Langmuir multilayers

Sugi M, Salto M, Fukui T and lizima S 1983 Effeot of dye oonoentration in Langmuir multilayer photooonduotors Thin Solid Films 99 17-20... 

N.V. Dubinin, S.G. Yudin, and L.M. Blinov, Quadratic Stark effect and orientation of molecules in polar Langmuir multilayers. Opt. Spektrosk. 59 92 (1985). 

In the present theory of van der Waals adsorption, the multilayer starts below the pressure P and builds up with increasing pressure, and the capillaries are not filled up even for pressures greater than this condensation pressure P, which contradicts the capillary condensation. This means that the multilayer theory based on van der Waals adsorption has an upper limit in the pressure range. Despite this limitation, the van der Waals theory puts all five types of adsorption isotherm shape into one framework, that is it can deal with unimolecular adsorption (Langmuir), multilayer adsorption (BET) and enhanced adsorption in capillaries (BDDT). 

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. 

Because of their prevalence in physical adsorption studies on high-energy, powdered solids, type II isotherms are of considerable practical importance. Bmnauer, Emmett, and Teller (BET) [39] showed how to extent Langmuir s approach to multilayer adsorption, and their equation has come to be known as the BET equation. The derivation that follows is the traditional one, based on a detailed balancing of forward and reverse rates. 

Another limitation of tire Langmuir model is that it does not account for multilayer adsorption. The Braunauer, Ennnett and Teller (BET) model is a refinement of Langmuir adsorption in which multiple layers of adsorbates are allowed [29, 31]. In the BET model, the particles in each layer act as the adsorption sites for the subsequent layers. There are many refinements to this approach, in which parameters such as sticking coefficient, activation energy, etc, are considered to be different for each layer. 

Patel H M, Didymus J M, Wong K K W, Hirsch A, Skiebe A, Lamparth I and Mann S 1996 Fullerates interaction of divalent metal ions with Langmuir monolayers and multilayers in mono-substituted Cgg-malonic acid J. Chem. Soc., Chem. Commun. 611-2... 

Saint Pierre M and Dupeyrat M 1983 Measurement and meaning of the transfer prooess energy in the building up of Langmuir-Blodgett multilayers Thin Solid Films 99 205-13... 

Jones R, Tredgold R H, Hoorfar A, Allen R A and Hodge P 1985 Crystal-formation and growth in Langmuir-Blodgett multilayers of azobenzene derivatives—optical and structural studies Thin Solid Films 134 57-66... 

Jones R, Tredgold R FI and Floorfar A 1985 Effeots of thiokness on surfaoe-potential and surfaoe oonduotivity in non-insulating Langmuir-Blodgett multilayers of porphyrins Thin Solid Films 123 307-14... 

Fukui M, Katayama N, Ozaki Y, Araki T and Iriyama K 1991 Struotural oharaoterization of phthalooyanine Langmuir-Blodgett multilayer assemblies by FTIR speotrosoopy Chem. Phys. Lett. 177 247-51... 

Laschewsky A, Ringsdorf H and Schmidt G 1985 Polymerization of hydroxocarbon and fluorocarbon amphiphiles in Langmuir-Blodgett multilayers Thin Soiid Fiims 134 153-72... 

Laschewsky A and Ringsdorf H 1988 Polymerization of amphiphilic dienes in Langmuir-Blodgett multilayers Maoromoieouies 21 1936-41... 

Tieke B, Enkelmann V, Kapp H, Lieser G and Wegner G 1981 Topoohemioal reaotions in Langmuir-Blodgett multilayers J. Macromol. Sol.—Chem. A 15 1045-58... 

Tieke B and Weiss K 1984 The morphology of Langmuir-Blodgett multilayers of amphiphilio diaoetylenes—effeots of the preparation oonditions and the role of additives J. Colloid Interface Sol. 101 129-48... 

Biddle M B, Lando J B, Ringsdorf H, Schmidt G and Schneider J 1988 Polymeric amphiphiles with hydrophilic main chain spacers—studies in monolayers and Langmuir-Blodgett multilayers Oollold Polymer Scl. 266 806-13... 

Erdelen C, Laschewsky A, Ringsdorf H, Schneider J and Schuster A 1989 Thermal-behaviour of polymeric Langmuir-Blodgett multilayers Thin Solid Films S0 153-66... 

Schneider J, Erdelen C, Ringsdorf H and Rabolt J F 1989 Structural studies of polymers with hydrophilic spacer groups. 2. Infrared-spectroscopy of Langmuir-Blodgett multilayers of polymers with fluorocarbon side-chains at ambient and elevated temperatures Macromolecules 22 3475-80... 

Spinke J, Liley M, Guder FI J, Angermaier L and Knoll W 1993 Moieouiar reoognition at self-assembled monolayers—the oonstruotion of multioomponent multilayers Langmuirs 1821-5... 

In the present study we try to obtain the isotherm equation in the form of a sum of the three terms Langmuir s, Henry s and multilayer adsorption, because it is the most convenient and is easily physically interpreted but, using more a realistic assumption. Namely, we take the partition functions as in the case of the isotherm of d Arcy and Watt [20], but assume that the value of V for the multilayer adsorption appearing in the (5) is equal to the sum of the number of adsorbed water molecules on the Langmuir s and Henry s sites ... 

Langmuir referred to the possibility that the evaporation-condensation mechanism could also apply to second and higher molecular layers, but the equation he derived for the isotherm was complex and has been little used. By adopting the Langmuir mechanism but introducing a number of simplifying assumptions Brunauer, Emmett and Teller in 1938 were able to arrive at their well known equation for multilayer adsorption, which has enjoyed widespread use ever since. 

During the remainder of the 1930s, Langmuir and Blodgett carried out a brilliant series of studies on multilayer films of a variety of chemicals, supplemented by studies in Britain, especially at the ill-fated Department of Colloid Science in Cambridge (Section 2.1.4). Then the War came, and momentum was lost for a couple of decades. After that, L-B films came back as a major topic of research and have been so ever since (Mort 1980). It is current practice to refer to molecular films, made by various techniques (Swalen 1991), but the L-B approach remains central. 

Brunauer further developed the Langmuir isotherm expression to include multilayer adsorption ... 

Mono- and Multilayers of Spherical Polymer Particles Prepared by Langmuir-Blodgett and Self-Assembly Techniques... 

Transfer experiments of the Langmuir films onto solid substrates and the preparation of LB films were investigated for 43. The deposition of films of 43 occurred regularly on quartz sHdes or silicon wafers with a transfer ratio of 1 0.05. The diblock structure of dendrimer 43 also appeared crucial for efficient transfers of the Langmuir films in order to obtain well-ordered multilayered LB films. Effectively, the transfer of the Langmuir films of the dendrimer 42 with the small polar head group was found to be difficult with a transfer ratio of about... 

Figure 5.19 shows an idealized form of the adsorption isotherm for physisorption on a nonporous or macroporous solid. At low pressures the surface is only partially occupied by the gas, until at higher pressures (point B on the curve) the monolayer is filled and the isotherm reaches a plateau. This part of the isotherm, from zero pressures to the point B, is equivalent to the Langmuir isotherm. At higher pressures a second layer starts to form, followed by unrestricted multilayer formation, which is in fact equivalent to condensation, i.e. formation of a liquid layer. In the jargon of physisorption (approved by lUPAC) this is a Type II adsorption isotherm. If a system contains predominantly micropores, i.e. a zeolite or an ultrahigh surface area carbon (>1000 m g ), multilayer formation is limited by the size of the pores. 

BET method. The most commonly used method for determining the specific surface area is the so-called BET method, which obtained its name from three Nobel prize winners Brunauer, Emmett and Teller (1938). It is a modification of the Langmuir theory, which, besides monolayer adsorption, also considers multilayer adsorption. The equation allows easy calculation of the surface area, commonly referred to as the BET surface area ( bet). From the isotherms also pore-radii and pore-volumes can be calculated (from classical equation for condensation in the pores). 

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