Macromolecular Spreading Sergei S. Sheiko, University of North Carolina at Chapel Hill , DMR 0606086

1. Macromolecular SpreadingSergei S. Sheiko, University of North Carolina at Chapel Hill, DMR 0606086 Our research program develops a molecular-level understanding of polymer spreading through visualization of individual molecules during flow. Our findings impact fluidics, lubrication, and surface coatings. We demonstrated that single brush molecules could be used as sensors of film pressure and friction in flowing monolayers of linear polymer melts.1 Flow-induced conformational changes were compared with static mononlayers by generalizing the Flory theorem for structurally asymmetric mixtures of brushes and chains of the same chemical structure.2 Unlike linear polymer melts, swelling of brushes is controlled not only by the degree of polymerization (DP) of the surrounding linear chains but also by the DP of the brush’s side-chains. We anticipate the utilization of such miniature sensors for probing flow properties on nanometer length scales. 1Adv. Materials 19, in press (2007) 2Phys. Rev. Lett. 99, in press (2007) Single-molecule pressure and friction sensors. AFM micrographs show single pBA brush molecules embedded in a melt of linear pBA. The molecules change conformation due to the pressure gradient within the flowing monolayer. (a) Molecules are coiled in the vicinity of liquid reservoir (melt drop) where the film pressure is high, while they get extended upon approaching at the film edge (b,c). After appropriate calibration, the visualized pressure gradient gives friction coefficient between the melt and substrate.

2. We have been involved in organization of science clubs at local schools including lectures and lab tours. Through the DMR project we raised this collaboration to a new level by involving 9-12 grade students as active participants into the proposed research program. Our goal is to identify and nurture prospective scientists. The students will be trained to carry out a full cycle of research activities including experiments, data analysis, weekly reports, and group seminars. In Summer 2006, our lab was fortunate to have Gregory Rubinstein from the Chapel Hill High School. The results of this experience were fantastic and truly surprising. After 3 months of passionate work, Gregory’s project culminated in a full paper in Phys. Rev. Lett. Gregory and his mentor Frank Sun (4th year GS) experimentally verified the Flory theorem for structurally asymmetric polymer mixtures that predicts three conformational regimes of a brush-like macromolecule embedded in a melt of linear chains. In 2007, Gregory was admitted as an undergraduate student to the California Institute of Technology. Macromolecular SpreadingSergei S. Sheiko, University of North Carolina at Chapel Hill, DMR 0606086 Gregory Rubinstein (12th grade, Chapel Hill High School) found three distinct conformational regimes of single molecular brush embedded in a melt of linear chains of the same chemical structure.