Effect of Salt and Temperature on Visco-Elasticity of Gelatin Hydrogels

Rheology studies, on aqueous gelatin gels, were performed below gelation temperature (T_g ≈ 28°C) in the temperature range, T= 5-25°C as a function of NaCl concentration (0.01-0.1M). In the low frequency domain and at a given temperature, both the storage (G') and loss (G") modulii exhibited power-law frequency dependence, G' ∼ ω^0.02±0.005 and G" ∼ ω^0.8±0.2. The network size, ξ estimated from low-frequency relaxation modulus, G₀ ≈ K_BT/ξ³ increased three fold as the temperature was increased from 5 to 25°C indicating thermal swelling of the network. The strain peaks were observed to shift to higher frequency as the temperature was lowered. Higher salt concentration had the same effect on the gel as higher temperature.