纳米液滴撞击润湿梯度表面的分子动力学模拟  

Molecular Dynamics Simulation of Nanodroplet Impacting on Wettability Gradient Surface

作　　者：潘伶[1] 谢旭清 郭锦阳 PAN Ling;XIE Xu-qing;GUO Jin-yang(School of Mechanical Engineering and Automation,Fuzhou University,Fuzhou 350108,China)

机构地区：[1]福州大学机械工程及自动化学院,福州350108

出　　处：《表面技术》2022年第11期395-404,共10页Surface Technology

基　　金：国家自然科学基金(51975123);福建省产学合作项目(2020H6025);晋江市福大科教园区发展中心科研项目(2019-JJFDKY-54)。

摘　　要：目的研究在液滴撞击固体表面的过程中,撞击速度和润湿梯度对液滴运动的影响。方法采用分子动力学方法模拟纳米液滴以不同初始下落速度v_(0)撞击带有润湿梯度的固体表面,通过改变固体表面纳米方柱的间隙来构建润湿梯度,方柱间隙越小则接触角越小、润湿性能越好。结果当v_(0)为0.3~1.1 nm/ps时,液滴撞击固体表面后沿固体表面朝着润湿性较强的方向移动;在v_(0)为0.7~1.1 nm/ps时,液滴出现了二次铺展;受到液滴的初始动能和钉扎效应的影响,液滴质心离开润湿梯度表面时的移动速度v_(t)出现了2个拐点。当v_(0)为1.2~1.5 nm/ps时,液滴在撞击固体表面后会发生弹跳,此时液滴在v_(0)垂直方向的速度分量随着v_(0)的增大呈线性增大趋势,而在v_(0)水平方向的速度分量为定值(0.017 nm/ps);液滴的弹跳速度v和弹跳角α会随着v_(0)的增大而增大。结论在液滴撞击带有润湿梯度的固体表面的过程中,最大铺展因子β_(max)与v_(0)近似呈线性关系;低速液滴撞击固体表面后会被捕捉,并沿着润湿性强的方向移动,提出了不同撞击速度区间中v_(t)与v_(0)的关系式;高速液滴在撞击后会沿着润湿性较好的一侧发生弹跳,提出了液滴弹跳速度、角度与v_(0)的关系式。The work aims to study the effects of different impact velocity and wettability gradient on droplet movement during the process of droplet impacting on solid surface.The specific data for spreading and bouncing droplets were obtained by molecular dynamics(MD)simulation,which was difficult to be measured quantitatively in the experiment and had reference value for guiding engineering practice.The MD method was used to simulate the nanodroplet impacting on solid surface with wettability gradient at different initial velocities v_(0).The behavior of droplet impacting on solid surface was affected by droplet impact velocity,presence of impurities in the droplet and solid surface characteristics.The solid surface characteristics mainly included wettability,surface roughness and temperature.The wettability of solid surface could be reflected by the contact angle of droplet surface.The wettability gradient was constructed by changing the gap of nano square columns on solid surface.The smaller the square column gap,the smaller the contact angle,and the better the wettability.When v_(0)=0.3-1.1 nm/ps,the droplet after hitting the surface moved along the direction of good wettability on the solid surface.When v_(0)=0.3-0.5 nm/ps,the droplet was hindered by the pinning effect and hardly spread.When v_(0)=0.7-1.1 nm/ps,the droplet underwent secondary spreading.Owing to the effect of initial kinetic energy and pinning effect of the droplet,two inflection points were observed in the curve of moving velocity v_(t) when the droplet centroid left the gradient surface.The x-direction velocity v_(t) of the droplet leaving the gradient surface was mainly related to the initial velocity v_(0) and the total spreading time T of the droplet.The x-direction velocity v_(t) increased with the increase of the initial kinetic energy of the droplet.v_(t) decreased with the increase of T,because the kinetic energy of droplets was consumed more in the spreading process.When v_(0)=1.2-1.5 nm/ps,the droplet bounced after hitting solid surface.At

关 键 词：纳米液滴 撞击 润湿梯度 分子动力学模拟 弹跳 铺展 

分 类 号：O552.4[理学—热学与物质分子运动论]