Control of initiation, rate, and routing of spontaneous capillary-driven flow of liquid droplets through microfluidic channels on SlipChip.
Control of initiation, rate, and routing of spontaneous capillary-driven flow of liquid droplets through microfluidic channels on SlipChip.
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DOI：
10.1021/la204399m
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发表时间：
2012-01-24
期刊：
影响因子：
--
通讯作者：
Ismagilov RF
中科院分区：
文献类型：
--
作者：
Pompano RR;Platt CE;Karymov MA;Ismagilov RF
本文介绍了利用毛细压力来启动和控制流经微流控通道的液液自发性流动的速度。与外部压力驱动的流动相比，毛细压力驱动的流动由界面现象主导，并且对流体和通道的化学成分和几何形状非常敏感。在疏水芯片上，毛细管力的逐步变化是通过将包含水滴的浅通道滑动到填充了不混溶油的略深的通道上来启动的。这一作用导致液滴自发流入更深的通道。基于净毛细管力与粘性流动阻力的平衡，以液-液表面张力、三相水-油表面接触线上的推进和后退接触角以及装置的几何形状为输入，建立了一个预测自流速度的模型。定量了接触角滞后、润滑层的存在或不存在以及表面活性化合物在液-液或液-固界面上的吸附的影响。得到了两种流型，并对两种流型进行了定量模拟，其中较快的流型(mm/S)是在油被流动的水溶液置换后可以通过连通的通道逃逸时获得的，而较慢的流型(微米/S)是在漏油主要限制在滑片之间的μm尺度间隙时获得的(“死端流”)。润滑层的破裂(使人想起Cassie-Wenzel转变)被认为是模型和实验之间存在差异的原因。稀盐溶液和复杂的生物溶液，如人体血浆，都可以使用这种方法流动。我们预计，在不需要外部电源、阀门或泵的微流体应用中，包括SlipChip和其他基于液滴或插头的微流体设备中，由毛细压力驱动的流动将有助于流量的设计和操作。此外，该方法可作为评价界面张力、接触角和芯片上润湿现象的一种灵敏方法。
This paper describes the use of capillary pressure to initiate and control the rate of spontaneous liquid-liquid flow through microfluidic channels. In contrast to flow driven by external pressure, flow driven by capillary pressure is dominated by interfacial phenomena and is exquisitely sensitive to the chemical composition and geometry of the fluids and channels. A step-wise change in capillary force was initiated on a hydrophobic SlipChip by slipping a shallow channel containing an aqueous droplet into contact with a slightly deeper channel filled with immiscible oil. This action induced spontaneous flow of the droplet into the deeper channel. A model predicting the rate of spontaneous flow was developed based on the balance of net capillary force with viscous flow resistance, using as inputs the liquid-liquid surface tension, the advancing and receding contact angles at the three-phase aqueous-oil-surface contact line, and the geometry of the devices. The impact of contact angle hysteresis, the presence or absence of a lubricating oil layer, and adsorption of surface-active compounds at liquid-liquid or liquid-solid interfaces were quantified. Two regimes of flow spanning a 104-fold range of flow rates were obtained and modeled quantitatively, with faster (mm/s) flow obtained when oil could escape through connected channels as it was displaced by flowing aqueous solution, and slower (micrometer/s) flow obtained when oil escape was mostly restricted to a μm-scale gap between the plates of the SlipChip (“dead-end flow”). Rupture of the lubricating oil layer (reminiscent of a Cassie-Wenzel transition) was proposed as a cause of discrepancy between the model and the experiment. Both dilute salt solutions and complex biological solutions such as human blood plasma could be flowed using this approach. We anticipate that flow driven by capillary pressure will be useful for design and operation of flow in microfluidic applications that do not require external power, valves, or pumps, including on SlipChip and other droplet- or plug-based microfluidic devices. In addition, this approach may be used as a sensitive method of evaluating interfacial tension, contact angles and wetting phenomena on chip.
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