Lucio Isa: Controlling Active Brownian Motion by Feedback
Plats: Kemicentrum, Lecture hall B
Kontakt: peter [dot] schurtenberger [at] fkem1 [dot] lu [dot] se
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A Physical Chemistry seminar by Professor Lucio Isa, Laboratory for Interfaces, Soft Matter and Assembly, Department of Materials, ETH Zurich, Switzerland.
Active Brownian Particles (ABPs) are colloidal objects capable of harvesting energy and converting it into directed propulsion by virtue of their internal asymmetry. In particular, they move ballistically at short times, with a propulsion velocity dependent on the available “fuel”, and diffusively at longer times, when rotational diffusion effectively randomizes the propulsion direction. If control over active trajectories by modulating the speed has already been established, the counterpart, where characteristic reorientation times are controlled, presents more challenges. Naturally, rotational diffusivity is set by temperature and by the geometry of the particle, leaving very little room for modulation. In this talk, I will show two different strategies to control ABPs by modulating rotational diffusivity using feedback. I will first show that we can realize ABPs with internal feedback. By composing active particle clusters comprising thermo-responsive colloids, we can achieve objects that reconfigure and adapt their geometry, and therefore their rotational diffusivity, depending on local temperature changes, e.g. achieved by light absorption. I will then describe the case of active magnetic particles with external feedback. By applying randomly oriented magnetic fields, we can effectively impose rotational diffusivities decoupled from the bath temperature. Moreover, by using real-time tracking of the particle position, we realize landscapes of spatially-varying rotational diffusion with dramatic consequences on particle dynamics. These results indicate that different kinds of feedback open new avenues to control ABPs towards the vision of realizing autonomous micro-devices.