# Symmetry Breaking in Chemical Systems: Engineering Complexity Through Self‐Organization and Marangoni Flows

## TL;DR

This study shows how chemical waves can form flower-like patterns around obstacles due to fluid flows, enabling control over chemical reactions for microfluidic devices.

## Contribution

The study demonstrates how solutal Marangoni flows can be used to engineer specific wave patterns in chemical reactions.

## Key findings

- Marangoni flows destabilize circular chemical waves into flower-like patterns around hydrophilic obstacles.
- Petal number increases linearly with obstacle diameter above a threshold.
- Solutal Marangoni forces dominate thermal ones in influencing wave patterns.

## Abstract

Far from equilibrium, chemical and biological systems can form complex patterns and waves through reaction‐diffusion coupling. Fluid motion often interferes with these self‐organized concentration patterns. This study examines the influence of Marangoni‐driven flows inside a thin layer of fluid ascending the outer surfaces of hydrophilic obstacles on the spatio‐temporal dynamics of chemical waves in the modified Belousov–Zhabotinsky reaction. These observations reveal that circular waves originate nearly simultaneously at the obstacles and propagate outward. In a covered setup, where evaporation is minimal, the wavefronts maintain their circular shape. However, in an uncovered setup with significant evaporation and resulting Marangoni flows, the interplay between surface tension‐driven Marangoni flows and gravity destabilizes the wavefronts, creating distinctive flower‐like patterns around the obstacles. Experiments further show that the number of petals increases linearly with obstacle diameter, though a minimum diameter is required for these instabilities to appear. Our complementary numerical analysis indicates that solutal Marangoni forces dominate thermal ones in this system. These findings demonstrate the potential to “engineer” specific wave patterns, offering a method to control and direct reaction dynamics. This capability is especially important for developing microfluidic devices requiring precise control over chemical wave propagation.

We show that solutal Marangoni flows in thin films climbing the outer surfaces of hydrophilic obstacles break circular Belousov‐Zhabotinsky waves into striking flower‐like patterns. Evaporation‐driven surface‐tension gradients, coupled with gravity, trigger the instability; above a threshold, petal number scales linearly with obstacle diameter, enabling programmable guidance and shaping of chemical waves for microfluidic applications.