402
11 Templated Systems
The phase diagrams of the lyotropic systems show a great variety but exhibit
a few uniform features [321, 323]. The critical concentration of the amphiphilic
material at which the L 1 phase is formed increases with temperature. In most of the
lyotropic systems used for electrodeposition templates, the Q 1 and Q 2 phases are
rather a narrow boundary region between the neighbouring phases. It may occur that
some of the phases are even missing. The general rule is that with the increase in
temperature, the concentration range in which either the I, H or Q phases are stable
get narrowing and finally become vanishing, and two liquid phases can coexist. For
the most commonly used non-ionic amphiphilic material in electrodeposition experiments, octaethyleneglycol monohexadecyl ether (often abbreviated as C 16 EO 8 ), the
H 1 phase is stable over a ~20 wt.% range around room temperature, which makes it
relatively easy to prepare.
Even though the phase diagrams are known for the mixtures of major polar and
amphiphilic molecules, the dissolution of the ionic components necessary for electrodeposition modifies the phase diagrams to significant extent. Hence, the phase
diagrams of the water–amphiphilic systems can be taken as a rough approximation
only, and the determination of a new phase diagram for the electrolyte solutions is
needed. In these cases, the quasi-binary approach is often applied. This means that
the aqueous component is not pure water but a solution of the electrolytes with fixed
concentrations, even though the distribution of the electrolytes between the possible
phases is not studied but assumed that the composition of the aqueous phase does not
change as various phases are formed. The identification method of the phases includes
polarized light microscopy and small-angle X-ray diffraction. For the latter, the periodicity of either the lyotropic system itself of the nanostructured deposit obtained
can be identified with a Bragg peak at 2 < 2° diffraction angle, corresponding to
the 6–15 nm periodicity.
Since lyotropic systems are in a dynamic equilibrium and are non-solid by nature,
they are easy to deform during the deposition process. Hence, the overall shape and
the internal structure of the lyotropic templates constantly change during the deposition process. This is the reason why deposits much thicker than the characteristic
length scale of the internal composition modulation in the lyotropic media often
exhibit either some surface undulation or a large-scale growth morphology unrelated
to the lyotropic material. However, the small-scale morphology within the large-scale
morphological units bears the fingerprint of the lyotropic template. This is the reason
why the SEM method is suitable for the observation of the large-scale morphology,
while the template-induced small-scale morphology with <15 nm periodicity can
be imaged with TEM only in most cases. An example for both the top and side
views of the pore structure in a deposit obtained from a H 1 type template is shown
in Fig. 11.19. For a similar comparison of Pt deposits, see Fig. 4 in Ref. [324].
11 Templated Systems
The phase diagrams of the lyotropic systems show a great variety but exhibit
a few uniform features [321, 323]. The critical concentration of the amphiphilic
material at which the L 1 phase is formed increases with temperature. In most of the
lyotropic systems used for electrodeposition templates, the Q 1 and Q 2 phases are
rather a narrow boundary region between the neighbouring phases. It may occur that
some of the phases are even missing. The general rule is that with the increase in
temperature, the concentration range in which either the I, H or Q phases are stable
get narrowing and finally become vanishing, and two liquid phases can coexist. For
the most commonly used non-ionic amphiphilic material in electrodeposition experiments, octaethyleneglycol monohexadecyl ether (often abbreviated as C 16 EO 8 ), the
H 1 phase is stable over a ~20 wt.% range around room temperature, which makes it
relatively easy to prepare.
Even though the phase diagrams are known for the mixtures of major polar and
amphiphilic molecules, the dissolution of the ionic components necessary for electrodeposition modifies the phase diagrams to significant extent. Hence, the phase
diagrams of the water–amphiphilic systems can be taken as a rough approximation
only, and the determination of a new phase diagram for the electrolyte solutions is
needed. In these cases, the quasi-binary approach is often applied. This means that
the aqueous component is not pure water but a solution of the electrolytes with fixed
concentrations, even though the distribution of the electrolytes between the possible
phases is not studied but assumed that the composition of the aqueous phase does not
change as various phases are formed. The identification method of the phases includes
polarized light microscopy and small-angle X-ray diffraction. For the latter, the periodicity of either the lyotropic system itself of the nanostructured deposit obtained
can be identified with a Bragg peak at 2 < 2° diffraction angle, corresponding to
the 6–15 nm periodicity.
Since lyotropic systems are in a dynamic equilibrium and are non-solid by nature,
they are easy to deform during the deposition process. Hence, the overall shape and
the internal structure of the lyotropic templates constantly change during the deposition process. This is the reason why deposits much thicker than the characteristic
length scale of the internal composition modulation in the lyotropic media often
exhibit either some surface undulation or a large-scale growth morphology unrelated
to the lyotropic material. However, the small-scale morphology within the large-scale
morphological units bears the fingerprint of the lyotropic template. This is the reason
why the SEM method is suitable for the observation of the large-scale morphology,
while the template-induced small-scale morphology with <15 nm periodicity can
be imaged with TEM only in most cases. An example for both the top and side
views of the pore structure in a deposit obtained from a H 1 type template is shown
in Fig. 11.19. For a similar comparison of Pt deposits, see Fig. 4 in Ref. [324].