List of Events

MRSEC SEMINARS-EVENTS

MRSEC Seminars are normally held at 4:00 p.m. in Abelson 229, unless otherwise noted. Find Abelson-Bass-Yalem building on the interactive map.



December 19, 2016
Room: Abelson 229
Time: 4 p.m.
Event: MRSEC Seminar
Speaker: Jeffrey Urbach, Professor at Georgetown University
Title: Localized Stress Fluctuations in Shear Thickening Suspensions
Abstract: The mechanical response of solid particles dispersed in a Newtonian fluid exhibits a wide range of nonlinear phenomena including a dramatic increase in viscosity with increasing applied stress. While the bulk rheological response of concentrated suspensions is well documented, there are many open questions about microscopic origins of shear thickening and the role of spatio-temporal fluctuations. We report direct measurements of spatially resolved surface stresses for shear thickening suspensions. Surprisingly, we do not observe a smoothly increasing uniform local stress during continuous shear thickening, a regime where the average viscosity increases smoothly with applied stress.  Instead we find that above a critical stress, there are clearly defined regions of substantially increased local stresses. The high stress regions appear intermittently and are highly dynamic. As the applied stress is increased further, these high stress regions become a larger fraction of the total surface area, and that increase accounts quantitatively for the observed shear thickening. The high stress regions are indicative of high viscosity fluid phases with a viscosity that is nearly independent of shear rate but that increases rapidly with concentration. The characteristic size of the high stress regions is approximately equal to the gap between the rheometer plates, with no observable stress variations on the particle scale. These observations suggest that continuous shear thickening arises from increasingly frequent localized discontinuous transitions from a low viscosity state to a high viscosity state, with the viscosities of the two states only weakly non-Newtonian, but separated by more than an order of magnitude.






January 13, 2016
Room: Rosenstiel Penthouse
Time: 5:30 p.m.
Event: TacoCat Social
*Grad students and postdocs only*


January 19, 2016
Room: Abelson 307
Time: 9:30 a.m.
Event: Executive Committee Meeting






February 10, 2016
Room: Rosenstiel Penthouse
Time: 5:30 p.m.
Event: TacoCat Social
*Grad students and postdocs only*




February 27, 2016
Room: Abelson 307
Time: 9:30 a.m.
Event: Executive Committee Meeting



March 10, 2016
Room: Rosenstiel Penthouse
Time: 5:30 p.m.
Event: TacoCat Social
*Grad students and postdocs only*



March 20, 2016
Room: Abelson 307
Time: 9:30 a.m.
Event: Executive Committee Meeting


April 14, 2016
Room: Rosenstiel Penthouse
Time: 5:30 p.m.
Event: TacoCat Social
*Grad students and postdocs only*



April 24, 2016
Room: Abelson 307
Time: 9:30 a.m.
Event: Executive Committee Meeting

May 12, 2016
Room: Rosenstiel Penthouse
Time: 5:30 p.m.
Event: TacoCat Social
*Grad students and postdocs only*