Stochastic migrations of Marangoni surfers between two lobes of a dumbbell-shaped confinement†

We report an experimental investigation on the stochastic migration dynamics of Marangoni surfers (camphor-infused paper disks) between the two lobes of a dumbbell-shaped chamber. We characterize the migration dynamics using survival analysis of a configuration, wherein a configuration represents a distinct distribution of disks between the lobes. We observe that a configuration's stability decreases with increasing pairwise interactions. Consequently, the configuration with equal partitioning of disks between the lobes—that is exactly one-half of disks in each lobe for even-numbered systems but with one extra disk in either of the lobes for odd-numbered systems—has the lowest pairwise interactions, thus is always the most stable configuration. Furthermore, all configurations exhibit a stretched exponential decay with time, which is ascribed to a disk's activity decay with time or “aging”—a phenomenon validated by modeling a camphor disk as a chiral active particle (CAP) as initially proposed by Cruz et al.