Structural evolution of surfactant-silica film-forming solutions, investigated using small-angle neutron scattering

Time-resolved small-angle neutron scattering has been used to investigate the evolution of micelles in the subphase of surfactant-templated silica film-forming solutions. Two samples have been prepared using cetyltrimethylammonium bromide (CTABr), as the structure-directing agent, and different amounts of tetramethoxysilane (TMOS) (CTABr/TMOS molar ratio 0.093, 0.139). The solutions have been reproduced at three different H2O/D2O contrasts and allowed to develop until a precipitate formed in the bulk. The surfactant initially forms micelles in solution while the hydrolyzed TMOS is dispersed uniformly through the aqueous phase. The micelles appear to have an ellipsoidal structure immediately after mixing, composed of a surfactant core surrounded by a thin, low-density silica film. The ellipsoidal micelles are typically 32 A in length and with time elongate and become “rodlike” silica-coated cylinders with length in excess of 150 A. This value is significantly larger in the composition containing more TMOS ...