Rheophysics of pastes: a review of microscopic modelling approaches

Pastes are materials intermediate between solids and liquids which are of great practical interest as they keep the shape they have been given. Despite their various internal structures it is possible to draw up a generic rheophysical scheme from which one qualitatively understands, from a physical point of view, their main mechanical characteristics, i.e. solid regime, solid-liquid transition, liquid regime, thixotropy and aging. Here we review in detail these different properties as they are generally observed with most pasty materials and the attempts to describe them using microscopic structure-based theoretical models. For real systems a unified, qualitative, conceptual description is provided. For some model systems (e.g., foams, colloidal gels...) there exist consistent microscopic approaches providing quantitative relationships between rheological parameters in the solid regime and physical parameters of the system. For the liquid regime and thixotropy the situation is more complex.