Soft Matter Engineering and Microfluidics Lab, Department of Chemical Engineering, Indian Institute of Technology Ropar, Rupnagar, Punjab, 140001, India.
Sci Rep. 2022 Feb 14;12(1):2395. doi: 10.1038/s41598-022-06202-x.
Many complex fluids such as emulsions, suspensions, biofluids, etc., are routinely encountered in many micro and nanoscale systems. These fluids exhibit non-Newtonian viscoelastic behaviour instead of showing simple Newtonian one. It is often needed to mix such viscoelastic fluids in small-scale micro-systems for further processing and analysis which is often achieved by the application of an external electric field and/or using the electroosmotic flow phenomena. This study proposes a very simple yet efficient strategy to mix such viscoelastic fluids based on extensive numerical simulations. Our proposed setup consists of a straight microchannel with small patches of constant wall zeta potential, which are present on both the top and bottom walls of the microchannel. This heterogeneous zeta potential on the microchannel wall generates local electro-elastic instability and electro-elastic turbulence once the Weissenberg number exceeds a critical value. These instabilities and turbulence, driven by the interaction between the elastic stresses and the streamline curvature present in the system, ultimately lead to a chaotic and unstable flow field, thereby facilitating the mixing of such viscoelastic fluids. In particular, based on our proposed approach, we show how one can use the rheological properties of fluids and associated fluid-mechanical phenomena for their efficient mixing even in a straight microchannel.
许多复杂流体，如乳液、悬浮液、生物流体等，在许多微纳尺度系统中经常遇到。这些流体表现出非牛顿粘性弹性行为，而不是简单的牛顿行为。为了进一步处理和分析，通常需要在小规模微系统中混合这些粘弹性流体，这通常通过施加外部电场和/或利用电渗流现象来实现。本研究提出了一种非常简单但有效的基于广泛数值模拟的混合粘弹性流体的策略。我们提出的设置由一个带有小面积恒定壁面 ζ 电势的直微通道组成，这些小面积的恒定壁面 ζ 电势位于微通道的顶壁和底壁上。一旦魏森贝格数超过临界值，微通道壁上的这种不均匀 ζ 电势就会产生局部电弹性不稳定性和电弹性湍流。这些不稳定性和湍流由系统中存在的弹性应力和流线曲率之间的相互作用驱动，最终导致混沌和不稳定的流场，从而促进了这些粘弹性流体的混合。特别是，基于我们提出的方法，我们展示了如何利用流体的流变性质和相关的流体力现象来实现其有效的混合，即使在直微通道中也是如此。
