Expanded Mesoporous Silicate Films Grown at the Air−Water Interface by Addition of Hydrocarbons

Abstract

We have examined the effect of addition of saturated straight-chain alkanes, Cn (n even and n = 8−16), and the aromatics toluene and benzene on the formation of mesoporous silicate films, which form at the air−water interface. The silicate films self-assemble by slowly condensing silicate oligomers attaching to templates formed by the alkyltrimethylammonium surfactants CnTAX (n even and n = 12−18, and X = Cl- and Br-) in solution. The collection of X-ray and neutron reflectivity profiles from these solutions shows that there is a chain length dependency to the formation of alkane-swollen hexagonal silicate films, which is manifest as a linear increase of the pore sizes of the films with increasing alkane chain length for Cn, n > 8, up to a limit of a hexagonal cell dimension of a100 = 80.8 A. The expansion is greatest when using decane as expander for all surfactant chain lengths examined. For C12 chain length surfactants a cubic phase results, C14 and C16 chain lengths form expanded hexagonal films, whil...