Liquid crystals in motion mimic biological systems

Liquid crystals are all around us, from phone screens and video game consoles to car dashboards and medical devices. Run an electric current through liquid crystal displays (LCDs) and they generate colors, thanks to the unique properties of these fluids: rearrange their shape, and they reflect different wavelengths of light.

As the lab of Chinedum Osuji, Eduardo D. Glandt Presidential Professor and Chair of Chemical and Biomolecular Engineering, recently discovered, these fascinating molecules may be able to do even more. Under the right conditions, liquid crystals condense into astonishing structures, spontaneously generating filaments and flattened discs that can transport material from one place to another, much like complex biological systems.

The insight may lead to self-assembling materials, new ways to model cellular activity, and more. "It's like a network of conveyor belts," says Christopher Browne, a postdoctoral researcher in Osuji's lab and the co-first author of a recent paper in Proceedings of the National Academy of Sciences (PNAS).

Originally, Osuji's lab partnered with ExxonMobil to investigate mesophase pitch, a substance used in the development of high-strength carbon fibers, like those found in Formula 1 cars and high-end tennis rackets. "Those materials are liquid crystals," says Osuji. "Or better stated, they are liquid crystalline over some period of their existence during processing." While experimenting with condensates at different temperatures, Yuma Morimitsu, another postdoctoral fellow in the Osuji Lab and the paper's other co-first author, noticed unusual behavior in the material.

Normally, when two immiscible, or not mixable, fluids are combined and then heated to a high enough temperature to force them to mix, during the cooling process the fluids will separate or "demix." In this case, the liquid crystal spontaneously formed highly irregular structures when separating from squalane, a colorless oil.

For Browne, the result's most exciting implication is that it brings together several traditionally disparate fields: the world of active matter research, which focuses on biological systems that transport material and produce motion, and the realms of self-assembly and phase behavior, which study materials that create new structures on their own and that behave differently when changing phase. "This is a new type of active matter system," says Browne.

Read more at Penn Engineering Today.