Mechanical spectroscopy of colloidal dispersions

Abstract

The mechanical properties of colloidal dispersions are closely related to their stability parameters. Unfortunately, the rheological characteristics which are normally used, such as viscosity and static elasticity, measure the global behaviour. It is extremely difficult to extract from such characteristics detailed information about the structure. Therefore, there is a need for more adequate experimental techniques.

The construction and the potential applications of a rheometer, in which an oscillatory movement is superimposed perpendicular to a steady shear flow, are discussed. Measurements on carbon black dispersions are carried out, and the relaxation spectra obtained for the sheared dispersions are compared with theoretical predictions based on a chain-like structural model. In this way, information concerning interaction forces and structural parameters is obtained.