Effect of the Molecular Structure on the Adsorption Properties of Cationic Surfactants at the Air-Water Interface

The surface activity and thermodynamic properties of adsorption at the air-water interface of two series of cationic surfactants based on isourea: the O-dodecyl-N, N'-diisopropylisourea hydrochloride, hydrobromide, and hydroiodide and the O-tridecafluorooctyl-N, N'-diisopropylisourea hydrochloride and hydrobromide were studied. The effect of structural parameters as the nature of the halide counter ion and the nature of the non-polar chain on the surface activity and thermodynamic properties of adsorption were investigated. The surface parameters, the maximum surface excess concentration (Gamma(max)), the minimum area per molecule (A(min)) at the aqueous solution-air interface, effectiveness of surface tension reduction (pi(CMC)), and efficiency of surface tension reduction (pC(20)) were estimated. The standard Gibbs free energy of adsorption, (Delta G degrees(ads)) change has been calculated at different temperatures.