Colossal barocaloric effects in plastic crystals (neopentylglycol)

Source: Nature (Lloveras/Tamarit et al., 2019, s41586-019-1042-5) + Nature Communications open-access companion (PMC6472423). Credibility: High (peer-reviewed, Nature family). Confidence: high.

Key points

• Colossal entropy change: ΔS ≈ 445-510 J/kg·K; adiabatic ΔT ≈ 30 K at 0.57 GPa, near room temp (~41 °C transition). Rivals commercial HFCs.
• Mechanism: pressure drives a plastic-crystal → ordered-crystal transition; extensive molecular orientational disorder (60 configurations vs 1), giant compressibility, ~4.9% volume change, latent heat 110-121 kJ/kg.
• NPG is cheap and abundant (paints/lubricants/cosmetics).
• Cons: pressures 0.25-0.57 GPa (2,500-5,700 bar) vs ~0.001 GPa for fluids; hysteresis ~10 K (needs management); poor thermal conductivity (proposed fix: graphite matrices).
• Lower-pressure variants exist: ammonium sulphate gives |ΔS| ~60 J/kg·K at only ~0.1 GPa (inverse barocaloric).

Relevance

The barocaloric member for solid-state-cooling: the largest entropy change of any caloric class, offset by high-pressure hardware and hysteresis.