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.

中文翻译：

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揭示天然橡胶中巨大压力作用的起源

压力效应（BCE）的特征是压缩产生的材料中的热响应（温度或熵的变化）。几种材料具有适合开发固态冷却装置的BCE，通常与压力引起的相变有关。已观察到天然橡胶（NR）的巨大BCE，这使其成为一种便宜且环保的候选材料。考虑到没有证据表明过程中存在相变，NR中BCE显着升高的原因仍然难以捉摸。本研究结合经典分子动力学（MD）模拟和热力学分析来研究NR中巨大BCE的起源。NR的绝热压缩循环的MD模拟是在变化的施加压力和初始温度下进行的，并且能够捕获BCE。对结果的详细分析帮助我们阐明了压缩状态下材料的结构转变以及由此产生的能量变化。MD等温压缩的结果以及热力学分析表明，NR的高可压缩性以及压缩后分子水平上势能的异常降低大大促进了BCE（由过程中的等温熵变化和绝热温度变化量化） ，这是其他材料中不常见的功能。这些发现可以扩展到其他聚合物，并且无疑将对具有增强的BCE的材料设计有用。