改性对硅胶纳米通道内流体传输特性影响研究

发布时间：2018-01-13 12:32

本文关键词：改性对硅胶纳米通道内流体传输特性影响研究　出处：《中南林业科技大学》2017年硕士论文　论文类型：学位论文

【摘要】：微/纳机电系统是微/纳米技术的重要分支,材料在微/纳机电系统中的性质和行为相对宏观尺度会发生不可忽视的变化。硅胶微粒内部空腔与微粒表面具有纳米级的输送通道,而改性后其通道壁面的化学组成也发生本质上的改变,改性后硅胶纳米通道所具有的“表面效应”会对流体水在纳米通道中的传输行为产生重大影响。因此,研究改性对硅胶纳米通道内流体传输特性的影响,对硅胶改性及其在微纳机电系统中的应用具有一定的理论指导意义。本文基于分子动力学方法建立了纳米流动模型,对流体水在硅胶纳米通道内的密度、速度、偶极取向分布进行模拟计算。分析了流体水与壁面间氢键的形成,并对流体水在纳米通道内的扩散行为和粘度性质进行了研究。首先,研究了改性对硅胶纳米通道润湿性的影响规律。计算了纳米通道内流体水的密度、速度以及电偶极矩取向分布,发现羟基化通道壁面呈强亲水性,而改性后硅烷化通道壁呈强疏水性,流体滑移长度与改性层烷基链长呈线性关系;羟基化纳米通道使得流体水偶极取向较为有序,与水分子间存在较强的氢键作用,而改性后硅烷化通道壁面使得流体水取向角变得相对无序,与水分子无氢键作用。其次,研究了改性对硅胶纳米通道内流体扩散行为的影响。计算了流体水的均方位移与扩散系数,发现流体水在羟基化硅胶纳米通道内的扩散系数远小于在硅烷化纳米通道内的扩散系数,但都要小于体相水,改性后硅胶纳米通道壁面特征的“表面效应”对流体水的传输占主导作用。进一步研究了纳米通道内流体水的局部扩散系数,结果表明纳米通道内流体水的局部扩散系数与其到壁面的距离相关。最后,研究了改性对硅胶纳米通道内流体粘度性质的影响。计算了流体水的粘度值,发现在羟基化硅胶纳米通道内流体的粘度值几乎为体相水的11倍;而改性后硅烷化纳米通道内流体水的粘度值仅为羟基化纳米通道内流体水粘度的1/5左右,约为体相水的2倍,并随着改性程度的增强,流体水在硅烷化纳米通道内的粘度值逐渐减小;进一步探讨了纳米通道内流体局部粘度的分布状况,结果显示纳米通道内流体水的局部粘度值与其到壁面的距离相关。
[Abstract]:Micro / nano electromechanical system is an important branch of micro / nano technology. The properties and behaviors of materials in micro / nano electromechanical systems can not be ignored on a macro scale. There are nano-scale transport channels in the cavity and surface of silica gel particles. The chemical composition of the modified channel wall also changed substantially. The "surface effect" of the modified silica gel nanochannel will have a significant impact on the transport behavior of fluid water in the nanochannel. The effect of modification on the fluid transport characteristics in silica gel nanochannels was studied. It has a certain theoretical significance for the modification of silica gel and its application in micro / nano electromechanical system. Based on the molecular dynamics method, a nano flow model is established, which can be used to determine the density and velocity of water in silica gel nanochannels. The dipole orientation distribution was simulated and the formation of hydrogen bond between fluid water and wall was analyzed. The diffusion behavior and viscosity properties of fluid water in nanochannels were studied. The effect of modification on the wettability of silica gel nanochannels was studied. The density, velocity and electric dipole moment orientation distribution of fluid water in the nanochannels were calculated, and it was found that the hydroxy channel wall was strongly hydrophilic. The hydrophobicity of the modified silanized channel wall and the linear relationship between the fluid slip length and the alkyl chain length of the modified layer were observed. The hydroxy nanochannels make the water dipole orientation of the fluid more orderly and have strong hydrogen bond with the water molecules, while the wall surface of the modified silanized channel makes the water orientation angle of the fluid become relatively disordered. Secondly, the effect of modification on the diffusion behavior of silica gel nanochannels was studied. The mean square displacement and diffusion coefficient of fluid water were calculated. It is found that the diffusion coefficient of water in hydroxylated silica gel nanochannels is much smaller than that in silanized nanochannels, but is smaller than that of bulk phase water. The "surface effect" of the wall characteristics of modified silica gel nanochannels plays a dominant role in the transport of fluid water. The local diffusion coefficient of fluid water in nanochannels is further studied. The results show that the local diffusion coefficient of fluid water in nanochannels is related to the distance from the surface to the wall. Finally, the influence of modification on the viscosity properties of silica gel nanochannels is studied, and the viscosity value of fluid water is calculated. It is found that the viscosity of the hydroxy silica gel nanochannels is almost 11 times that of the bulk water. The viscosity of water in the modified silanized nanochannels was only about 1/5 of that in the hydroxylated nanochannels, about 2 times that of the bulk water, and with the increase of the degree of modification. The viscosity of water decreases gradually in silanized nanochannels. The distribution of the local viscosity of the fluid in the nanochannel is further discussed. The results show that the local viscosity of the fluid water in the nanochannel is related to the distance from the water to the wall.
【学位授予单位】：中南林业科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TH-39;TB383.1

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