Trough, Langmuir

Large molecules, such as sodium stearate, which have no side chains are able to pack into a single monolayer as the pressure is increased. A complete 

This technique [40] can be useful where the adsorptive can be spread on an aqueous substrate to give a coherent film. The area occupied by the absorptive film, after evaporation of the solvent, is proportional to the amount of solute present. This method has been applied successfully by Hutchinson [41], Gregg [42] and Greenhill [43] to analysis of solutions of long-chain fatty acids and by Crisp [44] to alcohols and phenols in organic solvents such as benzene. Equal volumes of solution were spread on an aqueous substrate before and after adsorption. 

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Anotlier metliod applicable to interfaces is tlie detennination of tlie partial molecular area (7 of a biopolynier partitioning into a lipid monolayer at tlie water-air interface using tlie Langmuir trough [28]. The first step is to record a series of pressure 71-area (A) isotlienns witli different amounts of an amphiphilic biopolynier spread at tlie interface. 

The second step, Figure 32b, consists of the covering of the styli with cadmium arachidate LB films. Monolayers of arachidic acid (in principle, it is also possible to use stearic or behenic acids with practically the same results) were spread over the surface of 10 " M CdCli water subphase in a Langmuir trough. The monolayer was compressed to a surface pressure of 27 mN/m and transfered onto styli by a vertical dipping technique. Up to six monolayers were deposited. 

FIG. 27 Schematic (not to scale) of the SECM-induced transfer of oxygen across a 1-octadecanol monolayer, at the air-water interface, in a Langmuir trough. 

Monolayers of distearoylphosphatidylcholine spread on the water-1,2-dichloro-ethane interface were studied by Grandell et al. [52] in a novel type of Langmuir trough [53]. Isotherms of the lipid were measured at controlled potential difference across the interface. Electrocapillary curves derived from the isotherms agreed with those measured under the true thermodynamic equilibrium. Weak adsorption or a stable monolayer was found to be formed, when the potential of the aqueous phase was positive or negative respectively, with respect to the potential of the 1,2-dichloroethane phase [52]. This result... 

We also noticed that the initial surface pressure is relatively high for all subphase compositions. This is due to the fact that we used a rather small Langmuir trough and the presence of residual detergent in the sample. 

Langmuir trough (Cahn Instruments Surface Tension Accessory No. 099-002910-30) in which the film could be rapidly compressed and expanded at a linear rate by means of moving barriers at either end of the balance (Fig. 9). This equipment was redesigned to reduce leaks and to follow a linear rather than sinusoidal cycle. 

An unusually extensive battery of experimental techniques was brought to bear on these comparisons of enantiomers with their racemic mixtures and of diastereomers with each other. A very sensitive Langmuir trough was constructed for the project, with temperature control from 15 to 40°C. In addition to the familiar force/area isotherms, which were used to compare all systems, measurements of surface potentials, surface shear viscosities, and dynamic suface tensions (for hysteresis only) were made on several systems with specially designed apparatus. Several microscopic techniques, epi-fluorescence optical microscopy, scanning tunneling microscopy, and electron microscopy, were applied to films of stearoylserine methyl ester, the most extensively investigated surfactant. 

Hysteresis was generally observed in the compression-expansion cycles of the force-area isotherms, indicating that the timescale for relaxation of the fully compressed film back to its expanded state was slower than the movement of the barrier of the Langmuir trough. Our studies, like many others, imply that monolayers are metastable and that reversible thermodynamics can only be applied to their analysis with caution. 

Because the adsorbed HM-HEC molecules exhibit such slow rates of chain reorientation, the effects of molecular weight, amount of hydrophobic substitution and chain lengths of the hydrophobes on the interfacial properties of HM-HEC monolayers can be investigated by two kinds of dynamic experiments hysteresis and stress-jump, using a Langmuir trough film balance. 

An HM-HEC monolayer at the air/aqueous interface was formed by adsorption from an aqueous solution of the polymer placed in the Langmuir trough overnight. In "stress-jump" experiments, HM-HEC monolayers were placed under rapid compression to a large degree and surface pressure was measured as a function of time after compression was stopped. (The compressional "jumps" required a minute or two to complete, and in some cases were on the order of the polymer monolayer relaxation times. See later section for discussion). In hysteresis experiments, the adsorbed monolayers were subjected to continuous compression-expansion cycles at a specific speed, while surface pressure was determined as a function of surface area. 

Fig. 12. Two compartment Langmuir trough used in this study.

For the fabrication of noncentrosymmetric LB films, a two-compartment Langmuir trough, of which detail is given in the section 1.4, was used. Monolayers of pyrazine derivatives and arachidic add were spread on each compartmentalized subphase (BaC or CdCl aqueous solution, 2 x 10"4 M). The monolayers were compressed to 30 mNm 1, and then monolayers of pyrazine derivatives and arachidic acid were deposited fused quartz substrates in up stroke and down stroke, respectively. The aggregation structure in the LB films was studies by the absorption spectra and X-ray diffraction. 

The LB film depositions were performed using a Joyce-Loebl Langmuir Trough IV equipped with a microbalance for measurement of the surface pressure by the Wilhelmy plate method. Filtered deionized water with a pH of 7 was used for the subphase. For the electron beam lithography study, PMMA was spread on the water surface from a dilute benzene solution ( 10 mg PMMA in 20 ml benzene). The novolac/PAC mixtures were spread from solutions ( 20 mg solids in 10 ml solvent) of isopropyl acetate. For the fluorescence studies, the PMMA/PDA mixture was spread on fee water surface from a dilute benzene solution (1.75 mg PDA and 8.33 mg PMMA in 20 ml benzene). Prior to compression, a 20 min interval was allowed for solvent evaporation. The Langmuir film was compressed to the desired transfer pressure at a rate of 50 cm2/min, followed by a 20 minute equilibration period. The Cr-coated silicon wafers and quartz wafers were immersed into fee subphase before... 

Figures 8 and 9 ow two specially designed multicompartment Langmuir troughs that permit the treatment of a monolayer with a series of different subphase reagent solutions, thus producing a known series of chemical reactions in the film. Following these treatments, the films may be transferred to a solid support or subjected to quantitative analysis to determine the outcome of the reactions.

This way it has been possible to observe the anticipated conformational transition by experiment. Cylindrical brushes of polybutylacrylate-graft polymethacrylate were adsorbed on the surface of water from a CHCI3 solution on a Langmuir trough and studied by recording the tt-A (surface pressure vs molecular area) isotherm. At different stages of compression, the monolayer was... 

The remaining problem of the molecular mechanisms of this action was judged to be related to the conformation of the dicarboxylic acid at the interface. This conformation is usually determined directly with the use of a Langmuir trough (16-18). The disadvantage of such a method for the present problem lies with the restrictions of the environment of the molecule to be Investigated. The basic requirement is that the molecule must be virtually insoluble in the liquid substrate on which the monolayer is supported. For the dicarboxylic acid in question, this meant a pH value as low as 2 and also a high electrolyte content in the aqueous substrate. 

In a typical experiment, a small volume of an insoluble surface-active material (dissolved in a water-insoluble solvent such as benzene) is placed atop a clean water surface. As the solvent evaporates away, a film remains and the moving barrier can be adjusted so that the surface film exerts pressure on the mica float. A calibrated torsion balance is used to measure the force that the film exerts on the float. That force divided by the length of the float is the force per unit length or the surface pressure. For studies of lipolysis kinetics , a Langmuir trough can be constructed so that one can measure lipase action under first-order and zero-order conditions. 

LANGMUIR TROUGH AND BALANCE LAPLACE TRANSFORM LARMOR PRECESSION LASER-FLASH KINETIC ANALYSIS LATENT ACTIVITY LATENT HEAT Latent heat of fusion LATENT HEAT Latent heat of vaporization LATENT HEAT Lateral binding proteins,... 

LANGMUIR TROUGH AND BALANCE LIPOPROTEIN LIPASE MICELLES LIPID ACTIVATION Lipid mobilization kinetics,... 

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