Langmuir-trough apparatus

The isolation of the microbubble surfactant mixture from forest soil has been described in detail in preceding chapters. Quantitative examination of the surface properties of mono-molecular films of the isolated microbubble surfactant complex, at an air/water interface, were carried out using a modified Langmuir trough apparatus incorporating the surface tension method of Padday et al. (ref. 380). 

Fig. 3 Schematic depiction of the Langmuir trough apparatus and the positioning of the electrodes used in the lateral monolayer flow experiments. The inset shows the Au-coated glass slide working electrode modified with a self-assembled monolayer (SAM) of dodecanethiol. The working electrode is touching the air/water interface. A compound that forms a Langmuir monolayer is deposited on the water surface. It immediately spreads to cover the entire interface. Subsequently, the Langmuir film flows across the triple phase boundary into the SAM/water interface forming a bilayer. The lateral flow is completed when the entire electrode/solution interface is coated with a bilayer (from Ref 37).

Explore some commercial applications of surfactants as detergents and emulsifiers and familiarize yourself with the Langmuir trough apparatus. 

Because of the importance of surfactants in controlling and modifying the surface tension of fluids, it is appropriate here to describe methods for the measurement of surface tension and surfactant film characterization using the Langmuir trough apparatus. 

The Langmuir trough apparatus typically incorporates a mechanism for measuring the surface tension of the fluid interface (Figure 3.20). There are several methods used to achieve this measurement, and we review them briefly. Each involves exerting a force on the surface of the liquid in question and measuring the response. Surface tension of some common liquids at 25°C is shown in Table 3.2. 

A 5.2 X 10 -g sample of palmitic acid (C15H31COOH) is spread on a pure water surface as a solution in toluene and the solvent evaporated. Using a Langmuir trough apparatus, the monolayer is compressed to an area of 265 cm at which point it is known to form a close-packed monolayer. Calculate the area (in nm ) occupied by each molecule. 

An unusually extensive battery of experimental techniques was brought to bear on these comparisons of enantiomers with their racemic mixtures and of diastereomers with each other. A very sensitive Langmuir trough was constructed for the project, with temperature control from 15 to 40°C. In addition to the familiar force/area isotherms, which were used to compare all systems, measurements of surface potentials, surface shear viscosities, and dynamic suface tensions (for hysteresis only) were made on several systems with specially designed apparatus. Several microscopic techniques, epi-fluorescence optical microscopy, scanning tunneling microscopy, and electron microscopy, were applied to films of stearoylserine methyl ester, the most extensively investigated surfactant. 

The first to perform wave-damping measurements in a kind of Langmuir trough, i.e., under different compression status of the monolayer, was Agnes Pockels (1891). Ironically, she described for the first time an apparatus that was... 

The Langmuir trough used in this study has been described in detail recently [6, 7a, 7b]. Figure 1 illustrates the essential features of the apparatus. A solid PTFE frame, or barrier, hinged at the corners, provides a continuous, leak-free enclosure which can be used to reduce the area of an... 

The film balance (also called Langmuir trough) consists of a teflon (or teflon lined) rectangular trough (typically 20 cm x 10 cm x 1 cm). Teflon poly(tetraflouroethylene) (PTFE) allows one to keep the apparatus clean. A barrier of teflon is placed on one end of the trough, which is used as a barrier to compress the lipid molecules. Currently, there are many commercially available film balances. 

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