Interfacial measurement surface film

In the present study various surface measurements were made on interfacial lipid films to analyze in more detail the nature of interactions of lipids, Ca2+, ATP, and the glycolate esters. Surface pressure-area and surface potential-area diagrams were obtained on surface films of stearic acid, lecithin, and a mixture of brain lipids with Ca2+, ATP, and the drugs present in the subsolution, individually or in combination. Using radioactive Ca2+, ATP, and drug, quantitative measurements were made on the surface adsorption of these substances to lipid films. In addition, electron microscopy was performed on brain lipid films formed in the presence or absence of Ca2+ and ATP. Our objective was to establish the existence of surface complexes involving these substances with the hope... 

Adamson [15] and Miller et al. [410] illustrate some techniques for measuring surface shear viscosity. Further details on the principles, measurement and applications to foam stability of interfacial viscosity are reviewed by Wasan et al. [301,412], It should be noted that most experimental studies deal with the bulk and surface viscosities of bulk solution rather than the rheology of films themselves. 

Two experimental results indicate that there is an adsorption energy barrier related to the interfacial pressure. First, the presence of an energy barrier becomes evident only after an interfacial pressure of 0.1 mN m-1 is attained (Table II). In the second experiment, different compounds were spread at the air/water interface and the rate of adsorption of pepsin and lysozyme were measured under conditions where charge effects were minimized (MacRitchie and Alexander, 1963a). It was found that the rates of adsorption for these proteins were independent of the nature of the surface film and depended only on the surface pressure. 

Much progress has been made in understanding the role of surface films in air-sea gas transfer. Advances in both laboratory and field techniques have provided improved measurements and needed insight into this complex and important process. Current efforts focused toward better understanding the key physical mechanisms involved in interfacial gas transfer and the role of surfactants, along with innovative and interdisciplinary field and laboratory measurements, will help to further our present knowledge. 

It should be noted that in QCM measurement interfacial properties are determined by averaging over the length scale S. As a result one cannot distinguish between a true slip on the molecular level and an apparent hydrodynamic slip, which can arise from a shear thinning of the hquid near the surface. The latter leads to a steep velocity profile at the surface that appears as a slip, although the velocity is continuous at the surface. Indeed, a comparison between Eqs. 19-20 and Eqs. 16-17, which describe the effects of slip and surface film on the resonant frequency respectively, allow a relationship to be established between the apparent shp length and the film properties that give the same QCM response ... 

A under these conditions. The equivalent thickness of the top and interfacial layers as a function of ion bombardment energy are also shown in Fig. 41, bottom. The results of XPS measurements agree fairly well with the ellipsometric data. Surface films are all too common in electrochemical engineering, especially in corrosion. 

In this chapter, we report the influence of surface-active compounds on the stability of crude oil emulsions using the apparatus designed for bilayer lipid membrane studies. The electrical method we employed to measure the film lifetime and thickness of model oils and crude oils seems to be a convenient technique for monitoring the coalescence processes in emulsions. The results obtained show that the natural surface-active substances in crude oil, such as petroleum acids and asphaltenes, have a great effect on the film strength. The ionized acids formed by the reaction between the petroleum acids and the alkali can decrease the interfacial tension and accelerate the thinning and breakdown of the thin liquid film. The asphaltenes can adsorb on to the interface and improve the stability of the film. The order of stability of the films between different oils and alkaline solutions is as follows crude oil with asphaltenes removed < crude oil < crude oil with both asphaltenes and petroleum-acids removed (iv) < crude oil with petroleum acids removed. In addition. 

Singh (143) followed up this study to understand the performance of unidentified demulsifiers with a change in solvent properties. By noting the relative decrease in surface pressures resulting from added demulsifiers in various solvents, he found that benzene was the best in that it helped the demulsifier to lower the surface film pressures. The lowering of interfacial tension was measured at the same time and the results suggested that rapid adsorption occurred. It was concluded that structure, orientation, and film pressmes were the most important factors in demulsifier performance. 

The mechanical properties of asphaltene films at interfaces can be probed by a variety of rheological techniques. These methods provide valuable insight into the origins of stability of asphaltene emulsions and into the role of concentration, and solvation by resins and aromatic solvents on the adsorption and self-assembly of asphaltenes. Miller et al. provide a comprehensive review of methods for probing interfacial dilational and shear properties of adsorption layers at liquid interfaces (72). They describe devices that measure surface velocity profiles (indirect methods) or determine torsional stress values (direct methods). Indirect... 

Generally, the experimental data in Table 5.3 are consistent with these hypotheses. Firstly, the surface partition coefficient, is the ratio of the surface saturation concentration (T ) to the overall amount of surfactant needed to saturate the surface (keeping in mind that a significant amount of the surfactant remains solubilised). Therefore, at relatively constant T , should decrease as the solubility of the copolymer increases. This can be seen in Table 5.3. Secondly, the solvated volumes were not directly measured however, the diffusion coefficients were measured and they decreased as X increased. It is generally known that the diffusion coefficient varies as the inverse of the solvated volume [49]. From this relationship, one would conclude that the solvated volumes of the copolymers increased with X. Thirdly, the interfacial areas of the copolymers generally increased as X increased. Finally, we were not able to measure the surface viscosities of these materials in solution. ITowever, all of them yielded mobile-surfaced films. This means that their surface viscosities were relatively low, as expected. 

Ellipsometry is an experimental technique employed primarily for measurements of optical spectra of highly absorbing solids and of surface films on solid or liquid substrates. It is used mostly in a reflection mode. In electrochemical interfacial systems, the main use of ellipsometry has been for measurement of optical properties and the thickness of surface films formed on the electrode surface. These observations complement other interfacial information (e.g. electric charge associated with film growth, changes in interfacial capacitance following growth of film and impedance associated with the film conversion process). 

The LB trough is commonly used to measure surface pressure/area isotherms for a particular surfactant film. To carry out this measurement, the thin surfactant film is compressed by moving a barrier across the fluid surface at a constant rate while monitoring the surface tension. At a constant temperature the surface pressure Tt is measured as a function of the interfacial area available to each molecule as... 

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