Langmuir crystals

Electron diffraction studies are usually limited to transferred films (see Chapter XV), One study on Langmuir films of fatty acids has used cryoelectron microscopy to fix the structures on vitrified water [179], Electron diffraction from these layers showed highly twinned structures in the form of faceted crystals. 

Transmission electron microscopy (TEM) can resolve features down to about 1 nm and allows the use of electron diffraction to characterize the structure. Since electrons must pass through the sample however, the technique is limited to thin films. One cryoelectron microscopic study of fatty-acid Langmuir films on vitrified water [13] showed faceted crystals. The application of TEM to Langmuir-Blodgett films is discussed in Chapter XV. 

Other interesting Langmuir monolayer systems include spread thermotropic liquid crystals where a foam structure forms on expansion from a collapsed state [23]. Spread monolayers of clay dispersions form a layer of overlapping clay platelets that can be subsequently deposited onto solid substrates [24]. 

Ruths M, Steinberg S and Israelachvili J N 1996 Effects of confinement and shear on the properties of thin films of thermotropic liquid crystal Langmuir M 6637-50... 

Jones R, Tredgold R H, Hoorfar A, Allen R A and Hodge P 1985 Crystal-formation and growth in Langmuir-Blodgett multilayers of azobenzene derivatives—optical and structural studies Thin Solid Films 134 57-66... 

Penner T L, Schiidkraut J S, Ringsdorf H and Schuster A 1991 Oriented films from polymeric amphiphiles with mesogenic groups—Langmuir-Blodgett liquid-crystals/Macromo/ecu/es 24 1041-9... 

Adsorbed molecules are more strongly held at the sites where the weakest metal-metal bonding is to be found, and these conespond to the active sites of Langmuir. A demonstration of this effect was found in smdies of the adsorption of H2S from a H2S/H2 mixture on a single crystal of copper of which die separate crystal faces had been polished and exposed to die gas. The formation of copper sulphide first occuiTed on die [100] and [110] planes at a lower H2S partial pressure dran on die more densely packed [111] face. Thus die metal atoms which are less strongly bonded to odrer metal atoms can bond more strongly to die adsorbed species from die gas phase. 

The catalytic reaction of NO and CO on single crystal substrates, under ultra-high vacuum conditions, has been extensively studied. Neglecting N2O formation and CO desorption, the Langmuir-Hinshelwood mechanism of the NO + CO reaction can be described by the following sequence of steps [16,17] ... 

Self-Assembled Layers, Langmuir-Blodgett Layers, and Liquid Crystals... 

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. 

FIG. 16 Fomation of a Langmuir lipid monolayer at the air/subphase interface and the subsequent crystallization of S-layer protein, (a) Amphiphilic lipid molecules are placed on the air/subphase interface between two barriers. Upon compression between the barriers, increase in surface pressure can be determined by a Wilhelmy plate system, (b) Depending on the final area, a liquid-expanded or liquid-condensed lipid monolayer is formed, (c) S-layer subunits injected in the subphase crystallized into a coherent S-layer lattice beneath the spread lipid monolayer and the adjacent air/subphase interface. 

Protsailo, L.V., Fawcett, W.R., Russell, D. and Meyer, R.L. (2002) Electrochemical Characterization of the Alkaneselenol-Based SAMs on Au(lll) Single Crystal Electrode. Langmuir, 18, 9342-9349. 

Bohannan, E. W., Huang, L. Y Miller, F. S., Shumsky, M. G. and Switzer, J. A. (1999) In situ electrochemical quartz crystal microbalance study of potential oscillations during the electrodeposition of CU/CU2O layered nanostructures. Langmuir, 15, 813—818. 

Iwasita T, Xia X, Henero E, Liess HD. 1996. Early stages during the oxidation of HCOOH on single-crystal Pt electrodes as characterized by infrared spectroscopy. Langmuir 12 4260-4265. 

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