Lyotropic liquid crystals as templates for mesoporous silica materials

The paper considers the lyotropic liquid crystals and the role of their mesophases as templates to create the scaffold of mesoporous silica materials. It was in 1992 that a Mobil Research group disclosed a method to produce silica particles having a regular network of pores with hexagonal and cubic symmetries. The method was proposed as based on a liquid-crystal 'templating' mechanism. Since the symmetries resulting in the silica scaffolds are those observed in the mesophases of lyotropic liquid crystals, the Mobil Research group supposed the presence of a mesophase directly in a stage of the templating mechanism. Here we discuss the method as it was reported in 1992 and what is today defined as a true or direct liquid-crystal templating approach. It will be stressed that, in any case, the templating is a surfactant-assisted method, that can be better defined as supramolecular templating method. The template mainly happens in the form of a modified Stöber process. In this framework, the role of the curvature of silica-surfactant interfaces will be considered, the cubic phases of lyotropic liquid crystals analyzed in depth and the related surfaces with zero mean curvature discussed in detail.