2000-07-05
10:15 at ML H 43

From rheometry to rheology

T. Sridhar

Department of Chemical Engineering, Monash University, Australia

Using a variety of examples from the recent literature on extensional flow of polymer solutions, this talk shows that simple constitutive equations are unable to capture the diversity of chain conformations in such flows. Such diversity is a feature of extensional flows and arises because deformation leads to significant chain extension. Substantial local extension appears to occur even at low strains and the behaviour of these stretched out portions influences the dynamics of the chain and makes a dominant contribution to the stress. Both the distribution function and the chain conformation appear to follow different paths during stretching and relaxation. As a result the second moment of the distribution function does not contain enough information to correctly predict the dynamics. Resolution of this deficiency in simple constitutive models is one of the challenges for rheology.