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SUMMARY:Mixed active-passive suspensions: from particle entrainment to dem
 ixing - Marco Polin\, University of Warwick
DTSTART:20220513T150000Z
DTEND:20220513T160000Z
UID:TALK173483@talks.cam.ac.uk
CONTACT:Prof. Jerome Neufeld
DESCRIPTION:Understanding the properties of active matter is a challenge w
 hich is currently driving a rapid growth in soft- and bio-physics.  Some o
 f the most important examples of active matter are at the microscale\, and
  include active colloids and suspensions of microorganisms\, both as a sim
 ple active fluid (single species) and as mixed suspensions of active and p
 assive elements. In this last class of systems\, recent experimental and t
 heoretical work has started to provide a window into new phenomena includi
 ng activity-induced depletion interactions\, phase separation\, and the po
 ssibility to extract net work from active suspensions. Here I will present
  our work on a paradigmatic example of mixed active-passive system\, where
  the activity is provided by swimming microalgae. Macro- and micro-scopic 
 experiments reveal that microorganism-colloid interactions are dominated b
 y rare close encounters leading to large displacements through direct entr
 ainment. Simulations and theoretical modelling show that the ensuing parti
 cle dynamics can be understood in terms of a simple jump-diffusion process
 \, combining standard diffusion with Poisson-distributed jumps. Entrainmen
 t length can be understood within the framework of Taylor dispersion as a 
 competition between advection by the no-slip surface of the cell body and 
 microparticle diffusion. Building on these results\, we then ask how exter
 nal control of the dynamics of the active component (e.g. induced microswi
 mmer anisotropy/inhomogeneity) can be used to alter the transport of passi
 ve cargo.  As a first step in this direction\, we study the behaviour of m
 ixed active-passive systems in confinement. The resulting spatial inhomoge
 neity in swimmers’ distribution and orientation has a dramatic effect on
  the spatial distribution of passive particles\, with the colloids accumul
 ating either towards the boundaries or towards the bulk of the sample depe
 nding on the size of the container. We show that this can be used to induc
 e the system to de-mix.
LOCATION:MR2\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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