Adsorption of an anionic surfactant at air-liquid and different solid-liquid interfaces from solutions containing high counter-ion concentration

The self-assembly (adsorption) of the anionic surfactant, sodium dodecylbenzenesulphonate (SDBS), at air-liquid and different (octadecanethiol, β-mercaptoethanol, α-lipoic acid) solid-liquid interfaces from aqueous solutions containing high concentrations of counter-ion has been investigated. SDBS adsorption at the solid-liquid interfaces was obtained using surface plasmon resonance (SPR) while its adsorption at the air-liquid interface was extracted from surface tension measurements. The results have demonstrated that SDBS packing at the air-liquid interface is similar to its packing at the hydrophobic octadecanethiol-liquid interface. Additionally, SDBS packing at the three solid-liquid interfaces increases with increasing surface hydrophobicity, irrespective whether the surface is neutral or negatively charged. Nonetheless, SDBS adsorption is always within monolayer coverage (no evidence of bilayer or admicelle formation). The results have also revealed that SDBS affinity for the solid-liquid interfaces increases with increasing surface hydrophobicity. Furthermore, SDBS affinity for the air-liquid interface is more than 10-fold its affinity for the solid-liquid interfaces.