Title: Exploring active-passive mixtures at the microscale: simulations and experiments
When: Tuesday, May 20, 2025, 12:00
Place: Department of Theoretical Condensed Matter Physics, Faculty of Sciences, Module 5, Seminar Room (5th Floor)
Speaker: Horacio Serna / Marie Skłodowska-Curie Postdoctoral Fellow, Universidad Complutense de Madrid, Departamento de Estructura de la Materia, Física Térmica y Electrónica.
Mixtures of active and passive particles are ubiquitous at the microscale. Many essential microbial processes involve interactions with dead or immotile cells or passive crowders. When passive objects are immersed in active baths, their transport properties are enhanced and can be tuned by controlling active agents’ spatial and orientational distribution. Active-passive mixtures provide a platform to explore fundamental questions about the emergent behaviour of passive objects under simultaneous thermal and active noise and a foundation for technological applications in cargo delivery and bioremediation. In this work, we use computational simulations and experiments to study an active-passive mixture confined in microchannels designed with funnel-like obstacles that selectively allow the passage of passive particles. Active particles follow overdamped Langevin translational dynamics and run-and-tumble rotational dynamics. The experiments were carried out using suspensions containing the biflagellated green microalgae Chlamydomonas reinhardtii (~10 μm body length) and colloidal beads (~ 6 μm diameter) confined in microfluidic chambers with the same type of obstacles. We find that adjusting the tumbling rate of active agents and the microchannel geometry leads to a maximum in the passive particles’ diffusion coefficient, which correlates with the highest mixture sorting efficiency and the shortest response time.
