Analytical Sciences

Abstract − Analytical Sciences, 24(10), 1279 (2008).

Adsorption of 1-Decyl-3-methylimidazolium Bromide and Solvation Structure of Bromide at the Air/Water Interface
Makoto ARATONO,*1 Kei SHIMAMOTO,*1 Asuka ONOHARA,*1 Daiki MURAKAMI,*1 Hajime TANIDA,*2 Iwao WATANABE,*3 Toru OZEKI,*4 Hiroki MATSUBARA,*1 and Takanori TAKIUE*1
*1 Department of Chemistry, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan
*2 Experimental Facilities Division, Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan
*3 Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
*4 Department of Natural Sciences, Hyogo University of Teacher Education, Hyogo 673-1494, Japan
The adsorbed film of 1-decyl-3-methylimidazolium bromide (DeMIMB) at the air/water interface was investigated employing the surface tension measurement and the x-ray absorption fine structure method under the total reflection condition (TRXAFS). From the surface tension measurement, the surface excess concentrations of ions were determined. From the XAFS measurement, two solvation states of bromide ion were found in the adsorbed film, which were assigned to be “free-Br” and “bound-Br”. The hydration number of the former was estimated to be 6 while that of the latter was estimated to be 4. The results based on the XAFS analysis provided significant information on the formation of domains in the adsorbed film; the most conceivable situation is that the adsorbed molecules are definitely not homogeneously dispersed, but domains (islands or clusters) are dispersed in the adsorbed film. A regular and rather tight stacking of immidazolium rings may be formed in the domains.