A fractal analysis approach to viscoelasticity of physically cross-linked barley beta-glucan gel networks.

The structure and gelation kinetics of mixed linkage barley beta-glucans of varying Mw have been investigated. The fractal concept has been applied to describe the structure development of barley beta-glucan gels using a scaling model and dynamic rheometry data. The model supports that the gel structure consists of fractal clusters that upon aggregation lead to a three-dimensional network. The analysis showed that with increasing Mw a denser (more packed) network is formed as indicated by the corresponding fractal dimension (df) values. The microelastic parameter of the model, alpha, showed that all gel structures were in the transition regime implying structural reordering upon ageing. The description of the microstructure as a fractal network seems to be able to explain syneresis and other observations from large deformation testing of such systems. The molecular treatment of the gelation kinetics suggests that the gelling behavior is governed by the probability of collision of chain fragments with consecutive cellotriosyl units. This is greater for small chains due to their higher diffusion rates, for chains having lower amounts of cellulose like fragments and finally for those showing smaller degree of intrachain interactions. As a result, the faster gelling systems exhibit lower fractal dimensionality (more disordered systems) something that is in accordance with current kinetic theories.