1. Brownian Dynamics Simulations of Polymers in Good and Poor Solvents with Chain Non-Crossability in Flow Fields
Nazish Hoda and Ronald G. Larson, University of Michigan, Ann Arbor 48109
We developed and implemented a coarse-grained Brownian dynamics method of including short-range and long-range self-attractions and/or self-repulsions of a bead-spring model of a polymer chain in a solvent, representing solvent quality and/or electrostatic interactions. We accomplished this by imposing either attraction or repulsion between the beads and a long-range repulsion between springs. The repulsion between springs also prevents chain-chain crossings, and so imposes topological interactions (i.e., “entanglements”). We discovered that entanglements have only a minor effect on the chain deformation (see Fig. 1) in shearing flow. However, when spring-spring repulsion is added, and its effect on the no-flow radius of gyration is cancelled out by a bead-bead attraction, there is little deformation under a shearing flow, compared to a polymer with a similar no-flow radius, but with no interactions between either beads or springs (see Fig. 2). We find (Fig. 3) that under shear, the bead-bead attraction leads to a collapse of the chain configuration, as sticky beads are driven frequently into contact by the flow.
Fig. 1. Dependence of radius of gyration Rg on shear rate in a good solvent with and without topological constraints.
Fig. 2. Dependence of radius of gyration Rg on shear rate in a theta solvent with and without topological constraints.
Fig. 3. Snapshots showing the shear-induced collapse of a chain in a theta solvent. The chain has 20-beads and the dimensionless shear rate is 10.