Elongational viscosity of monodisperse and bidisperse polystyrene melts

The start-up and steady uniaxial elongational viscosity have been measured for two monodisperse polystyrene melts with molecular weights of 52 and 103 kg/mole, and for three bidisperse polystyrene melts. The monodisperse melts show a maximum in the steady elongational viscosity vs. the elongational rate, 4, of about two times the limiting value of 3h0 expected for a Newtonian fluid, whereas the bidisperse melts have a maximum of up to a factor of seven times the Trouton limit of 3770. The Wiest model which incorporates anisotropic drag and finite extensibility may be used to interpret the results in molecular terms.