Temperature-Induced Aggregate Transitions in Mixtures of Cationic Ammonium Gemini Surfactant with Anionic Glutamic Acid Surfactant in Aqueous Solution.

Abstract

The aggregation behaviors of the mixtures of cationic gemini surfactant 1,4-bis(dodecyl-N,N-dimethylammonium bromide)-2,3-butanediol (C12C4(OH)2C12Br2) and anionic amino acid surfactant N-dodecanoylglutamic acid (C12Glu) in aqueous solution of pH = 10.0 have been studied. The mixture forms spherical micelles, vesicles, and wormlike micelles at 25 °C by changing mixing ratios and/or total surfactant concentration. Then these aggregates undergo a series of transitions upon increasing the temperature. Smaller spherical micelles transfer into larger vesicles, vesicles transfer into solid spherical aggregates and then into larger irregular aggregates, and entangled wormlike micelles transfer into branched wormlike micelles. Moreover, the larger irregular aggregates and branched micelles finally lead to precipitation and clouding phenomenon, respectively. All these transitions are thermally reversible, and the transition temperatures can be tuned by varying the mixing ratios and/or total concentration. These temperature-dependent aggregate transitions can be elucidated on the basis of the temperature-induced variations in the dehydration, electrostatic interaction, and hydrogen bonds of the headgroup area and in the hydrophobic interaction between the hydrocarbon chains. The results suggest that the surfactants carrying multiple binding sites will greatly improve the regulation ability and temperature sensitivity.