液滴与旋转壁面的冲击动力学研究

A STUDY OF IMPACT DYNAMICS OF DROPLET ON THE ROTATING SUBSTRATE

屈冲

11849102

硕士

航天工程

邓巍巍

2020-05-28

2020-06-25

哈尔滨工业大学

深圳

液滴撞击固体壁面的现象普遍存在于自然界中，并且在航空航天、生物医学、电子制造等各个工业领域都有广泛的应用。目前在材料制膜领域普遍采用的旋涂方法，实际上就与液滴撞击旋转壁面的现象有关。银纳米线作为一种导电性、透光性良好的材料，是当下柔性透明电极制备领域的一个研究热点。本文以液滴撞击固体壁面的动力学过程作为研究对象，主要研究液滴撞击旋转壁面的过程，同时通过往液滴内部添加银纳米线，将液滴撞击过程与银纳米线排列结合起来。主要工作及结论如下：（1）搭建液滴撞击过程的可视化成像装置，从侧视、俯视角度观察了液滴撞击过程。对于液滴撞击旋转壁面的情况，发现液滴稍不对心就会不均匀铺开并产生“指状”不稳定分裂，通过改进装置实现了液滴的对心下落，从而使单个液滴旋涂后也能均匀铺开，重复性也有所保证。对比旋涂制膜领域为获得均一薄膜多采用过量液体，此方法在一定程度上可节省溶液。（2）探究了韦伯数、角速度对液滴旋涂铺展过程的影响，发现旋涂铺展过程可分为撞击铺展和旋转铺展两个阶段。韦伯数主要影响初始的撞击铺展阶段，转速则主要在旋转铺展阶段起作用。还发现了铺展过程中液膜边缘毛细脊的直径变化为先增大后减小，且韦伯数越大时毛细脊直径的峰值越小，且出现峰值的时间越早。（3）对撞击过程完成后的银纳米线排列情况进行了探究。发现液滴撞击固定壁面和旋转壁面后基板上的银纳米线都有沿径向排列的趋势。撞击固定壁面时由于液滴的回缩等行为可能导致排列不规则，而撞击旋转壁面后都有明显的沿径向排列的现象。这在一定程度上反映了液滴内部的流场变化，同时结合数值模拟对液滴撞击壁面过程进行了对比探究，获得了撞击过程的流场及剪切率信息。

The phenomenon of droplets impacting on solid surface is ubiquitous in nature, and is widely used in various industrial fields such as aerospace, biomedicine, and electronics manufacturing. At present, the spin-coating method is widely used in many research fields such as thin film solar cell fabrication. Dynamic spin coating is essentially a phenomenon of droplets impacting a rotating surface. On the other hand, silver nanowire is a research topic of intense study in the field of flexible transparent electrode because of its good conductivity and light transmittance. In this thesis, the dynamic process of droplets impacting on the solid surface is the key research object. The process of droplets impacting the rotating surface is studied experimentally. At the same time, by adding silver nanowires(Ag NWs) into the droplet, the droplet impact process is related to the directional arrangement of silver nanowires. The main work and conclusions are:(1) Build a visualization system for the droplet impact process, and observe the droplet impact process from the side and top views. For the case where the droplet impact the rotating surface, it is found that the droplet will spread unevenly and produce unstable fingering pattern if the impact point is slightly out of center. Once concentric alignment has been improved, a single droplet can spread evenly upon impacting on the rotating substrate. This work inspires a single drop spin coating method, which can reduce material waste by up to 90%.(2)The effects of Weber number and rotation speed on the droplet spreading on the rotating substrate are explored. It is found that the spreading process can be divided into two stages: the impact-spreading and the centrifugal-spreading. The Weber number mainly affects the initial impact-spreading stage, and the rotation speed mainly affects the centrifugal-spreading stage. It is also found that the diameters of the film rim first increase to a peak value and then decrease. The larger the weber number, the smaller the peak value of the rim diameters.(3)The arrangement of the silver nanowires after the impacting process is investigated. It is found that the silver nanowires on the substrate tend to be arranged in the radial direction for droplets impacting on both the fixed and the rotating substrate. When impacting on the fixed surface, due to the retraction of droplets after maximum spreading, the alignment of Ag NWs may be spoiled and become irregular. For droplets impacting on the rotating surface, there are obvious radial alignment phenomena because no recoil is involved. This suggests the Ag NWs response to the flow field inside the droplet to a certain extent. The numerical simulation using a commercial multiphysics software package COMSOL is carried out to compare the process of droplet impact on the stationary substrate.

液滴撞击 单液滴旋涂 液膜铺展 银纳米线排列 数值模拟

droplet impingement single droplet spin coating liquid film spreading silver nanowire arrangement numerical simulation

中文

联合培养

南方科技大学

屈冲. 液滴与旋转壁面的冲击动力学研究[D]. 深圳. 哈尔滨工业大学,2020.