The total-reflection XAFS measurement possessing bromide ion selectivity at the interfacial region was applied to the adsorbed film of hexadecyltrimethylammonium chloride (HTAC) and dodecyltrimethylammonium bromide (DTAB) mixture. The surface compositions XjH of individual ions j (j = HTA+, Cl-, DTA+, and Br -) were evaluated by combining the surface excess concentration of Br- estimated from the XAFS with the surface composition of the respective surfactants from the surface tension results. It is clearly shown that HTA+ and Br- are preferentially adsorbed to DTA + and Cl- at the air/water interface. The preferential adsorption was estimated numerically in terms of activity coefficient f i±H,p of component i and excess Gibbs energy of adsorption ĝprH,E. Then, the magnitude of ĝprH,E was compared with that of ĝinH,E attributable to intrinsic interaction between ions.
All Science Journal Classification (ASJC) codes
- General Materials Science
- Condensed Matter Physics
- Surfaces and Interfaces