Photon Correlation Spectroscopy Study of Diffusion of Gelatin Chains and Surfactant Complexes

Photon Correlation Spectroscopy (PCS) study carried out on semi-dilute, 4%(w/v) aqueous gelatin sols with the anionic surfactant, sodium dodecyl sulphate (SDS) showed three relaxation processes in the dynamic structure factor data; first an exponential process S (q,t) ~ exp (-D_f(q²t) at t ≤ 20 μs called the gel mode, was observed followed by an intermediate power law regime S(q,t) ~ t^-α(q) at 20 μS ≤ t ≤ 1 ms and finally a stretched exponential decay S(q,t) ~ exp -(t/τ_c)^β observed for t ≥ 1 ms. The power-law exponent (α) and characteristic time τ_c in stretched part were found to be q-dependent, α ~ q^X with x = 1.80 ± 0.09 in the sol state; and τ_c~q^-y, y = 2.05 ± 0.08 also in the sol state but independent of SDS concentration. The temperature dependence of α and τ_c was measured. With SDS the different characteristic length scales alter the conformation of gelatin. Our results agree with the predictions of anomalous Gaussian diffusion model in the sol state.