MONITORING FLOCCULATION IN-SITU IN STERICALLY STABILIZED SILICA DISPERSIONS USING RHEOLOGICAL TECHNIQUES

Flocculation of sterically stabilized colloidal dispersions is a technologically important and complex phenomenon. Often, a state of controlled, weak flocculation is desired to slow the aging of dispersions due to irreversible flocculation and subsequent sedimentation. Using theological techniques, we have characterized flocculation in situ in sterically stabilized fumed silica dispersions toward identifying those variables important to the control of the flocculated network strength. Both poly(methyl methacrylate) homopolymers and polystyrene/poly(methyl methacrylate) block copolymers have been used as stabilizers. Dynamic oscillatory measurements have been used to quantify the elastic moduli and hence the strength of the flocculated networks as a function of polymer surface coverage, molecular weight, architecture, and solvency as well as particle volume fraction. The results show that the flocculated network strength is weaker for complete surface coverage and when diblock copolymers are used as stabilizers, as expected. In addition, a sealing of the elastic modulus with particle volume fraction demonstrates weaker flocculation with increasing polymer molecular weight. This work illustrates the utility of theological techniques in studying the dynamic flocculation process.