TRANSIENT ELONGATIONAL RHEOLOGY OF POLYMERIC FLUIDS

The elongation viscosity of a high viscosity polymer fluid can be measured by equilibrium techniques. Low viscosity fluids require the use of non-equilibrium methods which produce an instantaneous value. Using two solutions of polyisobutylene in different solvents it can be shown that these instantaneous values of elongational viscosity are strongly dependent on the experimental method employed for the measurement. However. by considering the results in terms of a three-dimensional plot of elongational viscosity, strain and time of elongation, a three-dimensional surface can be produced. It is postulated that the different techniques merely trace out different lines on this surface. producing the apparently different data when projected onto a two-dimensional plot of elongational viscosity vs strain (or strain rate).