Events Calendar

AME - Department Seminar

Speaker: Chris Hogan, Assistant Professor in the Department of Mechanical Engineering at the University of Minnesota

Talk Title: Nanoparticle-Vapor Association and Dissociation Reactions in the Gas Phase

Abstract: The formation of nanoparticles (nucleation) in gas phase environments is of critical importance in a number of systems, including the ambient atmosphere and modern combustion engines. Unfortunately, prediction of nucleation rates is often not possible, with measured nanoparticle formation and growth rates differing from classical theoretical predictions by several orders of magnitude. In any environment, the rate of nucleation is defined as the net difference between the rate at which vapor molecules collide with and stick to growing nanoscale clusters (association) and the rate at which vapor molecules evaporate (dissociate) from such clusters. Therefore, to improve nucleation rate predictions, detailed study of association and dissociation reactions are necessary. In this talk, two new measurement systems used to examine nanoparticle-vapor molecule association and dissociation will be discussed. The first of these systems consists of a high resolution differential mobility analyzer (DMA) and time-of-flight mass spectrometer (MS), which enables in-series measurement of the collision cross sections and masses of 1-2 nm nanoparticles. Collision cross section measurements are made at atmospheric pressure, controlled vapor molecule (water vapor in the presented cases) concentrations, and controlled temperature. Shifts in the average collision cross section of mass-identified entities can yield the equilibrium binding coefficients of vapor molecules, as well as the Gibbs free energy change, enthalpy change, and entropy change brought about by vapor molecule sorption. The second presented system consists of two DMAs operated in series with a controlled temperature furnace connecting the DMAs. This system is used to examine single atom dissociation from 2-5 nm silver nanoparticles.

Biography: Chris Hogan is a McKnight Land-Grant Assistant Professor in the department of Mechanical Engineering at the University of Minnesota. He received a BS degree in Biological & Environmental Engineering from Cornell University in 2004, and a PhD degree in Energy, Environmental, & Chemical Engineering from Washington University in 2008. After studying as a Postdoctoral Associate at Yale University in 2008-2009, he joined the faculty at the University of Minnesota in July 2009. He is the recipient of the 2011 Sheldon K. Friedlander Award for "Outstanding PhD dissertation in a field of aerosol science and technology." Currently, his laboratory group, the Nanoparticle Physics Laboratory, focuses on the analysis of mass, momentum, and energy transport processes in nanoparticle-laden aerosols and colloids.

Host: Hai Wang

More Info: http://ae-www.usc.edu/seminars/1-23-13-hogan.shtml

Location: Seaver Science Library (SSL) - Room 150

Audiences: Everyone Is Invited

Contact: April Mundy

Event Link: http://ae-www.usc.edu/seminars/1-23-13-hogan.shtml