微流控装置中溶剂转移形成液滴的研究
Droplet Formation via Solvent Shifting in a Microfluidic Device
摘要：
溶剂转移是将非溶剂添加到溶剂/溶质混合物中并萃取溶剂的过程。溶剂和非溶剂是可混溶的。由于溶液过饱和，一部分溶质转变成液滴。本文基于这一过程，研究了微流控装置中液滴的形成及其径向运动，其中射流被注入并流液流中。由于层流，微流体设置使得能够研究径向方向上的扩散传质并获得明确定义的浓度分布。这些分布图与三元相图（TPD）一起给出了关于液滴形成条件以及它们在通道中的径向迁移的条件的详细信息。三元体系由乙醇（溶剂）、去离子水（非溶剂）和二乙烯基苯（溶质）组成。我们采用解析/数值解的扩散方程，以获得浓度分布的组件。我们表明，在所研究的系统中，液滴形成在区域的相图之间的双节线和旋节线，即通过热激活过程。液滴通过溶质Marangoni效应被驱动到通道中心线，但不能显著地渗透到单相区域中，在单相区域中液滴迅速溶解。因此，双节点表面的径向运动将液滴携带到中心线，在中心线处液滴被收集。
英文摘要：
Solvent shifting is a process in which a non-solvent is added to a solvent/solute mixture and extracts the solvent. The solvent and the non-solvent are miscible. Because of solution supersaturation a portion of the solute transforms to droplets. In this paper, based on this process, we present an investigation on droplet formation and their radial motion in a microfluidic device in which a jet is injected in a co-flowing liquid stream. Thanks to the laminar flow, the microfluidic setup enables studying diffusion mass transfer in radial direction and obtaining well-defined concentration distributions. Such profiles together with Ternary Phase Diagram (TPD) give detailed information about the conditions for droplet formation condition as well as their radial migration in the channel. The ternary system is composed of ethanol (solvent), de-ionized water (non-solvent) and divinyle benzene (solute). We employ analytical/numerical solutions of the diffusion equation to obtain concentration profiles of the components. We show that in the system under study droplets are formed in a region of the phase diagram between the binodal and the spinodal, i.e. via a thermally activated process. The droplets are driven to the channel centerline by the solutal Marangoni effect but are not able to significantly penetrate into the single-phase region, where they get rapidly dissolved. Therefore, the radial motion of the binodal surface carries the droplets to the centerline where they get collected.
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