Diffusing Wave Spectroscopy of aggregating and gelling systems

Diffusing Wave Spectroscopy is a relatively recent but rather under-utilized branch of light scattering. It has the advantage that it can be used in highly-scattering suspensions to measure the motions of the scattering particles. This means that it can be used to study food colloidal systems in their normal state, with no requirement for dilution of the samples. The motions of the particles in a suspension depends on their state (free or limited diffusion, gelation, phase separation, etc.). Therefore, analysis of the light scattering behaviour can give information not only on particle sizes, but on the mechanisms by which they aggregate. In addition to the dynamics of the particles, it is also possible to gather information about the interactions of the particles from the overall turbidity of the suspensions. This review describes the application of the DWS technique to the study of a number of food-related suspensions, and shows how the results can be interpreted for the different systems.