The team at Harvard's Wyss Institute for Biologically Inspired Engineering and John A. Paulson School of Engineering and Applied Sciences (SEAS) have used magnetic fields to control the molecular structure of liquid crystal elastomers (LCEs) to create microscopic three-dimensional polymer shapes that can be programmed to move in any direction in response to multiple types of stimuli. The work could be used for solar panels that turn to follow the sun for improved energy capture, actuators in soft robots or sticky surfaces where the stickiness can be switched on or off.
"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," said Yuxing Yao, a graduate student in the lab of Prof Joanna Aizenberg.
The microstructures created by Yao and Aizenberg's team are made of LCEs cast into arbitrary shapes that can deform in response to heat, light, and humidity, and whose specific reconfiguration is controlled by their own chemical and material properties. By exposing the LCE precursors to a magnetic field while they were being synthesized, all the liquid crystalline elements inside the LCEs lined up along the magnetic field and retained this molecular alignment after the polymer solidified. By varying the direction of the magnetic field during this process, the scientists could dictate how the resulting LCE shapes would deform when heated to a temperature that disrupted the orientation of their liquid crystalline structures. When returned to ambient temperature, the deformed structures resumed their initial, internally oriented shape.
Such programmed shape changes could be used to create encrypted messages that are only revealed when heated to a specific temperature, actuators for tiny soft robots, or adhesive materials whose stickiness can be switched on and off. The system can also cause shapes to