Dynamic Critical Phenomena in Aqueous Protein Solutions

We report our use of quasielastic light scattering to characterize concentration fluctuations in aqueous solutions of ${\gamma }_{\mathrm{II}}$-crystallin along the critical isochore. We find that the wave number and temperature dependence of the average rate of decay of the concentration fluctuations are consistent with the theory for critical dynamics in binary liquid mixtures only if we allow both the background viscosity and the background contribution to the decay rate to be unusually large. Furthermore, in contrast to the behavior seen in binary liquid mixtures, we find that the concentration fluctuations exhibit very significant deviation from exponential decay.