Phase equilibria of dodecylhexaoxyethylene glycol monoether in water

Abstract

Low-angle X-ray diffraction has been used to characterize the two lyotropic mesomorphic phases (neat phase and middle phase) which are formed in the dodecylhexaoxyethylene glycol monoether + water system. The occurrence of these two anisotropic mesomorphic phases does not affect the behaviour of the thermodynamic excess functions which have been interpreted in terms of solute-water interactions. Careful measurements of water vapour pressure have been necessary to establish the limited extent of the two phase co-existence regions which separate homogeneous mesomorphic phase regions from isotropic solution in this system. Volume and heat capacity measurements as a function of temperature across mesomorphic phase boundaries have confirmed that the neat phase/isotropic solution and the middle phase/isotropic solution transformations are first-order phase transitions with very small volume and enthalpy changes.