Polar-dielectrics with Giant Electrocaloric Effect and Their Related Cooling Devices

The direct and efficient coupling between the electric signals and the elastic, thermal, optical and magnetic signals in ferroelectric based electroactive polymers makes them attractive for exploiting a broad range of cross-coupling phenomena and applications which have great promise for new device technologies.  This talk will present the recent advances in developing electroactive polymers which may provide alternative cooling technology to replace the century old vapor compression cycle (VCC) based cooling which employs strong greenhouse gases as the refrigerants. Electrocaloric effect (ECE), which is the temperature and entropy change of insulating dielectric materials under electric fields, is attractive to realize efficient cooling devices.  However, the relatively small ECE observed in dielectrics in the last century make it unimpressive for any practical applications.  By making use of phase transitions and the high dipolar entropy in these polymers in the dipolar disordered state we demonstrated that a giant ECE can be achieved in a class of ferroelctric polymers. Moreover, by employing defects modifications to convert the normal ferroelectric into a ferroelectric relaxor a large ECE over a broad temperature range about room temperature can be obtained.  This talk will also discuss considerations on and present recent works in using nanocomposites to further enhancing the ECE beyond the pure relaxor polymers and on the giant ECE in a class of dielectric liquid. The works related to developing the chip-scale EC cooling devices, exploiting the newly discovered large ECE in ferroelectric polymers, will also be presented.