Colloidal Gas-Liquid-Solid Phase Diagram in Low Ionic Strength Solutions

Int. J. Microgravity Sci. Appl. 2011_s017
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Polystyrene latex particles showed gas-liquid condensation under the conditions of large particle radius (a >> κ-1) and intermediate κa, where κ is the Debye-Hückel parameter and a is the particle radius. The particles were dissolved in deionized water containing ethanol from 0 to 77 vol.% settled to the bottom of the glass plate within 1 hour and, then, laterally moved toward the center of a cell over a 20 hour period in reaching a state of equilibrium condensation. All the suspensions of 1 and 3 μm in diameter and of 0.01-0.20 vol.% in concentration realized similar gas-liquid condensation with clear gas-liquid boundaries. A phase diagram of the gas-liquid condensation was created as a function of KCl concentration at a particle diameter of 3 μm, 0.10 vol.% in concentration, and 50:50 water/ethanol solvent at room temperature. The miscibility gap was observed in the concentration range from 1 to 250 μM. There was an upper limit of salt concentration where the phase separation disappeared, showing near critical behavior of macroscopic density fluctuation from 250 μM to 1 mM. These results add new experimental evidence to the existence of colloidal gas-liquid condensation and specify conditions of like-charge attraction between particles.
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