title: Diffuse-double layer at a membrane-aqueous interface measured with x-ray standing waves.
abstract: The ion distribution in an electrolyte solution in contact with a charged polymerized phospholipid membrane was directly measured with long-period x-ray standing waves. The 27-angstrom-thick lipid monolayer was supported on a tungsten/silicon mirror. X-ray standing waves were generated above the mirror surface by total external reflection of a 9.8-kiloelectron volt x-ray beam from a synchrotron undulator. The membrane surface, which contained negatively charged phosphate headgroups, was bathed in a dilute ZnCl2 solution. The concentration of Zn2+ in the condensed layer at the membrane surface and the Zn2+ distribution in the diffuse layer were measured as a function of headgroup charge. The Debye length of the diffuse layer varied between 3 and 58 angstroms. The results qualitatively agree with the Gouy-Chapman-Stern model.
authors.affiliation: Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY 14853.
authors.forename: M J
authors.initials: MJ
authors.lastname: Bedzyk
authors.forename: G M
authors.initials: GM
authors.lastname: Bommarito
authors.forename: M
authors.initials: M
authors.lastname: Caffrey
authors.forename: T L
authors.initials: TL
authors.lastname: Penner
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004563:Electrochemistry; D004573:Electrolytes; D006863:Hydrogen-Ion Concentration; D008567:Membranes, Artificial; D010315:Particle Accelerators; D010743:Phospholipids; D011108:Polymers; D012996:Solutions; D014867:Water; D014965:X-Rays; D015032:Zinc / Q000032:analysis
chemical_list: D004573:Electrolytes; D008567:Membranes, Artificial; D010743:Phospholipids; D011108:Polymers; D012996:Solutions; D014867:Water; D015032:Zinc