Dresden 2011 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 35: Poster: Micro- and Nanofluidics

CPP 35.20: Poster

Mittwoch, 16. März 2011, 17:00–19:00, P2

A model for swimming active droplets — •Maximilian Schmitt¹, Shashi Thutupalli², Holger Stark¹, and Stephan Herminghaus² — ¹Institut für Theoretische Physik, TU Berlin — ²Max-Planck-Institut für Dynamik und Selbstorganisation, Göttingen

In a recent attempt to build an active microswimmer, a micron-sized droplet of bromine water was placed into a surfactant laden oil medium such that the surfactant molecules spontaneously assemble at the droplet interface. Experiments revealed that due to a bromination reaction, the chemical potential of the surfactant (mono-olein) increases causing the surface tension to increase locally. At the same time these surfactants with a higher surface tension are readily replaced by surfactants from the surrounding oil phase. As a result, a steady gradient of surface tension on the droplet is created. Since an interface with higher surface tension pulls more strongly on a surrounding liquid than one with a lower surface tension, the surface tension gradient on the droplet generates the so-called Marangoni flow. Measurements of the flow around a swimming droplet revealed a flow field similar to that of a squirmer, which is a model for a spherical micro-swimmer with prescribed flow velocity on the surface.

In this contribution we construct a first simple model of the swimming mechanism of the active droplets. We establish a reaction-diffusion system on a sphere which comprises the bromination of the surfactants and the flux of new surfactants from the oil phase to the droplet. In a second step we want to simulate the flow field created by the surface-tension gradient and compare it to the measured flow field.