【作者】 陈小燕；

【导师】 杨基明； 刘扬；

【作者基本信息】 中国科学技术大学 ， 流体力学， 2008， 博士

【摘要】 随着纳米科技的日益发展,迫切需要了解纳米尺度流体特性。本论文采用分子动力学模拟方法,对纳米通道中的流体流动及传质特性进行了研究,主要研究对象为平板形纳米通道、圆孔形纳米通道以及毛细血管壁简化模型等三种纳米通道。首先,以平板形纳米通道内的流体为研究对象,利用平衡态分子动力学模拟研究了其中的流体密度特性,重点考察了通道宽度、整体平均密度以及势函数等因素对流体密度分布的影响,并就密度振荡特性对流量的影响进行了考察。计算过程中,选择纳米通道从几个分子直径到上千个分子直径尺寸。结果表明,流体密度在近壁区会出现振荡,该振荡随流体平均密度增大而加剧;壁面与流体之间的吸引力部分对流体的密度分布影响较大。研究还发现,无论对通道宽度是微观尺度还是宏观尺度的流体系统,近壁区流体密度的振荡一直存在,当密度振荡区域长度与通道特征尺度相比很小时,壁面附近流体密度振荡对整体流体特性的影响基本可以忽略;当密度振荡区域长度与通道特征尺度相当时,壁面附近流体对通道内整体流体的影响强烈,从而导致纳米尺度流体特性发生显著变化。其次,以圆孔形纳米通道内的流体为对象,研究了加速度场、壁面与流体之间作用力对流动的影响,考察的主要信息包括流体的密度分布、速度分布,以及反映综合效果而且易于测量的流量。研究发现,对于憎水性壁面来说,管内远离壁面的相对均匀区的流体密度明显高于平均密度,这一趋势随着管径的减小和平均密度的降低而加剧;同时,对憎水性壁面来说,即使存在比管径小得多的壁面粗糙度,都会对管内流体产生显著的抑制作用;研究中还对整体平均密度不同时流体的流动特性进行了比较并重点考察了流量,发现在相同的加速度场下,存在密度较小而流量反而大的情况。此外,对圆孔形纳米通道中颗粒传输问题进行了简化模拟分析,发现流体与壁面之间的作用力对纳米颗粒在其中的传输影响显著,颗粒在壁面-流体作用力比较弱时会出现壁面吸附现象。最后,针对毛细血管输运问题,在二维简化的基础上,对纳米颗粒在纤维丛中的运动进行了模拟,考察了纳米颗粒通过纤维丛的传输特性。结果表明:在没有纤维丛的情况下,半径大小不同的纳米颗粒的传输特性差别很小,在考虑相应的宏观传输特性的时候,可以不考虑纳米颗粒尺寸大小引起的差别;而有纤维丛时,纳米颗粒的运动行为随其自身尺寸的不同表现出很大的差异,较大的颗粒在运动过程中受纤维丛的阻碍而减缓输运速度。进一步对颗粒群的研究表明,这种尺寸效应对颗粒群来讲更为显著,因为对较大的纳米颗粒来说,多颗粒之间以及颗粒与纤维柱之间的作用大大加剧了对输运的抑制。更多还原

【Abstract】 With the development of modern science and nanotechnology, the behavior of nanoscale fluid has been attracting more and more attention. In this thesis, an investigation based on three types of nanochannel, including slit, pore and a simplified model of microvessel wall, was carried out by using molecular dynamics (MD) simulation.Firstly, a comprehensive investigation on the density properties of confined fluid in nano slit was carried out, in which the density properties was comprehensively investigated by MD simulation, mainly focusing on the effect of channel width, average density and potential on density distribution. And the effect of density distribution on fluid flux was also considered. It was found that: density distribution depends on channel width /average density/potential. No matter nanoscale or macroscale, density oscillation always exists near the wall. With the increase of channel width, oscillation amplitude/length will become stable. The bigger average fluid density, the longer oscillation length. For WCA/LJ fluid, oscillation length is several molecular diameter long. The attraction force takes more effect on density distribution, compared with repulsive part.Furthere more, fluid behavior in nanopore was investigated, focusing on the effect of external force/wall-fluid interaction. We mainly pay attention to density and velocity distribution. At the same time, a comparison between the flow flux of different average fluid density was also carried out. It was shown that, the fluid of lower average density corresponds to bigger flux. Then the effect of wall roughness of sinusoidal type on flow was considered, which demonstrated that velocity can be apparently suppressed by wall roughness and the effect is stronger for weaker wall-fluid interaction. We also established a simplified model to trace the movement of nano particle, and found the wall-fluid interaction takes effect and the particle will be adsorbed to the wall when the wall-fluid interaction is weak.Finally, the structure of microvessel wall was simplified and the permeable characteristics of nano-particle in microvessel wall were investigated by molecular dynamics simulation. The study is focused on the effect of particle size on transport properties. Traces of particles with different radius was recorded and compared. The result shows size effect must be considered when considering the problem of microvessel permeability. To our knowledge, we reproduce the transport of colloidal particles in the presence of fiber matrix for the first time, which is helpful to understand drug delivery in microvessel.更多还原