Incorporating Particle-Scale Properties into Powder-Scale Adhesion Descriptions
Stephen Beaudoin and Caralyn Coultas-Mckenney
When a powder comprised of micron-scale particles adheres to a surface, the interplay between the properties of the surface and of each individual particle drive the observed powder-scale behavior. Of interest here are van der Waals forces that are influenced by nanoscale topographical features on the surface and the individual particles, as well as by the micron-scale variations in the shape of the particles. Colloidal probe microscopy studies, complemented by a computational model for the interactions between nano-scale features on the particle and surface, have been used to approximate the likely range of expected van der Waals adhesion interaction forces in such systems. While this approach can describe the adhesion of individual particles reasonably well, it is impractical for describing the complete range of expected behavior when a powder interacts with a surface. There are simply too many topographical variations on the individual particles within the powder to allow a complete description to be developed. To address this concern, an enhanced centrifuge method has been developed which involves measuring the adhesion force between milligram quantities of powder and surfaces of interest and using these measurements to tune a distribution of effective Hamaker constants that capture the effects of nano-scale topographical features on the particles and surface. When these constants are used in idealized models for van der Waals adhesion (perfectly smooth spheres on perfectly flat surfaces), they reproduce the observed van der Waals adhesion force distributions between the real powder and the surface. In this fashion, the enhanced centrifuge method allows particle-scale phenomena to be included in simple models that describe the powder-scale adhesion.
Stephen P. Beaudoin is a Professor in the School of Chemical Engineering at Purdue University, where he also serves as the Director of the Purdue Energetics Research Center (PERC). He received his B.S. from MIT in 1988, his M.S. from the University of Texas at Austin in 1990, and his Ph.D. from North Carolina State University in 1995. All of his degrees are in Chemical Engineering. Beaudoin has published roughly 100 articles in the refereed literature, with a focus on particle and powder adhesion. His work finds applications in explosives detection and optimization, and in microelectronics, food, and pharmaceutical manufacturing. Beaudoin has won the Faculty Early Career Development Award from the National Science Foundation, and has been named a Purdue University Faculty Scholar and Purdue University Provost Fellow (inaugural class). He has won numerous teaching and mentoring awards, including the Purdue University Student Government Teaching Excellence Award (inaugural recipient), the 2015 Outstanding Mentor Award from the Purdue University College of Engineering, the 2017 and 2020 Shreve Prizes for Outstanding Undergraduate Instruction in the School of Chemical Engineering at Purdue, and the 2017 Potter Award for Teaching Excellence from the Purdue College of Engineering. In 2018, Beaudoin was admitted into Purdue’s Teaching Academy. He currently serves as the Leader of the Trace and Vapor Sensors Research Thrust in ALERT (Awareness and Localization of Explosives-Related Threats), a U.S. Department of Homeland Security-sponsored Center of Excellence in Explosives Research.