Periodic square lattice, as seen under a polarizing microscope. [Image 8 of 12 related images. See Image 9.]
More about this Image
This periodic square lattice, seen under a polarizing microscope, occurs in a nematic fluid--the simplest form of a liquid crystal--when a thin film of the material is spread over the surface of an isotropic fluid (glycerine). The upper surface of the nematic film is free (in contact with air). In the nematic, the rod-like elongated molecules are free to move around but tend to remain 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. When the film is very thin--less than 1 micrometer--these distortions use too much energy and the system relaxes through periodic, in-plane director variations. The effect is similar to buckling instability of an elastic rod stressed at two ends; at some critical stress, the rod bulges. The periodic pattern illustrates a fine balance of elastic and surface anchoring forces. In this particular, rarely observed case, the director distortions adopt the form of square lattice; more often, one observes a periodic, one-dimensional pattern of stripes (see Polarization Microscope Image of Liquid Crystals (Image 1), for example).
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)