用于数字微流体的液滴内的调谐混合
Tuning Mixing within a Droplet for Digital Microfluidics
摘要：
产生有效混合的策略的设计对于各种应用是至关重要的，特别是使用小的“离散”流体体积（液滴）作为流体载体和微反应器的数字微流体装置。在最近的工作中，我们提出了一种方法，用于生成和控制内部的混合平移球形液滴。这是通过考虑Stokes流的液滴内进行下游，我们叠加时间依赖性（正弦）旋转。所获得的混合是材料线的拉伸和折叠的结果，材料线以指数方式增加试剂之间的表面接触。混合策略依赖于在流动的稳定和非稳定部分之间产生共振，这是通过调节周期性旋转的参数来实现的。在我们的系统中，这样的共振提供了控制液滴内混合区域的位置和尺寸的可能性，这对于制造不均匀的颗粒（例如Janus颗粒）可能是有用的。虽然周期性旋转的周期和振幅起主要作用，但这里通过使用三角函数示出了旋转的特定形状（作为时间的函数）具有较小的影响。这一发现证明了所提出的混合策略的鲁棒性，这是其实验实现的关键点。
英文摘要：
The design of strategies to generate efficient mixing is crucial for a variety of applications, particularly digital microfluidic devices that use small "discrete" fluid volumes (droplets) as fluid carriers and microreactors. In recent work, we have presented an approach for the generation and control of mixing inside a translating spherical droplet. This was accomplished by considering Stokes' flow within a droplet proceeding downstream to which we have superimposed time dependent (sinusoidal) rotation. The mixing obtained is the result of the stretching and folding of material lines which increase exponentially the surface contact between reagents. The mixing strategy relies on the generation of resonances between the steady and the unsteady part of the flow, which is achieved by tuning the parameters of the periodic rotation. Such resonances, in our system, offer the possibility of controlling both the location and the size of the mixing region within the droplet, which may be useful to manufacture inhomogeneous particles (such as Janus particles). While the period and amplitude of the periodic rotation play a major role, it is shown here by using a triangular function that the particular shape of the rotation (as a function of time) has a minor influence. This finding demonstrates the robustness of the proposed mixing strategy, a crucial point for its experimental realization.
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