Wetting hysteresis induces effective unidirectional water transport through a fluctuating nanochannel

TL;DR

This paper introduces a nanochannel water pump that uses asymmetric thermal fluctuations and hysteresis to achieve unidirectional water transport without osmotic pressure, with flow characteristics depending on the noise type and frequency.

Contribution

It demonstrates a novel mechanism for water transport driven by thermal fluctuation-induced hysteresis, expanding understanding of nanoscale fluid dynamics and energy conversion.

Findings

White noise inhibits channel wetting due to high-frequency components.

Pink and Brownian noises generate net flow through high-pass filtering.

Brownian fluctuation enhances water transport speed, pink noise overcomes osmotic pressure.

Abstract

We propose a water pump that actively transports water molecules through nanochannels. Spatially asymmetric thermal fluctuations imposed on the channel radius cause unidirectional water flow without osmotic pressure, which can be attributed to hysteresis in the cyclic transition between the wetting/drying states. We show that the water transport depends on fluctuations, such as white, Brownian, and pink noises. Because of the high-frequency components in white noise, fast switching of open and close states inhibits channel wetting. Conversely, pink and Brownian noises generate high-pass filtered net flow. Brownian fluctuation leads to a faster water transport rate, whereas pink noise has a higher capability to overcome osmotic pressure in the opposite direction. A trade-off relationship exists between the resonant frequency of the fluctuation and the flow amplification. The proposed pump can be considered as an analogy for the reversed Carnot cycle, which is the upper limit on the energy conversion efficiency.