Stability assessment of non-aqueous polymer dispersions through viscous flow and linear viscoelastic rheological tests

This work studies the microstructure and stability against aggregation of non-aqueous polymer dispersions. Styrene-co-acrylonitrile particles were sterically stabilized by block copolymer dispersants composed of one block adsorbed on the particle surface and the counter-part soluble in the continuous medium (a liquid polyether). A comprehensive rheological characterization (by steady and transient flow tests and linear viscoelastic measurements) and a microstructural study (by SEM microscopy, particle size distribution, etc.) were conducted on systems with different particle volume fraction, dispersant concentration and styrene to acrylonitrile ratio. A trend to particle aggregation, related to either low particle surface dispersant coverage or weakly dispersant adsorption onto the particle surface, has been identified through viscous flow tests, mainly assessing shear-thickening phenomena related to flow-induced particle aggregation, and by linear viscoelastic frequency sweep measurements. This work shows the use of rheological techniques as a powerful tool for stability testing and dispersant design of these sterically stabilized dispersions.