Disordered mesoporous silicates formed by templation of a liquid crystal (L3)
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Disordered mesoporous silicates formed by templation of a liquid crystal (L3) Abds-Sami Malik, Daniel M. Dabbs, Ilhan A. Aksay, Howard E. Katz1 Princeton University, Dept. of Chemical Engineering and Princeton Materials Institute, Princeton, NJ 08540 1 Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974 ABSTRACT For a wide range of technological applications the need for optically transparent, monolithic, mesoporous silicates is readily apparent. Potential areas of utility include filtration, catalysis, and optoelectronics among many others. This laboratory has previously reported on the synthesis of such materials that are formed through the addition of tetramethoxysilane to a liquid crystal solution of hexanol, cetylpyridinium chloride, and 0.2 M hydrochloric acid, and our investigation into the properties of these materials is a continuing process. We have achieved defect and fracture free material of suitable size (0.5 cm x 3 cm diameter disks) via supercritical drying of the silicate under ethanol or CO2. The dried materials are remarkably similar to ordinary glass in strength, texture, and clarity. They possess pore volumes of ca. 1.0 cm3/g, with BET surface areas >1000 m2/g. We can re-infiltrate the dried monolith with hydroxyethylacrylate, a photo-polymerizable monomer, to create an inorganic/organic nanocomposite. There is fracturing upon re-infiltration, but preliminary tests show that the polymerization proceeds despite the mechanical failure. These findings suggest many possible applications for these unique nanocomposites.
Water Water Silica layer
Water
Surfactant/hexanol
Liquid crystal bilayer wall Water
Silica layer
Silicified liquid crystal
Figure 1: A sketch of the L3 phase liquid crystal structure, derived from electron microscopy done on freeze fractured samples, as well as theoretical considerations. The pore diameters are uniform, but are randomly interconnected in all three dimensions resulting in short range order with long range disorder. The bilayer forming the liquid crystal can then be templated by a silica layer to capture the original liquid crystal structure as solid silica gel. (Source: McGrath et al., Langmuir, vol. 16, 2000, pp. 398-406)
GG7.5.1
INTRODUCTION In recent years, there has been an explosion of interest in mesostructured and mesoporous materials, partly because they are seen to have high potential for applications over a wide range of technological needs. Possible areas of use include filtration, biological separation, catalysis, and patterned thin film formation for use in optoelectronics. The need for optically isotropic, transparent, monolithic material is apparent, especially for optoelectronic applications. A liquid crystalline phase, termed the L3 phase, has been explored for a quasiternary system formed from hexanol, cetylpyridinium chloride, and 1 wt % aqueous NaCl solution.[1] This phase, which is optically isotropic and transparent, can be described as a surfactant bilayer that is convoluted to form a sponge-like structure with randomly distri
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