Department of Physics, University of Alberta, Edmonton, T6G 2G7, Canada.
Lab Chip. 2010 Jun 7;10(11):1436-41. doi: 10.1039/b925391b. Epub 2010 Mar 12.
The addition of minute amounts of chemically inert polyacrylamide polymer to liquids results in large instabilities under steady electro-osmotic pumping through 2 : 1 constrictions, demonstrating that laminar flow conditions can be broken in electro-osmotic flow of viscoelastic material. By excluding shear and imposing symmetry we create a platform where only elongational viscoelastic instabilities, and diffusion, affect mixing. In contrast to earlier studies with significant shear that found up to orders of magnitude increase in mixing we find that inclusion of polymers excites large viscoelastic instabilities yet mixing is reduced relative to polymer-free liquids. The absolute decrease in mixing we find is consistent with the understanding that adding polymer increases viscosity while viscoelastic flows progress towards elastic turbulence, a type of mild (Batchelor) turbulence, and indicates that electro-osmotic pumped devices are an ideal platform for studying viscoelastic instabilities without supplementary factors.
向液体中添加微量的化学惰性的聚丙烯酰胺聚合物，会导致在通过 2:1 收缩的稳定电渗流下出现大的不稳定性，这表明在粘弹性材料的电渗流中可以破坏层流条件。通过排除剪切并施加对称条件，我们创建了一个平台，在这个平台上，只有拉伸粘弹性不稳定性和扩散会影响混合。与早期具有显著剪切的研究相比，我们发现混合的增加幅度高达几个数量级，而我们发现聚合物的加入会激发大的粘弹性不稳定性，但与无聚合物的液体相比，混合会减少。我们发现的混合绝对减少与以下理解一致：添加聚合物会增加粘度，而粘弹性流动会朝着弹性湍流（一种温和的（巴切勒）湍流）发展，这表明电渗泵设备是研究粘弹性不稳定性的理想平台，无需额外因素。
