Langmuir monolayer films

In the case of Langmuir monolayers, film thickness and index of refraction have not been given much attention. While several groups have measured A versus a, [143-145], calculations by Knoll and co-workers [146] call into question the ability of ellipsometry to unambiguously determine thickness and refractive index of a Langmuir monolayer. A small error in the chosen index of refraction produces a large error in thickness. A new microscopic imaging technique described in section IV-3E uses ellipsometric contrast but does not require absolute determination of thickness and refractive index. Ellipsometry is routinely used to successfully characterize thin films on solid supports as described in Sections X-7, XI-2, and XV-7. 

In the third direction of their research. Miller and Bard also relied on HT voltammetry of Langmuir monolayer films to develop a trace analytic method of determination of water insoluble redox-active species [24]. They demonstrated that (iL volumes of such compounds can be deposited on the water surface in a miniature Langmuir trough, and then assayed electrochemically by HT voltammetry yielding detection limits of... 

Piwowar, A.M., GardeUa, J.A. Jr. (2007) Time-of-flight secondary ion mass spectrometric analysis of polymer tertiary structure in Langmuir monolayer films of Poly(dimethylsiloxane). Anal. Chem., 79,4126 134. 

Surface Micelles. The possibility of forming clusters of molecules or micelles in monolayer films was first proposed by Langmuir [59]. The matter of surface micelles and the issue of equilibration has been the subject of considerable discussion [191,201,205-209]. Nevertheless, many ir-a isotherms exhibit nonhorizontal lines unexplained by equations of state or phase models. To address this, Israelachvili [210] developed a model for ir-u curves where the amphiphiles form surface micelles of N chains. The isotherm... 

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. 

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... 

Guldi D M, Tian Y, Fendler J H, Hungerbuhler H and Asmus K-D 1995 Stable monolayers and Langmuir-Blodgett films of functionalized fullerenes J. Phys. Chem. 99 17 673-6... 

C2.4 Organics films (Langmuir-Blodgett films and self-assembled monolayers)... 

Films or membranes of silkworm silk have been produced by air-drying aqueous solutions prepared from the concentrated salts, followed by dialysis (11,28). The films, which are water soluble, generally contain silk in the silk I conformation with a significant content of random coil. Many different treatments have been used to modify these films to decrease their water solubiUty by converting silk I to silk II in a process found usehil for enzyme entrapment (28). Silk membranes have also been cast from fibroin solutions and characterized for permeation properties. Oxygen and water vapor transmission rates were dependent on the exposure conditions to methanol to faciUtate the conversion to silk II (29). Thin monolayer films have been formed from solubilized silkworm silk using Langmuir techniques to faciUtate stmctural characterization of the protein (30). ResolubiLized silkworm cocoon silk has been spun into fibers (31), as have recombinant silkworm silks (32). 

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]. 

FIG. 8 Phase diagrams for monolayer films on surfaces with boundary potential equal to 0.25 (a), 0.50 (b), and 0.75 (c). (Reprinted with permission from Langmuir 9 2562-2568, October 1993. 1993, American Chemical Society.)... 

The second way of preparing L-B monolayer structures, the horizontal lifting method, was introduced by Langmuir and Schaefer. In this method, a compressed monolayer first is formed at the water-air interface, and a flat substrate is then placed horizontally on the monolayer film. When the substrate is lifted and separated from the water surface, the monolayer is transferred onto the substrate, as depicted in Fig. 15(d). 

I. INTRODUCTION TO LANGMUIR MONOLAYERS AND LANGMUIR-BLODGETT FILMS... 

B. Langmuir Monolayers and Langmuir-Blodgett Films of Fatty Acids... 

Generation of nanoparticles under Langmuir monolayers and within LB films arose from earlier efforts to form nanoparticles within reverse micelles, microemulsions, and vesicles [89]. Semiconductor nanoparticles formed in surfactant media have been explored as photocatalytic systems [90]. One motivation for placing nanoparticles within the organic matrix of a LB film is to construct a superlattice of nanoparticles such that the optical properties of the nanoparticles associated with quantum confinement are preserved. If mono-layers of capped nanoparticles are transferred, a nanoparticle superlattice can be con-... 

FIG. 14 Measurements on monolayers and LB films of CdSe nanoparticles of narrow size distribution (a) II-A isotherms for Langmuir monolayers of CdSe nanoparticles of diameter 2.5 run (curve a), 3.0 mn (curve b), 3.6 mn (curve c), 4.3 mn (curve d), and 5.3 mn (curve e). The area per nanoparticle was determined by dividing the trough area by the estimated number of particles deposited on the surface, (b) Absorbance and photoluminescence spectra of the nanoparticles in solution (A, B) and in monolayers on sulfonated polystyrene-coated glass sbdes (C. D). The nanoparticle diameters are 2.5 nm (curves labeled a), 3.6 nm (curves labeled b), and 5.3 nm (curves labeled c). The excitation wavelengths are (a) 430 nm, (b) 490 nm, and (c) 540 nm. (Reproduced with permission from Ref. 158. Copyright 1994 American Chemical Society.)... 

The observation that Langmuir monolayers often exist as phase-separated domains has begun to be exploited as a means to produce LB monolayers with two-dimensional patterns. This approach aims to form, transfer, and stabilize these domains on appropriate substrates by combining the Langmuir-Blodgett method with the covalent bonding aspect of self-assembly. There are a small number of studies, and the possible further functionalization of the domains and use of different combinations of materials make this area promising for the construction of patterned films. 

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