Dependency of the Steady‐State and Transient Viscosity and First and Second Normal Stress Difference Functions on Molecular Weight for Linear Mono and Polydisperse Polystyrene Solutions

Abstract

Experimental data are reported for solutions of polystyrene in normal butyl‐benzene for concentrations, C, of 450 kg/m3 (with two exceptions). Polystyrene molecular weights, Mw, varied from 37,000 to 2×106, and molecular weight distributions, Mw/Mn, varied from 1.06 to 22. The solutions were sheared in cone‐plate geometry in steady‐state, oscillatory, and stress growth and decay shearing modes. For CMw>35,000, the viscosities depend on a molecular weight, M3,4. The first and second normal stress difference and related function dependences are similar. Both the first and second normal stress difference functions of the shear rate are similar and approach a constant “zero” shear rate asymptote. The ratios of the second to first normal stress difference coefficients for steady‐state shearing and the same ratios for the displacement and amplitude coefficients for oscillatory shearing have average values of −0.25, −0.225, and −0.22, respectively. The steady‐state shear compliances, Je0, computed from steady‐state “zero” shear rate first normal stress difference coefficients and the corresponding second normal stress difference properties are proportional to Mw(Mz/Mw)3,5 for CMw<critical. The normalized first and second normal stress differences grow and decay at the same relative rates upon the abrupt inception and discontinuance of steady‐state shearing.