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TRANSCRIPT
New Routes For Metal Protection Combining Conducting Polymers with SAMs
Luísa M. AbrantesCQB, Departamento de Química e Bioquímica
WorkshopElectrochemistry in Historical and
Archaeological Conservation January 11-15, 2010
Leiden
Contents
���� Introduction to Conducting Polymers
Basic aspects: polymerization, doping and conductiv ity
CP as Corrosion protective coatings- Why ?
CP film formation on metal surfaces
Corrosion protection ability of CP coatings
���� Conducting Polymers: A Versatile Route for novel an ti-corrosion coatings
���� Combining Conducting Polymers with Self-assembled M onolayers
Corrosion protection ability of CP coatings
Self-assembled adhesion promoters
Densely packed polymeric assemblies chemisorbed on solid surfaces
Incorporation of metal microparticles in CP matrice s
���� Concluding Remarks
From Plastics to Electronically Conductive Polymer s (ECP)
1960’s
“There can be no such things as Conducting Organic M aterials or Polymers ”
Introduction
19771977Oxidation of PA
� ‘doped ’ PA (conductivity 105 S/m)
A J. Heeger, A G. MacDiarmid and H. Shirakawa
2000 NOBEL Prize for Chemistry
“For the discovery and development of Conductive Pol ymers ”
Conducting Polymers – Most studied systems
Introduction
Conducting electric current ⇔⇔⇔⇔ free movement of electrons
PA
‘Doping ’
Introduction
Electrons removed / introduced
Oxidation with halogen (p-doping):
[CH]n + 3x/2 I2 → [CH]nx+ + xI3
-
Reduction with alkali metal (n-doping):
[CH]n + xNa → [CH]nx- + xNa +
Electrons removed / introduced
Need of “holes” for balloon propagationCharge can migrate along the polymer
Polymerization
Introduction
‘Dopant ’ not bound but ‘ near ’ the polymeric chain
Ionic participation assure the electroneutrality
The formed polymer is electrically charged
Conducting ( doped ) state can be reversibly reduced to the neutral fo rm
Conductivity of most known Conducting Polymers
Introduction
Conducting Polymers as Corrosion Protective Coating s
CP for novel anti-corrosion coatings
Why ?
•••• Reversible oxidation / reduction behaviour
•••• Reduced (neutral) form : semiconductor and hydropho bic
•••• Positive value of redox potential
���� coating gets noble character���� coating gets noble character
•••• Catalytic activity for oxygen reduction and simulta neous ability
to form a passivating oxide layer
•••• Metal dissolution and oxygen reduction processes se paration
���� prevent local pH increase
CP film formation on metal surfaces
CP for novel anti-corrosion coatings
•••• Addition of an oxidant to the solution ( e.g. FeCl 3)
���� suspension of polymer particles or colloids
Oxidative treatment of a monomer solution
•••• Anodic oxidation at the envisaged substrate
����polymer formed as a film on the electrode material
Oxidation potential of most monomers is in the range of metal dissolution
�
Metal dissolution competes with monomer oxidation
CP film formation on metal surfaces
CP for novel anti-corrosion coatings
Polymerization in the presence of passivating agent soxalic acid
p-toluene-sulphonic acid
sodium oxalate
sodium citrate
... /...
Substrate pre-treatment
PolymerSubstrate
PAni , PPy, PTh, PEDOTh, P(Amino -naphtol )
Iron /Steel
... /...
The inter-layer (pseudo-passive) supresses the metal dissolution
without preventing the electropolymerization process
P(Amino -naphtol )
PAni , PPy, PThAluminium
PPyZinc
PPyCopper
PAni , PPyTitanium
PAniNickel
PPyMagnesium
CP for novel anti-corrosion coatings
Electrosynthesis of PPy on Copper
Cyclic voltammogram of a copper electrode A1 : Cu 2O; A2 : Cu(II) species
Chelating agent
precipitated layerdiffusional barrierpartial inhibition
A3, A4 : adsorbed S, S ion oxidation0.1M sodium salicylate ( SS) 0.1M sodium salicylate ( SS) υυυυ=20mV/s (*)
1 M SS + 0.5 M Pyυυυυ=20mV/s (**)
_______________(*) A.C.Cascalheira, L.M. Abrantes, Electrochim. Acta 49 (2004) 5023(**) A.C.Cascalheira, S. Aeiyach, J. Aubard, P-C Lacaze,L.M. Abrantes, Russian J.Electrochem. 40 (2004) 294
In the presence of SS the oxidation of PPyoccurs at ~0.55 V
• before the oxidation of SS species
• after the surface modification
Successful polymerization
0.5 M pyrrole in 1 M sodium salicylate at 0.6 V vs. SCE
80
60
40
20
0
-20-1.0 -0.5 0.5 1.00 1.5
E / V vs. SCE
Polymer growth
I/ µ
A c
m-2
In-situ contact mode AFM
CP for novel anti-corrosion coatings
Electrosynthesis of PPy on Copper
in-situ AFM
globular morphology developinginto the typical “cauliflower”structure with film thickening(5 µµµµm x 5 µµµµm)
_______________A.C.Cascalheira, A.S. Viana, L.M. Abrantes, Electrochim. Acta 53 (2008) 5783
no corrosion observed
PPy / Cu PPy / Pt
CP for novel anti-corrosion coatings
Electrosynthesis of PPy on Copper
Polymer electrochemical behaviour not influenced by the substrate nature
Comportamento redox em SS 1 M; υυυυ =50 mV / s (*)
_______________(*) A.C.Cascalheira, Ph.D. Thesis, Univ. Lisboa (2004) (**) L.M.Santos, J.C. Lacroix, K.I. C. Ching, L.M. Abrantes, P-C Lacaze, J.Electroanal Chem. 587 (2006) 67
10 µµµµm
PPy deposited at 100 mA/cm 2 (600 mC/cm 2) (**)from SS tartrate
Polymer thickness depends on the growth conditions
Typical polarisation curves
CP for novel anti-corrosion coatings
Corrosion protection ability of CP coatings
PPy /Cu Polyaniline / steelPolymer prepared with 25 and 300 mC cm -2 (*)
NaCl 3.5%Coated steel
Polymer prepared from soluble doped PAni (Monsanto) (**)
NaCl 3 %
-0,1
0,0
0,1
0,2
Uncoated CuThin film(Thick film
vs.
SC
E
Ig = 1 mA cm-2
Bare steel
10 -9 10 -8 10 -7 10 -6 10 -5 10-4 10-3 10-2-0,5
-0,4
-0,3
-0,2
E /
V v
s.
I / A
_______________(*) A.C.Cascalheira, L.M. Abrantes, Corrs. Prot. Mater.,23 (2004) 6(**) D.E.Tallman, Y.Pae, G.P. Bierwagen, Corrosion,. 55 (1999) 779
Corrosion potential :shift to more positive values
Oxidation current: accentuated decrease
Anodic peak (CuCl formation): decreasesubstrate isolated from the aggessive anions
Combination of SAMs with CPs
Bifunctional molecules
� � Polymerizable terminal group
Densely packed polymeric assemblies
� head group
appropriate for self-assembly
_______________E. Jaehne et al., Progress in Organic Coatings.,61 (2008) 211
Bifunctional molecules
�������� Surface reaction of the terminal reactive group with further monomers
The introduction of polymerizable terminal groups allows in-situ surface polymerization
Combination of SAMs with CPs
Strongly bond layer
Densely packed polymeric assemblies chemisorbed ont o solid surfaces
Combination of SAMs with CPsModified copper electrodes
i) Adsorption of self-assembled monolayers (SAM) on Co pper
NN N N1 mM
solution
Cu substrates polished with alumina (down to 0.05 µm); washed in ultrasonic bath and transferred to the SAM adsorption solution.Cu
Densely packed polymeric assemblies
S
S
O
O
H
O
O
S SH
O
O
S SH
O
O
S SH
Cu
solution
~ 20 h
pyrrole lipoic acid derivative
(Py )
hexanethiol (C6), Py SAM C6 SAM
S-H
CH3
CuS
CH3
S
CH3
S
CH3
S
CH3
S
CH3
Electrochemical Characteristion of SAM modified cop per electrodes
0.1 M NaOH; 20 mV s-1Bare Copper
0.0
0.4
i / m
A c
m-2
Copper Modified with SAMs
0.0
0.3
0.6
i / m
A c
m-2
Cu / C6 SAM
Cu / Py SAM
Combination of SAMs with CPs
Densely packed polymeric assemblies
IEp red = - 0.460 V; IIEp
red = - 0.955 V C6 SAM : Ep
red = - 1.150 VPy SAM : Ep
red = - 0.980 V
-1.6 -1.2 -0.8 -0.4 0.0 0.4
-1.2
-0.8
-0.4
i / m
A c
m
E / V vs. SCE
I
II
C6 and Py derivative SAMs inhibit the copper oxide peaks
-1.6 -1.2 -0.8 -0.4 0.0
-1.2
-0.9
-0.6
-0.3
i / m
A c
mE / V vs. SCE
reduction peaks: SAMs reductive desorption
Combination of SAMs with CPsii) potentiostatic deposition of polypyrrole thin films onto
the Copper modified with Py SAM
N NN N NN
Pyrrole monomer
Densely packed polymeric assemblies
O
O
S SH
O
O
S SH
O
O
S SH
O
O
S SH
O
O
S SH
Cu
Potentiostatic polymerisation
Cu
0.5 M pyrrole em 1M sodium salicylate; Eg = 0.6 V
1.0
1.5
2.0
i / m
A c
m-2
CuCu / Py SAM
Cu / PPy
Densely packed polymeric assemblies
Combination of SAMs with CPs
0 20 40 600.0
0.5
t /s
Similar growth charges used to deposit Polypyrrole on bare copper (55 mC cm -2) and on
copper modified with Py SAM (57 mC cm -2). AFM images revealed thetypical globular morphologyobtained for polypyrrole films
Cu / Py SAM / PPy
Current transients for the potentiostatic depositio n of PPy
Densely packed polymeric assemblies
Combination of SAMs with CPsiii) Corrosion protection evaluation
-0.16
-0.14
-0.12
-0.10
Cu Cu/ PPy Cu/ SAM Py / PPy
E /
V v
s. S
CE
Open circuit potential
-0.2
-0.1
0.0
0.1
0.2
E /
V v
s. S
CE
Cu Cu/ PPy Cu/ Py SAM / PPy
Polarisation curves 0.5 M NaCl
0 750 1500 2250 3000 3750-0.22
-0.20
-0.18
-0.16
E /
V v
s. S
CE
t / s1E-9 1E-7 1E-5 1E-3 0.1
-0.5
-0.4
-0.3
-0.2
E /
V v
s. S
CE
i / A cm-2
ECA / V Ecorr / V i /(A cm -2) at - 0.075 V
Cu -0.204 -0.268 4.37 x 10 -4
Cu/ PPy -0.149 -0.180 7.02 x 10 -5
Cu/ Py SAM / PPy -0.115 -0.169 4.83 x 10 -5
best protection against Cu dissolution
PPy - PySAM /CuCorrosion protection evaluation (AFM analysis)
PPy / PySAM/Cu
3x3 µµµµm2
after polarisation curves in NaCl 0.5 M
2x2 µµµµm2
after 2 days in NaCl 0.5 M pH 1
3x3 µµµµm2
Densely packed polymeric assemblies
topography (z = 60 nm) Phase ( z = 44 º)
5x5 µµµµm2
z = 500 nm
1.7x1.7 µµµµm2 1.7x1.7 µµµµm2
bare copper after polarisation curves in NaCl 0.5 M : evident corrosion
Typical PPy morphology is obtained after the polari sation curvesPPy coating is still present after two days under h arsh conditions
Granular deposit might arise from corrosion of the underlying copper
5x5 µµµµm2
z = 80 nmCu
2x2 µµµµm 3x3 µµµµm
Incorporation of metal particles into CP films
Transition from active dissolving Fe-Cr alloy to th e passive state possible when the cathodic current ( reduction of oxygen or proton )
exceeds the critical anodic current necessary for t he alloy passivation
Protection of stainless steel (ss)
Acid solutions :
Combining CP with SAMs
considerable overpotentials for ORR and HER on ss
���� Fe-Cr alloys dissolve fairly
Decrease of overpotential in acid solution
���� small additions of Pt or Pd (0.1-0.5%) to Fe-Cr alloys
very efficient but too expensive
Incorporation of metal particles into CP films
The polymeric layer serves as a conducting matrix w hich supports, separates and stabilizes the metal clusters
PPy / Fe
Py electropolymerization from aqueous oxalic acid so lution PPy
Strongly adherent, smooth film
Physical barrier
Shift the potential of the coated metal ����
Lower the kinetics of corrosion
CP films incorporating metal microparticles
to stabilize the corrosion potential in the passive range
Cu2+ + Fe →→→→ Cu + Fe2+
mCu 2+ + 2PPyn+ →→→→ mCu + 2PPy (n+m)+
Cu – PPy / FeCementation process
Physical barrier����
Lower the kinetics of corrosion
Cu particles accelerate reduction of both protons a nd dissolved oxygen
SAMs
Ease adsorptionSelf-organization
Terminal reactive
CP
Work as oxidants New bifunctionalsystems
in -situ surface
Combining CP and SAMs
Concluding Remarks
Terminal reactivegroup
-SH, -S-S-, LA, Phophonic
thiophene, pyrrole
Passivation filmon metals
Steels, Al, Cu
Dopant anion, bi-layers, composites
in -situ surface polymerization
versatile corrosion resistant coatings
Novel anti-corrosion coatings
Acknowledgements
Joana Cabrita
António Cascalheira
Luís Santos
Franz-Peter Montforts
Pierre-Camille Lacaze
Ana Viana
Joana Cabrita
Christoph Eberle
Nina HeidaryFranz-Peter Montforts
Isabel Tissot