446
12 Localized or Spatially Selective Electrodeposition Methods
advantageous features, including that the size range of the polymer-coated particles may be limited since the metal nucleation on the polymer surface is much
hindered. An attempt to exploit this opportunity was given for silver particles and
polyphenylpyrrole [72]. In this case, N-phenylpyrrole was not only the polymerforming monomer but the electron donor that facilitated both the Ag
+ ion transfer
across the interface and its reduction to silver. Unfortunately, the direct observation
of the particles was not performed in this case. Further cases of the codeposition of
metals and polymers will be discussed in the next chapter.
Finally, it is worthwhile mentioning that the particles deposited at ITIES are not
necessarily supportless. If electrically conductive nanoobjects like carbon nanotubes
or carbon platelets containing a few layers of graphene sheet are accumulated
(adsorbed) at the ITIES, they can serve as a nucleation and accumulation platform
for the electrodeposited nanoparticles. While such a deposition method results in an
assembly of supported particles that are easier to collect than free-standing ones, the
electrosynthesis at the ITIES can still lead to ultrasmall particles with a narrow size
distribution [89, 91], hence retaining the general advantage of the particle electrodeposition at the ITIES. Possible catalytic application of such deposits has also been
anticipated [88].
12.3.3 Electrodeposition of Various Films at the ITIES
In the systems described in the previous chapter, an electrochemical activation (i.e.,
polarization of the interface) was necessary to initiate the nucleation of metallic
clusters. Since the experimental conditions were chosen in a way so that the partition
coefficient of the salts applied in both phases was extreme, the metal deposition
could not take place spontaneously. However, if the anion in the aqueous phase
could enter easily into the organic phase and the standard potential of the redox
reactions are close enough, the spontaneous metal deposition at the ITIES can also
happen. This was found for silver deposition at the water/n-octanol interface by
using ferrocene as reducing agent in the organic phase [103]. Depending on the
experimental conditions (e.g., by tuning the concentration ratio of the reactants),
the deposition of silver whiskers and smooth films covering practically the entire
ITIES was possible. Like any other electroless deposition reaction, the mechanism
was explained with electrochemical principles, although no external current source
was applied for the deposition itself. It is worth noting that no similar reaction was
achieved by electrochemical means for the liquid–liquid interface. Particle formation
was dominant, even if the coalescence of the particles and the formation of a spongy
loose network could be kept track of in some studies [88].
Although metals could not be electroplated at the ITIES as continuous films,
polymers may adopt this growth mode upon electropolymerization. Free-standing
tertiophene films were obtained with this method [80]. Since the deposition mode
at the ITIES was found to differ from the usual heterogeneous nucleation at metal
surfaces, the speculation was made that the intermixed solution layer may play a role
12 Localized or Spatially Selective Electrodeposition Methods
advantageous features, including that the size range of the polymer-coated particles may be limited since the metal nucleation on the polymer surface is much
hindered. An attempt to exploit this opportunity was given for silver particles and
polyphenylpyrrole [72]. In this case, N-phenylpyrrole was not only the polymerforming monomer but the electron donor that facilitated both the Ag
+ ion transfer
across the interface and its reduction to silver. Unfortunately, the direct observation
of the particles was not performed in this case. Further cases of the codeposition of
metals and polymers will be discussed in the next chapter.
Finally, it is worthwhile mentioning that the particles deposited at ITIES are not
necessarily supportless. If electrically conductive nanoobjects like carbon nanotubes
or carbon platelets containing a few layers of graphene sheet are accumulated
(adsorbed) at the ITIES, they can serve as a nucleation and accumulation platform
for the electrodeposited nanoparticles. While such a deposition method results in an
assembly of supported particles that are easier to collect than free-standing ones, the
electrosynthesis at the ITIES can still lead to ultrasmall particles with a narrow size
distribution [89, 91], hence retaining the general advantage of the particle electrodeposition at the ITIES. Possible catalytic application of such deposits has also been
anticipated [88].
12.3.3 Electrodeposition of Various Films at the ITIES
In the systems described in the previous chapter, an electrochemical activation (i.e.,
polarization of the interface) was necessary to initiate the nucleation of metallic
clusters. Since the experimental conditions were chosen in a way so that the partition
coefficient of the salts applied in both phases was extreme, the metal deposition
could not take place spontaneously. However, if the anion in the aqueous phase
could enter easily into the organic phase and the standard potential of the redox
reactions are close enough, the spontaneous metal deposition at the ITIES can also
happen. This was found for silver deposition at the water/n-octanol interface by
using ferrocene as reducing agent in the organic phase [103]. Depending on the
experimental conditions (e.g., by tuning the concentration ratio of the reactants),
the deposition of silver whiskers and smooth films covering practically the entire
ITIES was possible. Like any other electroless deposition reaction, the mechanism
was explained with electrochemical principles, although no external current source
was applied for the deposition itself. It is worth noting that no similar reaction was
achieved by electrochemical means for the liquid–liquid interface. Particle formation
was dominant, even if the coalescence of the particles and the formation of a spongy
loose network could be kept track of in some studies [88].
Although metals could not be electroplated at the ITIES as continuous films,
polymers may adopt this growth mode upon electropolymerization. Free-standing
tertiophene films were obtained with this method [80]. Since the deposition mode
at the ITIES was found to differ from the usual heterogeneous nucleation at metal
surfaces, the speculation was made that the intermixed solution layer may play a role