| Bird/Stewart/Lightfoot Programs | |
| Bird/Stewart/Lightfoot Lecture, 2008-2009 |
Lecture by Ole Hassager
Department of Chemical and Biochemical Engineering, Technical University of Denmark
Tuesday, April 28, 2009
Room 1610 Engineering Hall
Refreshments at 3:45 p.m.
Lecture at 4:00 p.m.
The nonlinear dynamics and rheology of entangled flexible polymers is an area of both industrial and fundamental interest. Landmark developments by Doi and Edwards and by Curtiss and Bird have laid the foundation for intense research on polymer melt rheology in the last 25 years. The ultimate purpose of this activity is to understand the connection between molecular structure and rheological properties, i.e., to master the field of molecular rheology. However, for entangled polymer systems, progress towards achieving this goal seems to be limited more by a lack of reliable experimental data than by a lack of model developments.
In this talk I will show how the Filament-Stretching Rheometer (FSR) developed at the DTU may be used to produce reliable data on the nonlinear extensional rheology of well defined model polymers. The FSR provides for probing polymer dynamics in a way that is not possible with the more conventional shear rheometry. Shear flows are weak in the sense that particles are separated linearly in time. Extensional flows on the other hand are strong in the sense, that particles are separated exponentially n in time. As a result, extensional flows are much more efficient than shear flows at orienting and stretching flexible chain molecules. It seems to be a generally accepted opinion, that shear rheology is easy and accurate while extensional rheology is more difficult and less reliable. I will show that, especially for highly entangled polymeric melts, the reverse is in fact true. I will present experimental results for model polymers such as monodisperse linear polymers, bi-disperse linear polymers and branched polymers, and I will indicate how the measurements contribute to our understanding of the molecular rheology of entangled polymer systems.
|
|
Ole Hassager is a professor in the Department of Chemical and Biochemical Engineering at the Technical University of Denmark (DTU). He received his M.Sc. at DTU and his Ph.D. from the University of Wisconsin-Madison. His research activities include small scale fluid mechanics, polymer physics and molecular rheology. He is director and founder of the Danish Polymer Center, which promotes interdisciplinary research and teaching in polymer chemistry and engineering. He serves on the editorial boards of the Journal of Non-Newtonian Fluid Mechanics and Rheologica Acta and is a member of the Danish National Research Council and the DTU Academic Council. His academic awards include the Statoil Award for Technical Research, and the Stichting Fund Research Award. He will be the 2009 ESR Weissenberg Award recipient in April 2009.
Professor Hassager coauthored the two-volume treatise Dynamics of Polymeric Liquids with R.B. Bird, R.C. Armstrong and C.F. Curtiss.
As the chemical engineering profession developed in the first half of the 20th century, the concept of “unit operations” arose as the natural organizing principle in educating chemical engineers. Particularly in undergraduate education, underlying theories of mass, momentum and energy transfer were presented only to the extent necessary for a narrow range of applications. Following World War II, chemical engineers moved into a number of new areas in which problem definitions and solutions required a deeper knowledge of the fundamentals of transport phenomena than those provided in the textbooks on unit operations.
In the 1950s, R. Byron Bird, Warren E. Stewart, and Edwin N. Lightfoot stepped forward to develop an undergraduate course at the University of Wisconsin to integrate the teaching of fluid flow, heat transfer, and diffusion. From this beginning, they prepared the landmark textbook, Transport Phenomena, published in 1960 by John Wiley & Sons.
This textbook, referred to by generations of chemical engineers simply as BSL after its authors, would remain in print for 41 years and see five translations. BSL changed fundamentally the organizing principle in chemical engineering curricula worldwide. The enduring strength of BSL is testimony to the vision and attention to detail of its authors.
In “retirement,” the three authors found time to thoroughly revise BSL, the second edition of which appeared in the summer of 2001. With new or revised discussions of such topics as two-phase systems, angular momentum, Taylor dispersion and turbulence, the revision promises to help prepare students well into the 21st century. The BSL Lecture was inaugurated in the fall of 2001 to honor the achievements of these outstanding chemical engineers.
 |
|
Copyright 2009 The Board of Regents of the University of Wisconsin System Date last modified: 19-Mar-2009 Date created: 19-Mar-2009 Content by: che@che.wisc.edu Accessibility Web services |