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 $\phi$.