Stability of mixtures of charged silica, silica-alumina, and magnetite colloids

J. L. Viota, M. Raşa, S. Sacanna, A. P. Philipse

Research output: Contribution to journalArticlepeer-review


We report experiments on the stability of aqueous mixtures of charged colloidal magnetite and charged silica and silica covered with alumina particles of similar size. First, positively charged magnetite dispersions were mixed with negatively charged silica dispersions at pH 4, at different volume ratios and low colloid volume fractions, producing mixtures which were stable over a period of weeks despite the expected electrostatic attraction between the oppositely charged particles. When magnetite particles were mixed with positively charged silica covered with alumina at pH 4 under exactly the same conditions, some of the systems separated to form a magnetite sediment. When the volume fraction of the initial dispersions was increased, the behavior of the mixtures was the opposite: positive magnetite/negative silica mixtures were unstable at intermediate volume ratios. The unexpected behavior of the mixtures was investigated by means of electrophoretic mobility, initial susceptibility, and dynamic light scattering measurements as well as sedimentation experiments.

Original languageEnglish (US)
Pages (from-to)419-425
Number of pages7
JournalJournal of Colloid And Interface Science
Issue number2
StatePublished - Oct 15 2005


  • Binary mixtures
  • Colloidal alumina particles
  • Colloidal silica particles
  • Heteroaggregation
  • Magnetic colloids
  • Magnetic fluids
  • Stability

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Surfaces, Coatings and Films
  • Colloid and Surface Chemistry


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