(574e) Simulation Studies of Surfactant Interactions with Carbopol-Type Ionic Polymer Gels

Surfactant-loaded polymeric gels are of great interest for the development of various consumer products. However, the physical-chemical mechanisms of gel stability and rheology are poorly understood, and the search for new formulations with improved properties is based mainly on empirical trial-and-error experimentation. We attempt to develop a molecular simulation approach aiming at a better understanding and quantitative predictions of morphological stability and rheology of gel-forming systems containing surfactants and cross-linked polymers like Carbopol. The multiscale approach includes molecular ab-initio optimization, thermodynamic modeling with Conductor-like Screening Model (COSMO), dynamics (MD) simulations of polymer-surfactant interactions at the atomic scale (2-5 nm), and dissipative particle dynamics (DPD) simulations at the mesoscale up to 50nm. We focus on gel-forming copolymers of highly hydrophilic polyacrylic acid and various hydrophobic compounds mixed with anionic surfactants p-(1-hexyl)heptyl benzenesulfonate (NaLAS), and sodium dodecylsulphate (SDS) and amino oxide (AO). SEM studies suggest that Carbopol forms a foam-like gel, which is destructed as the surfactant concentration increases. Our simulations shed light on this phenomenon. We demonstrate that surfactant molecules form micelles inside the polyacrylic acid structure without any appreciable interactions with the polymer. At the same time, surfactants interact intensively with hydrophobic linkers that may cause polymer network rapture. Using the DPD simulations, we show how the gel nanostructured morphology and the disjoining pressure in the polymer foam films depend on the chemical composition and surfactant concentration.