Growth kinetics of nanosize silica in a nonionic water-in-oil microemulsion: A reverse micellar pseudophase reaction model

Kwadwo Asare Osseo-Asare, F. J. Arriagada

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74 Scopus citations

Abstract

The growth kinetics of silica nanoparticles synthesized by the microemulsion-mediated alkoxide hydrolysis method was investigated with tetraethoxysilane (TEOS) as the silica precursor and polyoxyethylene (5) nonylphenylether (NP-5)/cyclohexane/ammonium hydroxide as the water-in-oil microemulsion system. The time evolution of the mean diameter of the silica particles was determined for different values of the water-to-surfactant molar ratio (R). Particle growth was found to be a slow process, where under typical experimental conditions at room temperature ([TEOS] = 0.024 M, 29.6 wt% NH3, water-to-TEOS molar ratio (h) = 7.8) the particles achieved their terminal size after several days. During the early stages of the reaction, particle growth followed first-order kinetics, and the observed first-order growth rate constants decreased with increase in R. A reverse micellar pseudophase model (which considered the partition of reactants between the reverse micellar pseudophase and the bulk oil phase) was developed to analyze the growth kinetics under the hypothesis that TEOS hydrolysis was rate controlling. The pseudophase model predicted an inverse relationship between the observed growth rate and R, in agreement with experiment. The roles of steric effects and the bound state of water molecules, in retarding the hydrolysis rate, were highlighted by examining the effect of R on the TEOS hydrolysis rate constant in the reverse micellar pseudophase.

Original languageEnglish (US)
Pages (from-to)68-76
Number of pages9
JournalJournal of Colloid And Interface Science
Volume218
Issue number1
DOIs
StatePublished - Oct 1 1999

All Science Journal Classification (ASJC) codes

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

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