410
11 Templated Systems
chemical composition. This notation is analogous to the occurrence of these names
in the relevant literature.
The concentration range of micellar solution of Pluronic-123 is 0.001 wt.% < c <
30 wt.%, and the average micelle diameter about 14 nm, although the pore diameter
of the resulting deposits was found to be smaller, 11 and 7 nm for Pd [368] and FePt
[369] deposits, respectively. The treatment of the micellar solution of Pluronic-123
does not require any special step due to the lack of any orientation preference in the
random micellar system. The addition of metal salts necessary for electrodeposition
does not change significantly either the limiting compositions of the phases or the
micelle diameter.
Irreversibly coagulated micelles as template. The periodicity of the self-assembled
templates prepared from particles ex situ and prior to the deposition process is limited
due to the interaction strength of the particles in the self-organization processes.
While the particle templates have a lower limit for the particle size (>100 nm),
micelles formed with the association of either tenside or polymer molecules in equilibrium with a true solution exhibit an upper limit for the particle size (<20 nm).
Polymer particles coagulated in situ by a sol–gel process fill up a size gap between
the above-mentioned template types.
The initial step of the particle formation is the dissolution of a diblock copolymer
in a suitable solvent. For the commonly used PS-b-PEO diblock copolymer (where
PEO stands for polyethylene oxide), tetrahydrofuran (THF) is a suitable solvent that
dissolves the polymer without any micelle formation. Then, ethanol and the plating
solutions to be used are added successively to the polymer solution. The gradual shift
of the solvent polarity leads to the precipitation of core–shell type polymer particles
in which the more hydrophobic component (here, PS) forms the core that is covered
with the more hydrophilic PEO as shell. The particle size can be controlled with the
concentration of the THF solution and the molar weight of the polymers in the 20–
60 nm range. In accord with the description of the method [370], the electrodeposited
cage-like metal framework and the polymer particle network serving as template are
produced in parallel in electrodeposition and electrophoretic assembly, respectively.
This can be the reason why the deposition potential (and hence, the deposition rate)
has a crucial role in the formation of the mesoporous structure [371]. A deposition
rate below the desired value leads to the formation of a bulky deposit since it pushes
ahead the polymer particles instead of growing in between them, whereas a too high
deposition rate leads to random nucleation and a layer without mesopores.
The deposit types reported for the precipitated diblock copolymer templates show
some great variety. The surface image of the deposits is in each case characteristic
of a random porous structure in which both the cavities and the walls percolate,
regardless of the material deposited (Au [370, 372, 373], Au–Cu alloy [374] or
Ni [371]). However, the cross-sectional images can differ in whether the pores are
randomly situated or form a vertical channel due to the linear arrangement of the
polymer particles during the deposition process [374]. With a purposefully chosen
substrate, hemispherical mesoporous Au particles can be grown in which the polymer
particles are the pore-directing agent [373].
11 Templated Systems
chemical composition. This notation is analogous to the occurrence of these names
in the relevant literature.
The concentration range of micellar solution of Pluronic-123 is 0.001 wt.% < c <
30 wt.%, and the average micelle diameter about 14 nm, although the pore diameter
of the resulting deposits was found to be smaller, 11 and 7 nm for Pd [368] and FePt
[369] deposits, respectively. The treatment of the micellar solution of Pluronic-123
does not require any special step due to the lack of any orientation preference in the
random micellar system. The addition of metal salts necessary for electrodeposition
does not change significantly either the limiting compositions of the phases or the
micelle diameter.
Irreversibly coagulated micelles as template. The periodicity of the self-assembled
templates prepared from particles ex situ and prior to the deposition process is limited
due to the interaction strength of the particles in the self-organization processes.
While the particle templates have a lower limit for the particle size (>100 nm),
micelles formed with the association of either tenside or polymer molecules in equilibrium with a true solution exhibit an upper limit for the particle size (<20 nm).
Polymer particles coagulated in situ by a sol–gel process fill up a size gap between
the above-mentioned template types.
The initial step of the particle formation is the dissolution of a diblock copolymer
in a suitable solvent. For the commonly used PS-b-PEO diblock copolymer (where
PEO stands for polyethylene oxide), tetrahydrofuran (THF) is a suitable solvent that
dissolves the polymer without any micelle formation. Then, ethanol and the plating
solutions to be used are added successively to the polymer solution. The gradual shift
of the solvent polarity leads to the precipitation of core–shell type polymer particles
in which the more hydrophobic component (here, PS) forms the core that is covered
with the more hydrophilic PEO as shell. The particle size can be controlled with the
concentration of the THF solution and the molar weight of the polymers in the 20–
60 nm range. In accord with the description of the method [370], the electrodeposited
cage-like metal framework and the polymer particle network serving as template are
produced in parallel in electrodeposition and electrophoretic assembly, respectively.
This can be the reason why the deposition potential (and hence, the deposition rate)
has a crucial role in the formation of the mesoporous structure [371]. A deposition
rate below the desired value leads to the formation of a bulky deposit since it pushes
ahead the polymer particles instead of growing in between them, whereas a too high
deposition rate leads to random nucleation and a layer without mesopores.
The deposit types reported for the precipitated diblock copolymer templates show
some great variety. The surface image of the deposits is in each case characteristic
of a random porous structure in which both the cavities and the walls percolate,
regardless of the material deposited (Au [370, 372, 373], Au–Cu alloy [374] or
Ni [371]). However, the cross-sectional images can differ in whether the pores are
randomly situated or form a vertical channel due to the linear arrangement of the
polymer particles during the deposition process [374]. With a purposefully chosen
substrate, hemispherical mesoporous Au particles can be grown in which the polymer
particles are the pore-directing agent [373].