Rheological response of polydisperse nematic polymethacrylates: Relaxation times and conformational transition

We investigated the rheological behavior of two nematic polymethacrylate homopolymer samples, S1 and S5, containing azobenzene side groups. They possessed different molar mass and molar mass distribution, which was fitted by a twocomponent molar mass distribution function. Creep and oscillatory measurements enabled us to obtain the temperature dependence of the zero shear viscosity. The time-temperature superposition principle was found to hold over large temperature intervals; in particular no discontinuities were detected at the isotropic-nematie transition in either sample. Moreover, temperature scans of the storage modulus of the polymers at a constant frequency were marked by glass and conformational transitions, the conformation transition being driven by the nematic order. The storage modulus and the distribution of relaxation times were analyzed in terms of the two components of the molar mass distribution.