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TitleNonequilibrium 2-hydroxyoctadecanoic acid monolayers: Effect of electrolytes
Publication TypeJournal Article
Year of Publication2011
AuthorsLendrum, C.D., Ingham B., Lin B., Meron M., Toney M.F., and McGrath K.M.
Pagination4430 - 4438
Date Published2011
ISSN07437463 (ISSN)
Keywords2-hydroxyoctadecanoic acid, Aqueous subphase, article, artificial membrane, Bicarbonate ions, Biological process, Biomineralization, Brewster angle microscopy, Calcium, Calcium carbonate, Calcium chloride, Calcium ions, Carbonates, Carbonation, carbonic acid derivative, Carboxylic acids, Cation binding, Chelation, chemistry, Combined effect, Crystallization, Dyes, electrolyte, Electrolytes, Electron energy levels, Electrostatics, Grazing incidence X-ray diffraction, hydrogen, hydrogen bond, Hydrogen bonding, Hydrogen bonding interactions, Hydrogen bondings, Hydrogen bonds, Hydroxy groups, Hydroxyacids, Low pressures, MATHEMATICAL MODELS, Membranes, Artificial, Monolayer structures, Monolayers, Non equilibrium, Non-equilibrium process, Ocean habitats, Phase behavior, phase transition, Positive ions, Pure water, Sodium bicarbonates, Sodium cations, Sodium chloride, static electricity, stearic acid derivative, Stearic Acids, Steric effect, Subphases, Surface active agents, Surfactant head groups, Surfactant solubility, Three phasis, X ray diffraction, X ray reflectivity
Abstract2-Hydroxyacids display complex monolayer phase behavior due to the additional hydrogen bonding afforded by the presence of the second hydroxy group. The placement of this group at the position α to the carboxylic acid functionality also introduces the possibility of chelation, a utility important in crystallization including biomineralization. Biomineralization, like many biological processes, is inherently a nonequilibrium process. The nonequilibrium monolayer phase behavior of 2-hydroxyoctadecanoic acid was investigated on each of pure water, calcium chloride, sodium bicarbonate and calcium carbonate crystallizing subphases as a precursor study to a model calcium carbonate biomineralizing system, each at a pH of ∼6. The role of the bicarbonate co-ion in manipulating the monolayer structure was determined by comparison with monolayer phase behavior on a sodium chloride subphase. Monolayer phase behavior was probed using surface pressure/area isotherms, surface potential, Brewster angle microscopy, and synchrotron-based grazing incidence X-ray diffraction and X-ray reflectivity. Complex phase behavior was observed for all but the sodium chloride subphase with hydrogen bonding, electrostatic and steric effects defining the symmetry of the monolayer. On a pure water subphase hydrogen bonding dominates with three phases coexisting at low pressures. Introduction of calcium ions into the aqueous subphase ensures strong cation binding to the surfactant head groups through chelation. The monolayer becomes very unstable in the presence of bicarbonate ions within the subphase due to short-range hydrogen bonding interactions between the monolayer and bicarbonate ions facilitated by the sodium cation enhancing surfactant solubility. The combined effects of electrostatics and hydrogen bonding are observed on the calcium carbonate crystallizing subphase. © 2011 American Chemical Society.

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