Science and Engineering at The University of Edinburgh

Seminars & Discussions

Week beginning 7 February 2016

Monday 8 Feb 16 - 1:00pm

Lunchtime Seminars

Spatially controlled activity of light-driven E. coli suspensions

Jochen Arlt (University of Edinburgh)

Suspensions of swimming bacteria, such as Escherichia coli, are widely used as model active colloids. But the swimming speed of bacteria normally cannot be easily tuned. However, E. coli can be genetically modified to swim only when illuminated with green light, potentially giving biological active colloids with an externally tuneable speed v. We studied several mutants of E. coli for which their swimming speed can be controlled by the intensity of incident green light and we specially engineered mutants which adjust their speed rapidly in response to changes in intensity. By projecting intensity patterns of light onto a suspension of such bacteria we are then able to spatially control the activity of these suspensions over large length-scales (~1 mm). In order to characterise our active suspensions we introduce a spatially resolved version of Differential Dynamic Microscopy. This allows us to extract key parameters, e.g. swimming speed v, relative changes in local cell density ?/?0 and the fraction of non-motile cells ?. We compare our quantitative findings with theoretical predictions that the local density is inversely proportional to the swimming speed.

Friday 12 Feb 16 - 11:30am

Journal Club

Liquid-Solid Nanofriction and Interfacial Wetting

Authors: Rong An, Liangliang Huang, Yun Long, Berc Kalanyan, Xiaohua Lu, Keith E Gubbins

Speaker: Iva Mansai

Using atomic force microscopy, the nanofriction coefficient was measured systematically for a series of liquids on planar graphite, silica and mica surfaces. This allows us to explore the quantitative interplay between nanofriction at liquid-solid interfaces and interfacial wetting. A corresponding states theory analysis shows that the nanofriction coefficient, µ = dFF/dFN, where FF is the friction force and FN is the normal force, is a function of three dimensionless parameters that reflect the intermolecular forces involved and the structure of the solid substrate. Of these, we show that one parameter in particular, β=ρsΔsσls2, where ρs is the atomic density of the solid, Δs is the spacing between layers of solid atoms, and σls is the molecular diameter that characterizes the liquid-substrate interaction, is very important in determining the friction coefficient. This parameter β, which we term the structure adhesion parameter, provides a measure of the intermolecular interaction between a liquid molecule and the substrate and also of the surface area of contact of the liquid molecule with the substrate. We find a linear dependence of µ on the structure adhesion parameter for the systems studied. We also find that increasing β leads to an increase in the vertical adhesion forces FA (the attractive force exerted by the solid surface on the liquid film). Our quantitative relationship between the nanofriction coefficient and the key parameter β which governs the vertical adhesive strength, opens up an opportunity for describing liquid flows on solid surfaces at the molecular level, with implications for the development of membrane and nanofluidic devices.
Langmuir 32 pages 743-750 (2016)
pdf version

Friday 12 Feb 16 - 11:30am

Journal Club

To be confirmed

Upcoming meetings

Monday 15 Feb 16 - 1:00pm - Room 2511 JCMB

Lunchtime Seminars

To be confirmed

Friday 19 Feb 16 - 11:30am - JCMB 2511

Journal Club

Observation of Gravitational Waves from a Binary Black Hole Merger

Authors: B.P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration)

Speaker: Richard Blythe

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