Structural properties and topological defects of swollen polymeric mesophases: Low angle X-ray diffraction and optical microscopic studies

Abstract

Homogeneous mesophases encountered in water-toluene mixtures stabilized by polystyrene-poly(ethylene oxide) graft copolymers in the presence of 2-propanol are investigated. In these four-component systems, mesomorphic phases are produced for fairly high values of the copolymer/2-propanol ratio close to the transition region between cloudy and transparent systems. Low angle Xray diffraction studies show evidence of lamellar and reversed hexagonal structures, according to the composition of the systems. By addition of 2-propanol, the birefringent phases undergo a transition to isotropic systems which have either a cubic structure or consist of reversed water-swollen micelles. The existence of mesomorphic phases was further confirmed by optical microscopic investigation. These dilute polymeric mesophases exhibit a great variety of textures similar to those encountered in low molecular-weight lyotropic systems (soaps). For lamellar structures, typical textures such as classical focal conics, oily streaks, or batonnets are described and discussed. In addition, well-resolved polygonal arrays, interpreted recently in terms of a parabolic focal conic structure by Rosenblatt et al., are also observed. The textures most commonly found for hexagonal structures include fan-shaped and striated ones. These observations have been complemented by flow birefringence measurements.