Flow rectification in a micro-nanochannel junction: Interplay of channel geometry and interfacial properties for directional transport

Abstract

The linear correspondence between flow rate and pressure drop for low Reynolds number hydrodynamics is often a constraint for the realization of miniaturized fluid circuits with selective junctions. Here we devise a micro-nanochannel junction with the directional flow in the nanochannel achieved by a combination of junction geometry and wall functionalization. The system can be compared to a fluid diode with parity-breaking between pressure drop and flow rate in the nanochannel junction with increasing flow rates in a particular configuration and negligible throughput in the reverse direction. This directional junction transport is tuned with slip length, characterizing channel wall functionalization as the bias parameter. Tuning the transport or leakage at a junction is key to engineering various applications. Such junctions are ubiquitous in systems like capillary blood flow, desalination systems, energy storage devices, etc. The resulting flow physics, thus unraveled, is an amalgamation of various factors which leads to a flow rectification system. We have delineated the effect of the confinement of the channel, the slip, and the geometry of the nanochannel towards the selective nature of the resulting configuration. We have successfully characterized a system to generate flow anisotropy while transporting fluid in different directions using numerical techniques. Additionally, our work demonstrates, for the first time, that a common definition of slip coefficient may be associated with three different flow regimes, which correspond to the order of magnitude of slip length relative to the channel dimensions thus providing a unifying key to engineer substrates and geometries towards designing fluid circuits.