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SUMMARY: Sinking droplet durotaxis\, engulfment and yield phenomena - Anne
  Juel\, University of Manchester
DTSTART:20220520T150000Z
DTEND:20220520T160000Z
UID:TALK173489@talks.cam.ac.uk
CONTACT:Prof. Jerome Neufeld
DESCRIPTION:Durotaxis refers to the spontaneous motion of objects along st
 iffness gradients of the supporting substrate. In droplet durotaxis migrat
 ion occurs down rigidity gradients towards the softer regions of the subst
 rate due to elasto-capillary interaction. We perform experiments in the li
 mit of very soft PDMS substrates\, where the cross-linked matrix of the ge
 l can yield under the capillary stresses exerted by the sessile droplet. W
 e find that the droplet moves towards the softest i.e. deepest parts of th
 e gel layer while also sinking into the gel and that droplet durotaxis is 
 much faster when engulfment is associated with the motion. For comparison\
 , we focus on engulfment of aqueous droplets deposited onto a substrate la
 yer of silicone oil. On substrates with a depth gradient\, we observe qual
 itatively similar behaviour to the sinking durotaxis case. \n \nOn deep la
 yers\, the droplet is ultimately engulfed in the oil layer. This involves 
 rapid submersion of the droplet driven by capillary forces in the oil surf
 ace\, followed by the much slower peeling of the droplet from the interfac
 e to which it is adhered. The later peeling stage is driven by a combinati
 on of geometric constraints at the apparent contact line and gravity pulli
 ng on the droplet. Gravitational effects are therefore essential to comple
 te engulfment\, even for micrometric droplets. Furthermore\, the opposing 
 effects of geometry and gravity result in the longest engulfment times for
  droplets of intermediate size.\n \nFinally\, if time allows\, I will also
  briefly discuss some recent results on the fluidisation of sessile drops 
 of elasto-viscoplastic fluids subject to vertical vibration and how such a
  system may be used to explore nonlinear viscoelastic effects near the yie
 ld threshold.
LOCATION:MR2\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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