(749j) Molecular Modeling of Microstructure, Solubilization and Micro-Emulsion of Block Copolymer Micelles By iSAFT

Block copolymer micelles have been the focus of much interest for both academia and industry over decades for extensive applications in enhanced oil recovery, cosmetic products, and drug delivery. The immiscibility of constituents causes micro-phase separation for high density block copolymer melts, and micellar aggregates when it is dissolved in a selective solvent. A few chemical potential models have been developed to predict sizes, aggregation number, solubilization ability, critical micelle concentration(CMC) etc. Most of the theories are phenomenological equation of state(EoS) types of theories and thus cannot fully capture the physics at a molecular level. We study the microstructures using inhomogeneous statistical associating fluid theory(iSAFT) a classical density functional theory iSAFT takes into account a range molecular interactions, including hard-sphere repulsion, chain connectivity, van der Waals attraction, and association.

iSAFT is demonstrated to predict different influences of hydrophobic tail and hydrophilic head of block copolymer surfactants on the size and CMCs of micelles. iSAFT showed that radii and CMCs of micelles are strongly dependent on the length of hydrophobic tail but not for the length of hydrophilic head. This agrees with experimental finding of Pluronic micelles. iSAFT also predicts the radii of triblock surfactant micelles is smaller than of diblock copolymer surfactants with the same head and tail groups. Similar agreement between theory and experiment results is also found for the CMCs of micelles of triblock and diblock copolymer surfactants.

Structure of solubilized micelles is similar to a surfactant micro-emulsion. By predicting the distribution of solute, solvent and surfactants within micelles by iSAFT, we are able to show the enhanced solubility of hydrocarbon in water with surfactants. iSAFT predicts the different solubility of normal alkanes and branched alkanes with different carbon numbers when using different surfactants.