LCDs are everywhere. They are used in a wide range of applications, such as cell phone screens, video game consoles, car dashboards and medical equipment. Due to the unique properties of these liquids, liquid crystal displays (LCDs) produce colors if an electric current is passed through them: rearrange their shapes and they reflect different wavelengths of light.

Under the right conditions, liquid crystals form stunning structures reminiscent of biological systems, as shown here in true color (left) and false color (right), with filamentous structures in light blue and flat disks in yellow. Photo credit: ChristopherBrowne

Now, researchers in the laboratory of Chinedum Osuji, Eduardo D. Grant Presidential Professor and Chair of the Department of Chemical and Biomolecular Engineering, have found that these extraordinary crystals may be able to do even more. Under the right conditions, liquid crystals condense into stunning structures, spontaneously creating filaments and flat disks that can transport materials from one place to another, much like complex biological systems. This insight could lead to new ways of assembling materials, modeling cellular activity, and more.

"It's like a conveyor belt network, and it was this chance observation of something that looked very realistic on the surface - that was the first clue that it might be something more general and interesting," said Christopher Browne, a postdoctoral fellow in Osuji's lab and co-first author of a paper describing the discovery recently published in the Proceedings of the National Academy of Sciences (PNAS).

Browne and Osuji are now members of an NSF-supported interdisciplinary group housed in the Laboratory for Research on the Structure of Matter (LRSM), led by Matthew Good, associate professor of cell and developmental biology in the Perelman School of Medicine, and Elizabeth Rhoades, professor of chemistry in the College of Arts and Sciences, studying condensation formation in biotic and abiotic systems.

A close-up of the filaments and flat disks produced by the new liquid crystal condensate. Source: Christopher Brown, Chinedum-Osuji

Initially, Osuji's lab worked with Exxon Mobil Corp. to study mesophase pitch, a substance used to develop high-strength carbon fibers such as those in Formula One racing cars and high-end tennis rackets. "These materials are liquid crystals," Osuji said of the chemical precursors to carbon fiber itself. "Or rather, during processing, they remain liquid crystals for a period of time during their existence." While conducting experiments on the condensate at different temperatures, Yuma Morimitsu, another postdoc in Osudera's lab and co-first author on the paper, noticed the material's unusual behavior.

Typically, if two immiscible (i.e., unmixable) fluids are brought together and then heated to a high enough temperature to force them to mix, if the mixture is then cooled, at some point the mixture will separate or "demix." Typically, this happens through the formation of droplets that coalesce into a separate layer, much like if you mix oil and water together, you'll end up with a layer of oil on top of the water.

Video showing liquid crystal condensation formation - false color used on the right to differentiate between filaments (light blue) and flat disks (yellow). Video is 60x real-time zoom and 5x zoom. Source: Christopher Browne, ChinedumOsuji Unique Phase Separation and Structure Formation

In this case, the liquid crystal -- 4'-cyano-4-dodecyloxybiphenyl (also known as 12OCB) -- spontaneously formed a highly irregular structure when separated from squalane, a colorless oil. "When liquid crystals phase separate from other components in the system, instead of forming droplets, they form a cascade of structures, starting with these filaments that grow rapidly and then forming another set of structures -- what we call raised disks or flat droplets," Osuji said.

To understand the system, the researchers used powerful microscopes to observe the movement of liquid crystals on the micron scale, or one millionth of a meter, which is equivalent to the width of a human hair. "The first time we saw these structures, the cooling rate was too high, causing the liquid crystals to condense together," Osuji recalls. "Only by slowing the cooling rate and amplifying it further did the researchers realize that the liquid crystals were spontaneously forming structures reminiscent of biological systems."

Interestingly, Brown found that several researchers came close to observing similar behavior decades ago, but the systems they studied either didn't have particularly obvious behavior or lacked microscopes powerful enough to see what was going on.

For Brown, the most exciting aspect of this result is that it brings together several traditionally disconnected fields: the field of active matter research, which studies biological systems that transport materials and generate motion, and the field of self-assembly and phase behavior, which studies materials that can generate new structures on their own and behave differently when they change phase. This is a new type of active material system.

He and Osuji also noted that the findings could be used to model biological systems to better understand how they work or to create materials. "Molecules are absorbed into the filaments and then continuously shuttled into these flat droplets," Osuji said, "although just looking at the system doesn't reveal any obvious activity. In fact, the flat droplets can function like small reactors, producing molecules that are then transported by the filaments to other droplets for storage or further chemical reactions."

The researchers also say their findings could reinvigorate research into liquid crystals themselves. When a field becomes industrialized, basic research tends to decline. But sometimes there are unresolved puzzles that no one can solve.

Compiled from /ScitechDaily