依赖于壁面电荷的壁面滑移对微通道内压力驱动粘弹性流体流动的影响

With the development of micro total ananysis system (µTAS) and micro electro mechanical system (MEMS), microfluid actuation and manipulation techniques have gained considerable attention. In microfluidic system, pressure gradient is often used to propel and manipulate the working fluid in microchannel. Microfluidic system has many applications in biology, medicine and chemistry. Many fluids in biology, medicine and chemistry are non-Newtonian fluids. New phenomena different from those in macroflow, such as electroviscous effect and wall slip, emerge in microflow due to the decrease of characteristic scale of microchannel. Although electroviscous effect and wall-slip effect have been widely studied, a few studies have considered the effect of surface charge on wall slip. We will use integral transform method and variable separation method to investigate the effects of surface-dependent wall slip on pressure driven flow and electrokinetic energy conversion efficiency of viscoelastic fluids in microchannels. This work can advance our understanding of the interactions between surface charge, wall slip, electroviscous effect, electric double layer, fractional viscoelastic fluid parameters (relaxation time, retardation time, order of fractional derivative) and flow fields and provide a foundational basis for the design, optimization and development of the microfluidic devices.

随着微全分析系统(µTAS)和微机电系统(MEMS)的发展，微流体的驱动和控制技术备受关注。微流控系统通常利用压力梯度来驱动并控制微通道内流体流动。微流控系统已在生物、医学和化学等领域获得了重要的应用。生物、医学和化学中大多数流体都属于非牛顿流体。由于流动特征尺度的变小，微通道间流体流动中会出现不同于常规尺度流动的新现象，如电粘性效应和滑移效应。目前有很多有关电粘性效应和滑移效应的研究，但考虑壁面电荷对壁面滑移的影响的研究少之又少。本项目拟采用积分变换法和分离变量法研究依赖于壁面电荷的壁面滑移对压力驱动粘弹性流体流动及电动能量转换效率的影响，深入了解壁面电荷、壁面滑移、电粘性效应、双电层、分数阶粘弹性流体的相关参数(松弛时间、迟滞时间、分数阶导数的阶数)和流场等的相互作用规律，为微流控设备的设计、优化、发展奠定理论基础。

随着微纳流控技术的发展，微纳通道间电渗流动和压力驱动流动备受关注。本项目研究了依赖于壁面电荷的壁面滑移对纳米通道间压力驱动流动及其能量转换效率的影响和pH-调节的微通道间Maxwell流体的电渗流。结果包括：当滑移长度依赖于壁面电荷时，周期压力驱动流的速度振幅和电动能量转换效率都减小；当壁面电势增加或离子浓度增加时，壁面电荷对流率的影响增加；当频率充分大时，时间周期压力驱动流的能量转换效率大于常压驱动流的能量转换效率；在电粘性效应的作用下，无滑移和滑移流的速度振幅都减小；当管道半径与双电层厚度之比较小时，能量转换效率较大；当振荡频率大时，能量转换效率大；边界滑移能显著提高能量转换效率；溶液pH值影响壁面电荷密度，进而也影响双电层电势分布、溶液离子浓度和溶液体积电荷密度，电渗流的速度分布。这些研究成果为微流控设备的设计和优化提供一定的理论基础。