Microfluidic investigation of gynamical surfactant rearrangement at the water/oil interface during single droplet formation

复杂流体和多相流（如胶体悬浮液、聚合物或乳液）的输送是所有长度尺度的自然过程和工业过程的共同特征。通过利用微流体典型的层流条件，可以实现对一系列流动特性的精确控制。微流体的一个主要好处是通过研究每个单个液滴形成的动力学来研究乳液的形成的可能性。特别地，在液滴形成期间，快速形成新的界面。乳液的稳定性由表面活性剂的存在保证。根据相对大小和与系统的亲和力，表面活性剂分子可以比界面本身产生的速度更快或更慢地向新界面迁移[Kovalchuk，Nowak，Simmons，Langmuir，32（20）：5069-77，2016]，尽管迄今为止还没有进行显微镜研究。对这一现象的研究是迷人的，其意义是非常有趣的，无论是工业和基础科学的原因是重要的。这个博士项目的预期成果之一将是实验研究的形成一个单一的液滴在两相系统（无论是水在油或油在水）在不同的表面活性剂的存在下，通过先进的光学技术。特别是，我们将设计和实现不同的微流体装置，我们将广泛使用光学显微镜和快速相机记录（每秒高达50，000帧），以评估分散相和连续相之间界面行为的差异。速度场将用一种称为幽灵粒子速度测定法的创新技术进行分析[Buzzaccaro等人，物理学评论快报，111，2013; Pirbodaghi，Vigolo等人，实验室芯片，15，2015]。它也将需要进行微流体中的乳液的生成和微流体装置内的单个液滴形成的流体动力学的计算建模的基础研究。

The transport of complex fluids and multiphase flows such as colloidal suspensions, polymers or emulsions is a common feature of natural as well as industrial processes at all length scales. By exploiting laminar flow conditions typical of microfluidics, it is possible to achieve precise control over a range of flow characteristics. One major benefit of microfluidic is the possibility to investigate the formation of emulsions by studying the dynamics of formation of each single droplet. In particular, during droplet formation, a new interface is formed rapidly. The stability of the emulsion is guaranteed by the presence of surfactants. Depending on the relative size and affinity with the system, the surfactant molecules can migrate towards the new interface faster or slower than the speed at which the interface itself is created [Kovalchuk, Nowak, Simmons, Langmuir, 32(20):5069-77, 2016], although no microscopic study has been performed so far. The investigation of this phenomenon is fascinating and the implications are extremely interesting and important for both industrial and fundamental science reasons.One of the expected outputs of this PhD project will be the experimental study of the formation of a single droplet in a two-phase system (either water in oil or oil in water) in the presence of different surfactants by means of advanced optical techniques. In particular, we will design and realize different microfluidic devices, and we will extensively use optical microscopy and fast camera recordings (up to 50,000 frames per second) in order to evaluate differences in the behaviour of the interface between dispersed and continuous phase. The velocity field will be analysed with an innovative technique called Ghost Particle Velocimetry [Buzzaccaro et al., Phys. Rev. Lett., 111, 2013; Pirbodaghi, Vigolo et al., Lab Chip, 15, 2015].It will also be required to perform a fundamental study on the generation of emulsions in microfluidic and the computational modelling of the fluid dynamics of the single droplet formation inside the microfluidic device.