0strain curve, dynamic mechanical thermal analysis, and dielectric

thermal analysis.

%tress/%trai, C)rve

&i()re 5.1* The ),stresse- polymer spo,ta,eo)sly forms a fol-e- str)ct)re7 )po,

applicatio, of a stress the polymer re(ai,s its ori(i,al le,(th.

tress strain curves provide information about the polymer3s mechanical properties such as the

brittleness, elasticity and yield strength of the polymer. This is done by providing a force to the

polymer at a uniform rate and measuring the deformation that results. An example of this

deformation is shown in Bigure @.". This techni1ue is useful for determining the type of material

brittle, tough, etc.-, but it is a destructive techni1ue as the stress is increased until the polymer

fractures.

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http://en.wikipedia.org/wiki/File:LCpolymersII.pnghttp://en.wikipedia.org/wiki/File:LCpolymersII.png


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Dy,amic mecha,ical thermal a,alysis +D'TA

Doth dynamic mechanical analysis is a non0destructive techni1ue that is useful in understanding

the mechanism of deformation at a molecular level. !n ;8TA a sinusoidal stress is applied to the

polymer, and based on the polymer3s deformation the elastic modulusand damping

characteristics are obtained assuming the polymer is a damped harmonic oscillator-. Elastic

materials ta4e the mechanical energy of the stress and convert it into potential energy which can

later be recovered. An ideal spring will use all the potential energy to regain its original shape

no dampening-, while a li1uid will use all the potential energy to flow, never returning to its

original position or shape high dampening-. A viscoelastic polymer will exhibit a combination

of both types of behavior.

Dielectric thermal a,alysis +DETA

;ETA is similar to ;8TA, but instead of an alternating mechanical force an alternating electric

field is applied. The applied field can lead to polarization of the sample, and if the polymer

contains groups that have permanent dipoles as in Bigure ".7-, they will align with the electrical

field. Thepermittivitycan be measured from the change in amplitude and resolved into dielectric

storage and loss components. The electric displacement fieldcan also be measured by following

the current. *nce the field is removed, the dipoles will relax bac4 into a random orientation.

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http://en.wikipedia.org/wiki/Elastic_modulushttp://en.wikipedia.org/wiki/Elastic_modulushttp://en.wikipedia.org/wiki/Damped_harmonic_oscillatorhttp://en.wikipedia.org/wiki/Permittivityhttp://en.wikipedia.org/wiki/Permittivityhttp://en.wikipedia.org/wiki/Electric_displacement_fieldhttp://en.wikipedia.org/wiki/Elastic_modulushttp://en.wikipedia.org/wiki/Damped_harmonic_oscillatorhttp://en.wikipedia.org/wiki/Permittivityhttp://en.wikipedia.org/wiki/Electric_displacement_field


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Chapter 8

APPICATION% O& EECTRO ACTI!E PO$'ER%

&i()re 8.1* Cartoo, -rai,( of a, arm co,trolle- 0y EAPs. "he, a volta(e is applie-

+0l)e m)scles the polymer e9pa,-s. "he, the volta(e is remove- +re- m)scles the

polymer ret)r,s to its ori(i,al state.

EAP materials can be easily manufactured into various shapes due to the ease in processing

many polymeric materials, ma4ing them very versatile materials. *ne potential application for

EAPs is that they can potentially be integrated into micro electro mechanical systems8E8- toproduce smart actuators.

Artificial m)scles

As the most prospective practical research direction, EAPs have been utilized in artificial

muscles. Their ability to emulate the operation of biological muscles with high fracture

toughness, large actuation strain and inherent vibration damping draw the attention of scientists

in this field

Tactile -isplays

!n recent years, Welectro active polymers for refreshable DrailledisplaysX(77)has emerged to aid

the visually impaired in fast reading and computer assisted communication. This concept is

19
http://en.wikipedia.org/wiki/Microelectromechanical_systemshttp://en.wikipedia.org/wiki/Microelectromechanical_systemshttp://en.wikipedia.org/wiki/Fracture_toughnesshttp://en.wikipedia.org/wiki/Fracture_toughnesshttp://en.wikipedia.org/wiki/Braillehttp://en.wikipedia.org/wiki/Electroactive_polymers#cite_note-Electroactive_polymers_for_refreshable_Braille_displays-22http://en.wikipedia.org/wiki/File:Artificial_Muscle.pnghttp://en.wikipedia.org/wiki/File:Artificial_Muscle.pnghttp://en.wikipedia.org/wiki/Microelectromechanical_systemshttp://en.wikipedia.org/wiki/Fracture_toughnesshttp://en.wikipedia.org/wiki/Fracture_toughnesshttp://en.wikipedia.org/wiki/Braillehttp://en.wikipedia.org/wiki/Electroactive_polymers#cite_note-Electroactive_polymers_for_refreshable_Braille_displays-22


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based on using an EAP actuator configured in an array form. 5ows of electrodeson one side of

an EAP film and columns on the other activate individual elements in the array. Each element is

mounted with a Draille dot and is lowered by applying a voltage across the thic4ness of the

selected element, causing local thic4ness reduction. Hnder computer control, dots would be

activated to create tactile patterns of highs and lows representing the information to be read.

&i()re 8.2* Hi(h resol)tio, tactile -isplay co,sisti,( of 7#2: +5:982 act)ator pi9els 0ase-

o, stim)li/respo,sive hy-ro(els. The i,te(ratio, -e,sity of the -evice is 2;8 compo,e,ts

per cm


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types of micropumps are 4nown, a diffusion micropump and a displacement micropump.

8icrovalves based on stimuli0responsive hydrogels show some advantageous properties such as

particle tolerance, no lea4age and outstanding pressure resistance. Desides these microfluidic

standard components the hydrogel platform provides also chemical sensors .and a novel class of

microfluidic components, the chemical transistors also referred as chemostat valves-. These

devices regulate a li1uid flow if a threshold concentration of certain chemical is reached.


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Chapter =

AD!ANTA>E% ? DI%AD!ANTA>E%

=.1 AD!ANTA>E%

oft and flexible, hence find wide application in bio0medical field

EAP3s can be mass produced. ?ence it results in low cost.

EAP3s can be easily fabricated in various shapes.

!nherent vibration damping.

Sighter compared to other actuators and sensors.

5esponse speed is significantly higher.

uperior fatigue characteristics

Sarge actuation strains


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=.2 DI%AD!ANTA>E%

o effective and robust EAP material is currently commercially available.

election of suitable and satisfying materials poses a problem as new and new materials emerge.

A compromise between stress and strain needed

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Chapter ;

CONCU%ION

mart materials such as EAP3s are the foundation of current state0of0the0art devices to convert

energy from chemical or electrical into mechanical energy to perform useful wor4. !n the field of

sensing, these devices can provide an efficient way of converting mechanical energy into

electrical or chemical forms. This seminar had summarized efforts on a number of potential

applications of ionic polymerI metal composite that have proven to be a viable alternative to

conventional means.

Electroactive polymers have emerged with great potential enabling the development of uni1ue

biomimetic devices. As artificial muscles, EAP actuators are offering capabilities that are

currently considered science fiction. ;eveloping such actuators is re1uiring development on all

fronts of the field infrastructure. Enhancement of the performance of EAP will re1uire

advancement in related computational chemistry models, comprehensive material science,

electro0mechanics analytical tools, and improved material processing techni1ues.

8a4ing robots that are actuated by EAP, as artificial muscles that are controlled by artificial

intelligence would create a new science and technology realities. hile such capabilities are

expected to significantly change future robots, significant research and development effort is

needed to develop robust and effective EAP0based actuators.

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Chapter 1:

RE&ERENCE

(") 5onald Sumia+ 8ohsen hahinpoor+ 8icrogripper design using electroactive polymers. Proc.

P!E %@@#, mart tructures and 8aterials "###/ Electroactive Polymer Actuators and ;evices,

%77 8ay 7&, "###-+ doi/"$."""CO"7.%=#@.

(7) Gaehwan >im and Fung D eo 7$$7 mart 8ater. truct. "" %::. doi/"$."$&&O$#@=0

"C7@O""O%O%$:. 5eceived "% ovember 7$$", in final form 7# 8arch 7$$7. Published "@ 8ay

7$$7.

(%) 5 Tiwari and > G >im 7$"% mart 8ater. truct. 77 $":$"C. doi/"$."$&&O$#@=0

"C7@O77O"O$":$"C5eceived 7C Guly 7$"7, in final form 7$ ovember 7$"7. Published "C

;ecember 7$"7. Y 7$"% !*P Publishing Std.

(=) Gaehwan >im et al 7$$@ mart 8ater. truct. ": C"#. doi/"$."$&&O$#@=0"C7@O":O%O$$C

5eceived "7 8ay 7$$:, in final form "C Bebruary 7$$@. Published : April 7$$@.

!*P Publishing Std

(:) 5eview of electro0active shape0memory polymer composite *riginal 5esearch Article


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seminar report on electro active polymers done by manojkumar mahadevan , india

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