Physicochemical study of cationic gemini surfactant butanediyl-1,4-bis(dimethyldodecylammonium bromide) with various counterions in aqueous solution

The effect of salts (inorganic and organic) on the characteristic solution properties of bis(quaternary ammonium) gemini surfactant butanediyl-1,4-bis(dimethyldodecylammonium bromide) (referred to as 12-4-12) was explored. The results showed that salt counterions induce synergistic effects and greatly enhance the efficiency of gemini in surface tension reduction as well as the ability of micellization. Furthermore, combinations of salt anions and gemini exhibited thickening of their aqueous solutions. The aggregate morphology is strongly dependent on the nature and size of the counterions. These were also attributed to the unique molecular structure of gemini surfactant, where the spacer (polymethylene chain) links the two quaternary ammonium head groups. The interaction and micellar growth of cationic gemini-salt systems with the inorganic salts have been found to obey Hofmeister series. Also, the anions of organic salts promote the hydrophobic interaction between the alkyl tails of gemini surfactant. In addition, the orientation of the substituents in the aromatic fragment is important too.