题　目: Mechanical Deformation and Adhesion of Electrospun Polymer Fibers

报告人: Shing-Chung Wong

　　　　　Department of Mechanical Engineering，The University of Akron

时　间：2011年5月30日（周一）下午14：30

地　点：李薰楼468会议室

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Mechanical Deformation and Adhesion of Electrospun Polymer Fibers

Shing-Chung Wong

Department of Mechanical Engineering
The University of Akron
Akron, OH44325-3903
Phone: 330-972-8275. Fax: 330-972-6027.
E-mail: swong@uakron.edu

Abstract

Hierarchical structures as inspired from nature, such as the fibrils on insects, induce strong molecular forces as a result of van der Waals (vdW) interactions. The subsequent extraordinary strong adhesion and coordination enable these insects to support body weight and large loads.The phenomenon motivated materials scientists and engineers to fabricate artificial fibrillar adhesives using materials ranging from stiff carbon nanotubes to soft polymers. To leap frog, it is critical to understand the mechanics and mechanisms of fiber-fiber interactions in terms of weak adhesive forces. Adhesion between electrospun polycaprolactone (PCL) microfibers was directly measured for the first time in a cross-cylinder geometry using a nano force tensile tester. The surface roughness of fibers was determined by an atomic force microscopy (AFM) and the structural factors were characterized by differential scanning calorimeter (DSC) and wide angle X-ray diffraction (WAXD). “Pull-off” force was found to be in the order of 10^-6 N and the adhesion energy 190 ± 7 mJ/m². Adhesion increases with decreasing fiber radius. The experimental data are analyzed by the classical Johnson-Kendall-Roberts (JKR) contact mechanics model. Microfiber structural orientation and molecular confinement of fine fibers, which influence the temporary charge distribution on the microfiber surfaces, were found to play an important role on the fiber-fiber adhesion. This work was subsequently extended to hollow fibers prepared by co-axial electrospinning. PCL and piezoelectric polyvinylidene (PVDF) fluoride were electrospun into hollow fibers. The ultimate goal is to fabricate "responsive" fibers in our laboratory.

About the speaker: Dr. Wong graduated in 1995 with an M.S.M.E. at UMass Amherst, working with Shanti V. Nair. Later he joined the group of Yiu-Wing Mai, FRS, at University of Sydney on identifying the roles of maleated block copolymers as a sequence of events in toughening nylon polypropylene blends.　 He later pursued an academic career in Singapore, teaching at the School of Materials Science and Engineering in Nanyang Technological University. He has since graduated 9 masters, 3 PhDs and 6 postdocs and received demonstrable external research funding in excess of $1.8 million as a PI, and an additional $979,029 as a co-PI. In addition to pursuing bio-inspired materials research, he has worked on mechanical behavior and functional properties of polymers, electrospinning, processing-structure-property relationships, coatings, bio- and nano-materials and composites. Dr. Wong has authored and coauthored ~ 60 articles in book, journal and patent literatures. His work is widely cited with a Hirsh index: 15. One of his pioneering papers on graphite nanocomposites was cited well over a hundred times. In 2007 he received the prestigious NSF CAREER award entitled "Electrospinning-Enabled Bio-Inspired Materials Research and Education" from the Program of Materials Processing and Manufacturing.　 He is presently an associate professor with tenure at the University of Akron and an honorary associate professor at the University of Sydney.