(262ai) Molecular Modeling of Nonionic Block Copolymer Micelles

Nonionic block copolymer micelles have been the focus of much interest for both academia and industry over decades. The immiscibility of constituent groups causes micellar aggregates when dissolved in a selective solvent. Over the years a large number of experiments have been done to study temperature and pressure effects onto critical micelle concentration. The development of theory to model micellar solutions is limited by inhomogeneity of micellar structures. Several early successes of modeling temperature effects follow Flory-Hugginsâ?? theory but ignores pressure effects. We investigate both how temperature and pressure can affect critical micelle concentration by inhomogeneous statistical associating fluid theory(iSAFT). iSAFT is a classical density functional theory based on statistical mechanics that uses physical molecular parameters. We found that iSAFT can capture the pressure and temperature effects onto critical micelle concentration in agreement with experimental data.

Beyond temperature and pressure, microscopic qualities of a block copolymer micelle e.g. polydispersity and chain architecture, can also influence critical micelle concentration and even result in a complex structure. Linear tiblock copolymer in fact has a higher critical micelle concentration than cyclic triblock copolymer. Microscopic entropic effect is significant in self-assembly. Classical thermodynamics, however, fails to take into microscopic effects since it ignores molecular configurations nor variation in microscopic densities. iSAFT is a suitable theoretical model to study local density effect and chain connectivity. We used iSAFT and molecular simulation tool to explain synergistic effects of mixed micellization and polydispersity induced complex micellar structures. The iSAFT theory agrees well with molecular simulation results. With iSAFT, molecular simulation, and physical parameters obtained from bulk fluids, we believe this is a new trend towards quantitative modeling of block copolymer micelles and soft material.