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SUMMARY:Flagellated bacterial motility in polymer solutions - Dr Vincent A
 . Martinez\, School of Physics and Astronomy\, University of Edinburgh
DTSTART:20150213T140000Z
DTEND:20150213T150000Z
UID:TALK57349@talks.cam.ac.uk
CONTACT:Dr Eileen Nugent
DESCRIPTION:The way microorganisms swim in concentrated polymer solutions 
 has important biomedical implications\, e.g. that is how pathogens invade 
 the mucosal lining of mammal guts. Based on early measurements\, it is wid
 ely believed that the swimming speed of many flagellated bacteria initiall
 y increases when high-molecular weight linear polymers are added to their 
 aqueous medium\, before eventually slowing down at high polymer concentrat
 ions. Pores in the polymer solution were suggested as the explanation. Qua
 ntifying this picture led to a theory that predicted such non-monotonic sp
 eed-concentration curves.\nUsing new\, high-throughput methods for charact
 erising motility\, we have measured the swimming speed and the angular fre
 quency of cell-body rotation of motile Escherichia coli as a function of p
 olymer concentration in polyvinylpyrrolidone (PVP) and Ficoll solutions of
  different molecular weights. We find that non-monotonic speed-concentrati
 on curves are the result of low-molecular weight impurities. Removing such
  impurities by dialysis allows us to observe two distinct behaviors in New
 tonian and Non-Newtonian solutions. Results at low molecular weight can be
  explained by Newtonian hydrodynamic theory\, which brings about striking 
 data collapse at different molecular weights. There is clear evidence for 
 non-Newtonian effects in the highest molecular weight PVP solution suggest
 ing that flagella can be seen as `nano-rheometers' for probing the non-New
 tonian behavior of polymer solutions on a molecular scale.\n
LOCATION:Small Lecture Theatre\, Cavendish Laboratory
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