Liquid Crystal "Sunflowers" Are Capable Of Some Truly Bizarre Stuff

Transition between nematic (left) and smectic A (right) phases observed between crossed polarizers. Wikimedia Commons

Liquid crystal elastomers (LCEs) are often talked about like some kind of material of the future, serving as a potential candidate for everything from artificial muscles and medical equipment to aerospace applications and gecko-like sticky suits.

However, researchers have often struggled to form these materials into three-dimensional structures – until now. As reported in the Proceedings of the National Academy of Sciences, scientists have used new insights to create three-dimensional LCEs that can shift shape in any direction in response to multiple types of stimuli.

In an especially cool demonstration of this feat, they have developed what they call “microscopic sunflowers” that could be placed onto solar panels and turn to follow the sunlight for improved energy capture.

The microstructure consists of tiny pillars made of a light-responsive liquid crystal elastomer. However, they also found similar structures that deform in response to heat and humidity, each controlled by their own chemical and material properties. Crucially, the microstructure also responded to magnetic fields. With this insight, they were able to deform the LCE shapes and manipulate their liquid crystalline structures into desired shapes.

"What's critical about this project is that we are able to control the molecular structure by aligning liquid crystals in an arbitrary direction in 3D space, allowing us to program nearly any shape into the geometry of the material itself," first author Yuxing Yao, a graduate student at the Wyss Institute for Biologically Inspired Engineering at Harvard, said in a statement.

The microstructures did, however, return to their original shape when exposed to an ambient temperature. You might see this as a downside of the discovery, however, the researchers argue it’s just another benefit. For example, it could be used to create encrypted messages that are only revealed under certain conditions or adhesive materials whose stickiness can be switched on and off.

That's just the beginning of liquid crystals' potential, however. Another study, also published this week, has used LCEs to create a material with an interesting and useful property: it is auxetic. This means that if you stretch it, it doesn’t get thinner, it gets fatter.

"Auxetics are also great at energy absorption and resisting fracture,” lead author Dr Devesh Mistry, from the University of Leeds in the UK, said in a statement. “There may be many potential applications for materials with these properties including body armour, architecture, and medical equipment. We have already submitted a patent and are talking to industry about the next steps."

 

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