Raman spectroscopic study of temperature dependence of water structure in aqueous solutions of a poly(oxyethylene) surfactant

Abstract

The temperature dependence of the water structure in aqueous solutions of a poly(oxyethylene) surfactant C12E5 was examined at concentrations 0, 20, 30, 45, 70 and 90wt% by Raman spectroscopy of the O–H stretching band. The ratio of the intensities of the component around 3200cm−1 (the collective in-phase O–H stretching vibrations of bonded aggregates) to the component around 3400cm−1 (the O–H stretches in which the phase relations are lost) was monitored in the temperature range from 0 to 39°C. The results show that the speed of the thermal destruction of the H-bond network increases as the concentration increases from 0 to 45wt%. This change is attributed to the existence of a substantial amount of water in the system that takes part in the hydrophobic hydration of the poly(oxyethylene) headgroups, despite their predominantly hydrophilic character. The conclusion that this kind of water, which is known to have restricted mobility, plays an important role in the surfactant–water systems is consistent with the high viscosity of the liquid crystalline phases.