Characterization, of LB films

Although characterization of LB films after deposited on a substrate or monolayers at the air-water interface have been studied in detail. However, characterization of LB films during a transfer... 

Transferring Insoluble Monolayers Fundamental Characterization of LB Films Applied Physics of LB Films... 

In this chapter, we characterize in situ vertical transfer process of LB films of cadmium octadecanoate and other amphiphiles by using a QCM as a dipping substrate. Experimental set-up is shown in Figure 1. A transfer amount of dry LB films (W, / ng), an incorporated amount of water during a lifting process (W2/ ng), and... 

LB films of five new hybrid dimethyidioctadecylammonium/heteropolyanions DODA/HPA (HPA=[PZ(H20)M0 03,], Z=Co, Cu, Mn, Zn, Ni) were prepared and characterized by it-A isotherms, UV-Vis absorption spectra, IR spectra, small-angle X-ray diffraction (SAXD), and atomic force microscope (AFM). The results show that these compounds have good film-forming property on the air-water interface. The collapse pressure of LB films is 28.7-37.5mN/m. The area per molecule is 28.18-49.07 nm mol". The LB films have lamellar structures in which the monolayers of the heteropolyanions alternate with bilayers of DODA to form centrally symmetrical LB films. 

Modifications of LB films, whether caused by the SPM probe or by some other external force, are easily characterized and can provide insight into film structure and -dynamics. With an AFM tip under high force it is possible to maike holes in an LB film. From the image of the hole the thickness per monolayer and number of monolayers can be determined. Virtanen et al. ) induced defect pores in bllayers of stearic acid and cadmium stearate by the application of electric pulses between an STM tip and film surface. Real-time STM images measuring the rates at which these pores refill , provide a means of determining the viscosity of nanometer-scale regions of deposited molecular films. 

D.K. Schwairtz, Langmuir-Blodgett Film Structure, Surf. Set Reports 27 (1997) 245-334. (Review on structural and thermod5mamlc properties of LB films brief description of characterization techniques.)... 

Among techniques used to characterize such LB CP films have been low angle x-ray diffraction, comparative transmission-mode and reflection-mode IR spectroscopy, near-edge X-ray absorption fine structure (NEXAFS), and of course, conductivities, determined by transfer of LB films onto special 4-electrode substrates. As expected especially for the LB CP films which include alternating non-conductive surface-active molecular layers, conductivities of such films are highly anisotropic. For example, the conductivity of Shimidzu et al. s poly(3-octadecyl 4-Me-pyrrole-3-carboxylate)/octadecane alternating layer film, described above, is 10 S/cm in-plane and 10 S/cm across the film, yielding a conductivity anisotropy of 10 . 

In summary, a vast number of materials has been used to fonn LB films. However, in the majority of cases an effort to characterize the film stmcture or even to show that a regular layer stmcture has been achieved is lacking. Work on the stmcture of films of disc-like molecules such as porjDhyrins and phthalocyanines is especially limited. Some references can be found in [29]. 

X-ray diffraction has been applied to spread monolayers as reviewed by Dutta [67] and Als-Nielsen et al. [68], The structure of heneicosanoic acid on Cu and Ca containing subphases as a function of pH has been reported [69], as well as a detailed study of the ordered phases of behenic acid [70], along with many other smdies. Langmuir-Blod-gett films have also been studied by x-ray diffraction. Some recent studies include LB film structure just after transfer [71], variations in the structure of cadmium stearate LB films with temperature [72], and characterization of the structure of cadmium arachidate LB films [73], X-ray [74,75] and neutron reflectivity [76,77] data on LB films can be used to model the density profile normal to the interface and to obtain values of layer thickness and roughness. 

Langmuir-Blodgett (LB) films of proteins (Tiede 1985, Hwang et al. 1977, Furuno et al. 1988, Lvov et al. 1991) and lipid-protein complexes (Fromherz 1971, Phillips et al. 1975, Mecke et al. 1987, Kozarac et al. 1988) were intensively studied and characterized by different techniques. 

Several experimental techniques were applied to characterize these objects. It was found that CdS was formed as small particles inside the LB film with sizes in the nanometer range. Similar work was carried out that resulted in the formation of PbS, CuS, HgS, etc. The sizes of the particles produced by such approaches turned out to be rather similar to that of CdS. The observed sizes suggest that the objects could be useful for the formation of nanogranules for room-temperature single-electron junctions. 

Organic compounds which show reversible color change by a photochemical reaction are potentially applicable to optical switching and/or memory materials. Azobenzenes and its derivatives are one of the most suitable candidates of photochemical switching molecular devices because of their well characterized photochromic behavior attributed to trans-cis photoisomerization reaction. Many works on photochromism of azobenzenes in monolayers LB films, and bilayer membranes, have been reported. Photochemical isomerization reaction of the azobenzene chromophore is well known to trigger phase transitions of liquid crystals [29-31]. Recently we have found the isothermal phase transition from the state VI to the state I of the cast film of CgAzoCioN+ Br induced by photoirradiation [32]. 

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