二维超顺磁胶体的摩擦特性研究

发布时间：2018-09-11 20:56

【摘要】：随着技术的提高和介观物理的发展,介观尺度下材料的摩擦特性,尤其是介观尺度活动部件的界面摩擦特性,引起了实验和理论研究工作者的广泛关注。系统研究介观尺度下界面的摩擦特性对于微型精密仪器的精确控制以及生物医药的靶向输运有着重要意义。本文第1章首先对宏观摩擦、介观摩擦、以及原子分子尺度摩擦进行概述。第2章简单介绍两种典型的超顺磁界面润滑材料。一种是磁流变液。由于良好的抗磨损性使磁流变液广泛应用于传动元件之间,并在仿生学中用来模拟人体手臂关节等运动。另一种是活性磁化胶体。活性胶体已成为近年来研究的热点,研究其摩擦特性能帮助我们实现活性胶体在介观尺度的自主、可控运输,并将这种机制运用于工程运用,如精确诊断、药物运输以及微型机构对血管骨骼的简单处理。本文在第3章利用郎之万分子动力学,以无序钉扎衬底上二维磁流变液和活性磁化胶体模拟介观尺度下两种超顺磁界面胶体润滑材料,并系统研究无序钉扎强度、磁场强度以及温度等因素对平均摩擦力和最大静摩擦力的影响。通过对平均静摩擦力的系统研究,发现:(1)弱钉扎下,系统会出现有序结构(磁流变液系统出现长链,活性磁化胶体系统出现岛状),平均摩擦力可以忽略,呈现出超润滑现象;随着钉扎强度的增加,系统有序结构完全被破坏,平均摩擦力出现,并随钉扎强度线性增加。(2)较高的磁场强度会导致磁流变液系统在较强钉扎下仍然维持超润滑状态,而活性磁化胶体系统则相反。(3)温度的升高也会导致出现超润滑现象,即使在强钉扎情况下也有可能出现超润滑现象。通过对最大静摩擦力的系统研究,发现:(1)最大静摩擦力随着衬底钉扎强度的增加而增加。脱钉点附近,磁流变液系统的链状和活性磁化胶体系统的岛状有序微观结构逐渐被破坏,直至消失。(2)磁流变液系统的最大静摩擦力随着磁场强度的增加而减小。脱钉点附近,系统开始出现长链、束链有序结构。当磁场增加到一定强度后,最大静摩擦力几乎不随磁场强度的改变而改变,此时,脱钉点附近开始出现贯穿整个区域的通链。进一步增加磁场强度,最大静摩擦力骤减为零,脱钉点附近的链状结构破碎。活性磁化胶体系统的最大静摩擦力随着磁场强度的增加,先增大后减小(即峰值效应)。脱钉点附近,系统在低场下的岛状有序结构随着磁场强度的增加逐渐消失。当磁场增加到一定强度(峰值处的值)后,进一步增加磁场强度,脱钉点附近,系统又由塑性无序结构逐渐转变为有序晶体结构。(3)升高温度,最大静摩擦力降低。脱钉点附近,低温下,随着温度的提升,系统形成更加有序的微观结构(磁流变液系统出现长链和束链;活性磁化胶体系统出现岛状)。进一步升高温度,有序结构反而被破坏,这是由于温度引起的热涨落与无序钉扎竞争的结果。这种热涨落与衬底钉扎的竞争关系在低钉扎强度时表现得尤为明显。上述结果对于研究外场等因素对介观器件摩擦特性的影响以及介观可控运输等提供理论指导。
[Abstract]:With the improvement of technology and the development of mesoscopic physics, the friction properties of materials at mesoscopic scale, especially the interfacial friction properties of mesoscopic moving parts, have attracted extensive attention of experimental and theoretical researchers. In chapter 1, macroscopic friction, mesoscopic friction and atomic-molecular scale friction are summarized. In chapter 2, two typical superparamagnetic interfacial lubricating materials are briefly introduced. One is magnetorheological fluid (MRF). Active colloids have become a hot research topic in recent years. The study of their friction properties can help us realize the autonomous and controllable transport of active colloids at mesoscopic scale, and apply this mechanism to engineering applications, such as accurate diagnosis, drug delivery and microcomputer. In Chapter 3, using Langevin molecular dynamics, two superparamagnetic interfacial colloidal lubricating materials on disorderly pinned substrates were simulated by two-dimensional magnetorheological fluids and reactive magnetized colloids at mesoscopic scales. The effects of disorderly pinning strength, magnetic field strength and temperature on average friction and maximum friction were systematically studied. The influence of static friction is studied systematically. It is found that: (1) under weak pinning, the ordered structure (long chain in MRF system and islands in active magnetized colloid system) will appear in the system, and the average friction can be neglected, showing super-lubrication phenomenon; with the increase of pinning strength, the ordered structure of the system will be completely destroyed. (2) Higher magnetic field strength will cause the MRF system to remain super-lubricated under stronger pinning, whereas the reactive magnetized colloid system will remain super-lubricated on the contrary. (3) Higher temperature will also lead to super-lubrication, even in the case of strong pinning. It is found that: (1) the maximum static friction increases with the increase of the pinning strength of the substrate. The island-like ordered microstructure of the chain-like and active magnetized colloidal systems of the magnetorheological fluid system is gradually destroyed near the pinning point until they disappear. (2) The maximum static friction of the magnetorheological fluid system increases with the magnetic field. When the magnetic field increases to a certain strength, the maximum static friction almost does not change with the change of the magnetic field strength. At this time, a through chain appears near the nail removal point. With the further increase of the magnetic field strength, the maximum static friction decreases sharply. The maximum static friction of the active magnetized colloid system increases first and then decreases (i.e. peak effect) with the increase of magnetic field intensity. The island-like ordered structure of the system disappears gradually with the increase of magnetic field intensity near the nail removal point. With the increase of magnetic field intensity, the system gradually transforms from a plastic disordered structure to an ordered crystal structure. (3) With the increase of temperature, the maximum static friction decreases. When the temperature rises further, the ordered structure is destroyed, which is the result of the competition between the thermal fluctuation caused by temperature and disordered pinning. And provide theoretical guidance for mesoscopic controllable transportation.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O648.1

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