On-demand cooling for small-scale systems

Researchers from Pennsylvania State University have developed a novel hybrid dielectric material that allows electrocaloric materials (EC) to hold absorbed heat even after an external field has been switched off. Their work has been described in the journal Applied Physics Letters.

Turn on an electric field and a standard electrocaloric material will eject heat to its surroundings as its internal dipoles reorder themselves. Do the same thing and a negative electrocaloric material will absorb heat, cooling the environment, thanks to the blend of ferroelectric polymers that make up each.

While these materials have been investigated as a method of on-demand microclimate control for quite some time, there’s a catch — the external field needs to remain active, which is energy-consuming and ends up heating the material. However, the researchers have developed a blend of ferroelectric polymers which can continue to hold this absorbed heat — a material which could be adapted for a variety of small-scale systems.

In a typical electrocaloric material, heating and cooling are only generated when the field is changing in response to a full electric pulse. Here, the amount of heating is slightly greater than the amount of cooling, with the difference depending on the material’s efficiency.

The researcher’s anomalous electrocaloric material flips this, generating cooling when the field is turned on but no subsequent heating when the field is turned off, other than the miniscule amount of heating generated in the dielectric material by the electric field.

According to Xiaoshi Qian, the primary investigator on the project, the material can be attached to a chip or a biological system in need of on-demand cooling. This allows the materials to either add or remove heat from a system through an internal reordering of dipoles — the separation of positive and negative charges.

The researchers’ electrocaloric material consists of a hybrid normal ferroelectric polyvinylidene fluoride-trifluoroethylene copolymer and a relaxor ferroelectric chlorofluoroethylene terpolymer. The bulkier third monomer CFE in the terpolymer introduces defects in its polymer chain, causing it to exhibit dipolar randomness rather than the ferroelectric ordering shown in the copolymer.

When these form a finely tuned blend, the resulting hybrid can be poled into one dipolar direction with an electric pulse, owing to the formation of strong macroscopic ferroelectric domains. Then, when subjected to a second, smaller pulse, the material becomes depoled, or randomly poled, and maintains this state. This allows their ferroelectric material to not only maintain a large cooling effect when a voltage is applied, but after it has been removed.

“We would like to improve the electrocaloric materials in the future so that the cooling generated upon an electric pulse in the EC material can be much larger,” Qian said. “This study is the first step toward that direction.”

Image caption: A dielectric material, when subject to an electric pulse, will absorb heat from or cool its surroundings. Image credit: X Qian and QM Zhang/PSU.

Originally published here.