| Abstract
| - A novel zwitterionic surfactant, N-dodecyl-N,N,N‘,N‘-tetramethylethylenediammoniopropanesulfonate bromide(DEPB), has been synthesized, and Br- involved in the micellar system has been characterized by potentiometry,NMR, and X-ray absorption fine structure (XAFS). Although the dissociation degree of Br- from the micelle evaluatedby potentiometry almost agrees with that determined by NMR, the former is significantly smaller than the latter overthe entire range of concentrations of DEPB. This is explained by assuming that the bromide ions in the micellar systemhave several different peripheral structures. XAFS has given significant insight into the hydration structures of Br-involved in the system. Some of the bromide ions partitioned into the micelle are dehydrated and are directly boundby the ammonium groups in the DEP molecules. However, some of the bromide ions are still completely hydratedeven when they are partitioned into the micelles. The average hydration number of the bromide ions directly boundby the ammonium groups was determined to be ∼3.3. The partial dehydration of Br- is possibly facilitated by thecharacteristic hydration circumstances provided by the charge-stacked structure of the surfactant and by the resultingthick palisade layer of the DEP micelle.
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