Structure under shear flow of thixotropic clay gels
Résumé
The thixotropic behavior of colloidal clay dispersions consisting of disc-shaped particles of nanometric size, was studied by using a combination of SAXS, SANS and SLS techniques and rheometric measurements. The aim here is to examine the influence of shear flow on structural changes at various length scales, involved in the thixotropic behavior, and link these with their macroscopic mechanical properties. At rest, the structure of the dispersions is composed of subunits measuring a few tens of nanometers that combine to form dense aggregates measuring about a micrometer. At larger length scales, these micrometer-sized aggregates are rearranged to form a continuous 3-dimensional isotropic structure that has a fractal behavior of dimension D, which gives the gels their texture. The gel state is reached above a volume fraction fv*, for a given ionic strength and gelation time. The influence of the volume fraction on the structure was correlated with the yield stress and the fractal dimension by means of a scaling law (Pignon et al. 1996 ; 1997 a).