Properties of Random Block Copolymer Morphologies: Molecular Dynamics and Single-Chain-in-Mean-Field Simulations

B Steinmuller and M Muller and KR Hambrecht and GD Smith and D Bedrov, MACROMOLECULES, 45, 1107-1117 (2012).

DOI: 10.1021/ma202311e

The equilibrium structure and ordering kinetics of random AB block copolymers is investigated using a Lennard-Jones bead-spring model and a soft, coarse-grained model. Upon increasing the incompatibility a disordered microemulsion-like structure is formed, whose length scale slightly increases with segregation. The structure factor of composition fluctuations, molecular conformations, single-chain dynamics and collective ordering kinetics are investigated as a function of the segregation between A and B blocks. The harsh repulsion of the Lennard- Jones potential gives rise to pronounced fluid-like packing effects that affect the liquid structure on the length scale of the bead size and, upon cooling and increase of the local density, result in an additional slowing down of the dynamics. The soft, coarse-grained model does not exhibit pronounced packing effects and the softness of the potential allows for a faster equilibration in computer simulation. The structure and dynamics of the two different models are quantitatively compared. The parameters of the soft, coarse-grained model are adjusted as to match the long-range structure of the bead-spring model, and it is demonstrated that the soft, coarse grained model can be utilized to generate starting configurations for the Lennard-Jones bead spring model.

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