Evolution of non-ergodicity during gel transition studied through probe particle diffusion

We report ergodic to non-ergodic transition as studied through the evolution of dynamic structure factor during a sol to gel transition process. The experimental system was 5% (w/v) aqueous solution of gelatin with latex spheres of diameter 90 nm added to it to a concentration of 10 μ g/cc. We have measured the kinetic properties of the medium from dynamic light scattering measurements and the results discussed within the frame work of the model proposed by Pusey and Van Megen [Pusey PN, Van Megen W. Physica A 1989;157:705]. The ergodicity parameter Y was measured to be Y=1 in the sol state, but as the onset of gelation took place it deviated strongly from its sol state value, signalling the transition to a non-ergodic state. The microscopic local viscosity, “seen” by the probe particle, ηl was observed to increase from its sol state value of ηl=1 to 5000 cP as the gel state was reached.