📝 SummarXiv

Abstract

The discovery of colossal barocaloric effects in neopentyl glycol (NPG) makes plastic crystals promising candidates for solid-state refrigerants that have lower environmental impact than traditional vapour compression fluids. However, optimising operational temperatures and low-pressure operability remains challenging without diminishing parameters including the accessible latent heat. Here, we implement a strategy to improve the viability of NPG derivatives as barocaloric refrigerants. We blend pentaglycerine with NPG to lower the phase transition temperature, then dope the blend with just 2% pentaerythritol to improve the phase transition reversibility. In comparison with NPG, this ternary system has a seven-fold increase in reversible isothermal entropy change ($|\Delta S_{it,rev}|$ = 13.4 J kg$^{-1}$ K$^{-1}$) and twenty-fold increase in operational temperature span ($\Delta T_{span}$ = 18 K) at pressures of 1 kbar. Synchrotron x-ray diffraction reveals that the temperature range of the first-order phase transition is broadened because the intermolecular hydrogen bond network is disrupted by the presence of molecular dopants. Dynamic effects are revealed by quasielastic neutron scattering, which shows reduced activation energies for the molecular rotational modes underpinning the entropic component of the barocaloric effect. We propose that exploiting the large compositional phase space of multi-component molecular blends is an effective strategy for designing practicable molecular BCs.