Symmetry Breaking in Chemical Systems: Engineering Complexity through Self-Organization and Marangoni Flows

TL;DR

This study explores how Marangoni flows influence chemical wave patterns in a reaction system, revealing ways to engineer specific wave structures for microfluidic applications.

Contribution

It demonstrates the control of chemical wave patterns through Marangoni flows, highlighting the role of obstacle size and evaporation conditions in pattern formation.

Findings

Marangoni flows destabilize wavefronts, creating flower-like patterns.

Number of petals increases linearly with obstacle diameter.

Minimum obstacle size is required for pattern instabilities.

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. In this study, we investigate 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. Our 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. Our analysis shows that here solutal Marangoni forces are more relevant than thermal ones. Our experiments further show that the number of petals formed increases linearly with the obstacle's diameter, though a minimum diameter is required for these instabilities to appear. 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.