PDMS表面上的蒸发液滴内部流动实验研究

发布时间：2018-04-11 06:39

本文选题：液滴蒸发 + 聚二甲基硅氧烷　；参考：《湖北工业大学》2017年硕士论文

【摘要】：随着新型材料的不断涌现和加工工艺的不断优化,以聚二甲基硅氧烷(polydimethylsiloxane,PDMS)为代表的软衬材料在微纳米加工技术、微纳机电系统和微纳流体系统等领域发挥着极为重要的作用。同时,液滴作为一种载体被广泛应用于这些系统中,但是由于液滴具有蒸发或挥发特性,一方面它将会影响这些系统的工作性能,另一方面它可用于实现一些新的功能。在液气界面张力垂直分量的作用下,软衬基底会产生一定的表面变形,这种变形将会影响液滴的蒸发行为,进而影响蒸发液滴的内部流动。为此,本文开展了PDMS表面上的蒸发液滴内部流动实验研究,主要内容如下:(1)开展了PDMS表面上的液滴蒸发实验,发现PDMS质量配比越大,基底弹性模量越小,常接触面积(constant contact area mode,CCR)蒸发阶段持续时间越长。在液滴为球冠状和具有均匀的浓度梯度的假设下,得到了液滴以CCR模式蒸发时的解析解;(2)采用微观粒子图像测速技术(micro-particle imaging velocimetry,Micro-PIV)观测了PDMS表面上的蒸发液滴的内部流动,揭示了质量配比对流型变化、速度分布和涡量分布的影响,并利用激光共聚焦显微镜对两种浓度下溶液液滴蒸发残留的图案进行观察,发现两者存在明显的差异;(3)采用粒子跟踪测速(Particle Tracking Velocimetry,PTV)技术观察了固液界面处的液体流动情况,发现在蒸发初始阶段液体由液滴边缘向液滴中心流动,而后运动发生反转。使用最小二乘法分析了接触线的运动特征,通过各种作用力和惯性力的量级比较,认为接触线处的微球的运动为准静态的,并建立了一种新的微球钉扎机制。
[Abstract]:With the continuous emergence of new materials and the continuous optimization of processing technology, the soft lining materials, such as polydimethylsiloxane polymethylsiloxane PDMSs, play an extremely important role in the fields of micro / nano machining, micro / nano electromechanical systems and micro / nano fluid systems.At the same time, droplets are widely used in these systems as a carrier, but due to the evaporation or volatilization characteristics of droplets, on the one hand, it will affect the performance of these systems, on the other hand, it can be used to achieve some new functions.Under the action of vertical component of liquid-gas interfacial tension, the soft liner substrate will produce a certain surface deformation, which will affect the evaporation behavior of the droplet, and then affect the internal flow of the evaporative droplet.In this paper, an experimental study on the internal flow of evaporated droplets on the surface of PDMS is carried out. The main contents are as follows: (1) the evaporation experiments on the surface of PDMS are carried out. It is found that the larger the mass ratio of PDMS is, the smaller the elastic modulus of the substrate is.The longer the evaporation stage of constant contact area mod.Under the assumption that the droplet is spherical and has a uniform concentration gradient, the analytical solution of the droplet evaporation in CCR mode is obtained. The micro-particle imaging velocimetric micro-PIV technique is used to observe the internal flow of the evaporated droplet on the PDMS surface.The effects of mass ratio convection distribution velocity distribution and vorticity distribution were revealed and the patterns of droplet evaporation at two concentrations were observed by laser confocal microscope.It is found that there is a significant difference between the two methods. The particle Tracking velocimetry (PTV) technique is used to observe the liquid flow at the solid-liquid interface. It is found that the liquid flows from the edge of the droplet to the center of the droplet at the initial stage of evaporation, and then the motion reverses.The motion characteristics of the contact line are analyzed by using the least square method. By comparing the magnitude of various forces and inertial forces, it is considered that the motion of the microsphere at the contact line is quasi-static, and a new pinning mechanism of the microsphere is established.
【学位授予单位】：湖北工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O35

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