Langmuir technique

Films or membranes of silkworm silk have been produced by air-drying aqueous solutions prepared from the concentrated salts, followed by dialysis (11,28). The films, which are water soluble, generally contain silk in the silk I conformation with a significant content of random coil. Many different treatments have been used to modify these films to decrease their water solubiUty by converting silk I to silk II in a process found usehil for enzyme entrapment (28). Silk membranes have also been cast from fibroin solutions and characterized for permeation properties. Oxygen and water vapor transmission rates were dependent on the exposure conditions to methanol to faciUtate the conversion to silk II (29). Thin monolayer films have been formed from solubilized silkworm silk using Langmuir techniques to faciUtate stmctural characterization of the protein (30). ResolubiLized silkworm cocoon silk has been spun into fibers (31), as have recombinant silkworm silks (32). 

Basu and Searcy [736] have applied the torsion—effusion and torsion— Langmuir techniques, referred to above for calcite decomposition [121], to the comparable reaction of BaC03, which had not been studied previously. The reaction rate at the (001) faces of single crystals was constant up to a product layer thickness of 1 mm. The magnitude of E (225.9 kJ mole-1) was appreciably less than the enthalpy of the reaction (252.1 kJ mole-1). This observation, unique for carbonates, led to the conclusion that the slowest step in BaC03 vacuum decomposition at 1160—1210 K is diffusion of one of the reaction components in a condensed phase or a surface reaction of C02 prior to desorption. 

Powell and Searcy [1288], in a study of CaMg(C03)2 decomposition at 750—900 K by the torsion—effusion and torsion—Langmuir techniques, conclude that dolomite and C02 are in equilibrium with a glassy phase having a free energy of formation of (73 600 — 36.8T)J from 0.5 CaO + 0.5 MgO. The apparent Arrhenius parameters for the decomposition are calculated as E = 194 kJ mole-1 and activation entropy = 93 JK-1 (mole C02)-1. 

Polymer monolayers on the aqueous subphase are studied using the Langmuir technique as is shown in Scheme 3.2. 

B. L. Moiseiwitsch How Opaque Is a Star M. J. Seaton Studies of Electron Attachment at Thermal Energies Using the Flowing Afterglow-Langmuir Technique, David Smith and Patrik Spanel... 

The Langmuir technique is used in order to characterize monolayer properties of surface-active materials. The instrumentation consists of a shallow rectangular container (trough) in which a liquid subphase is added until a meniscus appears above the rim, whereupon the film is spread. The barrier for manipulation of the film rests across the edges of the container. For a more thorough description of the experimental setup. Petty and Barlow (8) are recom-... 

The influence of chemical additives on asphaltene films on the water surface and at the oil/water interface have also been studied by means of the Langmuir technique. This was done in order to view the interaction between demulsifiers added and asphaltenes, and to show the importance of this on emulsion stability. 

Both the block lengths in the x-direction and the extension of the 2-D polymer in the y-direction will be on the macroscopic scale if the Langmuir technique is applied. 

The Langmuir and Langmuir-Blodgett techniques The Langmuir technique... 

The properties of Chi a in vitro greatly depend on its environment and state of aggregation, properties which have been studied in solution [28,29], in vesicles [30,31], in micelles [32,33] and in monolayers [34-42]. The maximum absorbances of various systems of Chi a recorded in the blue and red regions of the visible spectrum are summarized in Table 1. The bathochromic shifts noticed especially in the red region are clear evidence of the transformations that Chi a undergoes. Considering the importance of Chi a in photosynthesis, it is vital to understand how Chi a interacts with various chloroplast components and with itself. The Langmuir technique has proven to be valuable in the study of Chi a interactions because it is easier to control the specific interaction in a two-dimensional layer as opposed to a bulk three-dimensional system. 

Because of the very high temperatures and the low pressures involved, no Knudsen studies have been undertaken. Even the Langmuir technique should only be used at the congruent composition. In view of this, the metal pressure over TaC + C is best calculated from thermochemical data. This was done using the following information A/f (298.15 ) = — 34.0 kcal/mole (Huber et al, 1963) a heat of vaporization for the metal of 186.5 kcal/mole (Edwards et al, 1951b) the thermal values in Table 37, the JANAF (1963) tables for and Stull and Sinke (1956) for TU(g). The resulting equation... 

The W-C system loses carbon preferentially at all compositions and measured temperatures. For this reason it is not possible to obtain equilibrium pressures of either W or C using the Langmuir technique and very... 

The mass spectrometer is the only technique which allows the vapor composition to be determined, and this can be done rapidly and with great sensitivity. Beyond that, its usefulness for pressure measurements depends on how accurately the apparatus can be calibrated. In this regard, it has been common practice to use the known vapor pressure of Ag, Au, or sometimes Mo combined with the measured or calculated ionization cross sections for the various species. While this method and its variations can give satisfactory answers, a comparison with an absolute determination using the system of interest is better. For example, the pressure of many metallic elements is known or can be determined by the Langmuir technique. If the elements of the system of interest fall into this category. 

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