Attraction Between Latex Particles in the Presence of Excess Surfactant
When an excessive amount of a surfactant (50 ~100 times its critical micelle concentration) was added to a latex, an attractive interaction appeared between the particles as well as between the particles and the wall of the container, causing reversible phase separation and adsorption to the wall. This phenomenon was studied by microscopy. It was found that ionic (only anionic ones were tried) surfactants produced the effect by themselves while nonionic ones needed the presence of some indifferent electrolyte at concentrations more than 0.05 mole/1.
The particle-wall interaction gave rise to reversible adsorption of the particles onto the surface; under the microscope were observed two dimensional gas, liquid and solid phases with equilibrium features between them- Particle-particle interaction in bulk produced solid phase (reversible aggregates with ordered structure) which settled to form an iridescent sediment. This observed phase separation which seemed to be caused by an attractive interaction is apparently different from a Kirkwood-Alder transition. The phenomenon much resembles those observed in latexes containing Na-polyacrylate.
KeywordsCritical Micelle Concentration Surfactant Concentration Latex Particle Attractive Interaction Adsorbed Particle
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