Woodruff School of Mechanical Engineering

GT Courtesy Listing


Equilibrium and Dynamic Forces in Binary Colloidal Mixtures


Prof. John Y. Walz


Virginia Tech


Tuesday, March 9, 2010 at 3:00:00 PM


Love Building, Room 183


Professor Valeria Milam


This talk will describe a modeling and experimental study to better understand the nature of the forces in such systems. Direct measurements of the force between a single microparticle and a planar surface in a well-characterized system, obtained with the atomic force microscope, will be described. This includes both equilibrium forces, in which hydrodynamic interactions between the microparticle and surface are negligible, as well as forces measured at varying approach speeds to determine the impact of the nanoparticles on the separation-depended mobility of the microparticles. The equilibrium measurements show a well-defined oscillatory force profile, resulting from ordering of the nanoparticles in the confined region between the microparticle and surface. The dynamic measurements explored both the effect of microparticle motion on nanoparticle ordering, as well as the effect of the nanoparticles on the microparticle mobility.


John Walz is Professor and Head in the Department of Chemical Engineering at Virginia Tech. After receiving his B.S. degree in chemical engineering from Tulane in 1982, he worked for six years as a process support engineer for Shell Oil Company. In 1988, he left Shell to pursue a Ph.D. in chemical engineering at Carnegie Mellon, where he worked with Dennis Prieve on the development and use of the optical technique, Total Internal Reflection Microscopy, for measuring colloidal interactions. He then spent five years on the chemical engineering faculty at Tulane, followed by eight years on the faculty at Yale, including three years as Department Chairman. In 2005 he moved to Virginia Tech as Department Head. Walz’s research interest are understanding and controlling interfacial forces and colloidal stability, and he has published over 50 peer-reviewed papers and proceedings in these areas. He serves on the Council of the International Association of Colloid and Interface Science and is chairman-elect of the ACS Division of Colloid and Surface Chemistry. He is the recipient of both the CAREER and Research Initiation Awards from NSF, as well as the Arthur Greer Memorial Prize for Research at Yale.