Comportement rhéologique des liquides et suspensions

Directeur de Recherches au C.N.R.S. (Service de biophisiques, Institut Pasteur, Paris).

Résumé

After a review of a few general ideas on the viscosity of liquids the principal forms of macroscopic rheological liquid and suspension behaviour are outlined. Qualitatively, the general characteristics of various types of liquid (fully viscous, visco-elastic, visco-plastic and subject to ageing) are quoted, also the various possible aspects of their flow (Newtonian viscosity, rheo-fluidification, rheo-thickening, thixotropy and anti-thixotropy). Special reference is made to the Weissenberg effect. The general principles of various theories which have been suggested to explain liquid, solution and suspension viscosity on a molecular scale are stated, i.e. representation principles of the mechanisms on which the flow pressures are based. The Eyring theory is emphasized, which extends to viscosity the general assumptions made for activation processes involving conditions beyond the potential barrier, and which thus enables viscosity mechanisms to be compared to diffusion mechanisms and to any reaction in the wide sense of the term. The effect of thermal molecular vibration and the corresponding wave propagation in flow processes is brought to light in Holzmüller's research. The Mooney theory, on the other hand, links the effect of thermal waves with acoustic wave propagation to explain the critical expansion zone shift allowing the molecular rearrangements producing flow to occur. In the Goodeve and Gillespie theories the proposed model attributes a leading role to molecular interaction and particle collision in suspensions. Finally, a few remarks are added on the dissipated energy distribution in suspensions and solutions during flow and on various electro-viscous effects.