Effect of solvent quality on the rheological and rheooptical properties of flexible polymer solutions

The dynamics of dilute solutions of flexible polymer molecules with intramolecular excluded volume interactions are modeled using nonequilibrium Brownian dynamics (NEBD) and configuration-biased Monte Carlo (CBMC) simulations. The mathematical model consists of beads interacting through stretching and excluded volume forces under both shear and extensional flow. Various conformational and rheological quantities, such as birefringence, mean squared end-to-end distance, and viscosities, are calculated for steady-state and transient flows, with the primary independent variable being the solvent quality e*. The model predicts coil-stretch transitions in extensional flow. The molecular weight scaling of the critical extension rate is found to vary as M-1.6 under poor solvent conditions and M-2 in a good solvent, in qualitative agreement with experiments reported in the literature. Model calculations also qualitatively capture a number of other observed features, most notably higher elongational viscosities under good solvent conditions and faster relaxation behavior under poor solvent conditions.