Transport properties of nanoconfined fluids: A review

The diffusion coefficient, viscosity, and thermal conductivity of fluids serve as the primary metrics for characterizing mass, momentum, and heat transfer. However, these transport properties exhibit significant deviations from those of bulk fluids when confined in nanoscale environments. In this work, we present a comprehensive overview of the transport properties of nanoconfined fluids (NCFs) with a focus on simple confinement systems and water by integrating findings from previous and recent researches. This discussion begins with an examination of methodologies for assessing transport properties through molecular dynamic (MD) simulations, with a focus on the equilibrium MD method. Subsequently, we delineate the unique characteristics of NCFs' transport properties, which include anisotropy, size dependence, and layered distribution. Furthermore, we conduct a thorough analysis of the fundamental physical mechanisms that dominate these transport properties. We highlight that the diffusion coefficient, viscosity, and thermal conductivity are significantly affected by these rationales such as the displacement, friction, and collision frequency of molecular motions within the NCFs. We then identify various factors that may directly or indirectly influence these mechanisms and related transport properties, including surface electrostatic property, surface wettability, surface roughness, surface flexibility, and fluid composition. In conclusion, we provide a comprehensive summary and perspective on the research emphasis and challenges associated with the transport properties of NCFs. This review not only facilitates the comprehension of the fundamental mechanisms governing the transport properties of NCFs but also holds promise for informing a range of industrial applications, including seawater desalination, gas separation, and chip cooling.