Wetting hysteresis induces effective unidirectional water transport through a fluctuating nanochannel

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.

Automated summary

We propose a water pump that transports water molecules through nanochannels by utilizing spatially asymmetric thermal fluctuations. The pump achieves unidirectional water flow without osmotic pressure by exploiting hysteresis in the cyclic transition between wetting and drying states. Our study demonstrates that various types of fluctuations, including white, Brownian, and pink noises, affect the water transport process. The proposed pump operates through fast switching of open and close states to inhibit channel wetting in the presence of white noise, while pink and Brownian noises generate high-pass filtered net flow.