Dissipative particle dynamics study of translational diffusion of rigid-chain rodlike polymer in nematic phase

In this study, dissipative particle dynamics (DPD) method was employed to investigate the translational diffusion of rodlike polymer in its nematic phase. The polymer chain was modeled by a rigid rod composed of consecutive DPD particles and solvent was represented by independent DPD particles. To fully understand the translational motion of the rods in the anisotropic phase, four diffusion coefficients, D∥(u), D⊥(u), D∥(n), D⊥(n) were obtained from the DPD simulation. By definition, D∥(n) and D⊥(n) denote the diffusion coefficients parallel and perpendicular to the nematic director, while D∥(u) and D⊥(u) denote the diffusion coefficients parallel and perpendicular to the long axis of a rigid rod u. In the simulation, the velocity auto-correlation functions were used to calculate the corresponding diffusion coefficients from the simulated velocity of the rods. Simulation results show that the variation of orientational order caused by concentration and temperature changes has substantial influences on D∥(u) and D⊥(u). In the nematic phase, the changes of concentration and temperature will result in a change of local environment of rods, which directly influence D∥(u) and D⊥(u). Both D∥(n) and D⊥(n) can be represented as averages of D∥(u) and D⊥(u), and the weighted factors are functions of the orientational order parameter S2. The effect of concentration and temperature on D∥(n) and D⊥(n) demonstrated by the DPD simulation can be rationally interpreted by considering their influences on D∥(u), D⊥(u) and the order parameter S2.