Pressure balance at the liquid-liquid interface of micro countercurrent flows in microchips
Pressure balance at the liquid-liquid interface of micro countercurrent flows in microchips
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DOI：
10.1021/ac070031d
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发表时间：
2007-05-15
影响因子：
7.4
通讯作者：
Kitamori, Takehiko
中科院分区：
文献类型：
--
作者：
Aota, Arata;Hibara, Akihide;Kitamori, Takehiko
提出并验证了界面压力平衡模型，以阐明亲水-疏水选择性改性微通道中微逆流的物理机制。我们考虑了微流相分离的条件，其中相分离需要微通道的每个输出中存在单相流。在该压力平衡模型中，由于各相中的压力损失而导致的两相之间的压力差通过由分离相之间的液-液界面处的界面张力产生的拉普拉斯压力来平衡。当两相之间的压力差足够低时，两相之间的接触线被固定在亲水表面和疏水表面之间的边界处。由于接触角被限制在前进接触角和后退接触角之间的值，因此拉普拉斯压力有极限。当两相之间的压差超过极限拉普拉斯压力时，其中一相泄漏到另一相的输出通道中，相分离失败。为了通过实验验证这一物理图像，使用了具有不对称横截面的微芯片，其水力直径分别为19和102μm。在微芯片中，在上限6.9kPa和下限-9.3kPa之间的压差下实现了水-甲苯微逆流的相分离。上限与所提出的模型非常吻合。该模型也适用于并流，因此可用于连续流化学处理中的一般多相微流。
An interfacial pressure balance model was proposed and verified for the elucidation of the physical mechanism of micro countercurrent flow in a hydrophilic-hydrophobic selective-modification microchannel. We considered the conditions of the microflow phase separation, where the phase separation entails a single phase flow in each output of the microchannel. In this pressure balance model, the pressure difference between the two phases due to pressure loss in each phase is balanced by the Laplace pressure generated by the interfacial tension at the liquid-liquid interface between the separated phases. When the pressure difference between the two phases is sufficiently low, the contact line between the two phases is pinned at the boundary between the hydrophilic and the hydrophobic surfaces. Since the contact angle is restricted to values between the advancing and receding contact angles, the Laplace pressure has a limit. When the pressure difference between the two phases exceeds the limiting Laplace pressure, one of the phases leaks into the output channel of the other phase, and the phase separation fails. In order to experimentally verify this physical picture, a microchip with an asymmetric cross section, whose hydraulic diameters were 19 and 102 mu m, was used. In the microchip, a phase separation of a water-toluene micro countercurrent flow was achieved under pressure differences between an upper limit of 6.9 kPa and a lower limit of -9.3 kPa. The upper limit agreed well with the proposed model. The model is also applicable to cocurrent flows, so that it is useful for general multiphase microflows in continuous-flow chemical processing.