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SUMMARY:Active trapping of microswimmers in a foam - Florence Elias (Unive
 rsité Paris Diderot)
DTSTART:20200123T130000Z
DTEND:20200123T140000Z
UID:TALK138343@talks.cam.ac.uk
CONTACT:George Fortune
DESCRIPTION:The formation of massive persistent foam at the surface of sea
 water may be observed in various coastlines\, often concomitant with a los
 s of biodiversity in the seawater. In many cases\, the foam has a natural 
 origin and the presence of chemical pollutants is excluded. In this contex
 t\, the hypothesis that the phytoplankton biomass is mechanically retained
  in the foam has been suggested. The capture or sedimentation of solid par
 ticles in a liquid foam has been well studied. Many phytoplankton species\
 , however\, are flagellated\, hence motile.\n\nInspired by this problemati
 c\, we have studied\, in the laboratory\, the impact of the motility of fl
 agellated algae on their sedimentation dynamics within a liquid controlled
  foam. The model unicellular motile algae Clamydomonas rheinardtii (CR) wa
 s incorporated in a bio-compatible foam\, and the number of cells escaping
  the foam at the bottom was measured in time. Comparing the escape dynamic
 s of living and dead CR cells\, we found that living motile CR cells escap
 e from the foam much at a much slower rate than dead cells: after two hour
 s\, up to 60 % of the injected cells may remain blocked in the foam\, whil
 e 95 % of the initial liquid volume in the foam has been drained out of th
 e foam. Microscopic observation of the swimming CR cells in a chamber mimi
 cking the cross-section of foam internal channels revealed that swimming C
 R cells accumulate near channels corners. A theoretical analysis based on 
 the probability density measurements in the micro chambers have shown that
  this trapping at the microscopic scale contributes to explain the macrosc
 opic retention of the microswimmers in the foam.\n
LOCATION:MR12\, Centre for Mathematical Sciences\, Wilberforce Road\, Camb
 ridge
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