期刊
JOURNAL OF COLLOID AND INTERFACE SCIENCE
卷 386, 期 -, 页码 135-140出版社
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcis.2012.06.085
关键词
Rheology; Titania; Colloidal suspensions; Colloidal gel
资金
- NSF [CBET-0828905, CBET-1066904]
- YINQE
- NSF MRSEC [DMR-1119826]
- Directorate For Engineering
- Div Of Chem, Bioeng, Env, & Transp Sys [1066904] Funding Source: National Science Foundation
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. (c) 2012 Elsevier Inc. All rights reserved.
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