Science and Engineering at The University of Edinburgh

Seminars & Discussions

Week beginning 23 October 2016

Monday 24 Oct 16 - 1:00pm

Lunchtime Seminars

Microfluidic Pumping by Micromolar Salt Concentrations

Joost de Graff (University of Edinburgh)

Moving fluid around on the microscale is not as simple as taking a syringe off the shelf and pushing liquid through, because if you do this, things tend to break. In this talk, a colloidal ion-exchange-resin-based microfluidic pump is introduced and experimentally characterized. It operates in almost deionized water for periods exceeding 24h and effects fluid flows of um/s over hundreds of microns. This fluid flow displays a far-field, power-law decay which is characteristic of two-dimensional (2D) flow when the system is strongly confined in the vertical direction, and of three-dimensional (3D) flow when the system is less confined. Using theory and numerical calculations we show that our observations are consistent with electroosmotic pumping driven by umol/L ionic impurities in the sample cell, revealing the surprising impact of trace amounts of charge carriers. In addition, we explain how the power-law decay of the fluid flow can be understood on the basis of the confinement imposed by the sample cell. These two insights should benefit the design of a new class of microfluidic pumps that operate at low solute concentration.

Friday 28 Oct 16 - 11:30am - JCMB 2511

Journal Club

How Far from Equilibrium Is Active Matter?

Authors: Étienne odor, Cesare Nardini, Michael E. Cates, Julien Tailleur, Paolo Visco, Frédéric van Wijland

Speaker: Martin Evans

Active matter systems are driven out of thermal equilibrium by a lack of generalized Stokes-Einstein relation between injection and dissipation of energy at the microscopic scale. We consider such a system of interacting particles, propelled by persistent noises, and show that, at small but finite persistence time, their dynamics still satisfy a time-reversal symmetry. To do so, we compute perturbatively their steady-state measure and show that, for short persistent times, the entropy production rate vanishes. This endows such systems with an effective fluctuation-dissipation theorem akin to that of thermal equilibrium systems. Last, we show how interacting particle systems with viscous drags and correlated noises can be seen as in equilibrium with a viscoelastic bath but driven out of equilibrium by nonconservative forces, hence providing energetic insight into the departure of active systems from equilibrium.
PRL 117 article 038103 (2016)
pdf version

Upcoming meetings

Monday 31 Oct 16 - 1:00pm - Room 2511

Lunchtime Seminars

To be confirmed

Ana Fialho (University of Edinburgh)

Friday 4 Nov 16 - 11:30am - JCMB 2511

Journal Club

To be confirmed

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