Understanding Phase Stability in Silica/Surfactant Composites through the Study of a Curvature Driven Rectangular Intermediate

Abstract

Hydrothermal chemistry is used to alter phase stability in ordered silica/surfactant composites. These materials, which are studied using real time X-ray diffraction, display a direct hexagonal-to-lamellar transformation when heated in water. When treated in a pH 11 buffer, however, low angle X-ray diffraction (XRD) reveals an intermediate centered rectangular phase during the phase transformation. By examining the kinetics of this transformation under a range of temperature conditions, we can understand how silica chemistry, interfacial charge density, and surfactant packing interplay to control phase stability. For example, if a lower transformation temperature is used, a hexagonal-to-rectangular-to-lamellar phase progression is observed. Higher transformation temperatures display more complex phase behavior, showing both a direct hexagonal-to-lamellar phase transition and the hexagonal-to-rectangular-to-lamellar transformation occurring at the same time. The observed ordering of phases is consistent wi...