Rheology of textured rodlike polymeric systems under shear flow as revealed by brownian dynamics simulation

A Brownian dynamics simulation algorithm has been developed in this paper to study the rheology of rodlike polymers under shear flow. Through the introduction of the Lebwohl-Lasher potential and consideration of the nearest-neighbor interaction without mean-field approximation, the spatial inhomogeneity of the director field, stresses as well as the multiple-domain effect are automatically included. By this new algorithm, the transient rheological behaviors of textured and untextured (uniformly aligned) rodlike polymeric systems are investigated. The damped oscillations of stresses are reproduced and the negative first normal stress differences are found at the moderate shear rate, all of which agree with the experimental observations in literature very well. Our simulation also demonstrates that the textured initial states only affect the transient responses of stress etc. at early shear stage and that the multiple domains formed during shear flow started from both textured and untextured initial states are essentially the same. The multiple domains are, therefore, the inherent structures resulting from the instability of shear flow, which are not sensitive to the initial textures, and the so-called multiple domains are conceptually different from the rest textured structures.