Langmuir-Blodgett film characteristics

Fig. 10 (a) Schematic representation of the I-V measurement of the Cgo derivative based molecular rectifier, (b) I-V characteristics of the Langmuir-Blodgett film of the fullerene penta-pod showing current rectification at bias voltage of 1.0 V measured at different junction positions, with high rectification ratios (RR) registered at each junction. (Reprinted with permission from [98])... 

Kusano, H. Kimura Shin, L Kitagawa, M. Kobayashi, H. Application of Cellulose Langmuir-Blodgett Films as Humidity Sensors, and Characteristics of the Sorption of Water Molecules into Polymer Monolayers. Thin Solid Films 1997, 295, 53-59. 

Langmuir-Blodgett films may have value in many applied areas of traditional interest to the industrial chemist, such as adhesion, encapsulation, and catalysis. The permeability characteristics of monolayer assemblies may also find application as synthetic membranes for ultrafine filtration, gas separation, and reverse osmosis. For example, Albrecht et al. (44) proved the eflSciency of polymeric diacetylene monolayers on semipermeable supports in reducing the flow of CH4. One interesting possibility lies in using LB monolayers as lubricants in magnetic tape technology. Unpublished reports have indicated that frictional coeflScients can be reduced markedly when the tape is coated with a few monolayers. In applications such as those listed previously, difiSculties may well be encountered with the mechanical stability of the films. To date, relatively little research has been carried out in this area. 

Liquori et al. [23] first discovered that isotactic and syndiotactic PMMA chains form a crystalline stereocomplex. A number of authors have since studied this phenomenon [24]. Buter et al. [25,26] reported the formation of an in situ complex during stereospecific replica polymerization of methyl methacrylate in the presence of preformed isotactic or syndiotactic PMMA. Hatada et al. [24] reported a detailed study of the complex formation, using highly stereoregular PMMA polymers with narrow molecular weight distribution. The effect of tacticity on the characteristics of Langmuir-Blodgett films of PMMA and the stereocomplex between isotactic and syndiotactic PMMA in such monolayers at the air-water interface have been reported in a series of papers by Brinkhuis and Schouten [27,27a]. Similar to this system, Hatada et al. [28] reported stereocomplex formation in solution and in the bulk between isotactic polymers of / -(+)- and S-(—)-a-methylbenzyl methacrylates. 

For instance the characteristics of Langmuir-Blodgett films using noncentrosymmetrically substituted phthalocyaninato complexes carrying different substituents have been studied (Fig. 24) [189]. 

Langmuir-Blodgett films at gold the characteristic distance do may be of the order of 100 A [41]. Therefore, we can tentatively explain the dramatic increase in the amount of fluorescent radiation by moving from the aggregates desorbed from the single touch to the triple touch film in terms of an increasing distance between the majority of the fluorophore and the metal surface. 

After creation of the compressed film, it can be transferred to an electrode surface. The characteristics of the substrate can tremendously affect the quality of the resulting Langmuir-Blodgett film (20), and dictate how the initial layer is transferred. Figure 8.4 depicts a common film transfer method, where a hydrophilic substrate is vertically lifted through a Langmuir film. The attractive forces between the surface and the head groups result in transfer of the layer, such that the film physisorbs on the electrode surface. These... 

Paloheimo et al. [208] described the function of a P(3-hexyl-T) based field effect transistor (FET), whose I-V characteristics are shown in Fie. 23-29. Tliey also described the use of this device as a sensor for such analytes as ammonia. Paloheimo et al. also described [1013] novel FETs based on mixed Langmuir-Blodgett films of P(3-hexyl-T) and arachidic acid. In these, film thicknesses were single monolayers to 35 monolayers (ca. 3.7 to 130 nm), and the undoped CP was the active semiconductor. The FET channel width and length were 8 cm and 5 pm respectively. The primary application envisioned was gas sensing. Like other organic-based FETs,... 

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. 

Mono- and multilayer films of polyimides were successfully prepared using Langmuir-Blodgett technique. Monolayer films of polyamic acid long alkylamine salts were prepared at the air-water interface. The mono-layer films were deposited on appropriate plates to produce multilayer films of the precursor to polyimide films. Finaly, the polyimide multilayer films were obtained by treatment of the multilayer films of the polyamic acid amine salts with acetic anhydride and pyridine. The polyimide multilayer films had excellent coating ability giving a very smooth surface. They also exhibited insulating characteristics as reliable as polyimide thick films. 

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