Axisymmetry breaking, chaos, and symmetry recovery in bubble film thickness profiles due to evaporation-induced Marangoni flows

Understanding the dynamics of evaporating thin liquid films is of practical and fundamental interest. Practically, this understanding is crucial for tuning bubble stability, while fundamentally thin films are an excellent platform to study the characteristics of evaporation-driven two-dimensional (2D) flows. Here, we experimentally study, across a wide range of volatile species concentrations (c(0)), the spatial and temporal dynamics of film thickness profiles [h(r, theta, t)] over bubbles in binary liquid mixtures subjected to evaporation-induced Marangoni flows. Initially, we probe the spatial structure and show that the spatial symmetry of the film thickness profiles is non-monotonic functions of volatile species concentration with profiles being axisymmetric for both very low (similar to 1%) and very high (similar to 90%) concentrations. The temporal evolution of the film thickness fluctuations reveals a similar non-monotonic dependence between the species concentration and the spatial prevalence of fluctuation stochasticity. At a tested intermediate species concentration of 50%, we observe a complete breakdown in spatial symmetry and obtain film thickness fluctuations that are chaotic everywhere in space with spatially invariant fluctuation statistics and rapidly decaying spatial correlation. The observed non-monotonic behavior is a result of the system sensitivity to ambient perturbations scaling as Delta gamma c(0)(1 - c(0))/mu, where Delta gamma is the difference in equilibrium surface tension between the two species in the mixture and mu is the dynamic viscosity. These insights along with the reported experimental setup serve as an excellent platform to further investigate evaporation-driven 2D chaotic flows.

Automated summary

The experimental study investigates the spatial and temporal dynamics of film thickness profiles over bubbles in binary liquid mixtures across a wide range of volatile species concentrations. It shows a peak in fluctuation stochasticity and breakdown in spatial symmetry of film thickness fluctuations at an intermediate species concentration of 50%.