| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 608101 | Journal of Colloid and Interface Science | 2012 | 6 Pages |
Titania nanoparticles were modified by free-radical graft polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) at the particle surface, resulting in the formation of a 1–2 nm thick polymer brush. The zwitterionic nature of the polymer layer suggests that the suspension stability is a delicate function of pH, as well as volume fraction, salt concentration and the presence of charged or un-charged additives which may act as depletants or to screen charge interactions in the system. In this context, we characterized the suspension rheology as a function of volume fraction, pH, ionic strength and the concentration of surfactants in the suspension. Near-neutral pH, the brush layer is effective in stabilizing particles against aggregation with Newtonian behavior observed for volume fractions approaching 14%. Flocculation of particles and an onset of shear-thinning behavior was observed on decreasing pH from near-neutral. Conversely, suspension stability was maintained on increasing pH from near-neutral. Likewise, flocculation could be quickly induced by the addition of salt and cationic surfactant in small amounts, but the suspensions displayed greater stability to anionic and non-ionic surfactant additives. These results have important implications for the successful formulation of complex fluids employing zwitterionic colloids.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (50 K)Download as PowerPoint slideHighlights► Titania particles are modified using a biocompatible phosphorylcholine-based polymer brush. ► Modification provides improved biocompatibility and sensory characteristics. ► Rheology examined as function of volume fraction, pH, ionic strength, surfactant concentration. ► The suspension stability is asymmetric in its response to pH and surfactant charge.
