Langmuir trough applications

Anotlier metliod applicable to interfaces is tlie detennination of tlie partial molecular area (7 of a biopolynier partitioning into a lipid monolayer at tlie water-air interface using tlie Langmuir trough [28]. The first step is to record a series of pressure 71-area (A) isotlienns witli different amounts of an amphiphilic biopolynier spread at tlie interface. 

Interfacial and surface tensions are the most important chciracteristics of fluid-fluid interfaces and hardly any paper exists in which such tensions do not play a central role. In fact the entire present volume of FICS will be devoted to them. In chapter 2 a molecular Interpretation will be given. Chapters 3 and 4 deal extensively with liquid-fluid interfaces containing spread and adsorbed molecules, respectively and chapter 5 will treat three-phase contacts. For all these applications, measurement is a first and necessary element. Langmuir troughs, to be described in sec. 3.3.1, also involve a kind of interfacial tension determination since... 

There are many applications of ellipsometry in the measurement of mono-layer and sub-monolayer films. The theory of the optical signal to be expected from an adsorbed layer less than one monolayer thick has been placed on a firm footing by Smith [15] in some elegant experiments on adsorption in a Langmuir trough. Simultaneous ellipsometric and surface potential measurements were made on various molecules spread in thin layers on mercury as the surface pressure was varied. One conclusion was the simple result that the effective thickness divided by the thickness of the island molecules in the adsorbed islands was equal to the fractional coverage of the surface area. 

The exceptionally low sensitivity of PM IRRAS to atmospheric CO2 and H2O vapor prompted interest in the application of this technique to the study of insoluble surfactant monolayers at the air/water interface in a Langmuir trough [27, 71-78]. These studies significantly advanced the PM IRRAS technique. 

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

These monolayer films find many applications, e.g. reduction of water evaporation from lakes, estimation of the molecular weight of proteins (Equation 4.10), study of biological (cell) membranes, enzymes and the impressive Langmuir-Blodgett monolayer films, often studied with a technique called the Langmuir trough (Pashley and Karaman, 2004) (see case study below). 

In its initial application, a triple potential step was applied at a submarine UME placed in the aqueous subphase of a Langmuir trough, close (1-2 pm) to the monolayer. The technique involves generating an electroactive species (Ox) at the UME by diffusion-controlled electrolysis of a precursor (Red) in an initial potential step. Ox diffuses to, and reacts with, the redox-active amphiphile at the water-air interface resulting in the conversion of the solution redox species to its initial form (Red), which then undergoes diffusional feedback to the UME. In this first step, the rate constant for electron transfer between the solution mediator and the surface-confined species can be measured from the UME current-time transient. In the second period, the potential step is reversed to convert the electrogenerated species (Ox) to its initial form (Red). Lateral diffusion of electroactive amphiphile into the interfacial zone probed by the UME occurs simultaneously in this recovery period. 

Formation of the monolayer is usually done with a Langmuir-Blodgett trough. With the aid of a moveable barrier a dense monomolecular layer of the surfactant on the liquid phase is maintained and controlled with a thin WOhelmy plate, the force on which is proportional to the stuface tensions. A dipping device provides the application of the layer on the substrate. Depending on its quality (hydro- or lipophilic) the nature of the surface is reversed after sorption. Multiple immersions and emersions allow stacking of the layers. 

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