Asaf Dana, PhD, Postdoctoral Researcher, Department of Biomedical Engineering at Texas A&M University

Actuators are valuable components in various technologies, from artificial muscles in biomedical engineering to deployable devices in aerospace machines. Traditional actuators are typically rigid systems composed of various moving parts that tend to suffer from limitations such as low operation rates and sensitivity to wet environments.  Responsive materials are materials that change their physical properties in response to external stimuli (such as heat or electromagnetic fields). Such materials execute macroscopic response (at the device level) through microstructural changes (on the molecular level) carried out by solid-solid phase transitions, offering greater flexibility in operation conditions. This talk will cover two unique systems of responsive materials, shape memory alloys (SMA) and liquid crystal elastomers (LCE). In both parts, I will demonstrate how fundamental knowledge on the relations between microstructure evolution and macro-scale mechanical behavior can be applied to the development of useful engineering tools. First, we consider long-standing fundamental questions on the rate of the martensitic phase transformation in SMA under high driving forces. Two unique experimental setups employing time-resolved x-ray diffraction at synchrotron radiation along with high-bandwidth force measurements allow us to identify transformation mechanisms at small time and length scales. We then apply this knowledge to formulate design guidelines for high-rate and powerful SMA actuators and develop simulations that can serve as accurate design tools. The second part will demonstrate a dynamic ‘material’ that is made of a collective of individual LCE films. In such materials, functionality of the collective emerges through physical interaction of individual elements. Porous materials inherently suffer from the need for structural stabilization which limits the degrees of freedom available for response. Multifunctional LCE films with active magnetic heads are fabricated to exhibit a combination of induced motion driven by a rotating magnetic field along with temperature-induced three-dimensional bending and twisting. These facilitate entanglement into macroscopic porous solids that are expected to open the way for new dynamic systems composed of active elements.  To conclude, I will describe my future vision to study how basic knowledge of the relations between micro- and macro-scale responses can facilitate the bottom-up development of novel mechanical devices and advanced materials.