Colossal barocaloric effect achieved by exploiting the amorphous high entropy of solidified polyethylene glycol

The barocaloric effect (BCE) has emerged as an intense research topic in regard to efficient and clean solid-state refrigeration. Materials with solid-liquid phase transitions (SL-PTs) usually show huge melting entropies but cannot work in full solid-state refrigeration. Here, we report a colossal barocaloric effect realized by exploiting high entropy inherited from huge disorder of liquid phase in amorphous polyethylene glycol (PEG), which is solidified by introducing 5 wt.% polyethylene terephthalate (PET). Transmission electron microscopy (TEM) combined with X-ray diffraction (XRD) demonstrates the amorphous nature of the high-temperature phase after fixation by PET. Although PEG loses its –OH end mobility in amorphous solid, high entropy still retains owing to the retained high degrees of freedom of its molecular chains. The remaining entropy of amorphous PEG is up to 83% of that of liquid PEG in PEG10000/PET15000, and the barocaloric entropy change reaches ΔS p ∼ 416 J·kg −1 ·K −1 under a low pressure of 0.1 GPa, which exceeds the performance of most other BCE materials. Infrared spectra combined with density function theory (DFT) calculations disclose conformational change from the liquid to amorphous state, which explains the origin of the large entropy retained and hence the colossal BCE of the solidified PEG. This research opens a new avenue for exploring full solid-state barocaloric materials by utilizing genetic high entropy from huge disordering of liquid phases in various materials with SL-PTs. Refrigeration: Phasing out freon with flexible plastics A technique that turns liquid polymers used in medicine and industry into solid-state refrigerants could lower demand for hydrofluorocarbon-based coolants. Recent studies have shown that plastics which undergo energy-absorbing structural phase transitions in response to mechanical pressure show promise as non-toxic refrigerants. Zibing Yu from the Chinese Academy of Sciences, Beijing, and colleagues now describe a method for creating plastic refrigerants with polyethylene glycol (PEG), an inexpensive polymer used to stabilize substances ranging from laxatives to toothpaste. By adding a small proportion of an aromatic polyester to a solution of PEG, the team created a solid composite with an exterior stabilized by hydrogen bonds and an interior containing flexible hydrocarbon chains. The new composite’s liquid-like center offered similar amounts of solid-state cooling to contemporary plastic refrige