COLL 111 |
| Alice C. De Bellis and Stefan Zauscher. Department of Mechanical Engineering and Materials Science, Duke University, 144 Hudson Hall, Box 90300, Durham, NC 27708 |
| We use atomic force microscopy (AFM) to examine the friction behavior of end-grafted poly(N-isopropylacrylamide) (pNIPAAm) brushes. pNIPAAm is a stimulus-responsive polymer that undergoes a reversible phase transition near 32°C. Using a CH3 functionalized AFM tip, we found that friction increased significantly when the pNIPAAm brush went from an extended to a conformationally collapsed state. This was accompanied by a significant increase in surface roughness, which likely accounts for the unexpected increase in friction. Friction measurements of thin slab-gels in a rotary rheometer showed that the friction coefficient decreased by over one order of magnitude when the gels were collapsed. In this case, the friction reduction likely arises from a change in the state of entanglement of the interacting polymer gel layers. We expect friction between a polymer brush and a polymer brush functionalized colloidal probe to behave similarly. Results from these micro-friction experiments will be presented. The present work is significant because the triggered control of interfacial properties on the nanometer-scale holds promise for actuation and friction control of micrometer-scale devices in aqueous media. |
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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 |