Dielectric Properties and Structure of Aqueous Decaoxyethylene p-Isononylphenyl Ether Solutions

Abstract

The static permittivity es of aqueous decaoxyethylene p-isononylphenyl ether (NOP-10 grade) solutions is measured at surfactant concentrations of 1.14 and 4.97 wt % within 275–351 K temperature range; at concentrations of 9.96, 20, and 30 wt %, within 275–313 K range. Data on es are analyzed, using the models of dilute disperse systems of oil–water type containing spherical particles, oblate and prolate spheroids. At 30, 20, and 9.96 wt % NOP-10 content, fragments of hexagonal mesophase are still retained in the isotropic phase near the interface, where there is a certain orientation of micelles acquiring the shape of prolate spheroids instead of cylindrical micelles. Upon heating up to 313 K, micelles are disoriented and their shape changes in prolate spheroid → spherical micelle → oblate spheroid sequence. With a further rise in water content, the fragments of lamellar mesophase appear in the isotropic phase at 4.97 and 1.14 wt % NOP-10 near the melting points of these solutions. They can exist with equal probability as the regions where either spherical micelles are located in the nodes of cubic lattice or oblate spheroidal micelles are distributed at random. As the temperature approaches the cloud point of dilute solutions, the randomly oriented oblate spheriodal micelles tend to acquire the disc-like shape.