Water activity in aqueous solutions of inhomogeneous electrolytes

The activity of water in the bulk aqueous and surface regions of inhomogeneous solutions of electrolytes was determined by the method based on hydration of aldehydes. The inhomogeneous solutions of electrolytes used in the study were those of spherical and rodlike SDS micelles. It was established that in the bulk aqueous phase of the micellar SDS solution the change of the water properties was mainly determined by the anions of the electrolyte. Chloride and perchlorate ions were found to decrease the water activity. The change of water properties in the surface micellar phase of SDS solution is mainly determined by the cations of the electrolyte; sodium and ammonium ions decrease a(Ws), while potassium and magnesium ions increase it. From an analysis of the electrolyte concentration effect on the water activity the micellar sphere-rod transition has been estimated.