Molecular Dynamics Simulations of Capillary Dynamics at the Nanoscale

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

Abstract

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

CLC Number:

O647.6

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.

Figures/Tables 7

Fig.1 The simulation model for investigating capillary imbibition process

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

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

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.)

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

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.)

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

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