Langmuir-Adam surface balance

The Langmuir-Adam surface balance (or trough) uses a technique... 

Figure 4.18 The principle of the Langmuir-Adam surface balance...

Typically, these films are deposited using the following procedure. A flat, shallow container, such as a Langmuir-Adam surface balance, is filled with water (or other suitable liquid) and the substrate to be coated is immersed. Then a solution of the amphiphilic material, in a solvent that is insoluble in water, is deposited dropwise onto the water, thereby forming an oriented monomolecular surface film upon evaporation of the solvent. This film can then be compacted... 

Figure 8-8 (A) The Langmuir-Adam film balance. Tension on the moveable barrier is recorded for different areas of the surface between the barriers. This gives the surface pressure jt, which is the difference between the surface tension (y0) of a clean aqueous surface and that of a spread monolayer (y) K = ya-y. Courtesy of Jones and Chapman.81 (B) Surface pressure (7t)-area per molecule isotherm for a typical fatty acid (e.g., pentadecanoic acid C14H29C02H) at the aqueous-air interface. From Knobler.81a...

Surface Pressure and Surface Potential Measurements. The surface balance was Langmuir-Adam type with a glass trough as previously described (14), The sensitivity of the balance in terms of surface pressure was 0.1 dyne/cm. 

Film Balance A shallow trough that is filled with a liquid on top of which is placed material that may form a monolayer. The surface area available can be adjusted by movable barriers, and any surface pressure thus created can be measured by means of a float. Also called Langmuir Film Balance, Langmuir Trough, and Pockels—Langmuir—Adam—Wilson—McBain Trough or PLAWM Trough. 

For many years, the main experimental tool for these studies was the film balance (see Figure 4.19). Various workers, including Pockels, Langmuir, and Adam, made major contributions to its development (see Gaines, 1966). A small, known quantity of the surfactant to be studied is dissolved in a volatile solvent and deposited carefully by pipette on the surface of a pool of water. The solvent is chosen so that it spreads rapidly over the water and then evaporates, leaving the surfactant uniformly distributed as a monomolecular layer (or monolayer) in the region between the two barriers. One of the barriers is movable, so that the area occupied by the surfactant film can be varied. A torsion balance is provided to measure the surface pressure (i.e., the difference between the surface tension of pure water and that of the film-covered surface). More commonly in modem instruments, a Wilhelmy plate is used to measure surface tension in the film region. 

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