Time-resolved SAXS studies of mixture of anionic and cationic surfactants

Time-resolved SAXS spectra emerged from the nano-structure formed after mixing of cationic dodecyltrimethylammonium chloride (DTAC) and anionic sodium dodecylsulfate (SDS) solutions were investigated. The catanionics with equal length tails are known to exhibit a lamella structure at equilibrium. In the present investigation, however, we found that a vesicle structure formed immediately after mixing (t=0.038 see) and a lamella structure grew later with time elapsed after mixing. It is found that the peak intensity identified with vesicle exponentially decays with time. The decay time T increases with NaCl concentration of the mixture. This result indicates that the vesicles are stabilized by the shielding of the electrostatic interaction due to the added salt. On the other hand, the peak intensity identified with lamella is described by a power law of time and the exponent of the power function is found to increase with NaCl concentration.