Fast nanofluidics by travelling surface waves

During the past two decades, we see the fast development and wide applications of nanotechnologies such as micro-/ nanoelectromechanical systems (MEMS/NEMS) Ho and Tai (1996), Ho and Tai (1998), Gad-el-Hak (1999), Cao et al. (2009), biological chips and lab-on-a-chip Daw and Finkelstein (2006), Craighead (2006), Ding et al. (2013), Bocquet and Tabeling (2014). Nanoscale transport governs the behaviour of a wide range of nanofluidic systems, but it remains less understood due to the enormous hydraulic resistance associated with the nanoconfinement and the resulting minuscule flow rates in MEMS/NEMS. As a point of long-standing view, it is of great importance pursued by many researchers due to its implications in mass and momentum transport at micro-/nanoscales, and the micro-/nanoflow control is also important for practical applications: DNA profiling Insepov et al. (2006), optical filters and display technology Cecchini et al. (2008), thermal management of semiconductor elements and pollution monitoring Roosta et al. (2016). However, the huge surface–volume ratio up to 10 − 10 significantly affects the mass and momentum transport in micro-/nanoelements and makes this type of research challenging. Obviously, the challenge is to overcome the large surface and viscous forces that prevent the fluid from flowing at the nanoscale, wherein other driving forces can be ignored in most microfluidic systems Yeo and Friend (2009), Friend and Yeo (2011), Arash et al. (2015). There is no doubt that the inertia becomes significant in nanofluidic flows and results in the low efficiency of mass transport. Thus, fast flow in nanochannels and large flow rate are highly appreciated. Traditional approaches to reduce the skin friction and increase the flow rate are the use of hydrophobic or Abstract In this paper, we investigate the fast flow in nanochannels, which is induced by the travelling surface waves. The nanoscale fluid mechanism in nanochannels has been influenced by both amplitude and frequency of travelling surface waves, and the hydrodynamic characteristics have been obtained by molecular dynamics simulations. It has been found that the flow rate is an increasing function of the amplitude of travelling surface waves and can be up to a sevenfold increase. However, the flow rate is only enhanced in the limited range of frequency of travelling surface waves such as low frequencies, and a maximum fivefold increase in flow rate is pronounced. In addition, the fluid–wall interaction (surface wettability) plays an important role in the nanoscale transport phenomena, and the flow rate is significantly increased under a strong fluid–wall interaction (hydrophilicity) in the presence of travelling surface waves. Moreover, the friction coefficient on the wall of nanochannels is decreased obviously due to the large slip length, and the shear viscosity of fluid on the hydrophobic surface is increased by travelling surface waves. It can be concluded that the travelling surface wave has a potential function to facilitate the flow in nanochannels with respect to the decrease in surface friction on the walls. Our results allow to define better strategies for the fast nanofluidics by travelling surface waves.