Molecular Visualization: Spreading Kinematics and Dynamics Sergei S. Sheiko, UNC Chapel Hill, DMR-0306787

1. Molecular Visualization: Spreading Kinematics and DynamicsSergei S. Sheiko, UNC Chapel Hill, DMR-0306787 a Our research program develops a molecular-level understanding of spreading phenomena in thin films by visualizing individual molecules during flow.1,2 Our findings impacts microfluidics, lubrication, and surface coatings. Recently, we have discovered a dramatic phenomenon that wetting can induce scission of covalent bonds within branched macromolecules as they spread on a substrate.3 The macromolecule’s destruction occurs because its side chains stretch the polymer backbone to maximize the number of contacts with the substrate. This discovery opens intriguing opportunities for the design of macromolecules that induce tension and fracture on surfaces in a specific way. 1Phys. Rev. Lett. 93, 206103/1-4 (2004) 2Phys. Rev. Lett. 94, 237801/1-4 (2005) 3 Nature440, 191-194(2006) b Adsorption-induced degradation of macromolecules. (a) The molecular degradation of brush-like macromolecules with long side chains (n=140)was monitored using AFM after each sample was exposed for different time periods to a water/propanol (99.8/0.2 wt./wt.%) substrate. (b) The number average contour lengths measured after different exposure times t (●) are fitted assuming first-order reaction (solid line). The experimentally determined polydispersity index PDI=Lw/Ln (■) shows good agreement with the computer simulation of the scission process (dashed line).

2. We encourage broad participation of underrepresented groups in scientific research through Summer Pre-Graduate Research Experience (SPGRE), a highly successful program (http://www.ibiblio.org/res/) that attracts undergraduate students nationwide for a nine-week summer research experience. This program provides extensive scientific experience to the students and exposes them to mentors who have careers in science and engineering. As a part of the summer internship, students are required to make a joint presentation with her or his summer advisor at their home university or school. PFPE Mold Master Molecular Visualization: Spreading Kinematics and DynamicsSergei S. Sheiko, UNC Chapel Hill, DMR-0306787 In June-July 2006, Jonathan Alford continued his project on molding of single polymer molecules and block-copolymer micelles, which he had started last summer. The figure below shows a master of 30nm-sized spheres on a solid substrate (left) that were imprinted into a perfluoropolyether (PFPE) mold. Jonathan Alford (undergraduate student from the North Carolina A&T State University) learning AFM with his mentor Sherryl Yu (3rd year graduate student at UNC-CH)