Figure 5. Temperature dependence of the mechanical properties of the P1f hydrogel (at 1 mg ml^–1).

(a) Differential modulus against stress at different temperatures. The solid line shows the high stress limit m=3/2. (b) Plateau modulus G₀, as a function of temperature T (linear scale). In the gel at T≥22 °C, G₀ increases exponentially with T over the investigated temperature window; the solid line is a fit to Te^2βT with β≈0.08 K⁻¹. At T≤22 °C, G₀ increases fast with T, corresponding to the transition from liquid to gel. (c) critical stress σ_c (pink circles) and critical strain γ_c (blue squares) as a function of T; the solid lines are fits to Te^βT and e^−βT with β≈0.08 K⁻¹. Both σ_c and γ_c show a sharp decrease at T≤22 °C. (d) The stiffening index m as a function of T clearly shows three regimes. In the high temperature regime, m weakly scales linearly with T, and around the marginal regime (see text) m sharply decreases while it restores to 0.9 on further decreasing T. The values for m were recorded at stresses close to the critical stress (at σ=3σ_c). At higher stress, in particular at high temperature, m will approach 1.5 ref. 16, but such stresses are impossible to apply close to T_gel.