Self-Assembly of Ionic Surfactants in Polyelectrolyte Solutions:A Model for Mixtures of Opposite Charge

摘要

A thermodynamci model of polyelectrolyte/surfactant interactions is derived.The model considers the binding of polyion chains to the surface of oppositely charged surfactant micelles.The electrostatic interactions are treated within the Posson-Boltzmann cell model.The nonelectrostatic interactions are described as in earlier phenomenolgical models of charged micelles.An explicit expression for chemical potential of the surfactant in the micelles in derived.It is used to calculate the critical aggregation concentration (cac) in solutions o fhydorphilic anionic polyelectrolytes with flexible backbones.The results are compared with experiemntal data for cationic surfactants,bothmonovalent and divalent.A reasonable agreement is obtained when the repulsive energy between surfactant headgroups is assumed tovary as a constant/area per headgroup.The modelexplains why monovalent and divalent surfactants with the same hydrocarbon chain length have aoubt the same hydrocarbon chain length have about the same cac.It accounts for the increase of the cac with increasing salt and polyelectrolyte concentrations and explains a previously found correlation between the cac and the aggregation number for a given surfactant interacting with different polyelectrolytes.The paper contains a summary of experimental results and a detailed discussion of thenature of the interaction between polyions an dsurfactants.A mechanism for the surppression of overcharging of the nature of the interaction between poyions and surfactants.A mechanism for the suppressin of overcharging of the micelles by the polyion is discussed.