Different stages of droplet generation are reported in this paper with two immiscible liquids, silicone oil and deionized water, inside a flow-focusing device for hydrophobic and hydrophilic channel walls. Hydrophobic and hydrophilic channels of identical geometry are compared. In this first set of experiments, the efficacy of the hydrophobic channel is compared with a square cross junction for a continuous oil phase with low viscosity. In the hydrophobic case, the flow-focusing design with a diverging outlet delays jetting and allows for the use of higher flow rate ratios in the squeezing regime. For the hydrophilic case, stable and well-structured droplet and slug generation can be achieved using oil and water, resulting in an inverse emulsion. However, the morphology of the fluid interface displays an unusual behavior compared to that of a hydrophobic microchannel. The droplet generation in the hydrophilic channel occurs following the formation of single and double T-junctions, a phenomenon hitherto unreported in the literature. The results demonstrate that the uncoated hydrophobic channels generate monodisperse droplets at a higher capillary number when compared to the hydrophilic channels.

本文报道了在疏水和亲水通道壁的流动聚焦装置内部，两种不混溶的液体（硅油和去离子水）产生液滴的不同阶段。比较了相同几何形状的疏水和亲水通道。在这第一组实验中，对于低粘度的连续油相，将疏水通道的功效与方形交叉结进行了比较。在疏水性情况下，具有发散出口的集流设计可延迟喷射，并允许在挤压状态下使用更高的流速比。对于亲水性情况，使用油和水可实现稳定且结构良好的液滴和团粒生成，从而形成反相乳液。然而，与疏水微通道相比，流体界面的形态表现出不同寻常的行为。在亲水通道中产生的液滴是在形成单个和两个T型结之后发生的，这是迄今为止文献中未报道的现象。结果表明，与亲水性通道相比，未涂覆的疏水性通道在较高的毛细管数下会产生单分散液滴。