In anionic and cationic asphalt emulsions, the stability is mainly achieved by the electrical replusions provided by the charged surfactants. In non-ionic asphalt emulsions, what kind of forces provide the stability? What effect does the pH of asphalt, water, and surfactant have on the asphalt emulsion stability?
Steric forces stabilize emulsions coated with non-ionic surfactants. The layers formed by the water-soluble head groups are highly solvated. When droplets approach each other, these layers overlap, increasing the head group concentration and causing an osmotic pressure that tends to suck solvent into the overlapping volume. This osmotic pressure acts to push the droplets apart - a repulsion. In principle, pH will have no effect on this type of stabilization.
to add, in general (nonionic surfactant or not) alkaline pH will cause dissociation of phenolic and carboxylic groups adding to electrostatic repulsion. So with nonionic surfactants this will add to stability. Reverse case of destabilization by shifting pH to acidic will be less successful.
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