Speckle-correlation analysis of the dynamic scatterers in temperature-governed gelation

This study focuses on the analysis of the temperature-dependent dynamics of scatterers in aqueous solutions of gelatin with added scattering centers (submicron particles of titanium dioxide), whose characterized by high scattering efficiency, during the process of gelation. The technique of full field speckle-correlometry with a localized source of probing radiation and the spatial filtering of the speckle-modulated images of the medium surface was applied to investigate systems with different values of the volume fraction of scatterers. It was shown that the Arrhenius equations with significantly different values of the activation energy can describe the temperature dependencies of the correlation time of speckle intensity fluctuations for temperature ranges above and below the gelation characteristic temperature. Note that the correlation time of speckle intensity fluctuations is determined by the mobility of the scattering centers in the medium. This suggests the existence of transition between two different regimes of spatially limited diffusion of scattering centers in the probed medium under the condition of "sol-gel" transition. The estimated values of activation energy of spatially limited scatter diffusion in the studied systems at low temperatures correlate with the published values of the gelation activation energy for gelatin aqueous solutions.