Surface Activity and Micelle Formation of Anionic Azobenzene-Linked Surfactants

The adsorption phenomena and micellization of sodium 4-((4‘-alkylphenyl)azo)benzenesulfonates, C n AzoSO 3 Na (C n = C 2 H 5, C 4 H 9, C 8 H 17 ), and sodium 4-((4‘-alkylphenyl)azo)benzoates, C n AzoCOONa (C n = C 4 H 9, C 8 H 17 ), were studied by means of surface tension and cyclic voltammetric (CV) techniques and compared with the respective parameters of the standard sodium alkanesulfonates, sodium alkylbenzenesulfonates, and sodium alkanecarboxylates. The presence of the azobenzene moiety in the surfactant molecule as a link between the hydrophobic tail and the anionic head group improves the surfactant solubility in water and introduces the hydrophobic character comparable to the effect of 8.4 methylene groups of the main alkyl chain in the assumed standards. The hydrophobic nature of both phenylene groups attached to the azo entity depends upon the position of these groups in the hydrophilic/hydrophobic zones.