Environmental stimuli induced phase transition in the aqueous mixture solution of Gemini surfactants and sodium deoxycholate

• Phase behavior in a mixture of Gemini surfactants and SDC was investigated.
• The obtained aggregates were responsive to both temperature and pH.
• The Gemini surfactant structure has a great influence on mixture phase behavior.

The phase behavior in a mixture of a cationic Gemini surfactant (12-2-12) and an anionic sodium deoxycholate (SDC) in the aqueous solution was reported here. The microstructures of formed aggregates have been investigated by rheology, small angle X-ray scattering and transmission electron microscopy. Mediated by the hydrophobic and electrostatic interactions of 12-2-12 and SDC, the wormlike micelles and lamellar aggregates were formed successively with increasing the SDC concentration. Due to the presence of hydroxyl and carboxylate groups on SDC, these aggregates were temperature and pH responsive. At low SDC concentrations, the wormlike micelles could be transformed into lamellar aggregates at lower pH. While at high SDC concentrations, the lamellar aggregates would be transformed into wormlike micelles at elevated temperatures. The Gemini surfactant structure also played an important role here on such environment-responsive phase transitions. The obtained results suggest the possibility to form smart aggregates by utilizing simple molecules with certain functional groups.

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