Spreading troughs

If the spreading is into a limited surface area, as in a laboratory experiment, the film front rather quickly reaches the boundaries of the trough. The film pressure at this stage is low, and the now essentially uniform film more slowly increases in v to the final equilibrium value. The rate of this second-stage process is mainly determined by the rate of release of material from the source, for example a crystal, and the surface concentration F [46]. Franses and co-workers [47] found that the rate of dissolution of hexadecanol particles sprinkled at the water surface controlled the increase in surface pressure here the slight solubility of hexadecanol in the bulk plays a role. 

The material of interest is dissolved in a volatile solvent, spread on the surface and allowed to evaporate. As the sweep moves across, compressing the surface, the pressure is measured providing t versus the area per molecule, a. Care must be taken to ensure complete evaporation [1] and the film structure may depend on the nature of the spreading solvent [78]. When the trough area is used to calculate a, one must account for the area due to the meniscus [79]. Barnes and Sharp [80] have introduced a remotely operated barrier drive mechanism for cleaning the water surface while maintaining a closed environment. 

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. 

A convenient orbital method for describing eleetron motion in moleeules is the method of molecular orbitals. Molecular orbitals are defined and calculated in the same way as atomic orbitals and they display similar wave-like properties. The main difference between molecular and atomic orbitals is that molecular orbitals are not confined to a single atom. The crests and troughs in an atomic orbital are confined to a region close to the atomic nucleus (typieally within 1-2 A). The electrons in a molecule, on the other hand, do not stick to a single atom, and are free to move all around the molecule. Consequendy, the crests and troughs in a molecular orbital are usually spread over several atoms. 

The formation of CdS particles beneath monolayers of A-methyl-p-(p-tetradecyl-oxystyryl)pyridinium iodide, a cationic surfactant with a hemicyanine portion was studied [144]. The monolayers were spread on a circular glass trough coated with paraffin, and the trough was covered by ajar. The CdCL subphase also contained EDTA, so the Cd was... 

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. 

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... 

The diacetylene monomers can be spread as a monomolecular layer on the air-water interphase of a Langmuir-Blodgett trough. The molecules are well oriented because of the preferences of the hydrophilic head group of the monomer to be in coordination with the subphase. The monomers can be spread using a good solvent like chloroform. 

On the other hand, inclusion and/or adsorption of NaphSOsNa molecules from the aqueous subphase to the spread monolayer of p-CDNHC12H25 were examined by using the multicompartment trough. When the P-CDNHC12H25 mono-layer spread on the distilled water surface was compressed to the prescribed initial surface pressures of 5, 10, 20, and 30 mN/m and transferred onto the aqueous subphase containing 10 3 M NaphSCbNa, the surface pressure increased with time, air/aqueous solution interface under the suggesting the... 

Measurements of pressure-area (jc-A) isotherms and transfers of monolayers on a substrate were carried out by using a computer-controlled film balance system (San-Esu Keisoku, Co., Fukuoka, FSD-20). Maximum surface area on the trough was 475 X 150 mm2. The trough surface and the moving barrier were coated with Teflon, and the subphase was temperature-controlled with a thermostat (20 0.5 °C). The concentration of lipid solutions was 1 mg/ml and the spreading amount of lipid solutions was 50 - 150 pi. After solvent evaporation, the monolayer was compressed at the speed of 0.60 cm2 s-i. Measurements of n-A isotherms and transfers of monolayer on a QCM substrate were performed automatically with the usual manner [26,27]. 

Figure 16 shows the experimental arrangement for the measurement of the surface pressure. The trough (200 mm long, 50 mm wide and 10 mm deep) was coated with Teflon. The subphase temperature was controlled within 0.1 C by means of a jacket connected to a thermostated water circulator, and the environmental air temperature was kept at 18 °C. The surface tension was measured with a Wilhelmy plate of platinum(24.5 x 10.0 x 0.15 mm). The surface pressure monitored by an electronic balance was successively stored in a micro- computer, and then Fourier transformed to a frequency domain. The surface area was changed successively in a sinusoidal manner, between 37.5 A2/molecule and 62.5 A2/molecule. We have chosen an unsaturated phospholipid(l,2-dioleoyl-3-sn-phosphatidyI-choline DOPC) as a curious sample to measure the dynamic surface tension with this novel instrument, as the unsaturated lipids play an important role in biomembranes and, moreover, such a "fluid" lipid was expected to exhibit marked dynamic, nonlinear characteristics. The spreading solution was 0.133 mM chloroform solution of DOPC. The chloroform was purified with three consecutive distillations. 

The two compartment trough is schematically shown in Fig. 12. The trough is divided to two large compartment, where monolayer is spread, and a small buffer portion by two fixed barriers with a flexible gate. Compression of monolayers spread on each compartment is controlled independently by two movable polytetrafluoroethylene (PTFE) barriers. A substrate can move from a compartment to the other compartment by passing through the flexible gates... 

This trough allow the convenient and efficient preparation of noncentrosymmetric LB films. For the preparation of alternating LB films (hetero Y-type films), two different monolayers are spread on each compartment. After one monolayer is deposited on a substrate in down stroke, the substrate is transferred to the other compartment through the flexible gates. Then, another monolayer is deposited by withdrawing the substrate. One can obtain alternating LB films by repeating the deposition process. For the X-type or Z-type films, a monolayer is spread on one compartment and the other compartment is kept empty. The monolayers are deposited on substrate only in up or down stroke. 

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. 

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