Experimental and Numerical Studies of Biopolymers Out of Thermodynamic Equilibrium

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Wednesday, November 15, 2017 4:00pm - 5:00pm
Watson CIT - SWIG Boardroom (CIT241)

Derek Stein
Associate Professor of Physics
Associate Professor of Engineering
Brown University

Experimental and Numerical Studies of Biopolymers Out of Thermodynamic Equilibrium

Statistical mechanics away from thermodynamic equilibrium is an important frontier of physics. The subject is challenging because there is no clear way to generalize the state variables and concepts, like entropy, that are so useful for understanding systems at equilibrium. Nonequilibrium physics are vitally important in biology, because equilibrium, as the saying goes, is death.  

In this talk I will describe experiments and simulations which explored one of the few nonequilibrium phenomena that has been solved analytically. Giant acceleration of diffusion (GAD) is a dynamical phenomenon exhibited by a Brownian particle in a tilted periodic potential. The hallmark of GAD is that the effective diffusivity of the particle peaks at a critical value of the tilt, where it can exceed the diffusivity in a uniform potential by orders of magnitude. It was theoretically predicted that Brownian particles conveyed across entropic barriers could also exhibit GAD, but this had not been shown experimentally. The entropic case is remarkable because entropy is not well defined out of equilibrium; entropic barriers can change or even vanish as the system is driven away from equilibrium. In the experiments and computer simulations I will describe, we investigated giant acceleration of diffusion of DNA polymers in well-defined nanofluidic channels with topographic features that create a periodic entropic array barriers.