Insights from molecular simulations on liquid slip over nanostructured surfaces

The current study focuses on non-equilibrium molecular dynamics (NEMD) simulations to investigate the slip properties of water flowing over different nanostructured surfaces. A simulation protocol is developed that applies constant shear stress throughout the fluid before measuring the slip length. Using pseudo-data, the reliability of this protocol in terms of both accuracy and noise of the results for high-slip and multiphase systems is demonstrated. In contrast to the NEMD techniques available in the literature, the protocol also enables a convenient way to compare the slip lengths of different surface coatings. The fluid slip lengths of surface coatings comprising carbon nanotubes on platinum are predicted using the proposed protocol with nitrogen gas trapped in the interstitial gaps. The role of these gas pockets in determining surface slip properties is investigated. The NEMD results from the proposed model compare well with a macroscopic theoretical model for nano-patterned surfaces. Finally, it is concluded that entrapped gas within nanostructures may offer significant drag reduction only if the gas surface coverage is above 95%.