Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
Lab Chip. 2011 Nov 7;11(21):3603-8. doi: 10.1039/c1lc20534j. Epub 2011 Sep 9.
Droplet microfluidic techniques offer an attractive compromise between the throughput (of i.e. reactions per second) and the number of input/output controls needed to control them. Reduction of the number of controls follows from the confinement to essentially one-dimensional flow of slugs in channels which--in turn--relies heavily on the speed of flow of droplets. This speed is a complicated function of numerous parameters, including the volume of droplets (or length L of slugs), their viscosity μ(d), viscosity μ(c) and rate of flow of the continuous phase, interfacial tension and geometry of the cross-section of the channel. Systematic screens of the impact of these parameters on the speed of droplets remain an open challenge. Here we detail an automated system that screens the speeds of individual droplets at a rate of up to 2000 experiments per hour, with high precision and without human intervention. The results of measurements in channels of square cross-section (of width w = 360 μm) for four different values of the contrast of viscosities λ = μ(d)/μ(c) = 0.3, 1, 3, and 33, wide ranges of values of the capillary number Ca ∈ (10(-4), 10(-1)), and wide ranges of lengths of droplets l = L/w∈ (0.8, 30) show that the speed of droplets depends significantly both on l and on λ. The dependence on Ca is very strong for λ > 1, while it is less important both for λ ≤ 1 and for λ ≫ 1.
液滴微流控技术在通量（即每秒反应次数）和控制所需的输入/输出控制数量之间提供了一个有吸引力的折衷方案。控制数量的减少源于在通道中基本上一维流动的液滴的限制，这反过来又严重依赖于液滴的流动速度。该速度是许多参数的复杂函数，包括液滴的体积（或弹丸的长度 L）、它们的粘度 μ(d)、粘度 μ(c)和连续相的流速、界面张力和通道的横截面几何形状。对这些参数对液滴速度的影响进行系统筛选仍然是一个开放的挑战。在这里，我们详细介绍了一种自动化系统，该系统可以以高达每小时 2000 次实验的速度筛选单个液滴的速度，具有高精度且无需人工干预。在宽度为 w = 360 μm 的方形横截面通道中进行的测量结果表明，对于粘度比 λ = μ(d)/μ(c) = 0.3、1、3 和 33 的四个不同值、毛细数 Ca 的宽范围（10(-4)，10(-1))，以及液滴长度 l = L/w 的宽范围（0.8，30），液滴的速度显著取决于 l 和 λ。对于 λ > 1，速度对 Ca 的依赖性非常强，而对于 λ ≤ 1 和 λ ≫ 1，依赖性都不那么重要。
