COLL 108 |
| Zhiqun Lin, Sung Chul Bae, Yingxi Zhu, and Steve Granick. Departments of Materials Science and Engineering, Chemistry, and Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801 |
| Progress in making definitive connections between the organization of lubricant molecules at surfaces, and subsequent friction behavior, has been impeded by the paucity of methods available to explore molecular packing directly. In this talk we explore two methods designed to explore this question. First, we have constructed a new nanotribometer in which confocal Raman spectroscopy within a surface forces apparatus (SFA) is used to measure directly how molecules orient in molecularly-thin films. Using polarized radiation, we quantify how sliding polydimethylsiloxane (PDMS) causes molecules to align in the direction of shear. Intriguingly, confined chains at rest are also aligned – but in a direction that the system selects randomly, never the same from one experiment to the next. In a second series of experiments designed to explore the connection between friction and molecular packing, we investigate how friction in an SFA depends on the method used to produce single crystals of atomically-smooth mica. After surveying a large number of confined molecular fluids, we conclude that when mica is prepared without using a hot platinum wire to cut it to size, minimal viscosity enhancement is observed except for films of thickness 1-2 molecular dimensions. The exceptions are bis-2-ethylhexylsebacate and pentamethylheptane. We discuss tentatively why, using this new method to prepare mica for SFA experiments, these glass-forming liquids show viscosity enhanced by more than 6 orders of magnitude but other liquids display remarkable superlubricity.
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Friction, Lubrication, and Adhesion in Micro- and Nano-Scale Devices
8:30 AM-12:00 PM, Monday, March 29, 2004 Marriott -- Orange County 5, Oral
Division of Colloid and Surface Chemistry |