Enthalpic perspective on thermodynamic equilibrium of bulk and confined liquids: A review

Abstract Studying liquid transition to other states of matter encounters certain challenges. The phase transition containing a liquid phase embodies energetic change that can be quantitatively correlated to the equilibrium conditions. The challenges can be more complex if the liquid is geometrically confined in a narrow space in which the energetic interaction between the confinement and confined liquid might become more pronounced. Therefore, it is of great essence to probe the enthalpic perspective of an equilibrium in which at least one liquid phase exists. However, the challenges can be used as opportunities to characterize both the confined liquid as well as the confinement material in terms of phase transition, intermolecular interaction, and pore size distribution. In this article, enthalpic studies of liquid phase equilibrium are carefully discussed. The majority of the discussions address the confined thermodynamic equilibrium that includes a liquid phase, especially the liquid phase transition under confinement to and from vapor and solid phases is elaborated in great details. In addition, enthalpic overviews of bulk equilibrium of liquids are briefed where challenges and opportunities to calorimetrically study these equilibrium states are remarked. An integrative and instructive approach is closely followed in order establish a network of information that can be used not only for comprehensively reviewing the existing state-of-the-art, but also for providing invaluable insight and constructive inputs for future studies to bridge the gaps in the field.