CONTINUUM AND MOLECULAR INTERPRETATION OF IDEAL ELASTIC FLUIDS

Measurements of the storage modulus as a function of frequency and the steady shear viscosity and first normal stress difference as a function of shear rate are presented for ideal elastic fluids constructed by dissolving a high molecular weight polyisobutylene in a solvent composed of kerosene and a low molecular weight poly(l-butene). The data, presented for four concentrations and at two temperatures, are extrapolated to zero concentration to determine the intrinsic viscosity and intrinsic first normal stress coefficient. The intrinsic quantities are discussed in terms of molecular theories which include variable hydrodynamic interaction and excluded volume effects. While the intrinsic quantities show significant deviation from ideal elastic fluid behaviour in a molecular sense, they are well represented when viewed from a continuum point of view. The steady and dynamic shear properties are well predicted with the Oldroyd-B constitutive equation when the relaxation time of the solvent is included.