The Langmuir-Blodgett Technique

Although some LB materials are liquids, most are solids at room temperature and need to be dissolved in a solvent before spreading onto the subphase surface. The solvent should therefore be immiscible with the subphase, have a sufficiently high vapour pressure to smoothly evaporate from the spread film and not chemically interact (form adducts, complexes etc.) with the solute. Common solvents are alkanes (e.g. hexane), chlorinated alkanes (e.g. dichloromethane) and to a lesser extent aromatics (e.g. toluene). 

The values obtained for molecular dimensions by this technique agree well with those obtained by other techniques (e.g. from crystal diffraction studies), and indicate that the hydrocarbon chains adopt a linear extended conformation with their major axis normal to the layer planes. 

By monitoring the increase in surface pressure IT (defined in two dimensions as the pressure per unit length) against the decrease in surface area A at constant temperature, a Il A isotherm is obtained. For most materials at low surface pressure the following relationship is obeyed  

Before deposition of the material to form multilayers, the stability of the monolayer must be considered. The solid monolayer phase of most LB materials is formed at surface pressures above the equilibrium spreading pressure (ESP) of the material the ESP being defined as the pressure at which the monolayer and stable solid or liquid phases are in thermodynamic equilibrium. Consequently, the deposition of most LB materials occurs from a metastable state. This often presents no practical problems, since the approach to thermodynamic equilibrium is extremely slow. However, for some materials a loss of pressure or area is observed below the collapse pressure 11. These materials approach thermodynamic 

While monolayer collapse is usually the major cause of LB monolayer instability, other processes, such as subphase dissolution, chemical reaction, evaporation and degradation, can also be a source of material loss. However, since their kinetics (although sometimes complex) are sufficiently different, it is often possible to distinguish between these loss mechanisms. 

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

Orthmann E and Wegner G 1986 Preparation of ultrathin layers of molecularly controlled architecture from polymeric phthalocyanines by the Langmuir-Blodgett-technique 1986 Angew. Chem. Int. Edn. Engl. 25 1105-7... 

Dominguez, D.D.,Mowery, R. L., and Turner, N. H., Friction and Durabilities of Well-Ordered, Close Packed Carboxylic Acid Monolayers Deposited on Glass and Steel Surfaces by the Langmuir-Blodgett Technique, Tribal. Trans., yi. No. 1, 1994, pp. 59-66. 

Therefore, investigators have shown considerable interest in the adoption of the Langmuir-Blodgett technique, or its modifications, to make molecular electronic devices using, in particular, as an active component, a light-transducing protein, such as BR. In fact, the ability of BR to form thin films with excellent optical properties and the intrinsic properties themselves make it an outstanding candidate for use in optically coupled devices. 

Supported lipid bilayers on planar silicon substrates have been formed using S-layer protein from B. coagulans E38/vl and from B. sphaericus CCM 2177 as support onto which l,2-dimyristoyl-OT-glycero-3-phosphocholine (DMPC) (pure or mixtures with 30% cholesterol) or DPPC bilayers were deposited by the Langmuir-Blodgett-technique (Pig. 

Modified electrodes containing cyclam derivatives have been prepared. The approach utilizing cyclam incorporated in Nafion film on a carbon electrode shows that the catalytic efficiency of the system is much lower than observed when the catalyst is adsorbed on the mercury. With electrodes prepared following the Langmuir Blodgett technique, only the electrode materials that allow the orientation of the monolayer so that the tail points to the substrate were found to be electrocatalytically active.165... 

Fig. 3.5 Representation of a scheme of an experiment (upper set of drawings) and the obtained experimental results presented as AFM images (middle part) and cross-sectional profiles (bottom) that provides evidence of silica nucleation and shell formation on biopolymer macromolecules. Scheme of experiment. This includes the following main steps. 1. Protection of the mica surface against silica precipitation. It was covered with a fatty (ara-chidic) acid monolayer transferred from a water substrate with the Langmuir-Blodgett technique. This made the mica surface hydrophobic because of the orientation of the acid molecules with their hydrocarbon chains pointing outwards. 2. Adsorption of carbohydrate macromolecules. Hydrophobically modified cationic hydroxyethylcellulose was adsorbed from an aqueous solution. Hydrocarbon chains of polysaccharide served as anchors to fix the biomacromolecules firmly onto the acid monolayer. 3. Surface treatment by silica precursor. The mica covered with an acid mono-...

Here, we demonstrate that oriented PAV films with well-developed -conjugated system can be fabricated through the regulation of orientation of precursor polymer chains by use of the Langmuir-Blodgett technique, and that large and anisotropic third-order optical nonlinearity was observed in the oriented PAV films. 

Y Cimrova, M Remmers, D Neher, and G Wegner, Polarized light emission from LEDs prepared by the Langmuir-Blodgett technique, Adv. Mater., 8 146-149, 1996. 

In both cases the top layer of these layered polyelectrolyte films contains many ion sites that can bind redox ions by ion exchange vdth the electrolyte solution. Homo polypeptides such as poly(L-lysine) and poly(L-glutamic add) have been employed to form layered polyelectrolyte films with Fe(CN)6 " electrostatically adsorbed onto ammonium sites in poly(lysine) [45]. Modified electrodes with polyelectrolytes mono-layers have also been deposited using the Langmuir-Blodgett technique [46-48]. 

FIG. 7.1 Deposition of multilayers using the Langmuir-Blodgett technique (a and b) monolayer deposition and (c and d) multilayer deposition. 

The Langmuir-Blodgett technique for deposition of ordered multilayers has origins which, in a sense, go back to classical antiquity as the present author has discussed elsewhere [3], In 1774 Benjamin Franklin [4] demonstrated that a very small quantity of oil could influence the sur-... 

The simple arguments presented above are for a one-dimensional variation of order in a direction normal to the planes of a layer structure in which individual layers remain flat. Such a system is, of course, a gross over-simplification of a real three-dimensional system but nevertheless serves to illustrate the way in which deterioration of order influences the X-ray diffraction obtained from a layered structure such as is obtained, for example, by the Langmuir-Blodgett technique. 

More complex structures formed by the Langmuir-Blodgett technique... 

Beginning with a discussion of the necessary basic physics and chemistry, the book proceeds to a description of the main topics of current research in this field. The Langmuir-Blodgett technique, self-assembly, and methods of film deposition exploiting the ordered structure of mesophases are discussed. Separate chapters are devoted to the properties and computer modelling of both liquid crystals and films at the air/water interface. Order in biomemebranes is also discussed. 

We have studied the photoelectrochemical behavior of Chi a and Chi b on an n-type Sn02 (60) optically transparent electrode (OTE thickness of the Sn02 layer on the glass substrate, ca. 2000 A donor density, 1020-21cm-3). Chi monolayer assemblies, deposited by means of the Langmuir-Blodgett technique (20,21), were employed. The use of such monolayer assemblies as interfacial dye layers... 

Monolayers can be transferred onto solid substrates by the Langmuir-Blodgett technique giving rise to mono- or multilayers which can even have thicknesses in the range of the wavelength of visible light. The multilayer quality often depends on the quality of the first monolayer transfer. 

Monolayer Films of Phthalocyanine Derivatives. A series of organic derivatives of phthalocyanines were prepared that have two important characteristics of materials to be deposited by the Langmuir-Blodgett technique (1) they are soluble in volatile organic solvents, and (2) they form monomolecular films on the surface of water. Further study of deposited films of these phthalocyanine derivatives will be necessary in order to determine the exact orientations on the surface, but regardless of their orientations, they offer interesting possibilities for construction of thin films of ordered arrays of molecules on the surface of gas sensors. 

Figure 13.4 Transfer of a monolayer from an aqueous surface to a solid substrate via the Langmuir-Blodgett technique.

Yasuzawa M, Hashimoto M, Fujii S, Kunugi A, Nakaya T. Preparation of glucose sensors using the Langmuir-Blodgett technique. Sensors and Actuators B 2000, 65, 241-243. 

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