Phase behaviour of polyoxyethylene surfactants with water. Mesophase structures and partial miscibility (cloud points)

TLDR

Surfactant mesophase structure depends on surfactant volume fraction and micelle curvature, and a model phase diagram has been derived to capture this relationship. The study aimed to test this model by examining the phase behavior of various pure polyoxyethylene surfactants in water using optical microscopy from 0 to 100 °C. Optical microscopy was employed across 0–100 °C on a series of CnEOm surfactants, yielding phase diagrams for selected compounds and determining mesophase types and sequences for the rest.

Abstract

From a review of the major factors responsible for surfactant mesophase structure, a model phase diagram is deduced which shows phase structure as a function of surfactant volume fraction and micelle curvature. To test this model the phase behaviour of a series of pure polyoxyethylene surfactants (CnEOm) with water has been studied using optical microscopy over the temperature range 0–100 °C. The compounds studied were C8EO3, C8EO4, C8EO8, C8EO12, C10EO3, C12EO3-C12EO6, C12EO8, C12EO12, C14EO3, C14EO6, C16EO3, C16EO4, C16EO6, C16EO8, C16EO12, C9PhEO8 and C12(2-C10)EO10. Phase diagrams were determined for C8EO4, C12EO3-C12EO6, C12EO8, C16EO4, C16EO8 and C16EO12. With the other compounds optical microscopy was used to determine the number, sequence and type of mesophases.