Colossal Barocaloric Effect in Liquid Crystals via Cascade Order-Disorder Transitions.

The order-disorder transition plays a pivotal role in the exploration of barocaloric materials, exemplified by the recent discovery of colossal barocaloric plastic crystals. Among the various candidates undergoing order-disorder transitions, liquid crystals stand out as a particular category with cascade solid-smectic-nematic-liquid phase transitions, which endow them with great potential as high-performance barocaloric materials. Herein, we report the barocaloric properties and the underlying entropy change mechanism of a series of length-tunable liquid crystals (4'-alkyl-4-cyanobiphenyl, nCB, n = 5, 6, 7, and 8). These liquid crystals exhibit large isothermal entropy changes (200-540 J K-1 kg-1) and substantial adiabatic temperature changes up to 20 K at 1000 bar. Raman spectroscopy confirms enhanced intermolecular interactions and more ordered molecular packing under pressure with a notable peak narrowing and red shift. These liquid crystals also exhibit stable thermodynamic properties over multiple pressurization cycles, with an average entropy change of 275 J K-1 kg-1. Compared with other known barocaloric materials, liquid crystals show superior performance in terms of both pressure response and thermal stability, highlighting the significance of cascade order-disorder phase transitions in achieving colossal barocaloric performance.