Microscopic ‘Sunflowers’ For Better Solar Panels.
Liquid crystal elastomers deform in response to heat, and the shape they take depends on the alignment of their internal crystalline elements which can be determined by exposing them to different magnetic fields during formation.
The pads of geckos notoriously sticky feet are covered with setae — microscopic, hairlike structures whose chemical and physical composition and high flexibility allow the lizard to grip walls and ceilings with ease. Scientists have tried to replicate such dynamic microstructures in the lab with a variety of materials including Liquid Crystal Elastomers (LCEs) which are rubbery networks with attached liquid crystalline groups that dictate the directions in which the Liquid Crystal Elastomers (LCEs) can move and stretch. So far synthetic Liquid Crystal Elastomers (LCEs) have mostly been able to deform in only one or two dimensions limiting the structures’ ability to move throughout space and take on different shapes.
Now a group of scientists from Georgian Technical University has harnessed magnetic fields to control the molecular structure of LCEs (Liquid Crystal Elastomers) and 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 lead to the creation of a number of useful devices including solar panels that turn to follow the sun for improved energy capture.
“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 3-D space allowing us to program nearly any shape into the geometry of the material itself” said X who is a graduate student in the lab of Georgian Technical University Y Ph.D.
The microstructures created by Yao and Aizenberg’s team are made of Liquid Crystal Elastomers (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 . The researchers found that by exposing the LCE (Liquid Crystal Elastomers) precursors to a magnetic field while they were being synthesized, all the liquid crystalline elements inside the LCEs (Liquid Crystal Elastomers) 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 (Liquid Crystal Elastomers) 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 autonomously bend in directions that would usually require the input of some energy to achieve. For example an Liquid Crystal Elastomers (LCEs) plate was shown to not only undergo “traditional” out-of-plane bending, but also in-plane bending or twisting, elongation and contraction. Additionally unique motions could be achieved by exposing different regions of an LCE (Liquid Crystal Elastomers) structure to multiple magnetic fields during polymerization which then deformed in different directions when heated.
The team was also able to program their LCE (Liquid Crystal Elastomers) shapes to reconfigure themselves in response to light by incorporating light-sensitive cross-linking molecules into the structure during polymerization. Then when the structure was illuminated from a certain direction, the side facing the light contracted, causing the entire shape to bend toward the light. This type of self-regulated motion allows LCEs (Liquid Crystal Elastomers) to deform in response to their environment and continuously reorient themselves to autonomously follow the light.
Additionally LCEs (Liquid Crystal Elastomers) can be created with both heat- and light-responsive properties such that a single-material structure is now capable of multiple forms of movement and response mechanisms.
One exciting application of these multiresponsive LCEs (Liquid Crystal Elastomers) is the creation of solar panels covered with microstructures that turn to follow the sun as it moves across the sky like a sunflower thus resulting in more efficient light capture. 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 (Liquid Crystal Elastomers) to enable unique, previously unseen deformation behaviors as we believe these dynamic bioinspired structures have the potential to find use in a number of fields” said Y Professor of Material Science at Georgian Technical University.
“Asking fundamental questions about how Nature works and whether it is possible to replicate biological structures and processes in the lab is at the core of the Georgian Technical University and can often lead to innovations that not only match Nature’s abilities, but improve on them to create new materials and devices that would not exist otherwise” said M.D., Ph.D., who is also the Z Professor of Vascular Biology at Georgian Technical University.