Langmuir-Blodgett LB Films

Preparation methods to be used in organic thin film deposition can be roughly divided into two main categories quick and dirty deposition from solution and (ultra high) vacuum deposition from the gas phase, which is expensive and time-consuming but clean. In between lies the preparation of LB (Langmuir-Blodgett-) films of substituted amphiphilic molecules or unsubstituted molecules in mixed layers. 

Yonezawa, Y. Wataya, K. Hada, H. Preparation and spectroscopic properties of LB (Langmuir-Blodgett) films composed of polar matrix molecules and a xanthene or coumarin dye. Nippon Shashin Gakkaishi 1989, 52, 550-560 Chem. Abstr. 1990,113, 174067. 

A huge number of other applications exist, where the chemical and physical requirements are totally different. These applications include reflectors, temperature measurement with thermochromic materials, nonlinear optics, pol3mier materials, SAMs (self-assembled mono-layers) and LB (Langmuir-Blodgett) films, the use of Uquid crystals in template synthesis of porous materials, drug delivery, and many more. 

Langmuir-Blodgett films (LB) and self assembled monolayers (SAM) deposited on metal surfaces have been studied by SERS spectroscopy in several investigations. For example, mono- and bilayers of phospholipids and cholesterol deposited on a rutile prism with a silver coating have been analyzed in contact with water. The study showed that in these models of biological membranes the second layer modified the fluidity of the first monolayer, and revealed the conformation of the polar head close to the silver [4.300]. 

When some NC particles are surface treated to make them hydrophobic by, e.g., silylation and floated on the surface of water, a nanoparticle layer can be made on a solid substrate by a method similar to Langmuir-Blodgett film formation. Interparticle separation is well controlled by choosing an appropriate surface pressure prior to making LB film, as discussed next. 

Langmuir-Blodgett films prepared from arachidic acid Nanosized, cationic Fe204 sandwiched between polar headgroups in LB films Domain structures were recognized in magnetic particles 796... 

Figure 19. a) Simple representation of an amphiphile b) Langmuir monolayer in expanded and compressed states c) vertical and horizontal Langmuir-Blodgett film transfer d) X-, Y-, and Z-type LB films. 

Menzel, H., Hallensleben, M. L., Schmidt, A., Knoll, W., Fischer T., and Stumpe, J. Langmuir-Blodgett-Films of Photochromic Polyglutamates IV. Spectroscopic and Structural Studies on LB-Films of Copolyglutamates Bearing Azobenzene Moieties and Long Alkyl Chains. Macromolecules 26, 3644 (1993). 

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. 

On a conceptual level, the ideal format for thin-film materials for nonlinear optics is the Langmuir-Blodgett film. Molecularly engineered chrom-ophores with large hyperpolarizabilities can, in principle, be incorporated at high concentration, with well-defined orientations into films having thicknesses defined by molecular resolution. Extremely large resonantly enhanced values of have been reported in LB films several layers thick (30, 3i) thus the considerable promise of this approach is established. 

J.A. DeRose, R.M. Leblanc, Scanning Tunneling and Atomic Force Microscopy Studies of Langmuir-Blodgett Films, Surface Sci. Reports 22 (1995) 73. (Review concerning STM and AFM studies of LB films, covering 1987-1994.)... 

D.K. Schwairtz, Langmuir-Blodgett Film Structure, Surf. Set Reports 27 (1997) 245-334. (Review on structural and thermod5mamlc properties of LB films brief description of characterization techniques.)... 

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.)... 

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