Gas-Liquid-Solid Condensation of Gravitationally Confined Polystyrene Particles near a Charged Wall at Intermediate Screening Lengths

Abstract

Charged polystyrene particles, which were initially sedimented uniformly on a glass wall, spontaneously transformed into two-dimensional gas, liquid, and solid phases in aqueous solvents. Their relative stabilities could be determined by a common phase diagram consisting of gas-liquid and liquid-solid coexistence lines under the conditions of a large particle radius (a much greater than κ(exp -1) and intermediate screening length (a=1.5 μm and 10 nm less than κ(exp -1) less than 300 nm), where a is the particle radius and κ is the Debye-Huckel parameter. The gas-liquid miscibility gap which had a critical point was very stable over a wide range of salt concentrations. The radial distribution functions of colloidal particles in the liquid phase showed remarkable oscillatory damping and both short-range (approximately particle diameter σ) and long-range (greater than 10σ) decay lengths were found. The latter was attributed to the charge density wave (CDW) due to alternating layers of oppositely charged colloids and counterions along the radial coordinate. Because the charged glass wall had a similar surface charge density and sign as the particles, the repulsive levitation at the wall against gravity assisted the thermal rearrangement during phase separation. Further evaluation is promising for investigating the complicated physics of particle-wall interactions.