Mesophases and crystalline phases in fatty acid monolayers

Kenn, R. M.; Böhm, C.; Bibo, A. M.; Peterson, I. R.; Möhwald, Helmuth; Als‐Nielsen, J.; Kjær, Kristian

doi:10.1021/j100158a034

Cited by 319 publications

(251 citation statements)

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“…[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][32][33][34] Except for a few cases, which have hexatic order, most of these phases exhibit resolution-limited Bragg peaks characteristic of 2D crystalline phases. Figure 1͑b͒ contains a schematic illustration of the kinematics for the GID experiment.…”

Section: ͑1͒mentioning

confidence: 99%

“…1-3 A principal challenge in this general area of physics has been to identify real, well defined physical systems that are suitable for experimental studies. Examples of two-or quasi-twodimensional systems that have been investigated for this purpose in recent years include rare gases adsorbed on solid substrates, [3][4][5][6] freely suspended thin liquid crystal films, [7][8][9][10] and Langmuir monolayers 11,12 of simple long-chain molecules such as fatty acids, [13][14][15][16][17][18][19][20][21][22][23] alcohols, [24][25][26][27] esters, 28 etc. Related statistical phenomena at surfaces and interfaces that have been often studied for more practical motivations, include wetting, [29][30][31] premelting and reconstruction of crystalline surfaces, [32][33][34][35] and surface induced order at liquid surfaces.…”

Section: Introductionmentioning

confidence: 99%

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C 60 -propylamine adduct monolayers at the gas/water interface: A Brewster angle microscopy and x-ray scattering study

Fukuto

Penanen

Heilmann

et al. 1997

The Journal of Chemical Physics

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Brewster angle microscopy ͑BAM͒, x-ray specular reflectivity and grazing-incidence x-ray diffraction ͑GID͒ studies of C 60 -propylamine adduct monolayers at the gas/water interface as a function of molecular area are reported. At large molecular areas (AϾϳ150 Å 2 /molecule), BAM images reveal macroscopic heterogeneity in the film, consisting of the coexistence between regions covered with uniform solidlike monolayer and bare water surface. After compression to a limiting molecular area of 150 Å 2 /molecule, the film is observed to be homogeneous, with the uniform monolayer covering the entire available surface. Both the x-ray reflectivity results and the GID patterns are consistent with the formation of a uniform monolayer at Aϳ150 Å 2 /molecule, while the little dependence that the GID patterns have on the molecular area for AϾϳ150 Å 2 /molecule is consistent with the heterogeneity in the film. Upon further compression to higher densities (AϽϳ120 Å 2 /molecule), the x-ray reflectivity results suggest the formation of a partial layer either at the molecule/gas interface or at the molecule/water interface. In this high density regime, the shift in the observed GID pattern with molecular area is much smaller than would be expected if the film were to remain a homogeneous monolayer, also consistent with the formation of an inhomogeneous partial layer. The analysis of the broad GID pattern observed from a uniform monolayer in terms of a model 2D radial distribution function, implies a short range positional correlation, extending to only a few molecular distances. The average nearest neighbor distance (dϳ13 Å͒, extracted from the GID analysis, is consistent with the limiting molecular area (Aϳ150 Å 2 /molecule) assuming local hexagonal packing. These results together with the sharp facets observed in the BAM images demonstrate that the monolayer when uniform is a two-dimensional amorphous solid.

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Section: ͑1͒mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

C 60 -propylamine adduct monolayers at the gas/water interface: A Brewster angle microscopy and x-ray scattering study

Fukuto

Penanen

Heilmann

et al. 1997

The Journal of Chemical Physics

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“…Although many phase diagrams have been already proposed, [7][8][9][10][11][12][13] it is not clear that any of these are truly equilibrium diagrams. The question arises because, in almost all of the phase diagrams published, the monolayer is compressed continuously, at a constant rate, without allowing sufficient time for the surface pressure to relax to an equilibrium value.…”

Section: Introductionmentioning

confidence: 99%

“…24 Finally, Foster et al determined the phase diagram for a relaxed Langmuir monolayer of methyl eicosanoate ͑CH 3 ͑CH 2 ͒ 18 COOCH 3 ͒; and found that although the topology of the relaxed phase diagram for this long chain fatty ester is in good agreement with previous work published for this system, the relaxed monolayer exhibits an additional phase previously unreported. 25 An important difference between the work presented here and most of the others [7][8][9][10][11][12][13] is that thermodynamic information is collected simultaneously with x-ray measurement of the microscopic structure, and both are combined to ensure that the results are self-consistent.…”

Section: Introductionmentioning

confidence: 99%

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A determination of the phase diagram of relaxed Langmuir monolayers of Behenic acid

Bommarito

Foster

Pershan

et al. 1996

The Journal of Chemical Physics

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Grazing incidence x-ray scattering ͑GIXS͒ and Brewster angle microscopy ͑BAM͒ are used to determine the -T phase diagram of Behenic acid monolayers supported on the surface of water ͑pHϭ2.0͒ over the temperature range of 3°C to 20.6°C. The phase diagram is constructed from measurements taken during isothermal compressions in which the surface pressure relaxed to a stable value at each surface density, and during temperature scans at fixed average surface density. The phase diagram is different than those previously reported for Behenic acid primarily because of the surface pressure relaxation. For temperatures less than 12°C the phase diagram exhibits similar phases and topology as the published diagrams, although the location of the phases in the -T plane is different. Temperature scans combined with the isotherms, and the Clausius-Clapeyron relation are used to determine three coexistence lines that meet in a triple point. Changes in entropy across the phase boundaries are determined. Near room temperature ͑20.6°C͒ only one phase is measured over the range of surface pressure from 0 dynes/cm to the collapse pressure in contrast to reported measurements on monolayers out of equilibrium ͑i.e., when the surface pressure is not allowed to relax͒ that exhibit several phases near room temperature at pressures higher than the collapse pressure. Discrepancies are observed between the average area per molecule (A T ) and the area per molecule determined from measurements of the unit cell (A X ) in the close packed regions of the phase diagram. It is conjectured that the -A X plane is a better representation of the ordered equilibrium monolayer phases than the -A T plane. Isotherms plotted in the -A X plane are used to determine the compressibility of the ordered phases and the nature of the phase transitions.

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