Nanoconfined Fluid Critical Properties Variation over Surface Wettability

Abstract

The characterization of nanoconfined fluid critical properties is critical for nanoconfined fluid phase behavior and flow capacity evaluation. To date, fluid–surface interaction strength is considered as the original cause for the shift of fluid critical properties, which is closely related to pore size and surface wettability. However, the majority of research is devoted to investigating the impact of pore size, while investigations about surface wettability on nanoconfined fluid critical properties are lacking. In order to fill the knowledge gap, in-depth investigations have been carried out to shed light on the wettability effect on nanoconfined fluid critical properties. First, focusing on the relative strength between fluid–fluid interactions and fluid–surface interactions, a robust correlation is proposed to relate surface contact angle, a macroscopic form of wettability effect, to critical property shift. Then, a linear correlation between the wettability effect and the adsorption thickness is established, and as a result, effective pore size can be described as a function of wettability as well. Finally, a prediction model for nanoconfined fluid critical properties is developed, and its reliability is well-clarified against 86 cases, collected from previous molecular simulation results or experiments. The results show the following: (a) The magnitude of the shift of fluid critical property can reach as high as 60%, dominating the variation characteristics of nanoconfined fluid phase behavior. (b) Both the pore size shrinkage and strong fluid-affinity surface are underlying mechanisms for suppressed critical properties at nanoscale. (c) The confined effect arisen from the cylindrical geometry is 2.24 times greater than that for slit nanopores, essentially stemming from the fluid force condition exerted by the pore surface.