Unveiling the Origin of the Giant Barocaloric Effect in Natural Rubber

Abstract

The barocaloric effect (BCE) is characterized as thermal responses (variations of temperature or entropy) in a material resulting from compression. Several materials exhibit a BCE suitable for development of solid-state cooling devices, typically associated with pressure-induced phase transitions. A giant BCE has been observed for natural rubber (NR), which makes it a cheap and environmentally friendly candidate for such a purpose. The reason for the significant BCE in NR is still elusive, considering that there is no evidence of phase transitions in the process. The present study uses a combination of classical molecular dynamics (MD) simulations and a thermodynamic analysis to investigate the origin of the giant BCE in NR. MD simulations of adiabatic compression cycles for NR were carried out under varied applied pressures and initial temperatures and were able to capture the BCE. A detailed analysis of the results helped us to elucidate the structural transformations and resulting energy changes in the material under compression. MD results for isothermal compression along with the thermodynamic analysis showed that the high compressibility of NR combined with an unusual decrease in the potential energy at the molecular level upon compression favors significantly the BCE (quantified by isothermal entropy changes and adiabatic temperature changes in the process), a feature not commonly seen in other materials. These findings can be extended to other polymers and are certainly going to be useful toward the design of materials with an enhanced BCE.

Simple and Low-Cost Footstep Energy-Recover Barocaloric Heating and Cooling Device

“…In this regard, we found that this material exhibited a similar barocaloric effect to the reported barocaloric vulcanized natural rubber, whose main component was sulfured cis-1,4-polyisoprene, and that exhibited a barocaloric effect of ~3.0 K when applying a slightly larger pressure of 434 bar [29]. Moreover, these values were in agreement, showing slight ∆T differences, with the theoretical calculations obtained by molecular dynamics and thermodynamics modeling as observed in Figure 4 [40]. Additionally, such computational studies revealed that the barocaloric effects in polyisoprene were related to a polymer chains rearrangement upon compression, which led to a reduction in its free volume and chain mobility.…”

“…Meanwhile, the material's thermalization was a bit slower, needing around ~35 s to reach room temperature back. This relatively long thermalization time could be related to the very low thermal conductivity of polyisoprene, which shows a value of λ ~0.14 W m −1 K −1 [40]. It should be noted that the fast pressure-induced temperature change and…”

Colossal and Reversible Barocaloric Effect in Phase Change Materials n-Alkanes

“…2A and Fig. 2B for CnH2n+2 (n=14, 16 and 18) along with those reported for existing BC materials 10,[13][14][15][16][17]20,21,[29][30][31][32][33][34][35][36][37][38][39] . Here, the isothermal entropy change in references is mainly obtained by indirect method or quasi-direct method 6 .…”

Development of magnetocaloric coordination polymers for low temperature cooling

“…17 Barocalorics materials exhibit a thermal response due to isotropic compression from hydrostatic pressure, typically associated with a concurrent first-order phase transition. 18 The BCE has been identified in many materials, [19][20][21] including elastomeric polymers, 22,23 including natural rubber, 24,25 plastic crystals, 26 magnetic memory shape alloys 27 and coordination polymers, particularly inorganic-organic perovskites that have shown the socalled giant barocaloric effect, including [TPrA][Mn (dca) 3 ], 28,29 [(CH 3 CH 2 CH 2 ) 4 N]Cd[N(CN) 2 ] 3 ([TPrA]Cd[dca] 3 ) 30 and [(CH 3 ) 4 N]Mn[N 3 ] 3 . 31 The final group of caloric solids are magnetocalorics, which were first discovered by Weiss and Picard in 1917.…”