Bile Salt-Induced Vesicle-to-Micelle Transition in Catanionic Surfactant Systems: Steric and Electrostatic Interactions

The vesicle-to-micelle transition (VMT) was realized in catanionic surfactant systems by the addition of two kinds of bile salts, sodium cholate (SC) and sodium deoxycholate (SDC). It was found that steric interaction between the bile salt and catanionic surfactant plays an important role in catanionic surfactant systems that are usually thought to be dominated by electrostatic interaction. The facial amphiphilic structure and large occupied area of the bile salt are crucial to the enlargement of the average surfactant headgroup area and result in the VMT. Moreover, bile salts can also induce a macroscopic phase transition. Freeze−fracture transmission electron microscopy, dynamic light scattering, isothermal titration calorimetry, and absorbance measurements were used to follow the VMT process.