微装置中非牛顿流体流动现象及乳化的研究

Non-Newtonian multi-phase fluids, which are fluids with non-constant viscosities, are ubiquitous and of great importance in industrial productions. The science behind non-Newtonian multi-phase fluid dynamics is highly fascinating and has led to different physical phenomena. Due to the increasingly important applications of microscale non-Newtonian multiphase systems in biomedical engineering, food production, and energy applications, understanding of the unique phenomena observed in microscale systems is urgently needed. Among the various phenomena involving non-Newtonian multiphase fluids, the breakup of non-Newtonian fluid jets into droplets and the dynamics between dripping and jetting are particularly important. With the advances in microfluidic technologies, droplets are shown to be excellent templates for fabrications of microspheres, capsules and other functional materials as well as platform for studying biological processes. The performance of these droplets is often determined by the degree of control over the droplet size and size distributions. A systematic study of non-Newtonian multiphase fluid dynamics will enable control over the formation of the droplets and inspire novel opportunities in these applications...Controlled droplet formation and dispensing of non-Newtonian fluids are challenged by three common properties of the fluids involved, namely, low interfacial tension, high viscosity and changing viscosity. Our group has devised a new approach to address the problem of low interfacial tension and generated unprecedented emulsions based on the understanding. In this project, we will apply our expertise to address the problem of formation of droplets with uniform sizes with highly viscous solutions and with solutions whose viscosity varies with the shear rate. We will carry out the study in microfluidic devices both experimentally and numerically. The rheological model will be proposed and studied according to the appropriate flow properties of common non-Newtonian fluids. Apart from these, we will characterize and analyze the flow patterns regarding different non-Newtonian systems in these micro-devices and demonstrate the generation of monodisperse emulsions with variable but controlled sizes. This will enhance the ability to fabricate functional particles as well as to study important processes using a droplet-based approach for applications ranging from energy to biomedical sciences.

非牛顿流体及以非牛顿流体制备的乳液在我们生活和生产中有着重要的应用价值。非牛顿流体特殊的流变性质及其有趣的物理现象吸引了很多学者对其的研究，但这些研究大都是常规尺度下进行的。近些年，随着以非牛顿流体为流质的微流控体系在生物医学、食品加工等方面的地位日渐增加，开展对微装置内非牛顿流体流动现象的研究显得极其迫切和重要。.在该课题中，我们采用实验和数值模拟相结合的方法，提出了对微尺度下非牛顿流体的流变特性的研究，以及以共轴同向流微流控体系为平台，研究非其流动现象和乳化过程。我们将根据流场的特征对研究的非牛顿流体提出一个合适的流变模型。并将在共轴同向流体系中，对不同的非牛顿流体体系的流动现象进行表征和分析。同时我们还将研究每个非牛顿流体体系乳化过程，并探讨获得尺寸小、分散性好的乳液液滴的方法。这些研究将对我们以乳液液滴为平台对生物医学、能源方面的应用有着重要的价值和意义。

研究非牛顿流体在微流控装置中的流态和乳化行为不仅有助于拓展人们对于非牛顿流体在微管尺度下形变规律的认识，而且还可以将新的乳化技术应用于食品加工和药物胶囊生产等领域。本研究中,我们利用实验和数值模拟相结合的方法，建立了非牛顿流体在共轴同向的微流体管道中的流动模型，分析了从液滴流到射流转变的临界条件。我们发现：区别于牛顿流体在微流体管道中的乳化过程，非牛顿流体从液滴流到射流转变的过程中存在过渡区域，伴随卫星液滴产生。为了促使非牛顿流体以液滴流的模式产生尺寸可控的乳液，我们引入电场和机械振动的方法试图加快乳液产生的速率。结果表明，对于低张力、低粘度的体系，机械振动可加速射流转变成液滴流。然而，实际应用中的非牛顿流体通常具有很高的粘度，机械振动法对此类非牛顿流体并不适用。为了实现对高粘度非牛顿流体的乳化控制，我们采用电喷技术拓宽了液滴流机制的适用范围，制备了尺寸均一可控、成分结构连续可调的乳液。通过改变电场引入方式，我们还实现了对高粘度非牛流体的射流的形态和尺寸的控制，这克服了以往在微流体管道中单纯利用水压为驱动力难以调控高粘度非牛流体变形的问题。最后，我们还将上述技术应用于医药胶囊、细胞载体、液体弹珠和纤维的制备过程中，极大拓展了非牛流体在微尺度下的应用领域。