Thermal behavior of slip length in connection with fluid-solid chemical affinity

The relation between fluid slip on a solid surface and flow temperature is investigated with the help of molecular dynamics simulations. An atomistic Couette configuration, consisting of a Lennard-Jones fluid and two rigid walls, is prepared and evolved to its steady state, where the slip length can be readily extracted from the linear velocity profile. Simulations are carried out for a broad range of temperatures and for different magnitudes of the fluid-solid chemical affinity. This last parameter is found to affect the overall shape of the slip length vs. temperature curve. Depending on its value, three distinct types of thermal behavior are observed: slippery (unbounded and decreasing), critical (constant), and sticky (bounded and increasing). We find that the temperature dependence of the slip length in each of these cases is well described by a simple heuristic function, whose adjustable parameters have a clear physical interpretation. The present study is aimed at the development of material-specific boundary conditions and their use in multiscale simulations. In this context, our analysis, once extended to more complex substances, may aid in the design and optimization of microfluidic devices and nanostructured membranes set to operate at specific temperatures.