Regensburg 2016 – scientific programme

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BP: Fachverband Biologische Physik

BP 30: Microswimmers I (Joint Session with DY)

BP 30.2: Talk

Tuesday, March 8, 2016, 10:00–10:15, H47

Meandering liquid crystal droplet swimmers — •Carsten Krüger, Corinna Maass, Christian Bahr, and Stephan Herminghaus — Max Planck Institute for Dynamics and Self-Organization (MPIDS), 37077 Göttingen, Germany

Liquid crystal microswimmers immersed in an aqueous surfactant solution at concentrations above the critical micelle concentration show self-propelled motion. The droplets dissolve into surfactant micelles [1], producing an inhomogeneous surfactant distribution in the continuum, propelling the droplets via Marangoni flows at the interface [2,3].

Below the nematic-isotropic transition we observe regular meandering trajectories, which change to a persistent random walk when the droplets are made isotropic by heating. This offers a unique possibility to tune the swimming behavior. We observe a distortion of the nematic director field, with the central defect pulled towards the droplet apex, but angled away from the direction of motion. This is consistent with a constant torque caused by a distortion of the defect pattern by the external and internal flow fields, acting against the elastic field associated with the nematic order. It also gives rise to the twofold symmetry break required for helical motion, as proposed by theory, e.g. in [4].

We use polarized microscopy to observe defect structures, PIV to image flow fields and are able to track freely moving droplets in 3D with a light sheet setup. [1] K. Peddireddy et al., Langmuir 28, 12426 (2012). [2] S. Herminghaus et al., Soft Matter 10, 7008 (2014). [3] C. C. Maass et al., Annu. Rev. Cond. Mat. 7, in press (2016). [4] H. Crenshaw, Amer. Zool. 36, 608 (1996).