Avalanche degradation

1. Macromolecular SpreadingSergei S. Sheiko, University of North Carolina at Chapel Hill, DMR 0606086 Avalanche degradation Our research program develops a molecular-level understanding of polymer spreading through visualization of individual molecules during flow. This work impacts fluidics, lubrication, lithography, and surface coatings. For the first time, we have demonstrated that spreading may cause physical degradation of branched macromolecules.1 Scission of covalent bonds occurs during flow as the film tension increases along the flow direction. The effect of the film tension was calibrated by measuring the bond life-time as a function of the surface energy of the substrate.2 The exponential dependence of the rate constant on tension leads to an avalanche-type degradation once the tension exceeds a threshold value. We anticipate the utilization of these unique materials as sensors and bond activators in flowing monolayers. 1Nature Materials to be submitted (2008) 2J. Am. Chem. Soc. 130, 4228 (2008) flow Reservoir Avalanche degradation of flowing macromolecules. AFM micrographs show individual pBA brush molecules as they break during spreading on a mica substrate. The contour length of the flowing molecules drastically reduces at a well-defined distance from the reservoir (drop). The distance is determined by the increase of the film tension along the spreading direction above a threshold value of ~20 mN/m. This film tension results in a chain tension of about 3 nN, which is sufficient to break C-C bonds.

2. We actively participated in organization of the Science Spectrum Symposium "Science on the Edge" for high school students. The goal of this event was to explore the increasingly interdisciplinary nature of the sciences, and specifically, to highlight the new Applied Sciences and Engineering program at the UNC. We were able to reach students and teachers throughout North Carolina and attracted nearly 100 students from 6 schools that attended this Symposium. The two-day event included science lectures, lab tours, and zoom-in exhibits at the Morehead Planetarium. Macromolecular SpreadingSergei S. Sheiko, University of North Carolina at Chapel Hill, DMR 0606086 Welcome to Science Symposium Science on the Edge Tuesday, April 22, 2008 Watching molecules at work: S. S. Sheiko, professor of materials chemistry, will talk about imaging, science, and devices of single molecules