Stabilization Langmuir-Blodgett films

FIG. 13 Langmuir-Blodgett films of dioctadecyldimethylammonium bromide incorporating 6.0-nm-diameter CdS nanoparticles stabilized by 0.2 mM sodium hexametaphosphate. (a) Absorbance spectra for 2, 3, 4, 5, 6, 7, 8, and 13 layers (bottom to top) the inset shows the linearity of the absorbance at 450 nm versus the number of layers, (b) Fluorescence spectra (excitation wavelength = 400 nm) for 2, 3, 4, 6, 8, 13, and 18 layers (bottom to top) the inset shows the emission intensity at 480 nm versus the number of layers. (Reproduced with permission from Ref. 152. Copyright 1994 American Chemical Society.)... 

Langmuir-Blodgett films were prepared by spreading a 2 x 1(T4 M solution of the enantiomerically pure helicenebisquinone in chloroform onto a water surface. After evaporation of the solvent, the monolayer was compressed to a surface pressure of 20 mN/m. After stabilization for 30 min, the monolayers were transferred by the horizontal dipping method onto glass substrates, treated with octadecyltrichlorosilane to make them hydrophobic. 

Because of their electrical, optical, and redox properties as well as the thermal and chemical stability, the Pcs also have been tried in the detection of volatile organic compounds and poisonous gases, which is very important for environment and human health. In the past decades, the possible applications of Pc thin film as sensor for atmospheric gaseous pollutants have been extensively studied [73, 74], Langmuir-Blodgett films of some multinuclear and multidouble-decker lutetium Pcs have also been used for those measurements [75,76], More details about conductivity and sensing properties of Pcs can be found elsewhere [77,78]. 

Self-assembled monolayers have recently attracted much attention as a new methodology for molecular assembly [249, 342]. They enable highly organized chemical binding of molecules of interest to the surfaces of, e.g., metals, semiconductors, and insulators. The well-ordered structure of self-assembled monolayers is in sharp contrast with conventional Langmuir-Blodgett films and lipid bilayer membranes in terms of stability, uniformity, and manipulation. Functional molecules can be arranged unidirectionally at the molecular level on substrates when substituents which will self-assemble on the substrates are attached to a terminal of the molecules. The wide variety of examples reported to date include porphyrins and metalloporphyrins in self-assembled monolayers [299-339]. 

Langmuir-Blodgett films may have value in many applied areas of traditional interest to the industrial chemist, such as adhesion, encapsulation, and catalysis. The permeability characteristics of monolayer assemblies may also find application as synthetic membranes for ultrafine filtration, gas separation, and reverse osmosis. For example, Albrecht et al. (44) proved the eflSciency of polymeric diacetylene monolayers on semipermeable supports in reducing the flow of CH4. One interesting possibility lies in using LB monolayers as lubricants in magnetic tape technology. Unpublished reports have indicated that frictional coeflScients can be reduced markedly when the tape is coated with a few monolayers. In applications such as those listed previously, difiSculties may well be encountered with the mechanical stability of the films. To date, relatively little research has been carried out in this area. 

J.A. Zasadzinski, R. Viswanathan, L. Madsen, J. Gamaes and D.K. Schwartz, Langmutr-Blodgett Films, Science 263 (1994) 1726. (Comprehensive overview of the progress made in LB technology with SPM, in terms of film structure, stability, and the substrate influence on these. Speeifle results for Langmuir-Blodgett films of fatty acids.)... 

Nicolini C, Erokhin V, Antolini F et al. thermal stability of protein secondary structure in Langmuir-Blodgett films. Biochim Biophys Acta 1993 1158 273-278. 

Techniques for the fabrication of molecular films. The existing techniques for multilayer fabrication address these requirements to a different extent. Langmuir-Blodgett films allow for excellent control of film architecture but typically lack stability. Self-assembled multilayers are extremely stable since they generally represent covalently crosslinked networks, but it seems to be difficult to obtain p.-thick films of high quality. Freely-suspended liquid crystalline films can be obtainedas optical monodomains, but are... 

Brandi, D., Schoppmann, C.,Tomaschko, Ch., Schurr, M., Voit, H. (1995) Vacuum stability of Langmuir-Blodgett films of fatty acids and fatty acid salts. Thin Solid Films, 256,220-225. 

Keywords Langmuir-Blodgett films Cadmium arachidate Adhesional stability Wettability Atomic force microscopy... 

Meldrum, F., Kotow, N. and Fendler, J., Utilization of surfactant stabilized colloidal silver nanocrystallites in the construction of monoparticulate and multiparticulate Langmuir-Blodgett films, Langmuir, 10, 2035-2040 (1994). 

Note G. Ashwell has achieved high stabilities with a novel series of zwitterionic compounds described in Ashwell, G. J., Hargreaves, R.C., Baldwin, C. E., Bahra, G. S., and Brown, C. R., Improved second-harmonic generation from Langmuir-Blodgett films of hemicyanine dyes. Nature, 357, June 1992. 

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