Am 29. November 2016, 15.30 Uhr, im HG 0.20 wird im Physikalischen Kolloquium Herr Dr. Andriy Pototskyy (Swinburne University of Technology, Melbourne, Australia) zu Gast sein.

"Liquid films covered by a carpet of self-propelled surfactant particles"


Colonies of swarming bacteria in a thin layer of a viscous fluid in the presence of dynamically deformable interfaces represent a core part of several fundamental biological and bio-engineering processes, including the spreading of bacterial suspensions and crawling of living cells. Understanding the properties of the bacterial motion in liquid films is vital for the development of novel strategies for the fabrication of biocoating layers. Artificially created layers of living cells have a wide variety of applications in medicine and engineering, serving as prototypes of ”artificial skin”, self-cleaning coatings and biosensors. We consider a colony of self-propelled particles (swimmers) in a thin liquid film resting on a solid plate with deformable liquid-gas interface. The local surface tension of the liquid-gas interface is altered by the local density of swimmers due to the soluto-Marangoni effect. The steady state is characterized by a flat film with a homogeneous density of swimmers. We consider two different instability mechanisms: (i) Firstly, the bottom-heavy swimmers generate an excess normal pressure which “bulges” the interface locally. As a result, fluid flow drifts additional swimmers towards the bulge and the excess pressure increases further. The interface becomes unstable if the stabilizing Marangoni flow towards regions of smaller swimmer concentrations together with the stabilizing translational diffusion are too weak. (ii) Secondly, the instability may be induced by the short-range alignment and longer-range anti-alignment of the swimmers orientations.
We find several instability modes and show that the stability of the steady state is strongly affected by  the rotational diffusivity, the self-propulsion velocity and a nonzero rotation frequency of the circular motion of swimmers. In the nonlinear regime we find square arrays of vortices with either radial, or circular orientation of swimmers, travelling oscillating droplets, stripe-like density states and holes developing in the liquid film.

[1]. Swarming of self-propelled particles on the surface of a thin liquid film, A. Pototsky, U. Thiele and H.
Stark, in book Control of Self-Organizing Nonlinear Systems, Pages: 393-412, Springer-Verlag (2016)
[2]. Mode instabilities and dynamic patterns in a colony of self-propelled surfactant particles covering a
thin liquid layer, A. Pototsky, U. Thiele and H. Stark, Europ. Phys. J. E, 39, 51 (2016)
[3]. Stability of liquid films covered by a carpet of self-propelled surfactant particles, A. Pototsky, U.
Thiele and H. Stark, Phys. Rev. E, 90, 030401(R) (2014)

Einladung zum Sondertermin im Rahmen des Physikalischen Kolloquiums

Termin:Montag, 1. Februar 2016
Zeit: 11.00 Uhr
Ort: Hauptgebäude, Raum HG 4.29

"Optische Kontrolle von Exziton- und Phonon-Zuständen in Halbleiter-Quantenpunktstrukturen"

Prof. Dr. Tilmann Kuhn

Institut für Festkörpertheorie
Westfälische Wilhelms-Universität Münster