Neutrally Charged Gas/Liquid Interface by a Catanionic Langmuir Monolayer

TitleNeutrally Charged Gas/Liquid Interface by a Catanionic Langmuir Monolayer
Publication TypeJournal Article
Year of Publication2010
AuthorsVaknin D, Bu W
Journal TitleJournal of Physical Chemistry Letters
Date Published07/01
Type of ArticleBioinspired
ISBN Number1948-7185
Accession NumberISI:000279508200007
Keywordsadsorption, air-water-interface, arachidic acid monolayers, cations, diffraction, ions, reflection, spectroscopy, surface, x-ray-fluorescence

Surface-sensitive synchrotron X-ray scattering and spectroscopic experiments were performed to explore the characteristics of Langmuir monolayers of oppositely charged mixed amphiphiles. A premixed (molar 1:1 stearic acid/stearylamine) solution was spread as a monolayer at the gas/liquid interface on pure water and on mono- and divalent salt solutions, revealing that the negatively charged carboxyl groups and positively charged amine groups are miscible into one another and tend to bond together to form a nearly neutral surface. Similar control experiments on pure stearic acid (SA) and stearylamine (ST) were also conducted for comparison. Due to the strong bonding, hexagonal structures in small domains with acyl-chains normal to the liquid surface are formed at zero surface pressures, that is, at molecular areas much larger than those of the densely packed acyl chains. In-plane X-ray diffraction indicates that the catanionic surface is highly ordered and modifies the structure of the water surface and thus can serve as a model system for interactions of an amino acid template with solutes.

URL<Go to ISI>://000279508200007