"Phase transformations in colloidal alloys" Professor Benjamin Yellen

Phase transformations in colloidal alloys

Abstract: Phase transformations are difficult to characterize at the microscopic level, due to the inability to directly observe individual atomic motions.  Model colloidal systems, by contrast, permit the direct observation of individual particle dynamics and their collective rearrangements, which allows for real-space characterization of phase transitions.  Being sufficiently small to form thermally equilibriated phases at room temperature, but large enough for individual particle tracking, colloidal particles have been widely used to study system both near and far from equilibrium, including crystal growth mechanisms, melting in confined and unconfined geometries, and a few types of solid-solid phase transformations.  However, there has been less work on blends of different types of colloidal particles, which are similar to material alloys.  In this talk, I will provide an overview of the structures that we have observed in two-dimensional alloys of magnetic and nonmagnetic spheres confined inside a thin fluid film of ferrofluid.   The interactions between particles can be controlled with the strength and direction of an external magnetic field, which allow us to analyze melting transitions, and solid/solid martensitic phase transformations.  I will also discuss some recent unpublished work on processes that are far from equilibrium, including phase separation dynamics and mixing phenomena.

About the Speaker: Benjamin Yellen is an Associate Professor in the Department of Mechanical Engineering and Materials Science at Duke University, Durham, NC. Yellen received a BS in Chemistry in 1998 from Emory University, Atlanta, GA, and a PhD in Electrical & Computer Engineering in 2004 from Drexel University, Philadelphia, PA.  Yellen’s research lies at the intersection of electromagnetics, colloids and surface science, nonlinear dynamics and controls, with a focus on materials science, and life science applications.  During his academic career, Yellen has published more than 50 papers in various applied physics and engineering journals.  He has received funding from NSF, DARPA, and NIH to support his research on magnetic mechanisms for controlling large degree of freedom systems. 

http://www.mems.duke.edu/faculty/benjamin-yellen