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.
