Interfacial Structural Entropy (ISE): A Statistical Descriptor That Links Distributed Fluid Microstructures and Interfacial Properties

Fluids at the nano/microscopic interface, particularly when influenced by external fields, exhibit significant variations in microstructures, resulting in complex properties that differ markedly from those of single molecules and bulk fluids. The diversity in microstructures leads to unique interfacial transport and reaction phenomena. Notably, the microstructure is a group of molecular clusters with different configurations distributed at the interface in a balanced state, yet the governing factors that determine the cluster structure and their distribution remain to be understood. Herein, we introduce interfacial structural entropy (ISE) as a metric to capture the combined effects of solid surfaces and external fields on fluid microstructure. Specifically, ISE quantitatively characterizes fluid microstructures and connects them to interfacial properties, offering a new perspective from a fluid standpoint to comprehend interfacial phenomena. Using the hydrogen evolution reaction as a case study, we outline the methodology for constructing the ISE, elucidate general principles for its optimization, and describe technical strategies for future developments. The ISE provides statistical insights into fluid microstructures that relate to interfacial properties, which are anticipated to facilitate rational and high-throughput computational screening and the design of materials and manipulation methods under external fields.