Wormlike micelles formed by mixed cationic and anionic gemini surfactants in aqueous solution

The formation and the properties of wormlike micelles in aqueous solutions of mixed cationic and anionic gemini surfactants, 2-hydroxyl-propanediyl-alpha-omega-bis(dimethyldodecylammonium bromide) (12-3(OH)-12) and O,O'-bis(sodium 2-dodecylcarboxylate)-p-benzenediol (C-12 phi C-12), have been studied by steady-state and dynamic rheological measurements at 25 degrees C. With the addition of a small amount of C-12 phi C-12 into the solution of 12-3(OH)-12, the total surfactant concentration of which was always kept at 80 mmol L-1, the solution viscosity was strongly enhanced and its maximum was much larger than that of the mixed system of propanediyl-alpha-omega-bis(dimethyldodecylammonium bromide) (12-3-12) and C-12 phi C-12. The results of dynamic rheology measurements showed that 12-3(OH)-12/C-12 phi C-12 formed longer wormlike micelles in comparison with 12-3-12/C-12 phi C-12. This was attributed to the effect of hydrogen bonding occurring between 12-3(OH)-12 molecules, which was an effective driving force promoting micellar growth. As few C-12 phi C-12 participated in the micelles, the electrostatic attraction between the oppositely charged head groups of 12-3(OH)-12 and C-12 phi C-12 made the molecules in the aggregates pack more tightly. This reinforced the hydrogen-bonding interactions and greatly promoted the micellar growth. (C) 2010 Elsevier Inc. All rights reserved.