Department of Energy Systems Research, Ajou University, Suwon 16499, Korea.
Soft Matter. 2017 Aug 30;13(34):5656-5664. doi: 10.1039/c7sm01355h.
Biological samples having viscoelastic properties are frequently tested using microfluidic devices. In addition, viscoelastic fluids such as polymer solutions have been used as a suspending medium to spatially focus particles in microchannels. The occurrence of flow instability even at low Reynolds number is a unique property of viscoelastic fluids. In this study, we report the instability in viscoelastic flow for a channel having a 90° bent geometry, which is a characteristic of many microfluidic devices. Interestingly, we observed that the flow instability in aqueous poly(ethylene oxide) (PEO) solution occurs when the concentration of PEO is as low as 50 ppm. We systematically investigated the effects of the polymer concentration, flow rate, and elasticity number on the flow instability. The results show that the flow is stabilized in shear-thinning fluids, whereas the flow instability is amplified when both elastic and inertial effects are pronounced. We believe that this study is useful to design microfluidic devices such as cell-deformability measurement devices based on viscoelastic particle focusing.
生物样本具有粘弹性，经常使用微流控设备进行测试。此外，粘弹性流体（如聚合物溶液）已被用作悬浮介质，以在微通道中实现颗粒的空间聚焦。即使在低雷诺数下也会发生流动不稳定性，这是粘弹性流体的独特性质。在这项研究中，我们报告了具有 90°弯曲几何形状的通道中粘弹性流动的不稳定性，这是许多微流控设备的特征。有趣的是，我们观察到当聚氧化乙烯（PEO）溶液的浓度低至 50ppm 时，PEO 溶液中的流动不稳定性就会发生。我们系统地研究了聚合物浓度、流速和弹性数对流动不稳定性的影响。结果表明，在剪切变稀流体中可以稳定流动，而当弹性和惯性效应都很明显时，流动不稳定性会加剧。我们相信这项研究对于设计基于粘弹性颗粒聚焦的微流控设备（如细胞变形性测量设备）是有用的。
