Hexagonal to mesocellular foam phase transition in polymer-templated mesoporous silicas

We have investigated the phase transition between two distinct mesoporous s ilicas: SBA-15, comprising a hexagonally packed arrangement of cylindrical pores (6-12 nm in diameter), and mesocellular silica foams (MCF), consistin g of spherical voids (22-42 nm in diameter) interconnected by "windows" of similar to 10 nm. Both SBA-15 and MCF are formed using an amphiphilic tribl ock copolymer (Pluronic P123) as a template. The synthesis conditions for t he two materials are identical, except substantial trimethylbenzene is adde d to form MCF. We find that the phase transition occurs at an oil-polymer m ass ratio of 0.2-0.3. Although the pore structures and pore sizes change dr amatically, the mean surface curvature of the system remains essentially th e same throughout the transition.