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Posted 12-10-99
A collaboration between physicists in Case Western Reserve University's Department of Physics and the Ukraine recently was strengthened with a $14,500 grant from the National Research Council's Twinning Program. The grant will provide expenses for travel between the two countries to foster cutting-edge science to improve liquid crystal technology.
Kenneth Singer, professor of physics, will work with Yuriy Reznikov from the Institute of Physics at the National Academy of Science in Kiev and Vickor Reshetnyak from Kiev University to increase their understanding of the optical properties of liquid crystals and how they align to form images we see on the liquid crystal displays used in laptop computers and other equipment.
The scientists began work on what they call "liquid crystal on liquid crystal alignment" through a prior grant with the Advance Liquid Crystalline Optical Materials Center -- a National Science Foundation science and technology center involving CWRU, Kent State University, and the University of Akron. Liquid crystal on liquid crystal alignment is a new method of aligning liquid crystals within the cell.
In a liquid crystal display, a cell containing liquid crystal molecules is sandwiched between quartz or glass coated with transparent electrodes. This layer is needed on the surfaces in order to align the liquid crystals in the cell so that they can be switched by applying an electrical signal. Usually the liquid crystals in the cell, which are made of cigar-shaped molecules, lie flat on the surface with their long sides nearly aligned, says Singer.
According to Singer, the widely used alignment method of rubbing velvet over the surface of a polymer deposited on the glass leaves dust particles on the surface, causing problems in the manufacturing and performance of the displays.
"Because the entire cell also must be aligned in a single direction, the viewing angle of the display is limited, as is easily noted on a laptop computer," explains Singer.
The collaboration with the Ukrainians has brought together a team of experimental and theoretical physicists who tackled ways to solve this problem.
In the liquid crystal on liquid crystal alignment, only the liquid crystal material is needed. The layer of molecules directly on the surface can be aligned appropriately by exposing it to polarized ultraviolet light.
This method eliminates debris, simplifies manufacturing, and allows for pixilated alignment in cells so that they have large viewing angles.
Using a technique called surface optical second harmonic generation, Singer is able to probe the single layer closest to the surfaces and determine how the alignment takes place. This information will help to improve the process, and speed this technique to the marketplace.
"To our surprise, we found the liquid crystal molecules directly on the surface stand nearly on end, while the ones away from the surface lie nearly flat," explains Singer.
Because of the nature of the liquid crystal's molecular structure, which has a wiggly tail attached to benzene rings of carbon, it forms a layer on which the liquid crystals in the cell can lie.
"It's like a raked bed of hay," says Singer.
The next step is for the scientists to see if this procedure works with the electrodes rather than the bare quartz.
The new grant will enable the researchers to make five trips between the two countries. The Ukrainian researchers will come in October and next spring. Either Singer or graduate student Oksana Ostroverkhova will travel to the Ukraine next summer to continue the research work.
With the fall of the Soviet Union, the National Research Council has promoted collaborations with former Soviet countries. Singer sees this collaboration as the beginning of a long-term relationship with Ukrainian physicists.
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