The "time of observation" of .pi.-A isotherms. 2. A possiblility that so-called "solid films" in .pi.-A isotherms of monolayers of long-chain acids may not correspond to the two-dimensional solids but to the first-order phase transition regions from two-dimensional liquids to solids.

Kato, Takeshi; Hirobe, Y.; Kato, Motoko.

doi:10.1021/la00058a039

Cited by 54 publications

(35 citation statements)

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“…8,23,26,[28][29][30] Unfortunately, there are situations when the LM exhibits long relaxation times and, unless the compression rate is uncommonly slow, it is unlikely that the measured isotherm will correspond to thermal equilibrium. 24,25,[31][32][33][34] To circumvent this problem, isotherms are performed, in this study, using the relaxation technique, 24,25,35 in which is allowed to relax between small sequential compressions of the macroscopic area per molecule, A T . Typical compression steps are 1/4 Å 2 /mol.…”

Section: Methodsmentioning

confidence: 99%

The structure of a Langmuir monolayer of methyl eicosanoate as determined by x-ray diffraction and Brewster angle microscopy

Foster

Shih

Pershan

1996

The Journal of Chemical Physics

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Relaxed Langmuir monolayers of methyl eicosanoate were studied using Brewster angle microscopy ͑BAM͒ and grazing incidence x-ray diffraction ͑GIXD͒. The structure of the various phases in this system was determined and compared to previous isotherm and microscopy measurements. At low pressure and low temperature, a crystalline phase with tilt toward nearest neighbor, I(L 2 Љ), is observed. At a temperature of ϳ14°C and low pressure there is a transition to a phase with tilt toward next-nearest neighbor, F(L 2 Ј). Finally, as the temperature continues to be raised at low pressure, there is a transition to a phase where the two F(L 2 Ј) peaks have the same values of Q xy , here called the phase, with a Rotator IV-like structure. At high pressure and low temperature, an untilted, orthorhombic phase, UЈ(CS), is observed. As the temperature is increased, a second untilted, orthorhombic phase, U(S), is observed, beginning at ϳ12°C. Above 21°C and at high pressure, a Rotator-II-like phase is seen, with an undistorted, untilted structure. Finally, results from BAM measurements are used to monitor the texture of the film in the different phases.

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Section: Methodsmentioning

confidence: 99%

The structure of a Langmuir monolayer of methyl eicosanoate as determined by x-ray diffraction and Brewster angle microscopy

Foster

Shih

Pershan

1996

The Journal of Chemical Physics

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“…The largest surface pressure that an interfacial monolayer can sustain is the so-called fracture pressure π f . Fracture [10] will occur if during an on-going compression, the interfacial molecules are unable to 45 leave the monolayer, either because this is thermodynamically disfavored or because the compression is too fast [11]. A mechanical instability then results, in which the layer breaks up.…”

Section: Introductionmentioning

confidence: 99%

Stability of stearic acid monolayers on Artificial Sea Water

Brzozowska

Duits

Mugele

2012

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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Please cite this article as: A.M. Brzozowska, M.H.G. Duits, F. Mugele, Stability of stearic acid monolayers on artificial sea water, Colloids and Surfaces A: Physicochemical and Engineering Aspects (2010), Abstract We studied the formation and stability of Stearic Acid (SA) based films on aqueous sub-phases via Langmuir trough and imaging ellipsometry experiments. The aqueous phase was based on Artificial Sea Water (ASW), a multicomponent salt solution with a total molarity of 0.53. The composition of this 10 solution was varied via dilution (1, 10 and 100 times) and adjustment of the pH (3, 7, 10). Also water sub-phases without the ASW salts were studied. Pressure-area isotherms of the SA monolayers show an enhanced stability of the film against fracture when the pH and/or the salt concentration of the subphase are increased. Isobars of SA measured below the pressure needed for film fracture, indicate distinct mechanisms for loss of material: 1) at low pH and salt concentration, three dimensional (3D) 15 structures are formed at the air/water interface via nucleation and growth, and 2) at high pH and salt concentration, diffusion-controlled dissolution of molecules in the sub-phase occurs. The formation of multilayer structures was corroborated with ellipsometry images of the films after Langmuir-Blodgett transfer. 20 Highlights 615  Langmuir films of stearic acid can be stabilized by increasing salt concentration and/or pH of the sub-phase. 3D solid phase is formed under acidic conditions.  Dissolution of molecules into sub-phase occurs only at high pH and low salt concentration. The influence of multicomponent salt is a combination of ionic strength and specific ion effects.

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“…That relaxation effects in Langmuir monolayers are important in establishing true equilibrium has already been demonstrated by several researchers. [13][14][15][16][17][18][19][20][21][22][23][24][25] For example, Schlossman et al showed that when a Langmuir monolayer of tetracosanoic acid ͑CH 3 ͑CH 3 ͒ 22 COOH͒ at pHϭ2.0 and 25°C, is allowed to relax completely following each incremental compression, both the isotherm and the x-ray scattering results are different from those that are obtained when the film is not allowed to equilibrate. 21,22 Using infrared external reflection spectroscopy in comparison with x-ray dif-fraction, Buontempo et al demonstrated that collective tilt ordering is different in relaxed and unrelaxed monolayers of heneicosanol ͑CH 3 ͑CH 3 ͒ 20 OH͒.…”

Section: Introductionmentioning

confidence: 99%

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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The "time of observation" of .pi.-A isotherms. 2. A possiblility that so-called "solid films" in .pi.-A isotherms of monolayers of long-chain acids may not correspond to the two-dimensional solids but to the first-order phase transition regions from two-dimensional liquids to solids.

Cited by 54 publications

References 0 publications

The structure of a Langmuir monolayer of methyl eicosanoate as determined by x-ray diffraction and Brewster angle microscopy

The structure of a Langmuir monolayer of methyl eicosanoate as determined by x-ray diffraction and Brewster angle microscopy

Stability of stearic acid monolayers on Artificial Sea Water

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

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