Electropolymerization 04.12.16

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Protection of Metallic Substrates through
Electropolymerization
Dr. M.G. Sethuraman Professor and Director,
IQAC Department of Chemistry Gandhigram Rural
Institute DU Gandhigram 624 302 Dindigul,
Tamil Nadu, India mgsethu_at_rediffmail.com
International Conference on Material Sciences
(SCICON' 16), December, 19-21, 2016
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Need for Surface Protection

• Surfaces of all materials are corrosion-prone due
  to Climatic conditions Chemical factors
• Destruction of materials leads to economy losses
• Direct Indirect losses due to corrosion amounts
  to 13 billions per year

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Need for Surface Protection

• Prime concern is Conservation of Materials
• Worlds supply of materials is limited
• wastage / loss of materials leads to loss of
  
• energy, cost escalation etc.,
• Surface coating is an important strategy to
  protect materials which are prone to decay

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Impacts of Corrosion
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Copper An Engineering Material

• Copper has been commonly used in a wide range of
  applications in heat conductors, heat exchangers
  because of its excellent thermal conductivity and
  mechanical workability.
• Copper generally shows resistant against
  atmospheric corrosion and other forms of
  corrosion.
• However, copper becomes very susceptible to
  corrosion in a significant rate in media that
  contain chloride ions.

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Corrosion Protection Methods

• Barrier Protection

• Provided by a protective coating that acts as a
  barrier between corrosive elements and the metal
  substrate.

• Cathodic Protection

• Employs protecting one metal by connecting it to
  another metal that is more anodic, according to
  the galvanic series.

• Corrosion Resistant Materials

• Materials inherently resistant to corrosion in
  certain environments.

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ElectropoIymerization

• It is a polymerisation of organic molecules in
  the presence of an electrical current.
• It is a relatively new technique involving
  aspects of electrochemical engineering, polymer
  science, organic chemistry and coating/plating
  technology.

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ElectropoIymerization

• Prevention of corrosion in copper has attracted
  many Researchers and many strategies have been
  developed to protect copper.
• Among the available methods, electropolymerization
  techniques have become prominent nowadays due to
  its simplicity and wide range of applications.

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Protection through Electropolymerization

• Electropolymerization of an organic compounds
  (usually the heterocyclic compounds) under the
  influence of current.
• Electrodeposition of polymeric films at the
  surface of an electrode has opened up a new field
  at the convergence between two rich domains

• Electrochemistry of modified electrode
• Conjugated systems

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General Aspects of Electropolymerization

• Simple process
• Doesnt require any toxic solvent
• Films thickness can be controlled
• Different morphology can be produced by varying
  the scan rate
• It is enough to impose a sufficiently positive
  potential on a metallic electrode.
• By passing of an anodic current through the
  solution of monomer, film of the corresponding
  polymer progressively grows at the electrode
  surface.

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Factors Affecting Electropolymerization

• Solvent
• Electrolyte
• Bath composition and temperature
• pH
• Monomer concentration
• Hydrodynamic conditions (e.g., stirring or its
  absence)
• Pretreatment of its surface
• Electrode surface area
• Shape of the working electrode
• Current density

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Conjugated Polyheterocycles
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Electrodeposition can be done by any of the
following methods
Cyclic Voltammetry

• The working electrode potential is ramped
  linearly versus time.
• These cycles of ramps in potential may be
  repeated as many times as needed.
• The current at the working electrode is plotted
  versus the applied voltage

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Cont
Chronoamperometry

• Potential of the working electrode is stepped and
  the resulting current from faradaic processes
  occurring at the electrode is monitored as a
  function of time.
• The current density at the working electrode is
  plotted versus time.

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Cont
Chronopotentiometry

• The rate of change of potential at an electrode
  is measured at constant current.
• The working electrode potential is plotted
  against time.

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Work done in our lab...
Electrosynthesis of poly-3-amino-1,2,4-triazole/Ti
O2 (3-ATA/TiO2) on copper
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Electropolymerization of 3-amino-1,2,4-triazole
(3-ATA)

• Monomer Concentration - 0.1 M
• Electrolyte - 0.1M Methanol/NaOH
• Scanning potential - ? 0.2 to 1.6 V vs SCE
• Scan rate - 30 mV/s

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CV of 3-ATA on Cu in MeOH-NaOH
Addition of TiO2 increases the peak current
values suggesting the increase of rate of
polymerization
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Schematic representation of electropolymerization
of 3-ATA
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XRD pattern of (a) p-3-ATA (b) p-3-ATA/TiO2
FT-IR Studies

• XRD pattern of p-3-ATA showed a peak at 25o.
  This could be due to the polymer.
• The 2? values at 37o, 47o and 55o showed the
  presence of Ti in the polymeric matrix and these
  values proved that the crystalline behavior of
  TiO2 particles was not affected during
  electropolymerization.

• For bare TiO2, the strong absorption at 686 cm-1
  could be obtained due to Ti-O stretching .
• This band is weak in p-3-ATATiO2 composites due
  to the interaction of polymer with TiO2

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• The incorporation of TiO2 particles into the
  polymeric matrix was also confirmed by EDX
  analysis.
• The intense peak at 0.40 and 4.5 keV confirms the
  presence of Ti.

• SEM Suggests the incorporation of TiO2 particles
  in the polymeric matrix.
• The average particle size of TiO2 is 0.67 µm.

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Nyquist plots
Polarization plots
Materials Rct (O cm-2 ) IE () Icorr (µA cm-2) IE ()
Bare 1043 --- 97.94 -
0.1 M 3-ATA 5051 95.3 18.4 81.2
0.1 M 3-ATA 10-3 M TiO2 11549 98.8 0.982 98.9
Thus, the study revealed that the incorporation
of TiO2 at lower concentration decreases the
porosity of the polymer and significantly
increases the inhibition efficiency
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Work done in our lab...
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Electropolymerization of 4-methyl-3-mercapto-1,2,4
-triazole (MMTA)

• Monomer Concentration - 0.1 M
• Electrolyte - 0.5M Methanol/NaOH
• Scanning potential - 0 to 1.7 V vs SCE
• Scan rate - 10 mV/s

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CV of poly-MMTA on Cu
FT-IR spectrum
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XRD pattern of poly-MMTA/TiO2
The 2? values at 35, 55, 60, 63 and 70 indicated
the presence of TiO2 in the polymeric matrix. It
also confirmed the crystalline nature of the
incorporated TiO2.
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Corrosion Inhibition Studies of poly-MMTA/TiO2
Bare Cu
p-MMTA/TiO2/Cu
p-MMTA/TiO2/Cu
Bare Cu
Materials Rct (O cm-2 ) IE () icorr (µA cm-2) IE ()
Bare/Cu 1081 --- 70.12 ---
p-MMTA/Cu 2450 55.4 33.12 52.7
p- MMTA/TiO2/Cu 5201 79.1 15.62 77.7
The increase in Rct values and decrease in icorr
values suggested the higher IE of p-MMTA/TiO2
composite on copper
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Electrochemical synthesis of poly-3-amino-5-mercap
to-1,2,4-triazole (AMTA) on copper and its
protective effect in 3.5 NaCl medium (Res. Chem.
Intermed.)
M. G. Sethuraman et al. Res. Chem. Intermed., 41
(2015) 8041-8055
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Electropolymerization of 3-amino-5-mercapto-1,2,4-
triazole (AMTA)

• Monomer Concentration - 0.1 M
• Electrolyte - 0.5M Methanol/NaOH
• Scanning potential - ? 0.7 to 1.2 V vs SCE
• Scan rate - 10 mV/s

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CV of AMTA
Schematic representation
As the cycle increases, anodic peak current
decreases, suggesting the formation of polymer
film at the electrode surface
Schematic representation of electropolymerization
of AMTA on Cu
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FT-IR spectra of (a) AMTA and (b) p-AMTA film
The disappearance of S-H stretching for
p-AMTA suggested the formation Cu-S linkage.
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Effect of scan rate on electropolymerization of
AMTA
The anodic current density increases with the
increase of scan rate suggested the
polymerization process is diffusion controlled in
nature.
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Effect of Various Oxides on Corrosion Protection
Electrodes icorr IE
(µAcm-2) () A 39.87
-- B 13.63 65.8
C 11.73 70.5 D
7.02 82.3 E 4.97 87.5
F 3.14 92.1

• From the above results, it is clear that the
  incorporation on nnao TiO2 into polymeric matrix
  enhanced the protection efficiency.
• This is because, TiO2 being a metal oxide
  additive in the composite, could give better
  dispersion of the particles and also enhance the
  barrier properties of the coatings.

A Bare Cu B poly-AMTA-Cu C
poly-AMTA-La2O3-Cu D poly- AMTA-CeO2-Cu E
poly-AMTA-TiO2-Cu F poly-AMTA-nano TiO2-Cu
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Evaluation of Corrosion Protection of
Poly-4-amino-1,2,4-triazole and Its Composites
We have studied the effect of various inorganic
oxides (La2O3, CeO2, TiO2 and nano TiO2) on the
electropolymerization of 4-amino-1,2,4-triazole
(4-ATA).
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EIS Studies

• Nano TiO2 incorporated composite coatings shows
  higher Rct value compared to other inorganic
  oxides.

Nyquist plots for (a) bare (b) poly-4-ATA (c)
poly-4-ATA-La2O3 (d) poly-4-ATA-CeO2 (e)
poly-4-ATA-TiO2 and (f) poly-4-ATA-nano TiO2
copper electrode in 3.5 NaCl
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EIS Studies
Electrodes Rct (?.cm2) IE ()
Bare Cu 1184 --
poly-4-ATA 3508 56.2
poly-4-ATA-La2O3 4450 73.3
poly-4-ATA-CeO2 5673 79.1
poly-4-ATA-TiO2 9893 88.0
poly-4-ATA-nano TiO2 12435 90.4

• Addition of inorganic oxide particles have
  increased the Rct values which in turn increased
  the inhibition efficiency (IE).
• Nano TiO2 composite coatings could reduce the
  porosity of the coatings to a larger extent
  thereby increasing the IE.

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Polarization Studies
From the polarization curves, it is clear that
the addition of nano TiO2 particles into
polymeric matrix decreased the corrosion current
values (icorr) vales.
Potentiodynamic polarization curves for (a) bare
(b) poly-4-ATA (c) poly-4-ATA-La2O3 (d)
poly-4-ATA-CeO2 (e) poly-4-ATA-TiO2 and (f)
poly-4-ATA-nano TiO2 copper electrode in 3.5
NaCl
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Polarization Studies
Electrodes icorr (µAcm-2) IE ()
Bare Cu 71.24 --
poly-4-ATA 39.07 45.1
poly-4-ATA-La2O3 12.52 72.4
poly-4-ATA-CeO2 3.03 78.7
poly-4-ATA-TiO2 2.15 86.9
poly-4-ATA-nano TiO2 0.98 92.6

• The decrease in icorr value suggested the
  prevention of attack of corrosive chloride ions
  onto electrode surface.
• Nano TiO2 composite coatings showed higher IE.

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Reason for the higher IE of Composites

• Higher corrosion protection performance of the
  composites could be due to the filling-up of
  oxide particles in the pores/defects of the
  coatings.
• The use of inorganic oxide particles reduced the
  porosity and defects in the coatings thereby
  hindering the diffusion of corrosive ions onto
  the electrode surface.

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Reason for the higher IE of Composites

• Among the investigated oxides, nano TiO2
  incorporated composite coatings showed greater
  corrosion resistance property.
• This is because, TiO2 being a metal oxide
  additive in the composite, could give better
  dispersion of the particles and also enhance the
  barrier properties of the coatings.

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Reason for the higher IE of Composites

• Another plausible reason for the enhanced
  protection ability is polymer being the p-type
  offers large barrier for electron transport onto
  electrode surface, while TiO2 being n-type causes
  an obstruction against hole transport across the
  interface in the polymeric composites.
• The nano-sized particles could be easily
  impregnated into pores of the polymeric matrix
  and thus reduced porosity which could enhance the
  protection performance.

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Plausible schematic representation of protection
mechanism
The pores/defects of the coatings are filled by
the inorganic oxides thereby prevents the
diffusion of corrosive ions onto the electrode
surface
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Applications of Electropolymerization

• Electro catalysis
• Sensors
• Biosensors
• Energy storage ( batteries and supercapacitors)
• Anticorrosion
• Semiconductors
• Electrochromism

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Olny post by Maruthupandi
M Indian-TN-MDU