表面电荷调制及聚电解质层对微通道内电渗流动和传质/传热的影响

In recent years, micro nanofluidics technique has gained wide applications in biological and medical detection, drug delivery, energy harvesting and the design of heat and mass transfer system. Grafting or adsorbing polyelectrolyte materials onto the inner surfaces of the rigid microchannel and forming polyelectrolyte-grafted (PE-grafted) microchannel, also called soft microchannel, is one of the important means to improve the surface properties. PE-grafted microchannels have been widely used in biosensors, nanoelectronics, new energy and so on. So far, many investigations have been carried out on the flow and the transfer of mass or heat through rigid microchannels. However, theoretical studies on the electroosmotic flow and the transfer of mass and heat through the PE-grafted microchannel in the presence of modulated surface charges have not been carried out. Therefore, in the present proposal, by using variable separation method, integral transform method and finite difference method, the electroosmotic flow and the mass or heat transfer of Newtonian or non-Newtonian fluids through a PE-grafted microchannel in the presence of modulated surface charges will be studied theoretically. The variations of the flow field, the concentration field and the temperature field with relevant parameters will be studied. The influences of the modulated surface charges and polyelectrolyte layer on the electroosmotic flow, the solute diffusion and the heat transfer will be revealed. These results will provide meaningful contrast and suggestion for the experimental study on the transport of biofluids in the future.

近年来，微纳流控技术在生物和医学检测、药物传输、能量转化及热质传输系统的设计等领域得到了广泛应用。将聚电解质材料接枝或吸附在微通道的内壁形成聚电解质层接枝的微通道，也称作柔性微通道，是改善微通道表面性能的重要手段之一，已广泛应用于生物传感器、纳米电子、新能源等领域。目前，通常的刚性微通道内流体的电渗流动和传质传热研究已相对成熟。对于聚电解质层接枝的微通道，考虑表面电荷调制模式的电渗流动和传质传热特性的理论研究尚未开展。本项目拟利用分离变量法、积分变换法和有限差分法，考虑表面电荷调制及聚电解质层的影响，通过理论分析和数值模拟，研究微通道内牛顿/非牛顿流体的电渗流动和传质传热问题，发现流场、浓度场及温度场随相关参数的变化规律，揭示表面电荷调制及聚电解质层对于电渗流动、溶质扩散及热传导过程的影响机理，为开展生物微流体输运机理的实验研究提供有意义的理论参考和建议。

微流控系统中，在流体通道壁面内部添加聚电解质层形成聚电解质层接枝的微通道，是改善微通道表面性能的重要手段之一。在某些实际通道内，固壁表面可能会出现非均匀的壁面电势，形成表面电荷调制模式。本项目对于聚电解质层接枝的微通道，通过理论分析和数值模拟，开展了表面电荷调制模式的电渗流动和热质传输特性的理论研究。在流动过程中，电荷调制的壁面电势将引起垂直方向的速度分量。利用叠加原理，通过引进流函数计算得到速度分布的解析解，进而研究微通道内流体的电渗流动和传质传热问题，考虑表面电荷调制及聚电解质层的双重影响，讨论了流场及温度场随相关参数的变化规律。此外，我们对于非光滑的波纹壁面、壁面滑移及流向势对电渗流和电动能量转化效率的影响也展开了研究工作。结果表明：固壁表面的物理化学效应对流体的输运和控制具有非常重要的影响。