Soft interfaces including liquid/liquid interfaces are regarded as a model for biological membrane. One of the fascinating subjects is heterogeneity of interfacial films such as “raft” in biological membranes. In this paper, the structure and property of adsorbed films of fluorocarbon alcohols at oil/water interfaces were examined by interfacial tensiometry, Brewster angle microscopy, and X–ray refrectometry to understand the relation between condensed domain formation and line tension. It was found that the contact energy at domain boundary of pN (10–12 N) order affects appreciably the domain morphology. The liquid ordered (Lo)/liquid disordered (Ld) coexisting in lipid vesicle was also studied by quantifying the line tension on the basis of Fourier analysis of domain boundary. A low line tension (0.2~0.8 pN) in this system would be originated from a deviation of molecular orientation from spontaneous curvature at domain boundary.
