452
12 Localized or Spatially Selective Electrodeposition Methods
Hence, the source of the monomer is the organic phase while the absorbent
of the protons produced is the aqueous phase. In addition to the above reaction,
since the polymer is formed in an oxidative route, the polymer chain itself is also
oxidized, leading to a charged polymer chain for which the aqueous electrolyte
solution provides the counterions:
H−(EDOT) n −H(ITIES) + kAn
−
(aq)
H−(EDOT) n −H
k+ · An
−
k (ITIES) + ke
(12.12)
where the maximum of the n/k ratio is around 2…4 for various types of polymers.
The anion doping during the oxidation also makes the interfacial zone preferred
for the polymer formation site. The decrease in the hydration free energy of the
anion An
– in the aqueous phase promotes the ingress of this anion into either the
interfacial “mixed” solution layer or the polymer film being formed. Hence, the
decrease in the hydration free energy of the counterion as well as the decrease its
concentration favours the lateral growth of the self-standing polymer film as opposed
to its thickening.
The two basic approaches of the D3PIE reaction are similar to that of conventional
systems; i.e., either constant-potential polymerization (coupled with chronoamperometric record) or cyclic voltammetry is used. For the constant-potential polymerization, current increases with time in a manner defined by the experimental conditions.
For PEDOT formation by D3PIE, a nearly time-proportional surface area increment
was reported [64], while the diameter of the film showed a linear increase rate for
polypyrrole growth [63], which obviously means a quadratic surface area increment
with time. The determining factors of the growth mode are yet unclear. However, the
indication of the identical quality of the film along its diameter is shown by the fact
that the mass vs. polymerization charge functions are linear for the constant-potential
growth [63].
For the D3PIE films prepared with cyclic voltammetry, the current change during
the cycles may be anomalous in the sense that it is larger during the negative-going
sweep that in the preceding positive-going sweep (anomalous hysteresis [63–65]).
This is because the growth rate along the perimeter (with positive current contribution) is large enough for compensating the current originating from the redox and
capacitive properties of the film (that have negative current contribution). The anomalous hysteresis becomes more pronounced if the electrolyte(aq) vs. monomer(o)
concentration ratio increases [63].
The morphology of D3PIE-prepared films varies with the preparation method.
If CV is used, the film shows a tree-ring pattern due to the variation of the polymerization conditions with time [65], but constant-potential polymerization leads to
a laterally homogeneous structure [65, 90]. Regardless of the preparation method,
the morphology difference between the sides of the films is the same; moreover, it
shows the same trend as that was established for metal films. Namely, the film side
right at the ITIES is rather smooth, but the growing plane contacting the solution that
contains the precursor material is porous [65, 90]. The growing face of the polymer
12 Localized or Spatially Selective Electrodeposition Methods
Hence, the source of the monomer is the organic phase while the absorbent
of the protons produced is the aqueous phase. In addition to the above reaction,
since the polymer is formed in an oxidative route, the polymer chain itself is also
oxidized, leading to a charged polymer chain for which the aqueous electrolyte
solution provides the counterions:
H−(EDOT) n −H(ITIES) + kAn
−
(aq)
H−(EDOT) n −H
k+ · An
−
k (ITIES) + ke
(12.12)
where the maximum of the n/k ratio is around 2…4 for various types of polymers.
The anion doping during the oxidation also makes the interfacial zone preferred
for the polymer formation site. The decrease in the hydration free energy of the
anion An
– in the aqueous phase promotes the ingress of this anion into either the
interfacial “mixed” solution layer or the polymer film being formed. Hence, the
decrease in the hydration free energy of the counterion as well as the decrease its
concentration favours the lateral growth of the self-standing polymer film as opposed
to its thickening.
The two basic approaches of the D3PIE reaction are similar to that of conventional
systems; i.e., either constant-potential polymerization (coupled with chronoamperometric record) or cyclic voltammetry is used. For the constant-potential polymerization, current increases with time in a manner defined by the experimental conditions.
For PEDOT formation by D3PIE, a nearly time-proportional surface area increment
was reported [64], while the diameter of the film showed a linear increase rate for
polypyrrole growth [63], which obviously means a quadratic surface area increment
with time. The determining factors of the growth mode are yet unclear. However, the
indication of the identical quality of the film along its diameter is shown by the fact
that the mass vs. polymerization charge functions are linear for the constant-potential
growth [63].
For the D3PIE films prepared with cyclic voltammetry, the current change during
the cycles may be anomalous in the sense that it is larger during the negative-going
sweep that in the preceding positive-going sweep (anomalous hysteresis [63–65]).
This is because the growth rate along the perimeter (with positive current contribution) is large enough for compensating the current originating from the redox and
capacitive properties of the film (that have negative current contribution). The anomalous hysteresis becomes more pronounced if the electrolyte(aq) vs. monomer(o)
concentration ratio increases [63].
The morphology of D3PIE-prepared films varies with the preparation method.
If CV is used, the film shows a tree-ring pattern due to the variation of the polymerization conditions with time [65], but constant-potential polymerization leads to
a laterally homogeneous structure [65, 90]. Regardless of the preparation method,
the morphology difference between the sides of the films is the same; moreover, it
shows the same trend as that was established for metal films. Namely, the film side
right at the ITIES is rather smooth, but the growing plane contacting the solution that
contains the precursor material is porous [65, 90]. The growing face of the polymer