ORDERED MACROPOROUS MATERIALS BY EMULSION TEMPLATING

Ordered macroporous materials with pore diameters comparable to optica l wavelengths are predicted to have unique and highly useful optical p roperties such as photonic bandgaps(1-3) and optical stop-bands(4). Ti ght control over the pore size distribution might also lead to improve d macroporous materials (those with pores greater than approximately 5 0 nm) for application as catalytic surfaces and supports(5), adsorbent s, chromatographic materials, filters(6), light-weight structural mate rials(7), and thermal, acoustic(8) and electrical insulators(9). Altho ugh methods exist for producing ordered porous materials with pore dia meters less than 10 nm (refs 10, 11), there is no general method for p roducing such materials with uniform pore sizes at larger length scale s. Here we report a new method for producing highly monodisperse macro porous materials with pore sizes ranging from 50 nm to several microme tres. Starting with an emulsion of equally sized droplets (produced th rough a repeated fractionation procedure(12)), we form macroporous mat erials of titania, silica and zirconia by using the emulsion droplets as templates around which material is deposited through a sol-gel proc ess(13). Subsequent drying and heat treatment yields solid materials w ith spherical pores left behind by the emulsion droplets. These pores are highly ordered, reflecting the self-assembly of the original monod isperse emulsion droplets into a nearly crystalline array(14). We show that the pore size can be accurately controlled, and that the techniq ue should be applicable to a wide variety of metal oxides and even org anic polymer gels.