Interaction of dilute colloidal particles in a mixed solvent
- Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States)
We have measured the second virial coefficient {ital B}{sub 2} of very dilute colloidal dispersions of charge-stabilized polystyrene latex spheres in the one-phase region of the mixed solvent 2,6-lutidine plus water. These measurements were made as a function of temperature for two solvent compositions, both of which are richer in 2,6-lutidine than the binary liquid mixture`s critical composition. The temperature ranges started deep in the one-phase region and approached the coexistence curve but did not penetrate the region of reversible aggregation near the coexistence curve. Very large, positive (repulsive-interaction) virial coefficients are observed at temperatures far from the aggregation zone and for calibration samples whose solvent is pure water. These large values of {ital B}{sub 2} are impossible to model without invoking long-range repulsive interactions whose origin is difficult to explain. As the temperature is brought nearer to the aggregation zone, the virial coefficient plunges through zero to large negative (attractive-interaction) values. Crude modeling suggests that the observed changes in the interactions are not inconsistent with a temperature-dependent attraction arising from adsorption layer energetics operating at distances of a few solvent-fluctuation correlation lengths from the particle surfaces.
- DOE Contract Number:
- FG02-84ER45131
- OSTI ID:
- 55965
- Journal Information:
- Physical Review. E, Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, Vol. 51, Issue 6; Other Information: PBD: Jun 1995
- Country of Publication:
- United States
- Language:
- English
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