A liquid-gel transition measured for a polymerically stabilized dispersion as a function of solvent quality and particle volume fraction is compared with theoretical predictions of phase behavior. The experimental liquid-gel transition is interpreted from rheological measurements of 360 nm polystyrene (PS) particles with adsorbed F108 Pluronic (PEO-PPO-PEO) layers in aqueous 0.5 M NaCl as a function of temperature, which controls solvent quality for the adsorbed Pluronic. The measured liquid-gel transition occurs at temperatures when attractive interactions are not expected to occur from either core PS particle van der Waals forces or Pluronic mixing interactions. To consider an alternative temperature dependent attraction, an adhesive sphere (AS) phase diagram is constructed using a theoretical potential that includes the solvent quality dependent continuum van der Waals attraction due to the nonuniform dielectric properties of the adsorbed Pluronic. An impressive correspondence is found between the experimental liquid-gel transition and the theoretical AS percolation threshold with no adjustable parameters using the nonuniform film model. This work indicates conditions when adsorbed polymeric van der Waals interactions are critical for interpreting and predicting solvent quality dependent phase behavior in polymerically stabilized systems.

Using an extension of the Debye−Hückel theory for strong electrolytes, the thermodynamics, phase behavior, and effective pair colloidal potentials of deionized charged dispersions have been investigated. With the inclusion of colloid size effects, this model predicts the possibility of the existence of two critical points, one of which is thermodynamically metastable but can exhibit interesting behavior at high colloid charges. This analytic model also serves as a pedagogic demonstration that the phase transition is driven by cohesive Coulomb interactions between all charged species in the system and that this cohesion is not inconsistent with a repulsive effective pair potential between the colloidal particles.

The force between two parallel charged flat surfaces, with discrete surface charges, has been calculated with Monte Carlo simulations for different values of the electrostatic coupling. For low electrostatic coupling (small counterion valence, small surface charge, high dielectric constant, and high temperature) the total force is dominated by the entropic contribution and can be described by mean field theory, independent of the character of the surface charges. For moderate electrostatic coupling, counterion correlation effects lead to a smaller repulsion than predicted by mean field theory. This correlation effect is strengthened by discrete surface charges and the repulsive force is further reduced. For large electrostatic coupling the total force for smeared out surface charges is known to be attractive due to counterion correlations. If discrete surface charges are considered the attractive force is weakened and can even be turned into a repulsive force. This is due to the counterions being strongly correlated to the discrete surface charges forming effective, oppositely directed, dipoles on the two walls.

The mean spherical approximation ͑MSA͒ was used to investigate the phase behavior of charged colloidal systems with and without added salt. The competition between cohesive Coulomb interactions and stabilizing entropic and hard-core interactions controls the stability of the system and under certain circumstances, a liquid-gas-type phase transition can occur. The critical parameters and phase diagrams in the MSA obtained via the internal energy path, are compared with two-component Monte Carlo simulations and other theoretical approaches.