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| Home : Bird/Stewart/Lightfoot Programs | |
| Bird/Stewart/Lightfoot Lecture 2005-06 |
Lecture by William B. Russel
Department of Chemical Engineering, Princeton University
This year's BSL Lecture is dedicated to the memory of Warren E. Stewart, who passed away March 27, 2006
Monday, May 1, 2006
Room 1800 Engineering Hall
Lecture at 4:00 p.m.
Refreshments at 3:45 p.m.
An intriguing process, known in some parts as lithographically induced self-assembly (LISA), is initiated by positioning a template parallel to a flat silicon wafer that is coated with a thin polymeric film and then raising the temperature above the glass transition/melting temperature of the film. Electric fields, either natural or imposed, exert a force on the polymer–air interface, placing the film in either tension or compression. This static equilibrium is unstable to disturbances with wavelengths for which the electrostatic force overcomes the surface tension. Flow ensues, generating a pattern in the film with periodicity that generally reflects the characteristic length of the instability. The geometry of the pattern varies according to the nature of the mask, the ratio of the film thickness to the gap, and a number of other parameters. Examples include square or triangular arrays of pillars or concentric rings, depending on the topology of the mask. Under some conditions the inverse appears: circular holes in a continuous polymer film.
Our goal is to create a sound understanding of the mechanism to facilitate the conversion of these microstructures into nano-structures and from modest areas to wafer-scale coverage. The variety of patterns observed in experiments for polymers under both unpatterned and patterned masks stimulated theoretical and numerical analyses that define the role of a linear instability in setting the characteristic length scale and nonlinear effects in selecting the final pattern. In particular, the nonlinear regime involves interactions among different Fourier modes that favor the growth of hexagonal patterns under a featureless mask, in agreement with experimental observations and supported by numerical simulations based on the fully nonlinear model. Furthermore, simulations for longer times reveal several “kinetically stable structures” along the path to the thermodynamically stable state of minimum surface area. Patterns on the mask guide the patterns into conformity with the geometric shape and the spacing preferred by the instability. Finally, we exploit the simulations to design a mask capable of producing large areas of well-ordered patterns.
William B. Russel |
William B. Russel is the A.W. Marks '19 Professor in the Department of Chemical Engineering and Dean of the Graduate School at Princeton University. He joined the faculty at Princeton in 1974 after BA and MChE degrees from Rice University (where he also played baseball), a PhD from Stanford, and a NATO Postdoctoral Fellowship in the Department of Applied Mathematics and Theoretical Physics at Cambridge University. At Princeton he has served as chairman of chemical engineering and director of the Princeton Materials Institute and pursues research in the field of complex fluids. His research includes studies of the crystallization of colloidal dispersions (akin to the formation of opals) in microgravity aboard the Space Shuttle, theory and fabrication of micro-patterns in thin polymer films, and the drying and cracking of paint films. He is the author or coauthor of two books, the Dynamics of Colloidal Systems and Colloidal Dispersions. Sabbaticals have taken him to the Australian National University, the University of Wisconsin, Bristol University, Twente University, and Utrecht University.
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 1950's, 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.
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Copyright 2006 The Board of Regents of the University of Wisconsin System Date last modified: Tuesday, 11-Apr-2006 17:10:09 CDT Date created: 11-Apr-2006 Content by: che@che.wisc.edu Thank you for visiting! |
