Speaker
Description
Light-activated Janus microswimmers offer a programmable active-matter platform in which illumination modulates propulsion and enables controlled density modulations and localization [1,2]. We develop a continuum theory model that captures swimming pressure and the resulting dynamic pattern formation in spatially structured activity landscapes. Our framework couples a conservation law for the colloid concentration to a light-dependent swim speed, with swimming pressure acting as an effective nonequilibrium stress that biases fluxes and shapes interfaces.
From this model we extract three emergent timescales: (i) depletion in the bright (active) zone, (ii) filling in the dark (inactive) zone, and (iii) interfacial formation/relaxation in a shady transition zone. We further derive a Lyapunov functional for the coarse-grained dynamics, enabling direct determination of the quiescent-state concentration profile. Finally, when imposing a traveling-wave bright field (a moving activity pattern), we predict a net particle flux opposite to wave propagation direction and whose magnitude depends on the wave speed, yielding a tunable mechanism for rectified transport (“optical pumping”) under structured illumination protocols [3].
References
[1] Töpfer, U.; Bailey, M. R.; Schreiber, S.; Paratore, F.; Isa, L. Density Modulations in Active Colloidal Systems through Orthogonal Propulsion Control and Sensory Delays. ACS Nano 19, 39210–39219 (2025). DOI: https://doi.org/10.1021/acsnano.5c12596
[2] Palacci, J.; Sacanna, S.; Kim, S.-H.; Yi, G.-R.; Pine, D. J.; Chaikin, P. M. Light-activated self-propelled colloids. Philos. Trans. R. Soc. A 372 (2029), 20130372 (2014). DOI: https://doi.org/10.1098/rsta.2013.0372
[3] Chen, X.; Xu, Y.; Lou, K.; Peng, Y.; Zhou, C.; Zhang, H. P.; Wang, W. Programmable, Spatiotemporal Control of Colloidal Motion Waves via Structured Light. ACS Nano 16, 12755–12766 (2022). DOI: https://doi.org/10.1021/acsnano.2c04596
