SP Seminar 11.10 at SISSA: Gomez-Solano

[CM Section]

JOINT ICTP/SISSA STATISTICAL PHYSICS SEMINAR

Wednesday, 11th October - 11:00 am

SISSA, Via Bonomea, room 05

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Speaker: R. Gomez-Solano (University of Konstanz)

Title: Self-propelled Colloidal Particles in Viscoelastic Fluids

Abstract:
The motion of many natural microswimmers, e.g. bacteria and spermatozoa,
commonly takes place in viscoelastic fluids and under confinement close to
solid walls. The understanding of their swimming mechanisms has triggered
a lot of experimental and theoretical work in recent years as well as 
the development
of self-propelled colloidal particles. Although the motion of such synthetic
  microswimmers in Newtonian fluids has been extensively studied, and 
they are
nowadays a paradigm in non-equilibrium soft matter [1], so far only few 
investigations
have focused on the swimming of microorganisms in viscoelastic fluids 
[2]. In our work,
we experimentally investigate the dynamics of spherical colloidal 
microswimmers in
viscoelastic fluids, which are self-propelled by local demixing of a 
critical binary polymer
mixture induced by laser illumination. Unlike the motion in Newtonian 
liquids, we observe
a pronounced enhancement of rotational diffusion with increasing 
particle velocity [3],
thereby revealing an unexpected breakdown of the Stokes-Einstein 
relation for the particle
orientation. We demonstrate that this non-equilibrium effect originates 
from the coupling
between the directed particle motion, and the slow microstructural 
relaxation of the
surrounding fluid [4]. Furthermore, we show that such a coupling gives 
rise to a wealth
of new non-equilibrium phenomena with no counterpart in Newtonian 
liquids, e.g. for
  the particle translational and rotational dynamics close to solid 
walls, as well as for
collective motion in crowded environments.

References:
     [1] C. Bechinger, R. Di Leonardo, H. Lowen, C. Reichhardt, G. 
Volpe, and G. Volpe,
         Rev. Mod. Phys. 88, 045006 (2016).
     [2] A. Patteson, A. Gopinath, and P. E. Arratia, Curr. Opin. 
Colloid Interface Sci., 21, 86 (2016).
    [3] J. R. Gomez-Solano, A. Blokhuis, and C. Bechinger, Phys. Rev. 
Lett. 116, 138301 (2016).
    [4] J. R. Gomez-Solano, and C. Bechinger, New J. Physics 17, 103032 
(2015)