Temperature and molecular weight dependence of the viscometric properties of main-chain liquid crystal polymers in nematic solvents

The twist and bend viscosities of dilute nematic solutions in 4'-(pentyloxy)-4-cyanobiphenyl (5OCB) and in 4'-pentyl-4-cyanobiphenyl (5CB) of the main-chain liquid crystal polymers, TPB10 and TPB13, which have a mesogenic group, 1-(4-hydroxy-4'-biphenyl)-2-(4-hydroxyphenyl)butane, separated, respectively, by flexible decamethylene and tridecamethylene spacers, were determined via dynamic light scattering analysis. A theoretical expression for the increment of twist viscosity, γ 1 , derived by Brochard can be applied to interpret the experimental results in terms of changes in the mean square end-to-end distances parallel (R∥2) and perpendicular (R⊥2) to the nematic director