Anisotropy of diffusion in a liquid crystalline system of semi-flexible polymer chains

Molecular dynamic simulations are reported for semi-flexible systems consisting of rod-like linear molecules. The molecules are composed of eight tangent isotropic soft spheres, connected by continuous elastic springs into a linear chain. Rigidity is introduced by additional springs between each sphere along the chain. The elasticity of the springs is used to tune the flexibility of the molecule. The formation of only a nematic LC phase is shown for all systems considered. Persistence length dependences of the jump of the order parameter and boundary volume fractions in isotropic and nematic phases at LC transition agree well with predictions of the Khokhlov - Semenov theory and with available simulation data. The effect of the flexibility on the translational and rotational diffusion in the nematic phase is studied. The anisotropy of translational diffusion was observed. For the estimation of the rotational diffusion coefficient for molecules in a nematic phase the wobbling-in-a-cone model was applied. Anisotropy of translational diffusion and ratio of translational and rotational diffusion coefficients show universal dependences on the order parameter.