无阀纳米泵中水流的反常堵塞

Abnormal blockage of water flow in valveless nanopumps

对于颗粒物质,在锥形通道的窄口处容易发生堵塞现象,实验中通常利用机械振动进行疏通.而对于无孔不入的水却不同,即使在纳米尺度的碳纳米管中仍然可以快速通透.本文利用分子动力学模拟研究了由锥形碳纳米管与石墨烯平面构成的无阀纳米泵,发现水输运在一定条件下也会出现反常堵塞.与颗粒物质截然不同的是振动方法无法恢复水流,相反,它促使水在纳米水泵的通道窄口处发生堵塞.通过分析堵塞区水的密度分布、氢键寿命、水分子的结构特征,揭示了反常堵塞是由腔体中振动膜的高频振动引发水的结构相变造成的.

In the narrow orifice of a cone-shaped channel,blockage can occur for granular matter.However,water molecules can enter into and even permeate through carbon nanotubes of diameters down to 0.8 nm at ultrafast rates.Here we demonstrate by molecular dynamics simulations that clogging can also emerge unexpectedly in the water flowing through a nanoscale valve-less pump.The designed pump features two truncated carbon nanocones,with the narrowest region having a diameter of 1.2 nm(larger than that of(6,6)carbon nanotube),linked to a fluid cavity volume,and is powered by the vibration of a graphene sheet.In the low frequency range,water molecules can be driven through the nanocones effectively by the vibration of the graphene sheet.The maximum flux reaches 83 ns–1,which is approximately 20 times the measured value of(3.9±0.6)ns–1 for aquaporin-1.However,at higher frequencies,water molecules suffer blockage at the narrow exits.Much unlike granular matter,high-frequency vibration cannot restore water flow.The key to this phenomenon is that in the narrow exits of two nanocones acting as diffuser/nozzle,the number density of water molecules rapidly increases with frequency increasing,the tight hydrogen-bonding network is formed,and the mean lifetime of hydrogen bonds increases dramatically under high-frequency vibrations.High frequency fluctuations in the middle chamber make H-bond network between water molecules in the narrow exits more stable.The probability density distribution of water exhibits a non-equilibrium transition from a disordered state to ordered state.This work reveals a new mechanism of water flowing/blocking in a nanoscale valve-less pump based on two asymmetrical nanocones,offers valuable insights into understanding nonequilibrium jamming transition in nanoscale fluid.