One of the problems with solar panels is they stay stationary while the sun moves across the sky. To maximize efficiency requires two axis tracking mechanisms — a horizontal device that allows the panels to follow the sun on its diurnal journey and a vertical device that permits it to adjust to seasonal changes in the sun’s azimuth. Now researchers at the Harvard Institute for Biologically Inspired Engineering and School of Engineering and Applied Sciences say they have created shape-shifting polymers that respond to heat and light without any external power required.
The research began as an attempt to understand the how the pads on the feet of a gecko allow it to adhere to walls and ceilings. They found that setae — highly flexible microscopic hairlike structures — are the key. Attempts to recreate them using liquid crystal elastomers enjoyed limited success. The researchers could get them to stretch in one or two directions but not three.
The latest research uses magnetic fields during the creation of the LCEs to control their molecular structure. The result is microscopic three dimensional polymer shapes that can be programmed to move in any direction in response to multiple types of stimuli, according to Science Daily. One benefit of the new materials could be solar cells that turn to face the sun the way sunflowers do in nature.
“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,” says lead author Yuxing Yao. The research results were published in the Proceedings of the National Academy of Science on December 4. The entire report is available online and includes a number of interesting short videos showing how the LCEs respond in the laboratory. The research has been supported by the US Department of Energy and DARPA.
The research team was able to make LCE shapes that reconfigure themselves in response to light by incorporating light-sensitive cross-linking molecules into the structure during polymerization. This type of self-regulated motion allows LCEs to deform in response to their environment and continuously reorient themselves to autonomously follow the light. Other polymers can be made that respond to multiple stimuli such as light and heat simultaneously.
Other than solar cells that track the sun autonomously, what other uses might there be for these tiny shape-shifters? The technology could also form the basis of autonomous source-following radios, multilevel encryption, sensors, and smart buildings. “Our lab currently has several ongoing projects in which we’re working on controlling the chemistry of these LCEs to enable unique, previously unseen deformation behaviors, as we believe these dynamic bio-inspired structures have the potential to find use in a number of fields,” says Joana Aizenberg, a professor of material science at SEAS.
No doubt DARPA is interested in the encryption possibilities the new LCE polymers present, but the prospect of autonomous solar panels that track the sun without expensive mechanical systems will probably be the application most readers care most about.