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A series of three cationic surfactants with different chain lengths, i.e. O‐decyl‐, O‐dodecyl‐ and O‐tetradecyl‐N,N′‐diisopropylisourea hydrochloride were synthesized. The chemical structures of the prepared compounds were confirmed using chemical analysis, Fourier transform infra red spectroscopy and nuclear magnetic resonance spectra and chromatography coupled with mass spectrometry. Several surface properties of the synthesized surfactants were studied in aqueous solution. Surface tension, conductivity and the foaming power were measured and the critical micelle concentration (CMC) was determined at 25 °C. These results were correlated to the surfactant chemical structure. The surfactant that provided the best surface activity was the O‐dodecyl‐N,N′‐diisopropylisourea hydrochloride. The CMC was found to be significantly dependent on the hydrophobic chain length and decreased with increasing of the carbon number in the alkyl chain. The surfactants synthesized have an interesting foaming power. The surfactant with the longest alkyl chain exhibited the highest foamability.

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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 (Γmax), the minimum area per molecule (Amin) at the aqueous solution‐air interface, effectiveness of surface tension reduction (πCMC), and efficiency of surface tension reduction (pC20) were estimated. The standard Gibbs free energy of adsorption, (ΔG°ads) change has been calculated at different temperatures.