报告题目：Effect of Chain Architecture on Surface Fluctuations of Polymer Melt Films
报告人：Mark D. Foste 教授
美国Akron大学
报告时间：2012年5月29日（周二）下午2：30-3：30
报告地点：独墅湖校区907号楼1101报告厅
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报告内容：
The dynamics of the thermally stimulated surface height fluctuations in a polymer melt can be profoundly altered by tethering of the chains. One type of tethering is the tethering of one part of a molecule to another part of the same molecular. This is found in both long chain branched polymers and in macrocycles. We have studied the surface height fluctuations with X-ray Photon Correlation Spectroscopy for melts of well-defined, anionically polymerized polystyrenes of various architectures, including linear, 6 arm star, pom-pom, comb and cyclic. For linear chains, the variation of surface relaxation time with in-plane scattering vector can be fit using a hydrodynamic continuum theory (HCT) of thermally stimulated capillary waves with a nonslip boundary condition. Assuming the theory is applicable, apparent viscosities of the films may then be inferred from the XPCS data. For these linear chains, the viscosity inferred from XPCS data in this manner is the same as that measured by conventional bulk rheometry. The HCT does a reasonable job of describing the variation of relaxation time with scattering vector for branched chains also, but only if a viscosity much larger than that of the bulk is assumed. The discrepancy between the viscosity inferred from surface relaxation times using the HCT and that derived from conventional rheometry is different for each of five different long chain branched architectures. However, for densely branched combs and cyclic chains another behavior is found. The alteration of surface dynamics by designing the chain architecture has implications for wetting, friction, and adhesion.
Mark D. Foster教授简介：
Mark Foster earned a B.S. in Chemical Engineering at Washington University in St. Louis in 1981 and studied coal gasification with X-ray scattering for his Ph.D. research under Prof. Klavs Jensen in Chemical Engineering at the University of Minnesota. He then moved into the area of polymer science and accepted a postdoctoral fellowship with Prof. Erhard Fischer at the Max-Planck-Institute for Polymer Research in Mainz, Germany, where he initiated his research in polymer interfaces and performed early measurements of thin films with X-ray reflectivity. Dr. Foster returned to the University of Minnesota to work as a senior postdoctoral researcher with Prof. Frank Bates in the areas of block copolymer films and neutron scattering. He joined the faculty of the Department of Polymer Science at The University of Akron in late 1990, and currently holds the rank of professor, serving also as Associate Dean of the College of Polymer Science and Polymer Engineering and Director of the Akron Global Polymer Academy. His research interests currently include the study of structure and dynamics of polymer interfaces and thin films using various techniques, but particularly X-ray and neutron scattering methods and scanning probe microscopy methods. He has published more than 90 papers in refereed journals, 2 book chapters and 1 patent.
高分子科学与工程系
博彩平台
2012-5-25
