Levich Institute Seminar Announcement, 09/10/2013
Tuesday, 09/10/2013
2:00 PM
Steinman Hall, Room #312
(Chemical Engineering Conference Room)

Professor Karen Daniels
North Carolina State University
Department of Physics

"Tiny Sandpiles: Flow-Stabilized Solids in Microfluidics "


Disordered microscopic (Brownian) and macroscopic (granular) particulate matter share many similarities in their geometric structures, yet differ in the inter-particle interactions and the degree to which thermal fluctuations play a role in their statics and dynamics. We have developed a technique for assembling a flow-stabilized solid, formed by flowing a colloidal suspension towards a flat-topped ridge within a microfluidic channel. The resulting heaps are characterized by two distinct phases: a solid-like bulk phase in the interior and a highly fluctuating, liquid-like state which exists along its leading edge. We observe that heaps only form above a critical flow velocity (Peclet number) and that they are destroyed by thermal rearrangements when the flow ceases. The suspension flow-rate determines the heap size via the angle of repose (up to 7 degrees, even though the particles are frictionless). For steady-state heaps, we determine a large linear-elastic regime, and measure the elastic modulus via compressions or expansions due to fluid pressure steps.


Professor Daniels received her PhD in 2002 from Cornell University and spent 2002-5 as a postdoctoral research associate at Duke University. She joined the faculty of North Carolina State University in 2005, and was promoted to Associate Professor in 2011. She was a 2007 recipient of an NSF Faculty Early Career Development Program (CAREER) Award, and a 2011 recipient of an Alexander von Humboldt Fellowship which provided support for a sabbatical leave to the Max Planck Institute for Dynamics and Self-Organization in Göttingen, Germany.


Her main research interests center around experiments on the nonequilibrium and nonlinear dynamics of granular materials, fluids, and gels. These experiments have allowed her lab to address questions of how failure occurs, how non-trivial patterns arise, and what controls the transitions between different classes of behaviors. Several of these studies have used idealized systems to provide insight into biological and geological phenomena.

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