电场激励下表面润湿性可逆转变及其对润滑性能的影响

发布时间：2018-10-17 08:43

【摘要】：调控表面润湿性在微流体系统、可调焦液体透镜及润滑减阻等方面具有广泛的应用。电润湿是一种实时改变表面润湿性的有效方法,但是如何实现润湿性的可逆转变仍然是一个未解决的难题。为了理解电润湿工艺中润湿状态转变的机理和影响因素从而为润湿状态的可控转变提供理论指导,论文对电场激励下润湿性转变的动态过程进行了理论和试验研究,主要工作和结论包括:基于能量最小化方法,对外加电场、表面微观结构参数及表面能对润湿状态转变能垒的影响进行了理论推导,给出了不同表面微观结构条件及电场激励作用下润湿性转变的条件;从电动力学角度出发,将电场激励作为电动力耦合到流体动力学两相流方程作为润湿状态转变数值模拟的理论模型,为数值计算和试验结果分析提供了理论基础。基于相场法两相流模型,对电场激励作用下润湿状态转变的动力学过程进行了数值模拟。结果表明,电场激励作用下,润湿状态转变的驱动力主要源于气液界面的电动力和由于电场对界面表面张力系数的影响表现出来的电润湿效应;润湿状态转变的动态过程及最终结果主要由气液界面电场决定;影响电场的因素包括电压、介电层及表面微观结构形式;表面结构影响电场分布及润湿状态转变能垒,优化表面微观结构特征可以调控润湿状态转变过程。通过硅微加工工艺制备了不同几何特征的微结构阵列,对微观表面结构影响润湿性转变的规律进行了实验研究。结果表明,由于能垒的存在,不能实现表面润湿性的完全可逆转变;控制部分填充状态,可一定程度实现表面润湿性的可逆转变;可逆程度与部分填充程度存在一定关系,润湿性的可逆性有一定的可控性。通过激光加工在金属基底表面制备了具有多级微观结构的耐磨疏水表面,对疏水性影响摩擦性能的规律进行了初步的试验研究。结果表明,摩擦副表面疏水性在动压润滑条件下可以减小摩擦系数,但是在边界润滑条件下会使得摩擦系数显著增加。
[Abstract]:Surface wettability control has been widely used in micro fluid systems, focusing liquid lenses and lubricating drag reduction. Electrical wetting is an effective method to change the surface wettability in real time, but how to realize the reversible transformation of wettability is still an unsolved problem. In order to understand the mechanism and influencing factors of wetting state transition in electric wetting process, the dynamic process of wettability transition under electric field excitation is studied theoretically and experimentally. The main work and conclusions are as follows: based on the energy minimization method, the effects of applied electric field, surface microstructure parameters and surface energy on the wetting state transition barrier are derived theoretically. The conditions of wettability transformation under different surface microstructure and electric field excitation are given, and from the point of view of electrodynamics, The electric field excitation is coupled to the hydrodynamic two-phase flow equation as the theoretical model for the numerical simulation of the wetting state transition, which provides a theoretical basis for the numerical calculation and the analysis of the experimental results. Based on the two-phase flow model of phase field method, the dynamic process of wetting state transition under electric field excitation is numerically simulated. The results show that the driving force of the wetting state transition under the electric field excitation is mainly from the electrodynamic force of the gas-liquid interface and the electric wetting effect due to the influence of the electric field on the surface tension coefficient of the interface. The dynamic process and final results of the wetting state transition are mainly determined by the gas-liquid interface electric field, the factors affecting the electric field include voltage, dielectric layer and surface microstructure, the surface structure influences the electric field distribution and the transition barrier of the wetting state. The process of wetting state transition can be regulated by optimizing the surface microstructure. Microstructural arrays with different geometric characteristics were fabricated by silicon micromachining. The effect of microstructures on wettability transformation was studied experimentally. The results show that due to the existence of energy barrier, the complete reversible transformation of surface wettability can not be realized, and the reversible transformation of surface wettability can be realized to some extent by controlling the partial filling state, and the degree of reversibility is related to the degree of partial filling. The reversibility of wettability has certain controllability. The wear-resistant hydrophobic surface with multistage microstructure was prepared by laser processing on the surface of metal substrate. The effect of hydrophobicity on friction performance was studied. The results show that the hydrophobicity of the surface of friction pair can decrease the friction coefficient under hydrodynamic lubrication condition, but the friction coefficient can be increased significantly under boundary lubrication condition.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TH117.2

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