Phase diagram of tyloxapol and water — II

Abstract

The phase diagram of mixtures of tyloxapol, a nonionic liquid polymer of the alkyl aryl polyether alcohol type, and water and the corresponding liquid crystalline phases have been investigated by X-ray scattering. Below 35 wt% tyloxapol micellar solutions are formed. At 3 wt% they contain spherical micelles with a diameter around 7 nm. Increasing concentrations give rise to interparticle interactions that are clearly observable above 10 wt%. Complementary viscosity measurements indicate a pronounced hydration of the polyoxyethylene chains. From 37.5 to 65 wt% there is a lyotropic liquid crystalline hexagonal phase (middle phase, M 1 phase). Its lattice parameter increases nearly linearly with water concentration but is almost independent of temperature. There are no transitions of the hexagonal phases to thermotropic liquid crystalline phases at temperatures between 20 and 65°C. At 65°C all systems exhibit two broad diffuse reflections with a spacing ratio of 1: 1 2 . At all concentrations, samples heated to 65°C and cooled to room temperature return to the hexagonal phase. The X-ray data confirm the existence of a cubic phase in a narrow concentration range around 70 wt% below 30°C. Its three-dimensional structure, however, could not be determined from the eight reflections in the scattering pattern. Retransformation of the cubic phase from the melt is highly retarded. On cooling, the cubic phase which is closest to the hexagonal phase at 20°C forms a metastable hexagonal intermediate phase with a small lattice parameter. The melts of cubic phases which exist in the vicinity of the lamellar phase region form an intermediate lamellar phase. Between 74 and 80 wt% at room temperature there is a liquid crystalline lamellar phase. The reflections of the thermally unstressed samples are weak compared with the sharp reflections observed after cooling of molten samples. The melts of all three liquid crystalline phases are viscous liquids. Their scattering patterns display two broad maxima with spacings progressively decreasing from 5.3 to 4.6 nm and from 2.7 to 2.4 nm as the concentration increases from 37.5 to 77.5 wt%. No liquid crystalline phases were observed for the binary mixtures containing more than 80 wt% but these highly viscous liquids display a broad maximum around 4.2 nm.