Interfacial properties of nonionic micellar aggregates as a function of temperature and concentration

By means of density, dielectric spectroscopy and sound velocity measurement s we perform a systematic study on the polyoxyethylene C12E6 nonionic surfa ctant solutions as a function of temperature and concentration. Both densit y and sound velocity data, at about 34 degrees C, coincide with the value o btained for pure water. Above this temperature the density is lower than th e water density whereas below, it is greater, the opposite happens for the compressibility. Combining results from these different techniques we attem pt a detailed description of the evolution of the micellar interfacial prop erties with temperature. It is well known that nonionic surfactant solution s dehydrate with growing temperature. Our results indicate that this proces s is associated with a continuous change in the polymer conformation and in the local density of the micellar interface. (C) 2000 Elsevier Science B.V . All rights reserved.