Time-dependent mechanical and structural properties in colloidal clay gel
Résumé
Various types of complex behavior are encountered with colloidal dispersions. In the case of thixotropic behavior the rheological (i.e. mechanical and structural) properties of the material are dependent upon both time and shear rate. Thixotropy corresponds to the tendency of matter to exhibit a time-dependent change in its reference properties (reference viscosity, yield value, time scale, elacticity modulus, loss modulus, etc. or conductivity) when stresses are applied, and to recover these reference properties progressively when stress is relieved (Piau, 1997). Thixotropy has been observed for many years, but the physical mechanisms governing it are still poorly identified. Nevertheless, an understanding of these mechanisms at mesoscopic scale is of vital importance when using such materials and in controlling the industrial processes in which they are involved. Laponite was chosen for this study of thixotropic behavior. This is a synthetic clay of the hectorite type, consisting of anisotropic particles of nanometric size. The aims here are firstly to examine the influence of shear flow on structural changes in the thixotropic dispersions at various length scale and link these with their macroscopic mechanical properties, and secondly to define the various pertinent time and length scales that govern the mechanisms occurring in the thixotropic process.