A Predictive Model for Equilibrium Swelling of Thermoresponsive Gels in Aqueous Solutions of Surfactants

Surfactants are used in wastewater treatment, soil remediation, and pharmaceutical industry to disperse and dissolute poorly water-soluble compounds. Thermoresponsive (TR) gels loaded with surfactants are applied for removal of contaminants and controlled drug delivery. Design of gel-surfactant systems require quantitative predictions of the effect of surfactants on water uptake by TR gels. A simple model is developed for equilibrium swelling of TR gels in solutions of ionic and nonionic surfactants. Swelling and deswelling of the gels are driven by hydrophobic interactions between segments of chains and surfactant molecules. The model involves a relatively small number of parameters and can describe (and predict in some cases) the main phenomena observed in experiments: (i) an increase in the equilibrium degree of swelling below the volume phase transition temperature (VPTT), (ii) shift of VPTT to higher values, and (iii) weakening of the deswelling process above VPTT with an increase in mole fraction of surfactant. To find material parameters, equilibrium swelling diagrams are fitted on poly(N-isopropylacrylamide), poly(N-cyclopropylacrylamide), poly(N-ethylacrylamide), poly(N-vinylcaprolactam), and poly(vinyl methyl ether) gels. Results of numerical analysis reveal good agreement with experimental data.