Langmuir-Blodgett films diacetylene

Thin films of materials play an important role in modern electronics. Langmuir-Blodgett films (Mort, 1980) are prepared from surface-active molecules that adsorb at the surface of an aqueous solution. The surface is gently compressed to produce a close-packed monolayer, which can be coated on appropriate substrates by dipping at constant surface pressure. The layers so produced are of a precise thickness, and repeated dipping gives multilayers. For example, diacetylenes and other polymerizable... 

A membrane for a DNA-probe of a microelectronic biosensor based on Langmuir-Blodgett (LB) diacetylene film with covalently bonded DNA has been developed [86]. Diacetylene films formed on the surface of oxidized silicon by the LB method were used for covalent immobilization of DNA molecules, using the standard W./V -dicyclohexylcarbodiimide... 

Palto, S. P., Makhete, J., Germain, C., and Durand, G. On the Nature of Wiotoinduced Optical Anisotropy in Diacetylene Langmuir-Blodgett Films. Mol. Cryst. Liq. Cryst. 282, 451 (1996). 

Seki, T., Tanaka, K., and Ichimura, K. Phototropic discrimination of the polymerization behavior of diacetylene Langmuir-Blodgett films by an azobenzene-containing monolayers. Adv. Mater., 9, 563 (1997). 

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 Unpublished reports have indicated that frictional coeflScients can be reduced markedly when the tape is coated with a few monolayers.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. 

Photopolymerization in the Langmuir-Blodgett films provides a method to produce highly oriented monolayer films of polymers for application in Integrated optical and electronic devices. We have studied the photopolymerization of several diacetylenes in the Langmuir-Blodgett films (9,10)j Here results from two such studies will be presented. 

Tachibana, H., Yamaka, Y., Sakai, H., Abe, M., and Matsumoto, M. Structural and Morphological Changes and Polymerization Behaviors of Diacetylene Langmuir-Blodgett Films on Adding Water Soluble Polyallylamine in the Subphase. Polymer 42, 1995 (2001). Nishiyama, K., Kurihara, M. A., and Fujihira, M. Photochromism of Amphiphilic Azobenzene Derivative in its Langmuir-Blodgett Films Prepared as Polyion Complex with Ionic Polymers. Thin Solid Films 179, All (1989). 

Despite their potential importance, there are few spectroscopic studies of polymerizable surfactants. The only well-characterized polymerized surfactants are the polydiacetylenic fatty acids. The polymerization mechanism (1,4 addition) was only recently discovered as a result of studies on crystals of non-surfactant monomers which become brightly colored on polymerization [1], indicating the formation of polymer concurrent with a solid-solid phase transition. Several groups, particularly that of Ringsdorf, have pioneered the study of polydiacetylenic fatty acids [2-5]. A significant amount of spectroscopic work has been done on non-surfactant polydiacetylenes [6-9]. In addition, Lando and co-workers have used electron diffraction from mono- and bilayers of fatty acids to establish the conformation of the diacetylene backbone chains in this ordered surfactant system [10,11], and others have performed Raman spectroscopy on Langmuir-Blodgett films of similar surfactants [12]. This provides one with a powerful "basis set" of information from which to study other polydiacetylenic systems. 

The topochemical diacetylene photopolymerization is apphcable to various organized structures, including Langmuir-Blodgett films, liposomes, vesicles, and self-assembled monolayers (SAMs) on metal oxide or graphite surfaces. Scheme 3.14 depicts an assembly of diacetylene molecules and the subsequent photopolymerization at 254 nm. At ambient temperatures, the polymerization proceeds as a chain reaction by 1,4-addition, and results in alternating ene-yne polymer chains with exclusive trans selectivity. The quantum yield for initiation is low (about 0.01) [60]. 

S. Palto, J. Malthete, C. Germain, and G. Durand, On the nature of photoinduced optical anisotropy in diacetylene Langmuir-Blodgett films. Molecular Crystals and Liquid Crystals 282, 451 (1996). 

Besides single crystals, disubstituted diacetylene polymer thin films can be obtained for waveguide applications by evaporation, solidification, or deposition of the diacetylene monomers by the Langmuir-Blodgett approach, which allows film thicknesses to be controlled at the molecular level. These diacetylene films can be patterned using selective polymerization techniques such as developed for... 

Recently, the Langmuir-Blodgett (LB) technique has been recognized as a useful way of tailoring thin films of molecular thickness. Interest in the LB technique has led to a number of investigations of different types of materials. For example, the classic long-chain fatty acids and alcohols as well as polymerizable molecules, e.g. diacetylenic acids [211-213], aromatic hydrocarbons, e.g. substituted anthracenes [214, 215], TCNQ radical anion salts [216, 217] and charge transfer complexes [218-220] and dye substances can now all be produced as monomolecular layers. 

Molyneux, S., Matsuda, H., Kar, A. K., Wherrett, B. S., Okada, S., and Nakanishi, H., Third-order optical properties of poly-DCH thin single crystals. Nonlinear Opt., 4, 299, 1993. Kajzar, F. and Messier, J., Solid state polymerization and optical properties of diacetylene Langmuir-Blodgett multilayers. Thin Solid Films, 99, 109, 1983. 

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