Origin of the Instability of Octadecylamine Langmuir Monolayer at Low pH
It has been reported that an octadecylamine (ODA) Langmuir monolayer becomes unstable at low pH values with no measurable surface pressure at around pH 3.5, suggesting significant dissolution of the ODA molecule into the subphase solution (Albrecht, Colloids Surf. A 2006, 284-285, 166-174). However,...
| Veröffentlicht in: | Langmuir : the ACS journal of surfaces and colloids. - 1992. - 31(2015), 51 vom: 29. Dez., Seite 13753-8 |
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| 1. Verfasser: | |
| Weitere Verfasser: | , , , , , |
| Format: | Online-Aufsatz |
| Sprache: | English |
| Veröffentlicht: |
2015
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| Zugriff auf das übergeordnete Werk: | Langmuir : the ACS journal of surfaces and colloids |
| Schlagworte: | Journal Article Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. Amines Water 059QF0KO0R Sodium Chloride 451W47IQ8X stearylamine FFV58UNY7O |
| Zusammenfassung: | It has been reported that an octadecylamine (ODA) Langmuir monolayer becomes unstable at low pH values with no measurable surface pressure at around pH 3.5, suggesting significant dissolution of the ODA molecule into the subphase solution (Albrecht, Colloids Surf. A 2006, 284-285, 166-174). However, by lowering the pH further, ODA molecules reoccupy the surface, and a full monolayer is recovered at pH 2.5. Using surface sum-frequency spectroscopy and pressure-area isotherms, it is found that the recovered monolayer at very low pH has a larger area per molecule with many gauche defects in the ODA molecules as compared to that at high pH values. This structural change suggests that the reappearance of the monolayer is due to the adsorbed Cl(-) counterions to the protonated amine groups, leading to partial charge neutralization. This proposition is confirmed by intentionally adding monovalent salts (i.e., NaCl, NaBr, or NaI) to the subphase to recover the monolayer at pH 3.5, in which the detailed structure of the monolayer is confirmed by sum frequency spectra and the adsorbed anions by X-ray reflectivity |
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| Beschreibung: | Date Completed 12.10.2016 Date Revised 30.12.2016 published: Print-Electronic Citation Status MEDLINE |
| ISSN: | 1520-5827 |
| DOI: | 10.1021/acs.langmuir.5b03947 |