Probing Large Deformation and Fracture Behavior of Physically Assembled Gel System by Varying Polymer Concentration

Abstract

Physically assembled gels have promising applications in many fields because of their tunable mechanical properties. Here, we report the mechanical properties as a function of polymer volume fraction ($\phi$) for a physical gel system consists of poly(styrene)-poly(isoprene)-poly(styrene) [PS-PI-PS] in mineral oil. The PI-block molecular weight is higher than the entanglement molecular weight, which leads to the entanglement of PI-blocks at higher $\phi$. The micellar microstructure for all gels results in a similar stress relaxation mechanism, as captured by the superposition of stress-relaxation results. Tensile testing experiments reveal a strain-rate dependence mechanical response for the entangled gels. To capture the critical energy release rate ($\Gamma_0$) over a range of $\phi$, both cavitation rheology and fracture experiments were performed and we obtain $\Gamma_0\sim\phi^{2.0}$. The gel moduli scale with the volume fraction as $\phi^{2.39}$, where the exponent is likely dictated by the change in loop-to-bridge fraction with increasing $\phi$.