Syntheses of complex mesoporous silicas using mixtures of nonionic block copolymer surfactants: Understanding formation of different structures using solubility parameters

The use of block copolymer (BCP) nonionic surfactant mixtures (including Pluronic, Brij and Tetronic types) as templates for synthesizing porous silica materials of mixed pore sizes is explored here. These systems have important applications because combinations of pore sizes can allow rapid access of reactants (via large pores) whilst providing the very high surface area of small pores for higher reaction rates or size selectivity. Examples of the materials prepared here include pore size bimodal hexagonal p6mm channel structures and cubic Im3m cage structures. It is shown here that the chemical similarity, as indicated by the solubility parameter, of the surfactants is an important factor in determining the pore structure and size distribution (PSD) of the pores. Monomodal pore structures are usually obtained when the solubility parameters of the surfactants are similar and bimodal pore structures when the solubility parameters are reasonably different. When the interaction parameter is very high disordered porous systems are formed. Ternary co-surfactant systems, e.g. P123–25R4–P65, can also yield highly ordered bimodal mesoporous silica with a hexagonal structure.

A polymeric co-surfactant can form different mesoporous structure upon the packing ability of the both member components in the presence of silicate species.Figure optionsDownload high-quality image (134 K)Download as PowerPoint slideResearch highlights
► Formation of ordered mesoporous structures via a range of surfactant mixtures rather than single surfactants.
► Formation of complex bimodal pore size distributions in mesoporous materials via the different combination of two or three different types of surfactants.
► The use of solvent parameter theory to understand mesoporous structure formation in complex systems.