Hybrid-aligned nematic film
Hybrid-aligned nematic film.
More about this Image
Polarizing microscope texture of a thin, liquid crystalline film. This highly nonuniform structure reflects spatial distortions in molecular orientation that occur in a nematic fluid, the simplest form of a liquid crystal. The thin nematic film (1- to 2-micrometers thick) is spread over the surface of an isotropic fluid (glycerine). The upper surface of the film is free (in contact with air). In the nematic, the rod-like elongated molecules are free to move around but tend to be parallel to each other. The average direction of orientation is called the director. By placing the nematic film between glycerine and air, one creates director distortions in the vertical plane, as the nematic-air interface favors normal (perpendicular) orientation of the director and the glycerine-nematic interface favors tangential (parallel) orientation. Since the direction of alignment in the plane of the film is not fixed, the film exhibits numerous distortions, with the director changing from point to point. The interference colors of the film result from different director tilt and some variation in the thickness of the film. Very often, the director distortions collapse into "strings" of practically constant width, seen in the texture as parallel dark extinction bands. The dark bands mark the regions where the orientation of liquid crystal molecules is parallel to either the polarizer or analyzer.
This image was created by Oleg D. Lavrentovich, director of the Liquid Crystal Institute and professor of chemical physics in the Chemical Physics Interdisciplinary Program at Kent State University. The complex, 3-D molecular arrangements in liquid crystals and other soft materials reflect a rich variety of physical mechanisms that represent the focus of Lavrentovich's research.
Recent research in Lavrentovich's lab (supported by National Science Foundation grants DMR 05-04515, DMR 07-10544 and DMR 09-06751), explore what the physical mechanisms are behind the complex, 3-D molecular architectures; what controls the molecular order in space; and what controls the time dynamics of this order. The goal is to learn how to construct self-assembled complex materials with unique structural, electric and optical properties. Liquid crystals have already been a technological revolution through their liquid crystal displays, and much more is on the horizon of current knowledge if we were to explore and utilize more complex molecular arrangements than those in these displays. (Date of Image: exact date unknown)
Credit: Oleg Lavrentovich, Liquid Crystal Institute, Kent State University
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