Penn Researchers Develop a New Tool for Controlling Liquid Crystals

Penn researchers have developed a new way to control liquid crystals, which may lead to new types of antennas, sensors, or displays. Vicki and William Abrams Professor in the Natural Sciences in the Department of Physics and Astronomy Randall Kamien worked with Kathleen Stebe and Shu Yang of Penn Engineering on the research, which was published in the Proceedings of the National Academy of Sciences. 

The interdisciplinary team had already created a technique for controlling liquid crystals by means of physical templates and elastic energy, rather than the electromagnetic fields that manipulate them in televisions and computer monitors. Now the team has devised a new kind of template for rearranging particles and a new set of patterns that can be formed with them. 

Crystals are materials that have molecules arrayed in regular three-dimensional patterns; liquid crystals contain some but not all of these patterns, and their molecules can flow around one another and change the direction they face. This behavior allows for highly desirable “defects,” places on the surface where the molecular orientation of the liquid crystals is disrupted. If the location of the defects can be controlled, the change in pattern or orientation can be put to use. In a liquid crystal display, for example, the crystals’ orientation in different regions determines which parts of the screen are illuminated. 

In their new study, the team again started with a template consisting of microscopic posts to arrange the defects on the surface of the liquid crystals. Using a different kind of crystal, the researchers discovered that a ring-shaped defect encircled each of the posts at its midpoint. This ring then acts like another template, says Kamien, “a new way to tell what to go where.” The new set of shapes and patterns they can use adds to the toolkit of different structures they can make.

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