Twist viscosity coefficient of a dilute solution of the main-chain mesogenic polymer in a nematic solvent : an estimation of the anisotropy and the rotational relaxation time of polymer chains

The dynamics of Freederiks transition at bend deformation in the magnetic field was used to study the visco-elastic properties of a dilute solution of mesogenic main-chain polymer in a low molecular weight nematic liquid crustal pentylcyanobiphenyl (5CB). Analysis of obtained data based on Brochard's theory for polymer chains in the nematic environment provided the temperature dependences for the anisotropy $R_{\parallel}/R_{\perp}$ of chains (where $R_{\parallel}$ and $R_{\perp}$ are dimensions parallel and perpendicular to the nematic director) and for the rotational relaxation time of chains $\tau_{\rm R}$. The value of $R_{\parallel}/R_{\perp}$ decreased with temperature from 1.85 to 1.75 and $\tau_{\rm R}$ decreased according to the Arrhenius law