Nanostructured materials templating approach

Similar approach has also been taken by Ferain and Legras [133,137,138] and De Pra et al. [139] to produce nanostructured materials based on the template of the membrane with etched pores. Polycarbonate film was also of use as the base membrane of the template, and micro- and nanopores were formed by precise control of the etching procedure. Their most resent report showed the successful formation of ultrasmall pores and electrodeposited materials of which sizes were as much as 20 nm [139]. Another attractive point of these studies is the deposited materials in the etched pores. Electrochemical polymerization of conjugated polymer materials was demonstrated in these studies, and the nanowires based on polypyrrole or polyaniline were formed with a fairly cylindrical shape reflecting the side wall structure of the etched pores. Figure 10 indicates the shape of the polypyrrole microwires with their dimension changes by the limitation of the thickness of the template. 

Nanostructured materials can be synthesized from the so-called top down or bottom-up approach. In the first approach, features at the micron (or submicron) length scale are created on a substrate by masking and exposing selected regions of a radiation sensitive layer (typically a polymeric photoresist) to a UV source. This exposure is followed by various chemical treatments and mechanical steps to obtain the desired spatial pattern on a substrate. However, the feature sizes that can be obtained with this approach are limited to the length scale of the wavelength of the radiation employed. If features at the nanometer scale are desired, one must start from the bottom (i.e., use individual molecules or clusters) and assemble templates that will impart the nanostructure to the desired material. 

This chapter provides an overview of the use of H-bonds for the constmction of nanoporous materials. Systems are discussed where the formation of H-bonds directly induces porosity and approaches are presented where the mpture of H-bonds leads to porous materials. First, we describe the use of small molecules capable of forming H-bonds, which directly induces porosity in 2D and 3D H-bonded networks. Next, block copolymers are discussed which self-assemble in nanostructured materials. The removal of H-bonded template molecules leads to porous polymer materials. Finally, H-bonded polymerizable liquid crystals having even smaller pores are discussed. Molecular imprinted polymers that do not contain pores are beyond the scope of this chapter. 

Pillaring of metal sulfides has been achieved [91], and even metal-rich framework structures can be prepared [92]. Even for these materials template removal is not possible, they are still an interesting approach to nano-sized semiconductors, namely so-called anti-dot lattices where the semiconducting lattice surrounds template-filled voids of lower conductivity [86]. Template removal is probably not the essential problem for the design of a nanostructur-ed material, since often the goals of unusual size-dependent optical or electronic properties might be achieved with the composite of template and framework. 

The most exciting challenge is probably the preparation of BN nanostructures, including nanofibers and nanotubules, using the template-assisted PDCs route. Such an approach could allow us to control the morphology and size of the nanostructured BN materials to be incorporated into the BN matrix. This should significantly enhance the mechanical performance of the resulting composites compared to composites reinforced by BN microfibers. 

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