Soap-film type

Flowmeter. To monitor flow of carrier gas, a variety of devices are available, such as differential capillary, thermal conductivity, ionization, rotameters, and calibrated soap-film tubes Measurement of the flow may either be continuous or intermittent, and the flowmeter may be placed either in front of the column or at the carrier gas outlet. The soap-film type is most commonly used because of its economy and ease of operation. 

Fig. 2.2. Flow meters (a) soap film type (b) digital electronic type.

A. Flow Measurement by Displacement. A variety of flow meter designs are based on the positive displacement of a small amount of easily visualized material which does not alter the flow rate. A simple and easily constructed mass flow meter of this type, the soap-film meter, is based on timing the displacement of a soap film up a buret tube (Fig. 7.11). This type of flow meter is often placed at the exit of a gas chromatograph or small flow reactor. It is very... 

We shall examine properties of two systems of this type. Let the first system consist of a soap film stretched on two rings having the same diameter R (Fig. 28). 

In most cases e(electromagnetic spectrum. Fairly accurate interpolation formulas can be used for several systems. Numerical calculations have been made for soap films by Ninham and Parsegian. Their formula for e(w) was used to calculate the dispersion forces for our type of film. Results are given in Section VI. It is noteworthy that V h) is found to be not simply proportional to so that retardation effects cannot be neglected in our soap films. 

Although this contribution often cannot be neglected when the scattering of a single surface of a bulk liquid is measured, it is negligible for our type of thin film. To be more precise, the scattering of 1 cm of a 10% solution of the soap sodium dodecyl sulfate is 25 X 10 cm (for pure water it is 7.5 X 10 cm ). For 1 cm soap film, 300 nm thick, this is less than 1% of the surface scattering. 

Figure 12.11 Draining soap film showing interference colours from thicker films and silver and black bands from thin films. The two types of black film are not distinguishable.

Those researchers whose work have no direct connection with biomembranes perhaps are not acquainted with experimental lipid bilayers, commonly referred to as planar bilayer lipid membranes (BLMs) and spherical liposomes. These artificial systems have been extensively used in the past four decades as experimental models of cell membranes. The work began with D. O. Rudin and his associates in 1959 [1]. They first investigated lipid monolayers and multilayers of the Langmuir-Blodgett (L-B) type, and then they toyed with soap bubbles and films. It was realized that the structure of a soap film in air, in its final stage of thinning, has a structure that may be depicted as two lipid monolayers sandwiching an aqueous solution. That is a system which may be represented as ... 

One may rationalize emulsion type in terms of interfacial tensions. Bancroft [20] and later Clowes [21] proposed that the interfacial film of emulsion-stabilizing surfactant be regarded as duplex in nature, so that an inner and an outer interfacial tension could be discussed. On this basis, the type of emulsion formed (W/O vs. O/W) should be such that the inner surface is the one of higher surface tension. Thus sodium and other alkali metal soaps tend to stabilize O/W emulsions, and the explanation would be that, being more water- than oil-soluble, the film-water interfacial tension should be lower than the film-oil one. Conversely, with the relatively more oil-soluble metal soaps, the reverse should be true, and they should stabilize W/O emulsions, as in fact they do. An alternative statement, known as Bancroft s rule, is that the external phase will be that in which the emulsifying agent is the more soluble [20]. A related approach is discussed in Section XIV-5. 

Addition of chemicals without careful consideration may break an emulsion. An emulsion prepared with ionic surfactants should not be mixed with chemically incompatible materials of opposite charge. The pH of the emulsion should be alkaline if the emulsion is made with alkali soaps. At an acidic pH, the carboxylate ion of the soap is converted to the carboxylic acid, which is not water-soluble and an emulsifying agent. An alkali-soap stabilized O/W-type emulsion may be inverted to a W/O-type emulsion by adding a divalent electrolyte. The carboxylate ion reacts with the divalent electrolyte to form an alkali earth soap that is an oil-soluble surfactant. Addition of a common electrolyte to an emulsion prepared with ionic surfactants suppresses the ionization according to the Le Chatelier rule (e.g., ammonium oleate and ammonium chloride). The presence of noninteractive electrolytes in the emulsions alters the polar nature of the interfacial film. For example, the... 

As a result Bertrand and Vukasovitch of Climax Molybdenum carried out an intensive study of different cleaning techniques applied to various forms of molybdenum disulphide film. The types of film used were a burnished film from a sub-micron sized powder, a burnished film from a soap-containing molybdenum disulphide powder, an air-cured inorganic-bonded coating, and a film formed from a dispersion in oil. The films were formed on steel pins which were then pressed through an undersized bush. This ensured highly-loaded contact on the film, and consolidation of the film. The burnished powder and the resin-bonded films could be... 

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