Molecular Thermodynamic Model for Gibbs Energy of Mixing of Nonionic Surfactant Solutions

A segment-based molecular thermodynamic model for the Gibbs energy of polymer solutions or oligomer solutions is used to represent the Gibbs energy of mixing for aqueous nonionic surfactant solutions. In contrast to the mass-action models and pseudophase models, which are often discussed in the literature, the Gibbs-energy model provides an explicit account of the solution nonideality, including activity coefficients of monomeric amphiphiles in the aqueous phase. The equilibrium between monomeric amphiphiles and micellar amphiphiles is described by the equal-activity relationship. The Gibbs-energy model makes it possible to use a well-accepted molecular thermodynamic framework to correlate and represent phase behaviors of aqueous nonionic surfactant solutions.