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。由于润滑剂缺乏规则的原子尺度结构并且形成非常薄的层，因此使用标准表征技术难以研究原子尺度的弛豫和流动。然而，最近已经表明，由悬浮在溶剂中的微米大小的球体组成的胶体悬浮液表现出分子系统的许多标志性特征，包括气相、液相和结晶相的形成。这允许使用这样的悬浮液作为模型系统，用于研究原子尺度的润滑现象。研究胶体悬浮液中的润滑具有独特的优势。例如，除了测量摩擦力之外，还可以使用共焦显微镜和计算颗粒跟踪技术来确定颗粒的3D位置和运动。这甚至可以在剪切悬浮液时进行。此外，可以使用光刻机（例如Cornell Nanofabstract Facility可获得的光刻机）来图案化悬浮液所接触的表面。这允许对不同表面结构对润滑流的影响进行建模。 该项目将利用这些能力直接研究为什么润滑膜变得更加粘稠，当表面之间的颗粒少于10层时难以剪切，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，并将在多学科科学的未来职业生涯做好准备。此外，还将组织半年一次的纽约复杂问题讲习班。这些会议将促进来自锡拉丘兹、康奈尔、RIT、通用电气、柯达、康宁和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。研讨会将作为一个很好的机会，分享这个和其他研究项目的成果，并介绍研究生和博士后到当地的学术和工业研究界。

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.