X-ray diffraction study of heneicosanol monolayers on the surface of water

We have studied Langmuir monolayers of CH3(CH2)20OH (heneicosanol) using x-ray diffraction. Over the temperature range 7–55 °C, the monolayer isotherms show only one discontinuity, which may be either a ‘‘flat section’’ or a ‘‘kink;’’ we find that these are transitions between tilted and untilted ph...

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Bibliographic Details
Published in:The Journal of chemical physics 1992-09, Vol.97 (6), p.4485-4488
Main Authors: SHIH, M. C, BOHANON, T. M, MIKRUT, J. M, ZSCHACK, P, DUTTA, P
Format: Article
Language:English
Subjects:
360602 - Other Materials- Structure & Phase Studies
ADSORPTION
ALKYL RADICALS
Chemistry
COHERENT SCATTERING
DIFFRACTION
Exact sciences and technology
Gas-liquid interface and liquid-liquid interface
General and physical chemistry
HYDROGEN COMPOUNDS
HYDROXIDES
ISOTHERMS
LAYERS
MATERIALS SCIENCE
METHYL RADICALS
MOLECULES
ORGANIC ACIDS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PRESSURE DEPENDENCE
RADICALS
SCATTERING
SORPTION
Surface physical chemistry
SURFACE PROPERTIES
TEMPERATURE RANGE
TEMPERATURE RANGE 0273-0400 K
WATER
X-RAY DIFFRACTION
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Summary:We have studied Langmuir monolayers of CH3(CH2)20OH (heneicosanol) using x-ray diffraction. Over the temperature range 7–55 °C, the monolayer isotherms show only one discontinuity, which may be either a ‘‘flat section’’ or a ‘‘kink;’’ we find that these are transitions between tilted and untilted phases. There are several untilted phases, with hexagonal and distorted-hexagonal structures, as in monolayers of the corresponding (heneicosanoic) acid. However, in contrast to the acid, when the pressure is lowered the molecules tilt only towards a next-nearest neighbor. The dependence of the lattice spacings on pressure and temperature indicate that the monolayer does not form a ‘‘tilted hexagonal’’ phase, even at temperatures where the untilted phase is hexagonal (rotator-II).
ISSN:0021-9606
1089-7690
DOI:10.1063/1.463891