Rheological properties of mesomorphic polyorganosiloxanes

The rheological properties of three mesomorphic linear polyorganosiloxanes [poly(diethylsiloxane), poly(diphenylsiloxane), poly(hexylphenylsiloxane)] were studied by the method of capillary viscometry in a wide temperature ra nge. As was found, all the above polymers are viscoplastic bodies which are capable of plastic flow at shear stresses above a critical level tau (cr) (yield shear stress). The temperature dependences of tau (cr) were estimate d, and a relation between shear stress tau and shear rate (gamma) over dot was found to be described by a power law tau = k(gamma) over dot (n) as in the viscous flow of polymer melts. The temperature dependences of apparent viscosity upon viscous how eta = tau/(gamma) over dot were analyzed, and it was shown that at lower temperatures eta is primarily controlled by tau (c r).