Physicochemical Properties of Aryl Oleate Surfactants in Aqueous Solution

Abstract

Sodium and potassium aryl oleates, containing different aromatic rings on the straight aliphatic chain, were synthesized. Their surface properties at 25°C, surface tensions at CMC, γcmc, surface excess concentration, Γ m , the area per surfactant molecule at the air/water interface at surface saturation, A m , efficiency in surface tension reduction, pC20, effectiveness in surface tension reduction, ∏cmc, as well as standard free energies of adsorption, Δ G ads°, and of micellization, Δ G mic°, were determined. The CMCs and γcmcs of these surfactants increased with the increase of the size of aromatic ring from phenyl to a-methylnaphthyl. Introduction of aromatic rings to the alkyl chain decreased the efficiency and effectiveness in reducing water surface tension. The results indicated that the size of lipophilic group was important in effecting the interfacial surface area occupied by the surfactant molecules.