Effect of Salt and Charge Density on the Dynamics of Acrylamide-co-Sodium Acrylate Hydrogel

Abstract

We have investigated the diffusion dynamics in the charged gel matrix using dynamic light scattering measurements. Acrylamide-co-sodium acrylate was taken as the sample for polyelectrolyte gel with different charge densities, and the effect of salt on diffusion dynamics was explored. Due to the non-ergodic behavior of the sample, the direct ensemble averaged method was employed to obtain the correlation data. All the correlation curves were fitted with adequate accuracy by single plus stretched exponential functions from which the relaxation times corresponding to fast and slow relaxation modes were acquired. As we increase the charge density of the hydrogel sample without adding salt, an increase in mean relaxation time is noticed. However, when the samples were prepared with the addition of monovalent salt, a reverse trend was detected. Here, the mean relaxation time gradually decreases, implying that the gel network becomes more diffusive. Similar trend is seen for the fast relaxation mode.