Liquid crystal elastomer morphs on-demand
21 Dec 2018 by Evoluted New Media
Rice University researchers have developed a liquid crystal elastomer that morphs between two different shapes.
Shapes programmed into the shape-shifting polymer appear in ambient conditions and melt away with the application of heat. The process also works in reverse.
Materials scientist Rafael Verduzco said: “These are made with two-step chemistry that has been done for a long time. People have focused on patterning liquid crystals, but they hadn’t thought about how these two networks interact with each other.
“We thought if we could optimise the balance between the networks – make them not too stiff and not too soft – we could get these sophisticated shape changes.”
Once the material is given shape in a mould, five minutes of curling under ultraviolet light sets the crystalline order. When heated to a transition temperature of about 80 degrees Celsius, liquid crystals within the rubber band-like elastomer relax, and the material collapses into a flat sheet. When the heat is removed, the shape programmed into the liquid crystals dominates and the material reverts back to its original shape within minutes.
Rice graduate student Morgan Barnes said: "Instead of simple uniaxial shape changes, where you have something that lengthens and contracts, we're able to have something that goes from a 2D shape to a 3D shape, or from one 3D shape to another 3D shape."
The material could have applications for soft robots that mimic organisms, as well as biomedical applications requiring materials that take pre-programmed shapes at body temperature.
Barnes said that other possibilities include tactile smartphone buttons that appear when touched and reactive braille text for the visually impaired. The researchers are now focusing on lowering the transition temperature and developing a variant that reacts to light rather than heat.
"We want to make it photo-responsive," Barnes said. "Instead of heating the entire sample, you can activate only the part of the liquid crystal elastomer you want to control. That would be a much easier way to control a soft robot."
The scientists’ findings have been outlined in the Royal Society of Chemistry journal Soft Matter.
