Langmuir-Blodgett films, behavior

The area of colloids, surfactants, and fluid interfaces is large in scope. It encompasses all fluid-fluid and fluid-solid systems in which interfacial properties play a dominant role in determining the behavior of the overall system. Such systems are often characterized by large surface-to-volume ratios (e.g., thin films, sols, and foams) and by the formation of macroscopic assembhes of molecules (e.g., colloids, micelles, vesicles, and Langmuir-Blodgett films). The peculiar properties of the interfaces in such media give rise to these otherwise unlikely (and often inherently unstable) structures. 

Electrical Behavior of Langmuir-Blodgett Films Containing C60 and Derivatives... 

A benzo[18]crown-6 adduct (72) of Cgg (not shown) has been synthesized by the addition of the corresponding o-quinodimethane 71 in toluene [58]. The solubility of 72 in pro tic solvents such as MeOH strongly increases after the complexation of ions, as shown by extraction experiments. The combination of the crown ether and the fullerene moiety in 72 provides a highly amphiphilic character. This behavior allowed the preparation of Langmuir-Blodgett films of monolayers on mica of 72 and its complex. 

Amino-5-nitropyrimidine, cocrystallization, 455 Amorphous polymers, criteria for use in second harmonic generation, 250-251 Amphiphilic molecules polar Z-type Langmuir-Blodgett films, formation, 473-479 structures, transfer behavior, and contact angles, 474,476-477r Anharmonic oscillator models, nonlinear optical effect-microstructure relationship, 361... 

Verani and coworkers widely investigated stimuli-responsive soft materials with interesting optical and redox behaviors. Such materials are able to self-assembly in functional ordered structures, as Langmuir-Blodgett films and liquid crystals, and possess potential applications in molecular electronics and magnetic films as well. These compounds are mainly based on Co(II) (94), Co(III) (95), Cu(II) (96), Fe(II)/Fe(III) (97), and Ni (II) and Zn(II) (98). A recent overview dedicated to colloidal systems, and their application in different fields has recently appeared in the literature (99). 

Seki, T., Tanaka, K., and Ichimura, K. Phototropic discrimination of the polymerization behavior of diacetylene Langmuir-Blodgett films by an azobenzene-containing monolayers. Adv. Mater., 9, 563 (1997). 

Tachibana, H., Yamaka, Y., Sakai, H., Abe, M., and Matsumoto, M. Structural and Morphological Changes and Polymerization Behaviors of Diacetylene Langmuir-Blodgett Films on Adding Water Soluble Polyallylamine in the Subphase. Polymer 42, 1995 (2001). Nishiyama, K., Kurihara, M. A., and Fujihira, M. Photochromism of Amphiphilic Azobenzene Derivative in its Langmuir-Blodgett Films Prepared as Polyion Complex with Ionic Polymers. Thin Solid Films 179, All (1989). 

One core chiral system that shows dramatic amplification of its chiral structure is the substituted helicenes of Katz and coworkers [83]. In essence, this research cuts the helix into a number of six-helicene subunits that self-assemble (Figure 10). Only when these subunits, which look like lock washers, are prepared in optically pure form the material associates into supramolecular helical columns [84]. The assemblies have been synthesized with different amounts of substitution around the exterior. Depending on the helicenes substitution, the material exhibits hexagonally ordered soft-crystalline [84] or liquid-crystalline phases [85]. The liquid-crystalline versions of these molecules switch when electric fields are applied to neat and solution-phase samples and have been characterized as a dielectric response [85-87]. Upon association, these materials have enormous changes in their CD intensities and optical rotations [74]. In addition, this supramolecular chirality also significantly enhances the second-order nonlinear optical behavior of these materials in Langmuir-Blodgett films [88]. 

Using lateral force microscopy on Langmuir-Blodgett films, we found unexpected friction anisotropies and asymmetries in the frictional behavior. The data were found not to be related to the hexagonal packing of the molecules, but rather related to a small molecular tilt. 

The tip of an atomic force microscope makes a single point contact with a surface. Consequently, understanding tribological behavior becomes intellectually simpler. Friction has been shown to be correlated not with the magnitude of the adhesion between two bodies, but rather with the adhesion hysteresis [6]. Our recent study of a model system, a Langmuir-Blodgett film on mica [7], shows no dependence on adhesion hysteresis, but rather a dependence on molecular orientation [2]. 

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