ATTRACTIONS IN STERICALLY STABILIZED SILICA DISPERSIONS .3. EXPERIMENTS ON PHASE-SEPARATION INDUCED BY TEMPERATURE-VARIATION

On lowering the temperature initially homogeneous dispersions (in a variety of solvents) of silica coated with octadecyl chains show a separation into two phases of different concentration. The temperature of first instability is not strongly correlated with the solubility parameter of the solvent. Phase diagrams have been constructed for two dispersions in toluene and one in benzene. It is found that phase separation temperatures decrease with decreasing particle size. The concentration of the phases show a dependence on overall concentration. For the dilute phase this is in qualitative agreement with theoretical calculations for polydisperse systems.