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February 14, 2013

Polarizing microscope texture of smectic A liquid crystal

Polarizing microscope texture of a smectic A liquid crystal.

More about this Image
In smectic A, rod-like elongated molecules are arranged parallel to each other, forming layers of monomolecular length. The layers are stacked on top of each other and are flexible. When the smectic layers bend, they tend to preserve their equidistance, as it is fixed by the molecular length. The restriction of constant layer thickness leads to a peculiar geometry of deformations, so-called focal conic domains, in which the smectic layers are wrapped around line defects in the form of ellipses (seen in the figure) and hyperbolae (most of them are oriented normally to the plane of fiew). The ellipses form a fractal-type of structure, with smaller ones filling the gaps between the larger ones. The smectic order was discovered and correctly identified from optical observations of textures similar to the one shown here, on the basis of geometrical properties of ellipses and hyperbolae, before X-ray techniques were invented. The graphic Polarization Microscope Image of Liquid Crystals (Image 12) illustrates how the smectic layers are arranged around the ellipses and hyperbolae--bent, but everywhere else equi-distant to each other.

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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