Conformational and rheological dynamics of semiflexible macromolecules undergoing shear flow: A nonequilibrium Brownian dynamics study

Abstract

Nonequilibrium Brownian dynamics simulations (NEBD) are used to model the dynamics of semiflexible macromolecules undergoing shear flow. The mathematical model utilizes a discretized version of the Kratky–Porod wormlike (or persistent) chain as the building block, generalized to include flow. The Fokker–Planck equation resulting from such an analysis is converted to a stochastic differential equation from which the simulation algorithm for the NEBD is obtained. Various conformational and rheological quantities are monitored, under both steady-state and transient conditions, with the primary independent variable being the flexibility parameter β, the bending constant of the chain. The model qualitatively describes many of the experimentally observed effects in such systems, most notably birefringence overshoots, cessation effects, and various steady-state effects. In addition, many of the qualitative rheological features of both rigid rod (or flexible) polymers are captured as β is made very large (or small). The advantage of the NEBD over an analytical treatment is its ability to incorporate (analytically intractable) effects such as hydrodynamic interactions and its (natural) ability to obtain transient information, a facet useful in comprehending the differing dynamics of rigid and less rigid macromolecules.