Impact of Geometrical Constraints on Marangoni-Induced Instabilities in BZ Reaction Systems

In this study, we use computational fluid dynamics (CFD) to investigate how Marangoni effects, driven by chemical concentration gradients, influence free-surface dynamics in the Belousov-Zhabotinsky (BZ) reaction. We focus on how geometry—specifically hydrophilic cylindrical pillars placed inside a Petri dish—affects symmetry breaking and pattern formation. A custom solver was developed to couple hydrodynamics, chemical reactions, and three-dimensional Marangoni flows.

Our simulations show that these pillars act as centers for synchronized circular chemical waves. In covered setups, the waves remain circular and stable over time. However, in open setups where evaporation is stronger, surface tension gradients lead to Marangoni flows that break the wavefront symmetry and create flower-like patterns around the obstacles.

We also explore how pillar size affects the instability. A clear relationship is found between pillar diameter and the number of petals formed, with a critical size below which the instability does not occur. Our simulation results match well with experimental observations, supporting the model’s accuracy.

This work helps us understand how chemical waves can be controlled by adjusting geometry and surface properties. Such insights are useful for designing advanced microfluidic systems and for studying pattern formation in reactive fluids.