What do the following things have in common: an implanted medical device with its own power supply, a squishy human-like robot and how do we hear sound of different things? The answer to why these two dissimilar technology and biological phenomena are similar lies in how the materials they are made up of can change their size and shape significantly when an electrical signal is sent. Some materials in nature can act as an energy converter that deforms when an electrical signal is sent or provides electricity when they are stimulated. This is called piezoelectricity and is useful in the manufacture of sensors and laser electronics, among other things. However, these natural materials are rare and consist of rigid crystalline structures that are often toxic to human beings. Artificial polymers provide steps to alleviate these major drawbacks by eliminating material shortages and creating soft polymers that can bend and stretch, known as soft elastomers. Previously these soft elastomers lacked key piezoelectric properties. To overcome this drawback, a solution is offered by Kosar Mozaffari, a graduate student at the University of Houston Cullen College of Engineering, Pradeep Sharma, M.D. Anderson Professor and Chair of the Mechanical Engineering Department at the University of Houston, and Matthew Grasinger, LUCI Postdoctoral Researcher at the Air Force Research Laboratory.
“This theory makes a connection between electricity and mechanical motion in soft rubbery materials,” Sharma said. While some polymers are weakly piezoelectric, no soft rubbery materials possess piezoelectric properties. These scientists through their efforts tries to show that how flexoelectric performance can be increased in soft materials. “Flexoelectricity in most soft rubber materials is quite weak,” said Mozaffari , but by rearranging the chains in unit cells at the molecular level, our theory shows that elastomers could have flexoelectricity almost ten times higher than the conventional amount.”
The benefits of this new theory go beyond that. In the research process, the ability to design a unit cell that is stretch invariant or remains unchanged in the event of an undesired strain transformation arose. “For some applications, specific amount of electricity is needed to be generate irrespective of the stretch deformation, while for other applications, as much electricity as possible needs to be generated, and we designed for both,” said Mozaffari. “In our research, we discovered a method to make the elongation of a unit cell invariant. The tunable nature of the flexoelectric direction can be helpful in making smooth robots and smooth sensors” he further added. In other words, the amount of electrical energy generated by various stimuli can be controlled to allow devices to perform targeted actions. This could dampen the performance of self-sufficient electronic devices. In the next few steps, this theory would be tested in a laboratory using possible applications. In addition, efforts to improve the flexoelectric effect in soft elastomers would be the focus of further investigations.
