11.4 Soft Templates Formed by Molecular Self-assembly Processes
411
Electrodeposition from reverse micellar (L 2 ) systems. Various successful trials
have demonstrated that electrodeposition is possible from L 2 -type systems containing
reverse micelles, although the phase containing the reactant is not continuous.
However, the choice of the relatively non-polar continuous phase is usually such that
it has a limited ion transport capability, which makes it possible both to pass electrical current through the cells and to measure potential difference across the system.
Non-aqueous phases suitable for the reverse micelle electrodeposition include Triton
X-100 (i.e., p-octyl polyethylene glycol phenyl ether) as single component [375, 376],
and mixture of hexanol, hexane and Triton X-100 [377, 378], and cetyltrimethylammonium bromide with 1-butanol as co-surfactant [379, 380]. The water content of
the Triton X-100 phase, for instance, was reported to be 13 wt.%, and its proton
mobility was identified to be responsible for the electrical conduction [375].
The deposits formed from various L 2 systems show a large morphological variety.
Platinum deposited from L 2 -type lyotropic systems was mesoporous, i.e., morphologically analogous to those obtained with H 1 systems of polymer micelle solutions.
Nickel formed either cracked deposit layers or nanodots, depending on the water-tosurfactant ratio of the system [379], and cobalt showed a foamy or lamellar structure
[380]. The morphology of the metallic Ni and Co deposits does not bear a feature
size characteristic of the micelle size in the L 2 phase. The latter dissimilarity also
holds for non-metallic deposits such as ZnO [377] and Ni(OH) 2 [378], although these
deposits developed a significant porosity due to the exclusion effect of the less polar
phase in the L 2 system used. We can draw the conclusion that neither the diameter of
the reverse micelles nor their mean distance in the solution can be taken as a directly
applicable design factor for tuning the deposit morphology and porosity, although
the porosity itself is easily achievable with some optimization. Hence, the apolar
phase in the L 2 systems is not a comparable “template” to other systems listed in
the previous chapters in the sense that its mean thickness (the micelle-to-micelle
distance) usually cannot be recognized in the deposit.
11.4.7 Self-assembled Monolayers (SAMs) as Templates
Electrodes modified with self-assembled monolayers have long been studied in
relation to electrodeposition processes. For monolayers formed from molecules
anchored to the electrode through a sulphur atom (such as n-alkane thiols [381–384]
and mercapto-n-alkanoic acids [385]), two deposition mechanisms were identified,
namely deposition in the UPD state under the monolayer and deposition onto the
monolayer. In addition, it was revealed that the bulk deposition starts at the defect
sites of the substrate (e.g., terrace edges and crystal boundaries) and that the deposition can be accelerated by electrochemically induced desorption of the monolayer. In
each case, the experience was that the nuclei formed were fine-grained as compared
to the uncoated substrate. The experience for surfaces templated with a mixed layer
411
Electrodeposition from reverse micellar (L 2 ) systems. Various successful trials
have demonstrated that electrodeposition is possible from L 2 -type systems containing
reverse micelles, although the phase containing the reactant is not continuous.
However, the choice of the relatively non-polar continuous phase is usually such that
it has a limited ion transport capability, which makes it possible both to pass electrical current through the cells and to measure potential difference across the system.
Non-aqueous phases suitable for the reverse micelle electrodeposition include Triton
X-100 (i.e., p-octyl polyethylene glycol phenyl ether) as single component [375, 376],
and mixture of hexanol, hexane and Triton X-100 [377, 378], and cetyltrimethylammonium bromide with 1-butanol as co-surfactant [379, 380]. The water content of
the Triton X-100 phase, for instance, was reported to be 13 wt.%, and its proton
mobility was identified to be responsible for the electrical conduction [375].
The deposits formed from various L 2 systems show a large morphological variety.
Platinum deposited from L 2 -type lyotropic systems was mesoporous, i.e., morphologically analogous to those obtained with H 1 systems of polymer micelle solutions.
Nickel formed either cracked deposit layers or nanodots, depending on the water-tosurfactant ratio of the system [379], and cobalt showed a foamy or lamellar structure
[380]. The morphology of the metallic Ni and Co deposits does not bear a feature
size characteristic of the micelle size in the L 2 phase. The latter dissimilarity also
holds for non-metallic deposits such as ZnO [377] and Ni(OH) 2 [378], although these
deposits developed a significant porosity due to the exclusion effect of the less polar
phase in the L 2 system used. We can draw the conclusion that neither the diameter of
the reverse micelles nor their mean distance in the solution can be taken as a directly
applicable design factor for tuning the deposit morphology and porosity, although
the porosity itself is easily achievable with some optimization. Hence, the apolar
phase in the L 2 systems is not a comparable “template” to other systems listed in
the previous chapters in the sense that its mean thickness (the micelle-to-micelle
distance) usually cannot be recognized in the deposit.
11.4.7 Self-assembled Monolayers (SAMs) as Templates
Electrodes modified with self-assembled monolayers have long been studied in
relation to electrodeposition processes. For monolayers formed from molecules
anchored to the electrode through a sulphur atom (such as n-alkane thiols [381–384]
and mercapto-n-alkanoic acids [385]), two deposition mechanisms were identified,
namely deposition in the UPD state under the monolayer and deposition onto the
monolayer. In addition, it was revealed that the bulk deposition starts at the defect
sites of the substrate (e.g., terrace edges and crystal boundaries) and that the deposition can be accelerated by electrochemically induced desorption of the monolayer. In
each case, the experience was that the nuclei formed were fine-grained as compared
to the uncoated substrate. The experience for surfaces templated with a mixed layer