Polymer–surfactant complexes: solubilization of polymeric globule by surfactants

The behavior of polymeric globule in a solution containing surfactants is analyzed within the framework of the Flory lattice theory. The amphiphilic structure of surfactant molecule is modeled as two adjacent lattice cells with opposite interaction parameters. Therefore, model surfactants prefer the globule–solvent interface rather than regions inside and outside the globule. It is found that at surfactant concentrations below some Critical Solubilization Concentration (CSC), surfactant molecules are adsorbed on the globular surface of almost invariable spherical shape. The coverage of the globular surface by surfactants takes place in rather broad region of concentrations. If the surfactant concentration exceeds the CSC, the globule sharply transforms to a coil. The transition is found to take place in a very narrow surfactant concentration region, i.e. polymer chain bypasses intermediate globular shapes and can be approximately regarded as a chain of spherical blobs. In this case, the solvent quality and the surfactant concentration are two main factors inducing globule–coil transition. Reducing of the transition point with increasing surfactant concentration as well as the steepness of the transition is in qualitative agreement with the experimental data.