Dresden 2026 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 44: Poster: Active Matter, Soft Matter, and Fluids

DY 44.14: Poster

Wednesday, March 11, 2026, 15:00–18:00, P5

Dynamics of thermophoretic Janus particles in homogeneous light fields — •Samad Mahmoudi, Franziska Michaela Braun, and Regine von Klitzing — Institute of Condensed Matter Physics,TU Darmstadt, Hochschulstraße 8 64289 Darmstadt

We study the thermophoretic motion and orientational dynamics of individual Au-polystyrene Janus particles under uniform laser illumination. Light-driven Janus colloids serve as a model system for active Brownian motion and non-equilibrium transport in soft matter. The particles are illuminated by a defocused, approximately homogeneous laser spot and observed with dark-field microscopy. Image-processing routines in Python yield long-time trajectories, center-of-mass positions and in-plane orientations of the gold cap. From the mean-squared displacement we extract effective self-propulsion velocities and compare them with active Brownian particle models and simple expectations for thermophoretic motion. Our first measurements show that the tracking procedure resolves both translational and rotational motion of single Janus particles and yields thermophoretic velocities in the expected range for micrometer-sized swimmers. In future work, we will use this analysis to study how light gradients and cap design can create transient barriers for Janus particles and control their thermophoretic motion.

Keywords: Janus particles; Thermophoresis; Temperature gradient; Light-controlled propulsion; Active matter