Pore condensation in novel highly ordered mesoporous silica

The pore condensation of SF6 in two novel ceramic silica materials, obtained by templating lyotropic phases of nonionic surfactants and of amphiphilic block copolymers, has been investigated over a temperature range from below the triple point up to the critical point of the fluid. One of the materials represent an ordered array of cylindrical pores (mean pore size 29 Å); the sorption isotherms for this material exhibit no hysteresis in the entire experimental temperature range. For the other material, which is believed to constitute a more complex pore system (mean pore size 34 Å), a pronounced hysteresis loop is seen near the triple point temperature but not at higher reduced temperatures. For both materials pore condensation disappears well below the bulk critical temperature. The experimental isotherms are used to determine the coexistence curve and the critical temperature of the fluid in the confined pore space.