纳米受限流体的介尺度结构及壁面滑移机理

Because of its broad application prospect in membrane separation, nano-confined catalysis, and DNA sequencing, the fluid under nano-confinement has aroused wide attention. The stronger flow resistance originated from the more prominent wall effect is the key problem to be solved. According to the Navier equation, increasing the slip length is an effective way to reduce the mass transfer resistance. However, the current understanding of the wall slip phenomenon is still based on wall friction theory or gas phase gap model, the mechanism of wall slip is not clear. In recent years, people gradually realized that the inhomogeneties of the fluid near the wall were more prominent in nano channels, which provides a new way for further study of the wall slip mechanism. This project is intended to study the variation of the meso-sacle structure of nano-confined fluid using molecular simulation techniques. Introducing the inhomogeneties of the fluid near the wall into the Stokes equation, the theory model correlating the effects of the external field, the wall properties, and the meso-scale structure of nano-confined fluid and the slip distance will be established. On this basis, the methods for controlling the mass transfer resistance of nano-confined fluid by means of changing the geometrical configuration of the confined space, constructing the wall wetting gradient, and adding external field will be explored.

纳米受限流体因在膜分离、限域催化、DNA测序等领域的潜在应用引起了人们的广泛关注，壁面作用突出、流体传质阻力大是亟待解决的关键问题。根据Navier方程，增大滑移距离是减小传质阻力的有效途径，然而，目前对壁面滑移现象的认识仍基于壁面摩擦理论或气相间隙模型，对壁面滑移的机理认识尚不清晰。近年来，人们逐渐认识到，壁面附近流体性质的不均匀性在纳米孔道中更加显著，为深入研究壁面滑移机理提供了一种新的思路。本项目拟采用分子模拟技术深入研究壁面作用下纳米受限流体介尺度结构的变化规律，并将壁面附近流体性质的不均匀性引入Stokes方程，建立外场作用、壁面物化特性及流体介尺度结构等因素共同作用下的滑移距离理论模型。在此基础上，探索通过改变受限空间几何构型、构建壁面浸润梯度、增加辅助外场作用等手段调控纳米受限流体传质阻力的方法。

纳米受限流体因在膜分离、限域催化、DNA测序等领域的潜在应用引起了人们的广泛关注，实现对纳米受限流体滑移距离的调控是解决壁面作用突出、流体传质阻力大的主要途径。本项目采用分子模拟技术系统研究了纳米受限流体的介尺度结构及流动传质特性，建立了纳米受限流体滑移距离及通量模型，归纳了壁面作用、孔道结构、外场等因素的协同作用机制，具体如下：壁面附近异于宏观流体的介尺度有序结构及其对密度、粘度等流体性质的影响是纳米受限流体的主要特征，该介尺度结构仅与壁面润湿性相关；将该介尺度结构导致的密度、粘度等流体性质的不均匀性带入Stokes方程，建立了纳米受限流体的滑移距离及通量模型，揭示了纳米受限流体通量加速现象的微观尺度机理；开发了MD-DPD耦合模拟方法，用于表面接枝聚合物等复杂体系的模拟，建立了滑移距离与聚合物覆盖率、剪切应力之间的关联关系；深入研究了纳米通道内的毛细输运规律及调控机制，阐明了受限流体密度、滑移距离、毛细压力及蒸发速度等因素的协同作用机制；设计了一种基于润湿梯度的纳流二极管，正向润湿梯度可以加速流体而反向润湿梯度则阻碍流体通过。上述研究结果为纳米受限流体传质阻力的调控提供了理论指导。