Alkaline Lyotropic Silicate−Surfactant Liquid Crystals

Abstract

Multinuclear ( 2 H, 13 C, 29 Si, 81 Br) magnetic resonance spectroscopy, small-angle X-ray scattering, and polarized optical microscopy techniques have been used to investigate molecular and mesoscopic organization in silicate−surfactant lyotropic liquid crystals with hexagonal and lamellar morphologies under highly alkaline conditions. Such systems cooperatively self-assemble following the addition of a basic aqueous solution containing anionic silicate oligomers (e.g., double-four-ring species) to an isotropic micellar solution of cationic surfactant molecules (e.g., cetyltrimethylammonium bromide). Important similarities and differences are shown to exist between multicomponent silicate−surfactant and conventional binary lyotropic liquid crystals. Under highly alkaline conditions, the silicate−surfactant systems possess the characteristics of ordinary lyotropic liquid crystalline systems, though the balance of forces underlying their self-assembly is complicated by the richness of the aqueous silicate chemistry. This is the first comprehensive description of lyotropic silicate−surfactant liquid crystalline behavior, from which detailed insight is obtained into the molecular factors governing inorganic−organic mesophase formation in aqueous media.