Langmuir Blodgett

The Langmuir-Blodgett (L-B) assembly technique (8, 14, 15) offers a versatile way to prepare a modified electrode. L-B layers are created by transferring organized monomol-ecular films from a liquid phase in a Langmuir trough onto a soUd support. Attractive non-covalent interactions hold the film in a cohesive unit on the electrode surface. However, the weak nature of these forces limits adlayer stabihty. 

L-B films are useful in biological studies, as they can easily be prepared to act as mimics of hpid membranes. Thus, modified electrodes of this type are often used in studies of transport phenomena (16) and enzyme activity. These electrodes are also often used as molecular recognition sensors (17-20) and in molecular electronics (20-22). 

Functionalized aliphatic amphiphUes used to form Langmuir-Blodgett films  

Source Adapted from reference (8) with the permission of Cambridge University Press. 

The power of the L-B technique is the vast array of possible layer types and orientations. However, the forces that hold the film in a coherent unit on the substrate surface consist of van der Waals interactions. These forces are much smaller than those resulting in chemical bond formation. Thus, L-B layers may not be stable for long periods of time or in harsh environments. Moreover, specialized equipment is required to create than, and special care must be taken to ensure reproducible and well-ordered films. This approach is particularly demanding with respect to high-purity reagents and liquids, and surface preparation procedures. 

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A belief that solid interfaces are easier to understand than liquid ones shifted emphasis to the former but the subjects are not really separable, and the advances in the one are giving impetus to the other. There is increasing interest in films of biological and of liquid crystalline materials because of the importance of thin films in microcircuitry (computer chips ), there has been in recent years a surge of activity in the study of deposited mono- and multilayers. These Langmuir-Blodgett films are discussed in Section XV-7. 

Interferometry is based on the fact that light reflected from the front and back interfaces of a film travels different distances, producing interference effects. The method has been applied to Langmuir-Blodgett films (Section XV-7) and to soap films (Section XrV-8) [147-149]. 

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. 

Langmuir-Blodgett flint deposited on copper. From graphic integration of the data of Ref. 144. See Ref. 158. 

A. Ulman, An Introduction to Ultrathin Organic Films From Langmuir-Blodgett to Self-Assembly, Academic, New York, 1991. 

Macromolecular Surface Films, Charged Films, and Langmuir-Blodgett Layers... 

Films spread at liquid-liquid interfaces or on liquids other than water are discussed followed by the important effects of charged monolayers on water. Finally, the most technologically important application of Langmuir films, the Langmuir-Blodgett film deposited on a solid substrate, is reviewed. 

The transfer of Langmuir films from the air-liquid surface to a solid substrate has come to be known as Langmuir-Blodgett deposition, after its developers [130, 131]. The solid substrates are usually hydrophilic surfaces such as... 

Deposited Langmuir-Blodgett films take on many of the same stmctures as the Langmuir monolayers discussed in Section IV-4C, and they are often compared to the self-assembling monolayers described in Section XI-IB. The area... 

From what you know about wetting, contact angles, and spread monolayers, explain why a Langmuir-Blodgett layer will deposit as a F type if there are nonpolar fatty acids, yet will switch to a Z-type deposition if bipolar alcohols or amines are added (see Refs. 175, 176). What defines the critical contact angle for the deposition change ... 

G. G. Roberts, Langmuir-Blodgett Films, Plenum, New York, 1990. 

Flayden L M 1988 Looal-field effeots in Langmuir-Blodgett films of hemioyanine and behenio aoid mixtures Rhys. Rev. B 38 3718-21... 

Fu]iwara I, Ishimoto C and Seto J 1991 Scanning tunnelling microscopy study of a polyimide Langmuir-Blodgett film J. Vac. Sc/. Technoi. B 9 1148... 

Sotobayashi FI, Schilling T and Tesche B 1990 Scanning tunnelling microscopy of polyimide monolayers prepared by the Langmuir-Blodgett technique Langmuir 6 1246... 

Schwartz D K, Viswanathan R and Zasadzinski JAN 1993 Commensurate defect superstructures in a Langmuir-Blodgett film Phys. Rev. Lett. 70 1267... 

Bourdieu L, Ronsin O and Chatenay D 1993 Molecular positional order in Langmuir-Blodgett films by atomic force microscopy Science 259 798... 

Holmberg M ef al 1997 Surface force studies of Langmuir-Blodgett cellulose films J. Colloid Interface Sci. 186 369-81... 

Wang P, Maruyama Y and Metzger R M 1996 Superconductivity of Cgg Langmuir-Blodgett films doped with potassium low-field signal and electron spin resonance study Langmuir M 3932-7... 

Nakamura T, Tachibana H, Yumara M, Matsumoto M and Tagaki W 1993 Structure and physical properties of Langmuir-Blodgett films of Cgg with amphiphilic matrix molecules Synth. Met. 55 3131-6... 

Bulhoes LOS, Obeng Y S and Bard A J 1993 Langmuir-Blodgett and electrochemical studies of fullerene films Chem. Mater. 5 110-14... 

Goldenberg L M, Williams G, Bryce M R, Monkman A P, Petty M C, Flirsch A and Sol A 1993 Electrochemical studies on Langmuir-Blodgett films of 1-fert-butyl-1,9-dihydrofullerene-60 J. Chem. Soc., Chem. Commun. 1310-12... 

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