Interparticle interactions and direct imaging of colloidal phases assembled from microsphere-nanoparticle mixtures

Carlos J. Martinez, Jiwen Liu, Summer K. Rhodes, Erik Luijten, Eric R. Weeks, Jennifer A. Lewis*

*Corresponding author for this work

Research output: Contribution to journalArticle

40 Scopus citations

Abstract

We investigate the interparticle interactions, phase behavior, and structure of microsphere-nanoparticle mixtures that possess high size and charge asymmetry. 1 We employ a novel Monte Carlo simulation scheme 2 to calculate the effective microsphere interactions in suspension, yielding new insight into the origin of the experimentally observed behavior. 3 The initial settling velocity, final sediment density, and three-dimensional structure of colloidal phases assembled from these binary mixtures via gravitational settling of silica microspheres in water and index-matched solutions exhibit a strong compositional dependence. Confocal laser scanning microscopy is used to directly image and quantify their structural evolution during assembly. Below a lower critical nanoparticle volume fraction (φ nano < φ L,C), the intrinsic van der Waals attraction between microspheres leads to the formation of colloidal gels. These gels exhibit enhanced consolidation as φ nano approaches φ L,C. When φ nano exceeds φ L,C, an effective repulsion arises between microspheres due to the formation of a dynamic nanoparticle halo around the colloids. From this stable fluid phase, the microspheres settle into a crystalline array. Finally, above an upper critical nanoparticle volume fraction (φ nano > φ U,C), colloidal gels form whose structure becomes more open with increasing nanoparticle concentration due to the emergence of an effective microsphere attraction, 3 whose magnitude exhibits a superlinear dependence on φ nano.

Original languageEnglish (US)
Pages (from-to)9978-9989
Number of pages12
JournalLangmuir
Volume21
Issue number22
DOIs
StatePublished - Oct 25 2005

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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