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

By means of density, dielectric spectroscopy and sound velocity measurements we perform a systematic study on the polyoxyethylene C12E6 nonionic surfactant solutions as a function of temperature and concentration. Both density and sound velocity data, at about 34°C, coincide with the value obtained for pure water. Above this temperature the density is lower than the water density whereas below, it is greater, the opposite happens for the compressibility. Combining results from these different techniques we attempt a detailed description of the evolution of the micellar interfacial properties with temperature. It is well known that nonionic surfactant solutions dehydrate with growing temperature. Our results indicate that this process is associated with a continuous change in the polymer conformation and in the local density of the micellar interface.