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PROCESSING OF MACROPOROUS MATERIALS USING ORDERED POLYSTYRENE OR SILICA SPHERES AS TEMPLATES Two different types of macroporous materials were synthesized for use in electrophoretic applications. The first was a silica matrix templated with polystyrene spheres, the second was a PMMA (poly methylmethacrylate) matrix with silica spheres as templates. Monodisperse polystyrene spheres were synthesized via emulsion polymerisation and dispersed in water. Silica spheres were synthesized using the Stober Process and also dispersed in water. Polystyrene spheres were centrifuged for about 15 minutes at 5,000 RPM inside a .4 x 4 mm capillary tube to achieve ordering of the spheres (close packing). Silica spheres were centrifuged under the same conditions except at a lower speed (2,000 RPM). Samples were dried for 1-3 days in air and 1 day in a furnace at 60C which yielded minimal cracking. Another method to reduce cracking in polystyrene samples was to disperse the polystyrene spheres in methanol before centrifuging. Polystyrene templates were infiltrated with a mixture of TMOS (tetra-methyl-ortho-silicate), water and HCl (catalyst). Gelation of TMOS occurred in atmosphere after 40 hours. Following gelation, the polystyrene spheres were removed by calcination at 525C. The remaining structure was a periodic three-dimensional array of macropores in silica. Sizes can range from 300 nm to 1.5 microns based on the size of the polystyrene spheres used in templating. This method of processing worked moderately well, and final samples were analyzed with SEM. The structure was ordered as well as monodisperse with the expected pore size. Ordered silica spheres were infiltrated with a PMMA precursor rather than TMOS. The precursor was exposed to long range UV light for 2-4 hours to polymerize the PMMA. The silica was etched away (along with the glass capillary tube) in concentrated HF leaving a porous PMMA structure. Difficulties were encountered while etching and recovering PMMA material and analysis of the resulting structure is ongoing work.
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