压力驱动的纳米流体在接枝聚合物刷的微通道内流动特性研究

发布时间：2018-04-21 21:11

本文选题：聚合物刷 + 纳米流体　；参考：《吉林大学》2015年硕士论文

【摘要】：科技文明的迅速发展让越来越多的未知事物走入了人们的视野中，现代机械设计技术和制造工艺的日臻完善也不断改变着人们的生活。纳米流体作为新兴科技研究的代表成果，以其性能良好、制备便捷、用途广泛而越来越多地应用到各行各业中。先前的研究理论充分利用了纳米流体的传热特性，在多种热交换设备中显示出主导地位，随着对微观领域的不断开拓，更多鲜为人知的流体特性被开发出来，纳米流体是一种修正流道的有利工具，观察发现纳米颗粒会在流动中进行无规则运动，抵御颗粒沉降、凝聚和阻塞，其光滑的表面效应和空间小尺寸效应也极大地改善了机器设备的磨损，纳米流体可以保持长时间的平稳流动，不仅改善流动工况，同时还增加液体黏度，达到高效传送的目的。与此同时，高分子聚合物刷通过其独特的空间结构和材料性能也成为现代机械、化学、医疗等领域的研究重点。聚合物刷具有多种丰富的空间形态构象和运动规律，可以随着流体系统宏观性质的改变而做出反应，如光照强度、酸碱性和温度等，同时组成聚合物刷的单体大分子间长程作用力和短程分子势能的交互也为聚合物刷添加了更加多样的变化，在防止蛋白质凝结、润滑和“智能表面”等领域都有突出的应用场合。将纳米流体引入到接枝有聚合物刷的微流道中，纳米流体的流动特性就不再是原先单一的运动规律，聚合物刷扰动下的纳米流体会呈现出新颖的流动特性。二者的结合为是现代技术探索机械特性提供了新路径，两种介质的综合反应也为研究更多新产品提供了思路。通过分子动力学计算机模拟，可以跨越多种实验中难以企及的苛刻条件，简化工作量，并实时观测和读取研究数据信息，为研究纳米流体的流动特性提供了有利条件。本文首先采用分子动力学模拟方法研究压力驱动的纳米流体流动特性，同时微流道表面接枝中性聚合物刷。研究在多种接枝密度和纳米颗粒体积分数的条件下，流体速度变化以及粒子密度分布。随着接枝密度增大，整体速度呈现下降趋势，然而在流道中心速度却快速回升，说明聚合物刷的作用范围局限在靠近墙壁附近。纳米颗粒在流道中心起到了更具决定性的作用，溶液中添加的纳米颗粒越多，流体速度越慢，摩擦阻尼和粘滞效应表现得越强烈。不接枝聚合物刷的纳米流体和不添加纳米颗粒的纯流体作为参考。接枝聚合物刷可以有效地控制纳米流体的速度范围。驱动力的变化同样是一个重要因素，通过向每个粒子施加由大到小的驱动力来研究流动变化，虽然更大的驱动力可以提高流体速度，但是添加纳米颗粒的效果更能有效改变整个溶液的流动特性，其作用程度超过了驱动力的改变。在中性聚合物刷的基础上，进一步研究流道中接枝聚电解质刷后纳米流体的流动性质。接枝密度与纳米颗粒体积分数的变化同样会对流动速度产生巨大的影响力，从边界区域到流道中心稳步升高，并在流道中心趋于重合。水分子与反离子的分布区域依然相对稳定，随接枝密度的变化，聚电解质刷逐步伸展。纳米颗粒的含量越多就会越限制流速并降低。本文继续研究流体系统中的其他粒子作用效果，在添加单一价态的反离子和混合价态反离子后观察流体系统的流速变化，价态越高，则速度会有一定程度的提高，同时低价态的反离子分布范围更加宽泛，吸引了聚电解质刷的伸展，而混合添加不同比例的单价和三价反离子后速度没有明显变化，两种反离子的分布区域则受到静电吸引力的强弱规律而呈现稀疏到密集的分布。研究聚电解质刷的电荷序列对流动速度产生的影响，设定不同序列的电荷状态，并与中性刷对比，流速会随着电量的下降而被抑制减弱，而且单体伸展也有所不同，通过计算刷层高度反映出单体的空间塌缩形态。研究纳米流体的固液界面特性，通过计算得到流体的边界滑移长度和黏度特性以及分析相应的影响因素，接枝了聚合物刷的纳米流体系统会改善原有的流动性质。最后进行一个验证性流动实验，通过制作微流道和聚合物涂层，定性分析系统流量，并以此验证先前的模拟结果，保证研究结论真实可靠。本文使用分子动力学计算方法，采用模拟与实验相结合的研究体系，对接枝聚合物刷的流道中，纳米流体的流动特性进行全面细致的研究，分析了流动速度的变化趋势以及溶剂粒子、反离子和单体等密度变化范围，得到微观视野下纳米流体与聚合物刷结合后的流动效果，为今后二者的结合应用到实际机械设备中奠定了基础，并对微观探究更多流体性能提供了理论依据和技术支持，，具有广泛良好的应用前景。
[Abstract]:The rapid development of scientific and technological civilization has made more and more unknown things into the field of vision. Modern mechanical design technology and manufacturing technology are constantly changing people's life. As the representative achievement of new technology research, nanofluids have been applied to each other more and more with its good performance, convenient preparation, wide use and more and more applications. In all walks of life, the previous research theory made full use of the heat transfer characteristics of nanofluids, showing a dominant position in a variety of heat exchange equipment. With the continuous development of the micro field, more well known fluid characteristics were developed. Nanofluids are a favorable tool for correcting the flow channel. Irregular motion is carried out to resist particle sedimentation, condensation and blocking. The smooth surface effect and small space size effect also greatly improve the wear of the machine equipment. The nanofluid can maintain a long steady flow, not only improve the flow condition, but also increase the viscosity of the liquid body, and achieve the purpose of high efficiency transmission.
At the same time, the polymer brush has become the focus of modern mechanical, chemical, medical and other fields through its unique spatial structure and material properties. The polymer brush has a variety of abundant spatial conformation and motion laws, which can be reacted with the change of the macroscopic properties of the fluid system, such as light intensity, acid-base and temperature. At the same time, the interaction of the long-range force between the monomers and the short range molecular potential energy of the polymer brushes also adds a variety of changes to the polymer brushes. It has prominent applications in the fields of preventing protein condensation, lubrication and "intelligent surface". The flow characteristics of the rice fluid are no longer the original single motion law. The nanofluids under the disturbance of the polymer brush will present a novel flow characteristic. The combination of the two provides a new path for the modern technology to explore the mechanical properties. The comprehensive reaction of the two media provides a way of thinking for the study of more new products. The computer simulation can span the harsh conditions which are difficult to reach in many experiments, simplify the workload, and observe and read the data information in real time. It provides a favorable condition for the study of the flow characteristics of nanofluids.
In this paper, the flow characteristics of pressure driven nanofluids are studied by molecular dynamics simulation. At the same time, a neutral polymer brush is grafted on the surface of the micro channel. The velocity changes and the particle density distribution are studied under the conditions of the grafting density and the volume fraction of nanoparticles. With the increase of the grafting density, the overall velocity decreases. However, the velocity of the flow in the center of the flow path, however, increases rapidly, indicating that the scope of the polymer brush is limited to the vicinity of the wall. The nanoparticles play a more decisive role in the center of the flow channel. The more nano particles are added in the solution, the slower the fluid speed, the stronger the friction damping and viscosity effect. Rice fluid and pure fluid without nanoparticles are used as reference. Graft polymer brushes can effectively control the velocity range of nanofluids. The change of driving force is also an important factor, by applying a large to small driving force to each particle to study the flow change, although the greater driving force can improve the velocity of the fluid. The effect of nano particles can effectively change the flow characteristics of the whole solution, and its extent of action exceeds the change of driving force.
On the basis of neutral polymer brushes, the flow properties of nanofluids after the grafting of polyelectrolyte brushes in the flow channel are further studied. The change of the grafting density and the volume fraction of nanoparticles will also have a great influence on the flow velocity, which increases steadily from the boundary area to the channel center, and tends to coincide in the center of the flow channel. The distribution area of the sub is still relatively stable, with the change of the grafting density, the polyelectrolyte brush extends gradually. The more the content of the nanoparticles will limit the flow rate and decrease. This paper continues to study the effect of other particles in the fluid system, and observe the flow velocity change of the fluid system after the addition of the single valence state reverse ion and the mixed valence state reverse ion. The higher the valence state the higher the valence state, the velocity will be improved to a certain extent. At the same time, the distribution of the reverse ion in the low valence state is more extensive, which attracts the extension of the polyelectrolyte brush, but the velocity of the mixed adding of the different proportion of the monovalent and trivalent ions does not change obviously. The two kinds of reverse ion distribution regions are subject to the strong and weak law of the electrostatic attraction. It is sparse to dense distribution.
The effect of charge sequence on the flow velocity of polyelectrolyte brushes is studied, and the charge state of different sequences is set, and compared with the neutral brush, the flow velocity will be suppressed with the decrease of the quantity of electricity, and the extension of the monomer is also different, and the space collapse form of the monomer is reflected by the calculation of the height of the brush layer.
The characteristics of the solid-liquid interface of nanofluids are studied. The boundary slip length and viscosity characteristics of the fluid are calculated and the corresponding influencing factors are analyzed. The nanofluid system grafted with polymer brushes will improve the original flow properties. Finally, a confirmatory flow experiment is carried out, and the qualitative analysis is made by making the microfluidic and polymer coatings. System flow, and verify the previous simulation results to ensure that the conclusions are true and reliable.
In this paper, the molecular dynamics calculation method is used to study the flow characteristics of the nanofluid in the flow channel of the graft polymer brush. The change trend of the flow velocity and the variation range of the density of the solvent particles, the reverse ion and the monomer are analyzed, and the nanometers in the microscopic field of vision are obtained. The flow effect of the combination of the fluid and the polymer brush has laid a foundation for the application of the two in the future to the actual mechanical equipment, and provides a theoretical basis and technical support for the micro exploration of more fluid performance, and has a broad and good application prospect.

【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1

【参考文献】