纳米尺度下毛细流动的分子动力学模拟

doi:10.19596/j.cnki.1001-246x.8366

摘要/Abstract

摘要：

采用分子动力学模拟研究纳米尺度下壁面润湿性对毛细流动的影响，主要考虑纳米通道两侧壁面润湿性相同与不同两种情况。研究表明：两侧壁面润湿性相同条件下，毛细流动随着壁面润湿性增强而加快, 毛细高度随时间的变化早期偏离Lucas-Washburn理论，但后期与其预测符合。在纳米通道两侧壁面润湿性不同的情况下，液面会发生振荡，两侧壁面毛细高度也不相等，且液面振荡的幅度和两侧壁面毛细高度差都随着两侧壁面润湿性差异的增大而增大。基于能量转化分析，提出两侧壁面湿润性不同情况下纳米通道中毛细流动发生的条件以及毛细流动快慢的判别依据。研究结果加深了对纳米尺度下毛细流动机理的认识，并为相关工程应用提供理论参考。

关键词: 毛细流动, 纳米尺度, 润湿性, 分子动力学模拟

Abstract:

Molecular dynamics simulations are utilized to systematically investigate the effects of wettability on capillary imbibition process at the nanoscale. We consider two sets of scenarios. In the first set, the two sidewalls of a nanochannel have the same wettability. We find that the capillary imbibition rate increases with the hydrophilicity of capillary and that the imbibition dynamics deviates from the Lucas-Washburn theory at the early stage but agrees with it at the late stage. In the second set where the two sidewalls have different wetting conditions, the liquid-vapor interface oscillates, and there exists a difference between the capillary height of the two sidewalls. The amplitude of the liquid-vapor interface oscillation and the capillary height difference increase with the wettability contrast between the two sidewalls. We determine the critical condition for the occurrence of capillary imbibition in the nanochannel with inhomogeneous wettability, and propose a method to estimate the evolution of the capillary height. Our findings deepen the understanding of capillary dynamics at the nanoscale and could be useful for relevant engineering applications.

Key words: capillary dynamics, nanoscale, wettability, molecular dynamics simulations

中图分类号:

O647.6

阿湖宝, 杨志兵, 胡冉, 陈益峰. 纳米尺度下毛细流动的分子动力学模拟[J]. 计算物理, 2021, 38(5): 603-611.

Hubao A, Zhibing YANG, Ran HU, Yifeng CHEN. Molecular Dynamics Simulations of Capillary Dynamics at the Nanoscale[J]. Chinese Journal of Computational Physics, 2021, 38(5): 603-611.

图/表 7

图1 毛细流动现象模拟体系示意图

Fig.1 The simulation model for investigating capillary imbibition process

图2 液滴静态平衡接触角θS与势能函数参数εS-L的关系

Fig.2 Relation between the static equilibrium contact angle θS and εS-L

表1 模拟纳米通道中毛细流动时采用的参数

Table 1 Parameters used in simulating capillary imbibition process

组别	算例	壁面	ε_S-L/(kcal·mol^-1)	θ_S/(°)	cos θ_S	∑cos θ_S	Δ cos θ_S
1	1	下壁面	0.466 2	76.90	0.23	0.45	0.00
	1	上壁面	0.466 2	76.90	0.23	0.45
	2	下壁面	0.543 9	56.80	0.55	1.10
	2	上壁面	0.543 9	56.80	0.55	1.10
	3	下壁面	0.582 8	43.12	0.73	1.46
	3	上壁面	0.582 8	43.12	0.73	1.46
	4	下壁面	0.637 1	30.18	0.86	1.73
	4	上壁面	0.637 1	30.18	0.86	1.73
2	5	下壁面	0.155 4	135.41	-0.71	0.15	1.58
	5	上壁面	0.637 1	30.18	0.86	0.15	1.58
	6	下壁面	0.466 2	76.90	0.23	1.09	0.64
	6	上壁面	0.637 1	30.18	0.86	1.09	0.64
	7	下壁面	0.543 9	56.80	0.55	1.41	0.32
	7	上壁面	0.637 1	30.18	0.86	1.41	0.32
	8	下壁面	0.310 8	105.26	-0.26	-0.04	0.49
	8	上壁面	0.466 2	76.90	0.23	-0.04	0.49

图3 纳米通道两侧壁面润湿性相同时毛细高度h随时间t的变化 (插图(a)为t=0.1~1 ns内h变化的双对数曲线，(b)和(c)分别是算例2和算例3中t=10 ns时模拟体系的构型。)

Fig.3 Evolution of the imbibition length h as wettability of the two sidewalls is the same (Inset (a) shows the early evolution of h in the log-log scale; Insets (b) and (c) are snapshots of the simulation system at t=10 ns in Cases 2 and 3, respectively.)

图4 纳米通道两侧壁面润湿性不同时毛细高度hU、hL随时间t的变化

Fig.4 Evolution of the capillary imbibition length (hU and hL) on sidewalls of a nanochannel as wettability of the two sidewalls is different

图5 纳米通道两侧壁面润湿性不同时两侧壁面毛细高度差(hU- hL)和润湿性差异Δ cos θS间的关系 (插图(a)、(b)和(c)分别为算例5、6和7中t=10 ns时模拟体系的构型。)

Fig.5 Relation between (hU- hL) and Δ cos θS (Insets (a), (b) and (c) show snapshots of the simulation system at t=10 ns in Cases 5, 6 and 7, respectively.)

图6 纳米通道两侧壁面毛细高度平均值have随时间t的增长

Fig.6 Evolution of the average of hU and hL over time t

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