Nonlinear stress relaxation of a styrene–butadiene random copolymer

Abstract

The isothermal uniaxial stress relaxation response in the vicinity of the glass‐to‐rubber transition has been measured for a lightly crosslinked poly(styrene–butadiene) random copolymer, 85% styrene by weight. The volume change during stress relaxation was determined by measuring the time‐dependent lateral contraction of the specimen with a Hall‐effect proximity detector. The specimen exhibited an instantaneous dilation upon application of the strain and a subsequent time‐dependent volume decrease. The stress relaxation behavior and the associated volume relaxation were determined for a variety of strains and temperatures in both the linear and nonlinear viscoelastic regime. As the applied strain was increased the isothermal tensile modulus decreased and the shape of the log(modulus) vs. log(time) curve was altered. At equal levels of strain the tensile modulus exhibited increasing deviations from the linear viscoelastic response as the temperature was decreased. The maximum difference between the nonlinear tensile modulus and the linear viscoelastic response was observed at short times. Subsequently, the nonlinear tensile modulus began to approach the linear viscoelastic modulus with increasing time. Both the instantaneous dilation and the magnitude of the time‐dependent part of the volume change increased as the level of applied strain was increased and/or as the temperature was decreased. The observed nonlinearity in the tensile stress relaxation response has been quantitively related to the experimentally measured volume relaxation with a free‐volume model.

Arrhenius-type temperature dependence of the segmental relaxation below Tg

“…1,5,10,[12][13][14][15][18][19][20][21][22]27,29,30 Here we provide the relevant definitions for the analysis used in this study. The superposition principle is based on the assumption that the shape of the viscoelastic spectrum, and therefore that of the relaxation modulus, does not vary with the relevant parameter, e.g., aging time t e or temperature T. In the framework of the KWW function ͓Eq.…”

“…5,[15][16][17][18][19][20][21][22] Therefore, it is important that measurements of the relaxation response be performed in such a way that the equilibrium response is obtained. We assure this by performing physical aging experiments using Struik's 22 protocol ͑described subsequently͒ for times as long as 23d(2 ϫ10 6 s) to assure equilibration of the mechanical response.…”

Hedgehog signaling controls Soma‐Germen interactions during Drosophila ovarian morphogenesis

“…The data in Figures 2 and 3 are qualitatively consistent with an increase in creep compliance for nylons and cellulosic fibers at higher jump stress 15, 42. Watanabe et al,29 Osaki et al,30 and Merriman and Caruthers43 report decreasing stress relaxation moduli at larger strain in the nonlinear regime above 10% strain. For comparison with the stress relaxation data of Kraton™ D‐1101 in Figure 2, Merriman and Caruthers measured nonlinear stress relaxation in lightly crosslinked styrene–butadiene random copolymers in the vicinity of the glass transition temperature 43.…”

“…Watanabe et al,29 Osaki et al,30 and Merriman and Caruthers43 report decreasing stress relaxation moduli at larger strain in the nonlinear regime above 10% strain. For comparison with the stress relaxation data of Kraton™ D‐1101 in Figure 2, Merriman and Caruthers measured nonlinear stress relaxation in lightly crosslinked styrene–butadiene random copolymers in the vicinity of the glass transition temperature 43. The volume decrease during stress relaxation, that follows the instantaneous dilation upon deformation, was measured experimentally, and nonlinearity in the transient viscoelastic response was correlated with volume relaxation via fractional free volume 43.…”

Nonlinear stress relaxation in palladium(II) complexes with triblock copolymers of styrene and butadiene

“…For comparison with the stress relaxation data of Kraton™ D-1101 in Figure 2, Merriman and Caruthers measured nonlinear stress relaxation in lightly crosslinked styrenebutadiene random copolymers in the vicinity of the glass transition temperature. 43 The volume decrease during stress relaxation, that follows the instantaneous dilation upon deformation, was measured experimentally, and nonlinearity in the transient viscoelastic response was correlated with volume relaxation via fractional free volume. 43 Matsuoka et al 44 report that polycarbonate dilates under tensile deformation in the glassy state, and Poisson's ratio decreases from 0.45 to 0.375 at higher strain.…”