Soap film method

The determination of the volumetric flow rates is easily performed by a flowmeter and a stopwatch (by soap-film method). It is necessary to consider the pressure drop when the gas bubbling through the saturator to yield calibration curves as a function of the soap-film burette method. 

Interferometry is based on the fact that light reflected from the front and back interfaces of a film travels different distances, producing interference effects. The method has been applied to Langmuir-Blodgett films (Section XV-7) and to soap films (Section XrV-8) [147-149]. 

Water-in-oil macroemulsions have been proposed as a method for producing viscous drive fluids that can maintain effective mobility control while displacing moderately viscous oils. For example, the use of water-in-oil and oil-in-water macroemulsions have been evaluated as drive fluids to improve oil recovery of viscous oils. Such emulsions have been created by addition of sodium hydroxide to acidic crude oils from Canada and Venezuela. In this study, the emulsions were stabilized by soap films created by saponification of acidic hydrocarbon components in the crude oil by sodium hydroxide. These soap films reduced the oil/water interfacial tension, acting as surfactants to stabilize the water-in-oil emulsion. It is well known, therefore, that the stability of such emulsions substantially depends on the use of sodium hydroxide (i.e., caustic) for producing a soap film to reduce the oil/water interfacial tension. 

It is also practically constant if the gas, enclosed in a soap bubble, is ignited in the center by means of a small electric spark (Method of Stevens, as described in Ref 13, p 384). In this case a spherical flame front is created and as resistance of soap film is very small, the pressure and burning rates are practically constant... 

The method used by Hutchinson (11) allows the measurement of the composition of soap films, the constituents of which are labelled with radioactive elements. Such a film may be formed by raising a platinum ring through the surface of the solution of the soap. The radiation emitted by the tagged molecules of the film is measured and the concentration of the last ones in the film are calculated. 

Equilibrium of Adsorption, (a) The Soap Films. The isotherms of adsorption of the organic cations of the soaps are reproduced on the Figure 2. Classical methods (20) are used to obtain the surface densities of the soaps I and IV. 

The methods of eliminating the effect of gravity on the form of the surfaces were two Plateau used soap films, which are practically weightless and he suspended masses of olive oil in a mixture of alcohol and water of practically the same density. By the latter device, spheres many centimetres in diameter were obtained. 

In an effort to eliminate wall effects, two spherical methods were developed. In the one discussed here, the gas mixture is contained in a soap bubble and ignited at the center by a spark so that a spherical flame spreads radially through the mixture. Because the gas is enclosed in a soap film, the pressure remains constant. The growth of the flame front along a radius is followed by some photographic means. Because, at any stage of the explosion, the burned gas behind the flame occupies a larger volume than it did as unbumed gas, the fresh gas into which the flame is... 

This is the shortest roadway encountered. Is it the shortest If it is the shortest road linking the four towns, how is it possible to prove that there is no shorter road system Alternatively, if it is not the shortest system, what is the shortest roadway configuration and what is its length This problem can be simply solved using an analogue method based on the minimization property of the area of a soap film. 

All the problems discussed in this chapter have been solved by analogue methods based on the minimization property of the surface area of soap films. We shall now solve using analytic means one of the simpler problems, the problem of finding the minimum path linking three points. 

The methods of Euler and Lagrange consider a continuous sequence of surfaces, contained by the boundary, which deviate from the extremum surface. For the soap film problem the extremum surface is the minimum area surface. A differential equation is then derived for the extremum surface. The solution to the differential equation will give the required surface. 

The differential equations of Poisson and Laplace occur in many branches of physics, other than the fields of membranes and soap films. We can thus use the soap film as an analogue method of solving these equations. It must be remembered that soap films satisfy (6.53) and (6.54) providing the small gradient conditions, (6.52), are satisfied at all points on the surface. 

Let us examine the procedure for solving one of the previous differential equations using the soap film analogue. Once the method has been outlined for one particular problem the application to the other problems, with the same form of differential equation, will be clear. The electrostatic potential equation, (6.55), is probably the equation that is most widely known. In order to use the soap film analogue we need to replace V, in (6.55), by z in soap film Eq. (6.53). Let us write. 

If a material could be made extremely thin, for example, to the level of a single layer of molecules, this thin layer would transmit almost all of the infrared radiation, so that its infrared transmission spectrum could be measured. In fact, it is possible to measure a mid-infrared transmission spectrum from a thin soap film. It is usually practically difficult, however, to maintain such a thin film without it being supported by a substrate. For a thin film supported on a substrate, its infrared spectmm is often obtained by utilizing a reflection geometry. Two reflection methods are available for measuring infrared spectra from substrate-supported thin films, depending on the dielectric properties of the substrates used. External-reflection (ER) spectrometry, which is the subject of this chapter, is a technique for extracting useful information from thin films on dielectric (or nonmetallic) substrates, while reflection-absorption (RA) spectrometry, described in Chapter 10, is effective for thin films on metallic substrates [1]. In addition to these two reflection methods, attenuated total-reflection (ATR) spectrometry, described in Chapter 13 and emission spectroscopy, described in Chapter 15 may also be useful in some specific cases. 

Though foam and emulsion films might exist for a long time, on some timescale they will collapse. The rupture of foam and emulsion films has been studied by various methods both experimentally [797] and theoretically [798]. It is obvious that the stability of foam films is influenced by surface forces. For example, in 1924 Bartsch reported that electrolytes decrease the life time of certain foams [799], presumably by decreasing electrostatic stabilization. Surface forces alone, however, do not determine the life time of a soap film. 

EXPERIMENTAL The sampling and analytical method employed in determining the various solvent vapor concentrations in air are described in detail by White etal (A)and NIOSH (2), Four Bendix National Environmental Instruments Model BDX 30 Personal Samplers were used daily (one in each laboratory) with large size charcoal tubes (SKC cat no. 226-09-100) which contained two sections of activated charcoal per tube (a 400 milligram section followed by a 200 mg backup section to indicate when "breakthrough" of the main section has occurred). The sampling pumps were operated at a rate of one liter per minute and were calibrated by means of an Environmental Compliance Corporation Model 302 Universal Pump Calibrator (a device that generates a thin film of soap which is carefully timed as it traverses a very... 

There are static and dynamic methods. The static methods measure the tension of practically stationary surfaces which have been formed for an appreciable time, and depend on one of two principles. The most accurate depend on the pressure difference set up on the two sides of a curved surface possessing surface tension (Chap. I, 10), and are often only devices for the determination of hydrostatic pressure at a prescribed curvature of the liquid these include the capillary height method, with its numerous variants, the maximum bubble pressure method, the drop-weight method, and the method of sessile drops. The second principle, less accurate, but very often convenient because of its rapidity, is the formation of a film of the liquid and its extension by means of a support caused to adhere to the liquid temporarily methods in this class include the detachment of a ring or plate from the surface of any liquid, and the measurement of the tension of soap solutions by extending a film. 

X-ray diffraction and electron microscopy may be i d separately or together. X-ray diffraction was applied at first in Strasbourg to systems copolymer/solvent as a generalization of the study of systems soap/water and both experimental technics and structural interpretation methods were extended to copolymers. Electron microscopy has been very popular in Japan. The Japanese authors have generally studied films obtained by evaporation of a dilute solution of copolymers but, in that case, the structures observed may be influenced by the nature of the solvent and its speed of evaporation Low angle X-ray diffraction and electron microscopy have been systematically applied together to systems copolymer/solvent and to dry copolymers in Orleans and to oriented dry copolymers in BristoF ... 

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