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

Flocculation of sterically stabilized colloidal dispersions is a techn ologically important and complex phenomenon. Often, a state of control led, weak flocculation is desired to slow the aging of dispersions due to irreversible flocculation and subsequent sedimentation. Using theo logical techniques, we have characterized flocculation in situ in ster ically stabilized fumed silica dispersions toward identifying those va riables important to the control of the flocculated network strength. Both poly(methyl methacrylate) homopolymers and polystyrene/poly(methy l methacrylate) block copolymers have been used as stabilizers. Dynami c oscillatory measurements have been used to quantify the elastic modu li and hence the strength of the flocculated networks as a function of polymer surface coverage, molecular weight, architecture, and solvenc y as well as particle volume fraction. The results show that the flocc ulated network strength is weaker for complete surface coverage and wh en diblock copolymers are used as stabilizers, as expected. In additio n, a sealing of the elastic modulus with particle volume fraction demo nstrates weaker flocculation with increasing polymer molecular weight. This work illustrates the utility of theological techniques in studyi ng the dynamic flocculation process.