Knowledge of the thermodynamic potential in terms of the independent variables allows to characterize the macroscopic state of the system. However, in practice, it is difficult to access this potential experimentally due to irreversible transitions that occur between equilibrium states. A showcase example of sudden transitions between (meta)stable equilibrium states is observed for soft porous crystals possessing a network with long-range structural order, which can transform between various states upon external stimuli such as pressure, temperature and guest adsorption. Such phase transformations are typically characterized by large volume changes and may be followed experimentally by monitoring the volume change in terms of certain external triggers. Herein, we present a generalized thermodynamic approach to construct the underlying Helmholtz free energy as a function of the state variables that governs the observed behaviour based on microscopic simulations. This concept allows a unique identification of the conditions under which a material becomes flexible.

中文翻译：

---

热力学洞察软多孔晶体的刺激响应行为。

关于自变量的热力学势的知识允许表征系统的宏观状态。但是，实际上，由于平衡状态之间发生不可逆转，因此很难通过实验获得这种潜力。对于具有长程结构网络的软多孔晶体，观察到了（亚）稳定平衡状态之间突然转变的一个示例，该多孔晶体可以在外部刺激（例如压力，温度和客体吸附）下在各种状态之间转换。这样的相变通常以大的体积变化为特征，并且可以通过在某些外部触发条件下监视体积变化来进行实验跟踪。在此处，我们提出了一种广义的热力学方法，以构造潜在的亥姆霍兹自由能作为状态变量的函数，该状态变量基于微观模拟控制着观察到的行为。该概念可以唯一确定材料变柔韧性的条件。