Density Measurements on C12Ej Nonionic Micellar Solutions as a Function of the Head Group Degree of Polymerization (j = 5−8)

Density measurements have been performed on water solutions of nonionic surfactants oligooxyethylene glycol−monoether (C12Ej with j = 5, 6, 7, 8) in a wide range of temperatures and concentrations. The densities of the pure surfactants in their liquid state were measured too. The observed values are almost a linear combination of the densities of an oil and of an oxyethylene (EO) bulk liquid phases. The deviation from ideality reduces as j increases and may be reflects an entropic contribution due to a partial mixing of the oil and EO termination. A temperature (Tcross), at which the C12Ej aqueous solution density coincides with the solvent one up to 50 wt % has been found in all the Ej species. The Tcross of the different Ej results to be scaling temperatures for the excess density of these surfactants. The sphere-to-rod transition temperatures are scaling temperatures too; thus it is expected that the differences between these two temperatures be constant for each of the Ej species. In the case of j = 6...