(233i) Multiscale Molecular Modeling of Flory-Huggins ?-Parameter Calculation and Simulation of Structural Transformation of Photo-Regulated Multicompartment Micelle

There has been a growing interest in designing and synthesizing polymer nanostructures with degrees of complexity and controlling over the composition for various applications, which includes diagnostic imaging, and gene and drug delivery. Although much progress has been made in drug delivery systems, the design of a suitable carrier for the delivery of hydrophobic drugs is still a challenging problem. Overcoming such problem in designing drug carrier, multicompartment polymeric micelles, comprised of block copolymers with two or more monomeric species, have emerged as a solution since a desirable micellar architecture can be achieved by tuning polymer properties. Due to the complexity of the multicompartment micelle structure, molecular modeling and simulation have been widely used as powerful tools to characterize the structures and behaviors of micelles consisting of many amphiphilic multiblock copolymers in solution state. In this regard, the structural transformation of multicompartment micelle consisting of amphiphilic A-b-(C-spiropyran) diblock copolymer in water, induced by the photo-regulated transition between hydrophobic non-ionic spiropyran and hydrophilic zwitterionic merocyanine, is investigated using a set of computational methods such as density functional theory (DFT), molecular dynamics (MD) simulation, and dissipated particle dynamics (DPD) simulation. By employing a new computational framework for Flory-Huggins -parameter, which is improved by considering solvation free energy, it is demonstrated that the -parameter for a merocyanine-water pair is significantly smaller than that for a spiropyran-water pair, indicating that hydrophobic spiropyran becomes hydrophilic merocyanine through the photo-switched transition. Our computational procedure of -parameter calculation is further validated by investigating the deprotonation of acrylic acid in water. Finally, using a set of calculated -parameters, DPD simulations are performed employing two different block copolymers with two different block length: A₁₀-b-(C₆-Spiro₁₂) (Micelle I) and A₆-b-(C₁₀-Spiro₁₂) (Micelle II), demonstrating that both micelles undergo distinctive inside-out transformations as a function of the block length ratio. Through the structure analysis, it turns out that Micelle I keeps a well-defined core-shell structural feature before and after the transformation, whereas Micelle II loses such structural feature because short Block A is not capable of forming the core of micelle.