On the need for multi-parameter theories in the analysis of thixotropic behaviour

Viscoelastic and dielectric measurements are discussed that prove a difference in structure between recovery under shear and recovery at rest. The data include both systems with intermolecular and with interparticulate structures. The difference in structure can be explained on the basis of a three-dimensional network which develops after cessation of flow, whereas under shear the structure consists usually of isolated elements of varying size and shape. This picture is in agreement with the measured spectra. Finally a simple experiment is suggested which allows one to estimate the necessity for a multi-parameter description of a given thixotropic system.