But chip-cooling devices will take a while to arrive. It now takes 120 volts to get the polymer to change its atomic arrangement, and that figure would need to be much lower if the material is to be used in laptops. “Ideally, you want it to work at voltages common within the realm of a notebook, in the tens of volts or less,” Mongia says. The researchers will also need to engineer a working device containing the thin films.
Electrocaloric materials could make fridges greener. Current household fridges use a vapor-compression cycle, in which a refrigerant is converted back and forth between liquid and vapor to absorb heat from the insulated compartment. The need for mechanical compression lowers the fridge’s efficiency. “Vapor-cooled fridges are 30 to 40 percent efficient,” Mathur says. But because electrocaloric materials have no moving parts, they could lead to cooling devices that are more energy efficient than current fridges. What’s more, current hydrofluorocarbon refrigerants contribute to global warming.
Refrigerators that use electrocaloric materials would have an advantage over the magnetic cooling systems that some companies and research groups are developing. Electric fields large enough to produce substantial temperature changes in electrocaloric materials are much easier and cheaper to produce than the magnetic fields used in experimental refrigeration systems, which require large superconducting magnets or expensive permanent magnets. However, refrigerators need temperature spans of 40 °C, which is a tall order for electrocaloric materials right now, Mathur says. “The main sticking point in terms of the technology is that we have thin films, and you can’t cool very much with a thin film.”
Zhang and his colleagues are now trying to design better electrocaloric polymers. They plan to study polymers made from liquid crystals, which are used in flat-panel displays. Liquid crystals contain rod-shaped molecules that will align with an electric field and revert to their original arrangement when the field is removed. Zhang says that this property could be exploited to make materials that absorb and release large amounts of heat in response to electric fields.
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