Colossal barocaloric effects in liquid crystals

Dr Guillaume Nataf
Research Fellow 2018

Dr Guillaume Nataf
University of Cambridge

Cooling is essential for perishable food, medicine, buildings and electronics. Current cooling technologies exploit large thermal changes that occur in fluids when driving liquid to gas phase transitions with pressure. However, these vapour-compression technologies are harmful to the environment and display low energy efficiencies. By contrast, cooling based on pressure driven thermal changes in solids, i.e. barocaloric effects, promise novel environmentally friendly cooling technologies with high energy efficiencies close to the thermodynamic maximum limit. While several major breakthroughs have been recently reported, solid barocaloric materials are still in their infancy, and their thermal response is still far from the performance of fluids, because they all operate at solid-solid phase transitions with limited pressure-induced changes in entropy.

The aim of the proposed project is to experimentally study barocaloric effects in liquid crystals (LCs). LCs have properties between those of conventional liquids and those of solid crystals, and are widely used in displays. For instance, a LC may flow like a liquid, but its molecules may be oriented in a crystal-like way.

"promise novel environmentally friendly cooling technologies with high energy efficiencies "

Thus far, these materials have been widely ignored by the research community working on caloric materials, despite LCs exhibiting the key ingredients required to achieve an outstanding barocaloric response: they show:

  1. extremely large (colossal) thermally driven changes in entropy;
  2. very small thermal hysteresis; and
  3. extremely large shifts of their transition temperatures with pressure, which when combined all together in the same material promise pressure-driven thermal changes similar to those observed in fluids.

This research will develop a new framework to design and optimise LCs with colossal barocaloric properties that outperform those observed in state-of-the-art barocaloric materials. These findings will be the foundation for a new cooling technology that is environmentally friendly, energy efficient and affordable.