title: Structures of langmuir-gibbs films consisting of long-chain fatty acid and water-soluble surfactants.
abstract: The structures of Langmuir-Gibbs (LG) films at the air-solution interface were studied using surface tensiometry, Brewster angle microscopy (BAM), and infrared external reflection spectroscopy (IR-ERS). The LG films were fabricated by forming Langmuir films of deuterated arachidic acid (D19A) and then injecting a water-soluble surfactant, sodium dodecyl sulfate or octaethylene glycol monododecyl ether, into the subphase. The presence of the LG films at the air-solution interface affected the surface tension of water. BAM observations revealed the formation of phase-separated monolayers consisting of D19A monolayers and expanded monolayers of water-soluble surfactant at low concentrations of the water-soluble surfactant. The presence of phase-separated structures was supported by the IR-ERS results. At high concentrations, the water-soluble surfactants adsorbed to the domains of D19A monolayers, forming bilayers under the monolayers. The IR-ERS results suggest the penetration of the water-soluble surfactants into the domains of D19A monolayers and the diffusion of D19A molecules into the bilayer regions of the water-soluble surfactants. At concentrations greater than the critical aggregate concentration and/or critical micelle concentration, D19A molecules were solubilized in the solution. In some cases, the multilayers were kinetically stabilized and were present even 24 h after the injection of the water-soluble surfactants into the subphase.
authors.affiliation: Department of Materials Science and Technology, Faculty of Industrial Science, Tokyo University of Science, Tokyo, Japan.
authors.forename: Kenichiro
authors.initials: K
authors.lastname: Oka
authors.forename: Hirobumi
authors.initials: H
authors.lastname: Shibata
authors.forename: Satoshi
authors.initials: S
authors.lastname: Watanabe
authors.forename: Kenichi
authors.initials: K
authors.lastname: Sakai
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe
authors.forename: Mutsuyoshi
authors.initials: M
authors.lastname: Matsumoto
mesh_terms: D000388:Air; D004537:Eicosanoic Acids; D005227:Fatty Acids / Q000737:chemistry*; D008567:Membranes, Artificial; D008823:Micelles; D011092:Polyethylene Glycols; D012967:Sodium Dodecyl Sulfate; D012995:Solubility; D012996:Solutions; D013055:Spectrophotometry, Infrared; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry*; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D004537:Eicosanoic Acids; D005227:Fatty Acids; D008567:Membranes, Artificial; D008823:Micelles; D012996:Solutions; D013501:Surface-Active Agents; D014867:Water; C017272:dodecyloctaethyleneglycol monoether; D012967:Sodium Dodecyl Sulfate; D011092:Polyethylene Glycols; C094477:arachidic acid