CONFORMATIONAL AND RHEOLOGICAL DYNAMICS OF SEMIFLEXIBLE MACROMOLECULES UNDERGOING SHEAR-FLOW - A NONEQUILIBRIUM BROWNIAN DYNAMICS STUDY

Nonequilibrium Brownian dynamics simulations (NEED) are used to model the dynamics of semiflexible macromolecules undergoing shear how. The mathematical model utilizes a discretized version of the Kratky-Porod wormlike (or persistent) chain as the building block, generalized to i nclude how. The Fokker-Planck equation resulting from such an analysis is converted to a stochastic differential equation from which the sim ulation algorithm for the NEED is obtained. Various conformational and rheological quantities are monitored, under both steady-state and tra nsient conditions, with the primary independent variable being the fle xibility parameter beta, the bending constant of the chain. The model qualitatively describes many of the experimentally observed effects in such systems, most notably birefringence overshoots, cessation effect s, and various steady-state effects. In addition, many of the qualitat ive rheological features of both rigid rod (or flexible) polymers are captured as beta is made very large (or small). The advantage of the N EED over an analytical treatment is its ability to incorporate (analyt ically intractable) effects such as hydrodynamic interactions and its (natural) ability to obtain transient information, a facet useful in c omprehending the differing dynamics of rigid and less rigid macromolec ules. (C) 1998 The Society of Rheology. [S0148-6055(98)00602-6].