12.3 Deposition at the Liquid–Liquid Interface
449
where R
and R
mean various alkyl chains. It is to be noted that the reaction product
of the electrochemical process in the condensation of the alkoxysilane compound
is not a net reaction partner but a catalyst. This electrochemically assisted reaction
pathway was shown to lead to various nanostrucures: (i) hydrophobic films at the
ITIES if n-octyltriethoxysilane is used as a reactant in the organic phase [93]; (ii) a
hydrophobic but electrically conducting spongy nanocomposite if the ITIES contains
carbon nanotubes [94]; and a few nanometre-thick silicate film on conducting electrodes if the electrode is slowly withdrawn from the organic phase during the gel
formation process [95]. The latter method is particularly promising to achieve a
large coverage of an electrode with a layer containing bulky functional groups.
12.3.5 Tip- and Filament-Assisted Deposition
at the Liquid–Liquid Interface
Making use of the properties of ITIES is also possible if an electrode is applied for
defining the nucleation spot of the newly formed phase. In this case, the nucleation
is followed by the growth of the new phase. However, in contrast to the classical
deposition systems with metal–solution interfaces, the ITIES here has a growthregulating impact, and the growth often follows the interface. The hydrophilicity of
the interface close to the nucleation site of a growing film was also demonstrated
for polymer-coated metal electrodes [104]. The experience was that the polypyrrole
film exhibited a preferred growth direction along the three-phase boundary where the
non-conducting surface close to the growth front was hydrophobic, and the growth
rate of the polymer near the hydrophobic surface much exceeded the rate far from
the growth-regulating surface. A similar impact can be seen for ITIES, which works
surprisingly not only for polymer films but sometimes for metals, too.
In the studies where the ITIES served merely as an interface-forming component to act as a growth regulator, the organic phase does not have to contain any
electrolyte. Hence, the properties of the organic phase are not of importance, except
for that it should exhibit a negligible specific conductivity. This is a strongly distinguishing feature of the tip-assisted metal deposition studies at the ITIES as compared
to systems discussed in the previous chapters. However, if electropolymerization is
carried out at the interface, the organic liquid may contain the monomer. Therefore, methods dealing with the deposition of either metals or polymer layers will
be discussed separately. In spite of the substantial difference between the metal
and polymer growth, their common feature is the orientation effect of the interface
concerning the growth direction of the phase being deposited.
Concerning the metal deposition methods at the ITIES, the aqueous phase can
contain the reactant metal salt at a high concentration without any supporting electrolyte. The organic solution is always the top one if tip-assisted metal deposition is
in the focus of interest. The metal tip serving as cathode must be positioned accurately at the surface approaching from the organic (non-conducting or upper) phase
449
where R
and R
mean various alkyl chains. It is to be noted that the reaction product
of the electrochemical process in the condensation of the alkoxysilane compound
is not a net reaction partner but a catalyst. This electrochemically assisted reaction
pathway was shown to lead to various nanostrucures: (i) hydrophobic films at the
ITIES if n-octyltriethoxysilane is used as a reactant in the organic phase [93]; (ii) a
hydrophobic but electrically conducting spongy nanocomposite if the ITIES contains
carbon nanotubes [94]; and a few nanometre-thick silicate film on conducting electrodes if the electrode is slowly withdrawn from the organic phase during the gel
formation process [95]. The latter method is particularly promising to achieve a
large coverage of an electrode with a layer containing bulky functional groups.
12.3.5 Tip- and Filament-Assisted Deposition
at the Liquid–Liquid Interface
Making use of the properties of ITIES is also possible if an electrode is applied for
defining the nucleation spot of the newly formed phase. In this case, the nucleation
is followed by the growth of the new phase. However, in contrast to the classical
deposition systems with metal–solution interfaces, the ITIES here has a growthregulating impact, and the growth often follows the interface. The hydrophilicity of
the interface close to the nucleation site of a growing film was also demonstrated
for polymer-coated metal electrodes [104]. The experience was that the polypyrrole
film exhibited a preferred growth direction along the three-phase boundary where the
non-conducting surface close to the growth front was hydrophobic, and the growth
rate of the polymer near the hydrophobic surface much exceeded the rate far from
the growth-regulating surface. A similar impact can be seen for ITIES, which works
surprisingly not only for polymer films but sometimes for metals, too.
In the studies where the ITIES served merely as an interface-forming component to act as a growth regulator, the organic phase does not have to contain any
electrolyte. Hence, the properties of the organic phase are not of importance, except
for that it should exhibit a negligible specific conductivity. This is a strongly distinguishing feature of the tip-assisted metal deposition studies at the ITIES as compared
to systems discussed in the previous chapters. However, if electropolymerization is
carried out at the interface, the organic liquid may contain the monomer. Therefore, methods dealing with the deposition of either metals or polymer layers will
be discussed separately. In spite of the substantial difference between the metal
and polymer growth, their common feature is the orientation effect of the interface
concerning the growth direction of the phase being deposited.
Concerning the metal deposition methods at the ITIES, the aqueous phase can
contain the reactant metal salt at a high concentration without any supporting electrolyte. The organic solution is always the top one if tip-assisted metal deposition is
in the focus of interest. The metal tip serving as cathode must be positioned accurately at the surface approaching from the organic (non-conducting or upper) phase