【作者】 常银霞；

【导师】 张思祥；

【作者基本信息】 河北工业大学 ， 机械制造及其自动化， 2012， 博士

【摘要】 作为一种新兴技术，数字微流控凭借试剂用量小、可配置、可并行处理和易实现自动化等优势在生物、医药、化学和检测等领域展现出良好的应用前景。本文通过理论分析、建模仿真、实验验证和模型改进四个步骤，探讨了在基于介电润湿的封闭式数字微流控系统的基本性能和液滴的运动特性。论文的主要内容包括：1）研究了介电润湿的基础理论，对液滴的运动过程进行了受力分析；2）为系统建立流体力学的数学模型，通过二维仿真研究了电场的分布情况、介质层厚度的影响和接触角随驱动电压的变化等系统基本特性；3）建立三维模型，分析了液滴移动和分裂过程中接触角的变化、液滴的压强和速度、液滴的拉伸情况，讨论了电极形状、电极尺寸和上下极板间隙对液滴动态过程的影响；4）搭建了系统平台对系统的基本性能和动态性能进行验证，包括接触角的变化、介质层厚度的影响、疏水层的影响、接触角的滞后、阈值电压、液滴运动速度、液滴运动的可重复性和介质层的击穿现象等。然后验证了介质层厚度、不同电极形状和不同液滴半径对运动的影响。5）根据实验数据求出了接触线摩擦系数和极板剪切阻力的系数，并将改进后模型的预测值和实验数据进行对比。本文的主要创新点包括：1）在对液滴运动进行受力分析的基础上推导了液滴运动的最优体积，得出在理想状态下，当液滴半径r与方形电极的边长L之间满足r≤2L时，液滴所受到的驱动力随半径r增加而变大；当r>2L时，液滴所受到的驱动力保持不变。因为随着液滴半径的增长，液滴之间的互相干扰会增加，不容易准确控制，因此当r=2L，液滴的驱动效果最好。2）据作者所查文献，目前已见采用VOD方法进行仿真，采用水平集方法对开放式系统的仿真，采用水平集方法的二维模型对接触角变化的仿真，未见采用水平集方法对液滴运动和分裂过程的研究报道。本文采用有限元仿真软件、水平集动态界面追踪方法，以Navier-Stoke方程为基本模型对基于介电润湿的封闭式数字微流控系统进行了仿真，研究了系统的静态和动态特性。3）通过三维模型的仿真，讨论了电极形状和上下极板间隙对液滴运动的影响，得出结论：与方形电极相比，叉指型电极可以降低液滴运动的阈值电压，但对液滴运动的平均速度无明显影响；液滴分裂时，液滴体积越小分裂速度越快；当体积固定时，在液滴直径R与上下极板间隙h比例大约为6-17的范围内，电极尺寸越大，上下板间隙约小越容易分裂，小于此比值范围会分裂失败，大于此比值范围会出现细碎液滴，影响分裂效果。4）根据实验数据改进模型，将接触线摩擦力和上下极板的剪切阻力考虑在内，利用两组实验结果求出相应的摩擦系数，使仿真结果与实验数据更吻合。5）采用激光雕刻PCB板作为下极板的电极阵列，线间间距可以精确到50μm左右，用ITO导电玻璃作为上极板的导电层，上下极板上沉积一层最薄为0.5μm的派瑞林作为介质层和疏水层，该方式制作芯片相对于无尘室的芯片加工，大大降低了实验成本，同时又明显改善了常规PCB制版方式的精度，降低了驱动电压，对低成本高精度的实验芯片进行了探索。更多还原

【Abstract】 As an emerging technology, digital microfluidics has a good prospect in the field of biology,medicine, and chemical with the advantage of less reagent consumption, configurable, parallelprocessing and easy to automate. The basic performance and dynamic characteristics of closedelectrowetting on dielectric(EWOD) digital microfluidic system was studied through theoreticalanalysis, modeling and simulation, experimental validation and model improvement. The majorcontent includes:1) Research on the basic theory and stress analysis of the droplet motion.2) The hydrodynamic model was established and basic performances such as distributionof the electric field, effect of the dielectric layer thickness and the contact angle change withvariation of driving voltage were discussed based on the two-dimensional model.3) Dynamic characteristics including the changes of contact angle, the pressure and speedof the droplets, the stretch of droplet, the impact of electrode shape, electrode size and gasbetween plate were studied based on three-dimensional model.4) The experimental system was set up and the characteristics including the contact anglechanges with variation of applied voltage, saturation of the contact angle, the effect of dielectriclayer thickness, the influence of the hydrophobic layer, contact angle hysteresis, the thresholdvoltage, velocity under different voltages, repeatability of movement and the breakdownphenomenon of dielectric layer were validated.5) With experimental data, the coefficient of the contact line friction and shear resistancewith plates was calculated. Then the predictive value based on improved model was comparedwith experimental data. The main innovatin points including:1) Derivation of the optimal initial volume for droplet movement based on force analysis.In ideal situation, when the radius r of droplet and the length L of square electrode satisfied therelationship of r≤2L, driving force increased with r, while r>2L, the driving force isconstant. With increasing of radius, the droplets might interfere each other and couldn’t becontrolled accurately. In a word, the driving efficient was the best when r=2L.2) In most simulation reported about digital microfluidic system based on EWOD, VODwas adopted to tracking the interface of droplet. Some researchers used level set method to studythe open system and some others discussed the contact angle change with2D model. To theknowledge of author, it hadn’t been reported about simulating the moving and splitting processof droplet with level set method.3) Influence of electrode shape, electrode size and gas between plates were discussed with3D model, and some conclusions were drawn, including: while the threshold voltage ofinterdigital electrodes was a little lower than the square electrodes’, the shape of electrode didn’taffect the average velocity obviously. The splitting velocity grew faster with the decreasing ofdroplet volume. When the volume was fixed and the ratio of droplet the diameter R to gapbetween plates was in the range of6-17, the smaller of ratio, the easier to split. Out this range,splitting would fail if the ratio was smaller and broken daughter droplets were produced if theratio was bigger.4) The contact line friction and shear resistance with plates were taken into account inimproved model, which increased the accuracy of simulation result greatly.5) Laser engraving PCB board was adopted in chip fabrication and the smallest distancebetween lines was about50μm. ITO glass was used as top plate, and a thin film of paryleneabout0.5μm was coating as dielectric layer. Laser engraving PCB method reduced the costgreatly comparing with the clean room processing. Also, the fabrication precision was improvedsignificantly comparing with conventional PCB. It might lead a new way to relative low-cost andhigh-precision experiment method.更多还原