On the colossal barocaloric effect in higher n-alkanes

Abstract

In this work we present a combination of experimental, theoretical and computational analyses to demonstrate the colossal barocaloric (BC) effect in long-chain linear n-alkanes (paraffins). Adiabatic compression experiments with eicosane (C₂₀H₄₂) show that substantial temperature changes (as high as 38 K) are achieved for applied pressures up to 218 MPa, which are enhanced upon the occurrence of a liquid–solid pressure-induced phase transition. A thermodynamic analysis using accurate pressure–volume–temperature data from the literature shows that the same behavior is observed for other long-chain linear n-alkanes such as hexadecane (C₁₆H₃₄) and dodecane (C₁₂H₂₆), and that large isothermal entropy changes can be achieved upon compression under conditions near the phase transition. Molecular dynamics simulations were used to carry out adiabatic and isothermal compression tests, aimed at computing temperature and entropy changes for other n-alkanes (n from 12 to 32) and investigating relevant structural and energetic changes at the molecular level. These simulations helped to explain the reasons for the remarkable temperature and entropy changes, even in the absence of the phase transition (in this case, enhanced by a decrease in the intermolecular potential energy upon compression), and showed that an increase in the chain size leads to a decrease in these changes for the same reference temperature. In summary, our results show that these linear paraffins exhibit a BC performance superior to most of those reported for other materials so far, and are promising candidates toward the development of efficient refrigeration systems based on the BC effect.