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 language | English (US) |
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Pages (from-to) | 9978-9989 |
Number of pages | 12 |
Journal | Langmuir |
Volume | 21 |
Issue number | 22 |
DOIs | |
State | Published - Oct 25 2005 |
Externally published | Yes |
ASJC Scopus subject areas
- General Materials Science
- Condensed Matter Physics
- Surfaces and Interfaces
- Spectroscopy
- Electrochemistry