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DY: Fachverband Dynamik und Statistische Physik

DY 21: Pattern Formation

DY 21.5: Vortrag

Mittwoch, 2. April 2014, 16:00–16:15, HÜL 186

Phase separation by Marangoni flow drives active droplet — •Max Schmitt and Holger Stark — Institut für Theoretische Physik, Technische Universität Berlin, 10623 Berlin, Germany

One possible design of a spherical microswimmer is a water droplet in an oil phase with surfactants at the interface [1]. Bromine inside the droplets catalyzes a reaction, which saturates the double bond in the surfactant molecule, making it a weaker surfactant with a higher surface tension. The resulting binary mixture of surfactants will then demix due to Marangoni flow, initiated by and directed along a surface tension gradient. Thus a so-called squirmer results, which reaches a steady swimming state, when the surface is covered with only two domains that cannot demix any further.

We have extended our recently developed model based on a reaction-advection-diffusion equation for the surfactant mixture on an axisymmetric sphere [2], by considering a sphere without axisymmetry and by adding thermal noise. This allows us to trace back the random walk of the squirmer visible in its swimming trajectory to local fluctuations in the surfactant mixture. Furthermore, we investigate the time-dependence of the coarsening dynamics of the surfactant mixture and compare it to results from the classical Cahn-Hilliard theory for phase separation.

[1] Thutupalli S. et al New J. Phys. 13 073021 (2011)

[2] Schmitt M. and Stark H., Europhys. Lett. 101 44008 (2013)