POLYELECTROLYTES IN SHEAR AND EXTENSIONAL FLOWS - CONFORMATION AND RHEOLOGY

The conformational and rheological dynamics of dilute solutions of pol yelectrolyte macromolecules undergoing shear and extensional flow are modeled using Nonequilibrium Brownian Dynamics (NEBD) and Configuratio n-Biased Monte Carlo (CBMC) simulations. The mathematical model utiliz es a bead-spring chain with charged beads that interact through a scre ened Debye-Huckel potential, and that also interact through stretching and bending forces. The diffusion (or Fokker-Planck) equation for the probability density of the positions of the beads of the chain is con verted to a Stochastic Differential Equation (SDE), from which the sim ulation algorithm for the NEBD is obtained. The CBMC is used in the in itial chain generation and in determining steady-state properties in e longational flows. Various conformational and theological quantities, such as the stress and birefringence, are monitored, under both steady -state and transient conditions, with the primary independent variable being the salt concentration (parametrized through the Debye length) and the strength of interact:ion q, related to the degree of ionizatio n of the chain. It is found that this model is able to describe qualit atively many of the experimentally observed features in such systems. (C) 1998 John Wiley & Sons, Inc.