MPI-DS Colloquium: Symmetry breaking in chemical systems: engineering complexity through self-organization and Marangoni flows

In this study, we investigate the impact of a periodic array of hydrophilic cylindrical obstacles on the spatio-temporal dynamics of chemical waves in the bubble-free Bel-ousov-Zhabotinsky-1,4-cyclohexanedione (BZ-CHD) oscillatory chemical reaction. We find that the thin fluid layer ascending the outer surfaces of these hydrophilic obstacles is crucial for influencing wave dynamics. We observe that circular waves begin almost simultaneously at these obstacles and spread outward. In a covered setup where evapo-ration is minimal, these wavefronts retain their circular shape. However, in an open setup where evaporative cooling is more pronounced, thermal Marangoni flows trigger wavefront instabilities, leading to the formation of distinctive flower-like patterns around the obstacles. Our experiments also show that the number of petals formed in-creases linearly with the diameter of the pillars, though a minimum diameter is re-quired for the instabilities to manifest. These results highlight the ability to 'engineer' specific wave patterns, offering a strategy to control the reaction dynamics. This capa-bility is particularly crucial for the development of microfluidic devices that demand precise control over chemical wave propagation.