Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F59: Recent Advances in Single Polymer DynamicsInvited
|
Hide Abstracts |
Sponsoring Units: DPOLY GSNP Chair: Charles Schroeder, University of Illinois at Urbana–Champaign Room: LACC Petree Hall D |
Tuesday, March 6, 2018 11:15AM - 11:51AM |
F59.00001: Surprises Upon Watching Single Macromolecules in Real Time Invited Speaker: Steve Granick This is the age when one risks rolling back Boltzmann’s advances: what can we learn from inspecting individual molecules in favour of the ensemble-average? I will present 2 examples. Using fluorescence correlation spectroscopy in super-resolution mode (STED-FCS) we find that the enhanced diffusivity of enzymes is a “run-and-tumble” process analogous to that performed by swimming microorganisms, executed in this situation by molecules that lack the decision-making machinery of microorganisms. The result is that enzymes display “anti-chemotaxis” when they turn over substrate; they migrate in the direction of lesser reactant concentration. In a second example, we developed methods to image macromolecules in solution using transmission electron microscopy (TEM) in liquid environments where they display interesting properties because of their motions and relaxations. Our recent work shows that liquid samples wrapped between atomically-thin graphene sheets can be imaged so that macromolecules can be imaged one-by-one in real time. A picture emerges in which simple experiments, performed using new experimental methods, lend insight into important matters relevant to soft matter physics. |
Tuesday, March 6, 2018 11:51AM - 12:27PM |
F59.00002: Low-force single-molecule elasticity of complex polymers Invited Speaker: Omar Saleh Stretching a polymer with a force f introduces a new length scale, the tensile screening length, equal to kT/f. As the stretching force decreases below a piconewton, the tensile screening length increases above a nanometer. This means that low-force single-molecule stretching measurements can sense chain structure and intra-actions on relatively long length scales. I will discuss application of this method to the structure of complex polymer geometries, including polyelectrolytes dominated by long-range electrostatic interactions, and comb polymers whose structure is determined by side-chain repulsions. |
Tuesday, March 6, 2018 12:27PM - 1:03PM |
F59.00003: Microscopic origin of the elastic instabilities during flow of polymer solutions Invited Speaker: Pouyan Boukany Polymeric fluids exhibit a number of intriguing flow phenomena such as vortex formation, die swelling, stress overshoot, and drag reduction when the flow rate exceeds a certain critical value (typically when flow rate is larger than reciprocal of relaxation time of polymeric fluid or Wi >1.0). The exact molecular picture behind many of these complex flow responses is not known yet and it is still under debate. This limits the design, control and optimization of the technological processes related to polymer products. To overcome these technological limitations, it is required to develop novel methods that can relate the macroscopic flow with the molecular conformation. Recently, the direct visualization of stained DNA inside microfluidics provides a unique opportunity for us to create a conceptual framework for nonlinear polymer rheology in the fast flow rate regime (Wi>1.0). For instance, we recently employed single molecule experiments to study the necking and pinch-off dynamics of polymeric droplets by combining microfluidics and single DNA observation. We demonstrated that the individual polymer molecules suddenly stretch from their coiled conformation at the onset of necking. The extensional flow inside the neck is strong enough to stretch polymer chains. Furthermore, we have unraveled the molecular process leading to dead-zone formation during flow of shear thinning polymer solutions through porous media by a similar approach. We believe that these single-molecule experiments allow us to develop a realistic theoretical picture of polymer solutions during flow in porous media. |
Tuesday, March 6, 2018 1:03PM - 1:39PM |
F59.00004: How molecules behave in a squeeze Invited Speaker: Sabrina Leslie How biomolecules behave in a squeeze - whether in response to confining |
Tuesday, March 6, 2018 1:39PM - 2:15PM |
F59.00005: Conformational Averaging as a Route To Understanding Out-of-Equilibrium Polymer Solutions in Flow Invited Speaker: Charles Sing Solution-processing methods typically involve polymer concentrations in the semidilute range, where polymer coils impinge on each other and ‘overlap’. This is particularly true when polymers are driven out-of-equilibrium by strong processing flows, and polymer dimensions are extended in the flow direction. Despite the practical importance of such systems, they are difficult to simulate due to the computational expense required to include hydrodynamic interactions (HI); yet, HI is necessary to capture the correct polymer dynamics. We have developed a new “Conformational Averaging” (CA) method for incorporating HI into semidilute polymer dynamics, in a way inspired by classical theoretical efforts in single-molecule kinetic theory. CA is an iterative procedure that uses an averaged hydrodynamic tensor in Brownian Dynamics simulation, which is used to get a new hydrodynamic tensor averaged over the simulation trajectory. We are able to simulate semidilute solutions rapidly, and explore molecular diffusion and relaxation, as well as hydrodynamic screening. We show standard scaling laws in equilibrium, including how HI screening length behaves as polymer concentration increases. We also demonstrate how polymers stretch in semi dilute solutions under steady-state flow conditions, and how this affects the behavior of hydrodynamic screening. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700