Electrocaloric Refrigeration: A Polymer-Based Alternative to Conventional Technologies
A polymer is a long, chain-like molecule built from smaller components called monomers. When grouped together, these polymer chains form a solid that is light-weight, flexible, and easy and inexpensive to make. When an electric field is applied to some polymer solids, it makes the monomers rotate. This rotation causes the material's temperature to increase. Removing the electric field causes the monomers to rotate back to their original positions and the material's temperature decreases. The ability to increase and decrease temperature using an electric field is called the electrocaloric effect. Its presence in polymers indicates that they can be used to build a refrigeration system with no moving parts, very different from the vapor compression cycle that is ubiquitous in household, commercial, and industrial applications. Estimates suggest very high efficiency for electrocaloric refrigeration. The objective of this work is to use computer modeling and experiments to develop an understanding of the origin of the electrocaloric effect in polymers. The work will provide guidance in how to optimally select the monomers used to build the polymers and the ideal conditions for making the materials. To complement the research, outreach activities based on next-generation cooling technologies will be developed and presented to middle-school and high-school students. An undergraduate mechanical engineering course in fluid mechanics will be flipped, whereby the initial student learning is done outside the classroom and class time is devoted to active learning, where students engage directly with the material through problem solving, discussion, and small group projects.
The objective of this research program is to determine how the nanostructure and microstructure of PVDF-based polymer thin films drive their electrocaloric cooling performance The electrocaloric effect is a phenomenon in which polarization-related temperature and entropy changes occur when an electric field is applied/removed from certain ferroelectric materials, causing the rotation of internal monomer dipoles. The large electrocaloric effect measured in environment-friendly polymers points to untapped potential for application to thermal management. Atomistic calculations, kinetic Monte Carlo simulations, and experimental characterization tools will be applied to build fundamental knowledge of how composition and structure across length scales from nanometers to microns contribute to the electrocaloric effect. Specifically, (i) the mechanisms and energetics of the dipole flipping events will be investigated using nudged elastic band method calculations, and (ii) the correlation between the microstructure of the crystalline and amorphous regions to the electrocaloric temperature change will be explored using kinetic Monte Carlo simulations and experimental characterization. This knowledge will inform what cooling performance is possible and strategies for implementation into next-generation cooling technologies. The electrocaloric effect has the potential to transform cooling and thermal management at micro and macro scales. By combining scalable manufacturing, excellent performance, and inexpensive, abundant, and light-weight materials, electrocaloric-based devices will rival thermoelectrics as a next-generation solid-state cooling technology.