Adjustable capillary imbibition enhancement in double-walled nanotubes with concentric tube length difference

YC Lu and YJ Wang and JG Chen, JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT, 2021, 053204 (2021).

DOI: 10.1088/1742-5468/abfcb4

Capillary imbibition of water plays a significant role in various applications at both the macroscopic and microscopic scales. However, it is still unclear whether capillary imbibition could be manipulated by the geometry structure of the nanotubes. In this paper, we adjust the concentric tube length difference increment Delta L of the double-walled nanotubes (DWNTs) to manipulate the capillary imbibition by molecular dynamics simulations. Three configurations are considered, i.e. increment Delta L = 0 (the common DWNT structure, labeled as configuration I), increment Delta L < 0 (configuration II, the inner tube is shorter than the outer tube), and increment Delta L > 0 (configuration III, the inner tube is longer than the outer tube). By comparing with the single-walled nanotube, it is found that the imbibition velocities of the water molecules in the DWNT are weakened 9.1% in configuration I and enhanced 30%-46.5% in configuration II and 10% in configuration III. By analyzing the microscopic structure of the water molecules, it is found that the imbibition velocity adjustment originates from the potential energy difference of the water molecules in the water reservoir and at the entrance of the nanotube at the nanotube cylindrical pore. An exponential relation between the imbibition velocity v(L) and the potential energy difference Delta E is obtained as v(L)(t) similar to e(kBT)(-)(Delta E). Furthermore, it is found that imbibition velocity is independent from the radius differences in all three configurations. Our results suggest a possible way to manipulate the capillary imbibition behavior and it has significant implications for water treatment, nano-switches, catalysis engines and biological sensors.

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