Modeling Atomic and Nano Scale Lubrication Phenomena Using Sheared Colloidal Suspensions

了解流体润滑两个表面时所涉及的分子尺度过程仍然是工业和科学上的重要问题。由于润滑油缺乏规则的原子尺度结构，形成的层非常薄，因此很难使用标准表征技术来研究原子尺度的弛豫和流动。然而，最近已经表明，由微米大小的球体组成的胶体悬浮液悬浮在溶剂中，表现出许多分子系统的标志性特征，包括气相、液相和结晶相的形成。这允许使用这种悬浮液作为模型系统来研究原子尺度的润滑现象。研究胶状悬浮液的润滑提供了独特的优势。例如，除了测量摩擦力外，还可以使用共聚焦显微镜和计算粒子跟踪技术确定粒子的3D位置和运动。即使悬架被剪断，这也可以做到。此外，光刻机（如康奈尔纳米制造设施的那些）可用于与悬浮液接触的表面的图案。这允许模拟不同表面结构对润滑流动的影响。该项目将利用这些能力，直接研究为什么当表面之间的颗粒层数少于10层时，润滑膜变得更加粘稠和难以剪切，微观事件如何串通在薄润滑膜中产生粘滑运动，以及不同长度尺度下表面粗糙度的作用。从更广泛的角度来看，这项研究应该会导致新的尚未解决的现象，这些现象与薄膜和涂层的工业处理和制造有关。该项目广泛使用了各种实验技术，包括粒子合成、光刻、共聚焦显微镜以及跟踪和分析算法的开发。因此，研究生将接触到一系列的技术，并为未来在多学科科学领域的职业生涯做好充分的准备。此外，将组织半年一次的纽约复杂问题讲习班。这些会议将激发来自锡拉丘兹、康奈尔、RIT、通用电气、柯达、康宁以及该地区其他机构和工业实验室的软物质和统计物理研究人员之间的互动。研讨会将提供一个很好的机会，让大家分享这个项目和其他研究项目的成果，并向当地的学术和工业研究界介绍研究生和博士后。

Understanding the molecular scale processes entailed when a fluid lubricates two surfaces remains an industrially and scientifically important problem. Because lubricants are devoid of regular atomic scale structure and form layers that are very thin, atomic scale relaxations and flows have been difficult to investigate using standard characterization techniques. Recently however, it has been shown that colloidal suspensions comprised of micron sized spheres suspended in a solvent exhibit many of the hallmark features characteristic of molecular systems including the formation of gaseous, liquid, and crystalline phases. This allows for using such suspensions as model systems for investigating atomic scale lubrication phenomena. Investigating lubrication in colloidal suspensions offers unique advantages. For example, in addition to measuring the friction forces, the 3D positions and motions of the particles can be determined using confocal microscopy and computational particle tracking techniques. This can be done even while the suspension is sheared. In addition photolithography machines such as those available at the Cornell Nanofabrication Facility can be used to pattern surfaces with which the suspension is in contact. This allows for modeling the effects of different surface structures on lubricating flows. This project will take advantage of these capabilities to directly investigate why lubricating films become much more viscous and difficult to shear when there are fewer than 10 layers of particles between the surfaces, how microscopic events collude to produce stick slip motion in thin lubricating films, and the role of surface roughness at different length scales. From a broader prospective the research should lead to new as of yet unaddressed phenomena that have relevance for the industrial handling and fabrication of thin films and coatings. This project makes extensive use of a variety of experimental techniques that include particle synthesis, photolithography, confocal microscopy, and the development of tracking and analysis algorithms. Therefore, graduate students will be exposed to a range of techniques and will be well prepared for future careers in multidisciplinary science. In addition semiannual New York Complex Matter Workshops will be organized. These meetings will stimulate interaction among soft matter and statistical physics researchers from Syracuse, Cornell, RIT, General Electric, Kodak, Corning and other institutions and industrial labs in the area. The workshops will serve as an excellent opportunity for sharing results from this and other research projects and introducing graduate students and post docs to the local academic and industrial research community.