The counterion distribution of cationic surfactants at aqueous solution/air interface and the structure of oil soluble alcohols at hexane solution/water interface were examined by means of the synchrotron X ray analysis, from which the adsorbed films were suggested to often have heterogeneous structure. From the X-ray Absorption Fine Structure (XAFS) analysis of the adsorbed films of dodecyl- (DTAB) and hexadecyltrimethylammonium bromide (HTAB) and 1-decyl-3-methylimidazolium bromide (DeMIMBr), it was revealed that in all cases there exist two kinds of hydrated bromide ions in the adsorbed films; fully hydrated ones by six water molecules (free) and partially dehydrated ones but bound to surfactant head group (bound). The dependence of the ratio of bound Br to the free ones on the surface density was examined. From the X ray reflection analysis of the adsorbed films of 1H,1H,2H,2H-perfluorodecanol (FC10OH) and 1H,1H,10H,10H-perfluorodecane-1,10-diol (FC10diol), it was clarified that for FC10OH the condensed monolayer has a two dimensional solid-like structure and the expanded monolayer was not homogenous but heterogeneous with small condensed domains and for FC10diol, the films transformed their structure from the flat condensed monolayer anchored by two OH groups to the condensed multilayer. Furthermore the film structure of FC10OH and FC10diol mixture was also examined.

Spread monolayers of lipids at the air/water interface have been used as simplified cell membrane model systems for studying intermolecular interactions and lipid membrane-related biological phenomena under controlled environments. In addition, the monolayers have also served as biomimetic platforms which allow adsorption and/or self-organization of not only biological molecules but also artificial compounds. In this review, fundamental properties of lipid spread monolayers and features in studies with the monolayers are briefly presented, and then evaluation methods for adsorption phenomena and structures in the monolayer systems are explained with some examples.

Ionic liquids (ILs) are expected to be promising alternatives for molecular organic solvents in various fields. It is of crucial importance to clarify the structures at IL interfaces and furthermore to design the functions of IL interfaces. This novel liquids that do not contain neutral molecules have been found to have specific structures at their interfaces. In the present paper, a series of studies on the structure at IL interfaces by the author will be introduced. Two methods that can selectively and sensitively extract the information of interfacial structure, X-ray reflectometry (XR) and molecular dynamics simulation (MD), are complementarily used to reveal the structure at IL interfaces.