Aggregation and gel formation in biopolymer solutions

Abstract

We report an investigation of the microscopic structure and dynamics of biopolymer gels and relate them to the macroscopic viscoelastic properties of such systems. Biopolymer solutions and gels represent one of the most interesting class of gelling systems since they are of major industrial and scientific interest. We performed a systematic study using concentrated solutions of casein micelles which we destabilized and investigated during the process of gelation using diffusing wave spectroscopy (DWS) and rheological measurements. An analysis of the light scattering data shows a significant increase in the characteristic decay time of the correlation functions during the sol—gel transition. For the analysis of the DWS data we developed an algorithm which, based on the so-called microrheology approach, determines the viscoelastic properties G′(ω) and G′'(ω) of the gel. A comparison of the results obtained with DWS and measurements with a rheometer shows excellent agreement of both approaches. We demonstrate that we can clearly link the changes observed in the microscopic dynamics to the formation of a macroscopic gel with drastically modified viscoelastic properties.