Donaldson Lectures 2005–06
Department of Chemical Engineering, Department of Materials Science, and Department of Biomolecular Science and Engineering
Associate director, Materials Research Laboratory
University of California at Santa Barbara
Adhesion and Friction Forces in Everyday Life
April 6
4:00 p.m., 100 Smith Hall
Reception will follow in Dale Shephard Room, Campus Club
ABSTRACT: If there were no adhesion, we would fall apart; if there were no friction, we would not move forward when we walked, and no sound would come from a violin. We take these forces for granted and make use of them instinctively, without thinking—they are part of our biological makeup. The talk will attempt to to give a readily understandable but scientific background to the origin, history, and present-day understanding of why things stick (adhere) to each other, why they sometimes fall apart, and it will discuss the role of friction and lubrication forces in all of this.
Adhesion and Friction of Surfaces: Recent Nano- and Micro-scale Studies on the Transition from Liquid-like to Solid-like Behavior
April 7
2:30 p.m., 100 Smith Hall
ABSTRACT: Recent experiments using the Surface Forces Apparatus have been conducted on the adhesion and friction of polystyrene (PS) surfaces and films in air. Both cross-linked and uncross-linked PS were studied in the molecular weight range from 590 to 3,000,000, thereby spanning the purely liquid-like to glassy and elastomeric regimes. Our aims were (1) to see whether the adhesion and friction/lubrication forces for liquid PS (T››Tg) are determined by the surface tension and bulk viscosity (they are), and (2) how each of these interactions change on passing through Tg, ending up in the solid state at T‹‹Tg, where adhesive failure and friction are now determined by completely different material properties. We find that the deformation of the surfaces play a very important role in these processes and transitions. Preliminary comparisons will be made with similar experiments conducted on small, non-chain molecules of sugars whose viscosities can change by many orders of magnitude over a narrow temperature range, thereby making them ideal for these kinds of studies.
The lectures are free. For more information contact Professor Ilja Siepmann (612-624-1844 or siepmann@umn.edu) or Professor Joachim V.R. Heberlein (612-625-4538 or jvrh@me.umn.edu).
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