Multi-Scale Modelling Efforts for Diblock Copolymers
Sharon Loverde1, Vanessa Ortiz, Dennis E. Discher2, and Michael Klein3. (1) Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19103, (2) Chemical and Biomolecular Engineering, University of Pennsylvania, Room 129 Towne Building, 220 South 33rd Street, Philadelphia, PA 19104-6393, (3) Center for Molecular Modeling, University of Pennsylvania, Philadelphia, PA 19103
Amphiphilic block copolymers self-assemble into vesicles and worm-like micelles in the aqueous phase with several unique characteristics--high stability and morphological tunability, as well efficient integration of hydrophobic drugs. In this simulation study, the thermodynamic stability of worm-like micelles are examined using a complete multiscale modelling effort -- starting from atomistic molecular dynamics that are matched with coarser models, and then progressing to mesoscopic simulations of entire worm-like micelles. Several key issues are addressed: assembly and disassembly, equilibrium scaling of the core size with the hydrophobic length of the copolymer, as well as dynamic limitations on time scales of DPD (dissipative particle dynamics). To begin with, examinations of the phase stability of the micelles probe the worm to spherical micelle crossover region. Fundamental properties of the copolymers in the micelles—including the radius of gyration, end to end distance, as well as the diffusional behavior—are examined. Simple polydisperse mixtures are then used to gain insight into the coupling between local curvature and concentration, as well as the stability of the micelles. Break-up of these mixed assemblies proceeds through dynamic undulation and budding from the end-cap region of the worm-micelles, in agreement with experimental observations.