Concentration Dependences of Nonlinear Viscoelastic Functions for Polystyrene Solutions

Abstract

Concentration dependences of viscoelastic functions G (t, s),η (t, κ), and η (t, κ) were examined on solutions of two polystyrenes (M_ω=3.10×10⁶ and 5.53×10⁶) in diethyl phthalate. Here G is the relaxation modulus, s is the magnitude of shear, and κη and κη are shear stresses after the start and cessation, respectively, of steady shear flow with the rate of shear κ. When the concentration c was relatively low, i. e., when cM_ω,<10⁶g/cm³, the reduced functions η/η⁰and /η/η⁰ obteined at various c were unique functions of two reduced variables t/τ₁⁰ and κτ₁⁰. Here η⁰ is the zero shear viscosity and τ₁⁰ is the longest relaxation time. The reduced function G/G₁⁰, where G₁⁰is the relaxation strength corresponding to τ₁⁰, was also a unique function of two variables, t/τ₁⁰and s, in the same range of c as above. In this case, however, a slight dependence of G/G₁⁰, on c remained uneliminated at relatively short times. These results may indicate that in the description of nonlinear viscoelastic effect, the strain rate is most properly expressed in reference to the rate of stress relaxation 1/7τ₁⁰. This method of reduced variables was not applicable when the concentration was higher than the values stated above.