Dresden 2026 – scientific programme

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BP: Fachverband Biologische Physik

BP 32: Statistical Physics of Biological Systems III (joint session BP/DY)

BP 32.2: Talk

Thursday, March 12, 2026, 15:15–15:30, BAR/SCHÖ

Size control and fluctuations of chemically active droplets — •Guido Kusters and David Zwicker — Max Planck Institute for Dynamics and Self-Organization, Göttingen, Germany

Biological cells use liquid-liquid phase separation to dynamically compartmentalize their environment for various applications, many of which require size control. This process is challenging because (i) large droplets tend to grow at the expense of smaller ones, and (ii) thermal fluctuations can disturb droplets since cells are typically small and soft. Chemical reactions can, in principle, control droplet sizes, but there are no clear guidelines on how to robustly achieve size control. To provide guidelines, we consider a binary fluid model driven out of equilibrium by chemical reactions. We reveal two different classes of size-controlled droplets, depending on the ratio of droplet radius to the reaction-diffusion length. Moreover, we determine parameter regimes in which droplets become small. To study fluctuations in this case, we use fluctuation-dissipation arguments to predict the size fluctuations of size-controlled droplets, consistent with our numerical simulations. Taken together, our theory allows us to predict the chemical reactions necessary for maintaining small droplets, e.g., in biological cells or synthetic applications.

Keywords: Active droplets; Phase separation; Chemical reactions; Size control; Thermal fluctuations