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. (c) 2006 The Society of Rheology.