Molecular Weight Dependence of the Rotational Diffusion Constant and the Rotational Viscosity of Nematic Side-Group Polymers

Abstract

A combination of dielectric relaxation spectroscopy and measurements of the rotational viscosity by director reorientation experiments was used to study nematic side-group polymethacrylates with different molecular weight. The contribution γ₁^m of the mesogenic groups to the total rotational viscosity γ₁^t is estimated on the base of Marrucci's theory from the rotational diffusion constant D_r obtained by relaxation frequency determinations. γ₁^m then is used to separate the contribution Δγ₁ of the friction due to rearrangements of anisotropic ordered polymer backbones to γ₁^t. The molecular weight dependence of Δγ₁ can be described by a power law, as predicted by Brochard's theory. The resulting exponent gives evidence for the presence of nonentangled random coil conformations.