Transition in the Driving Mechanism of Self-Propelled Liquid Marbles Containing an Aqueous Alcohol Solution

The self-propulsion mechanisms of liquid marbles containing aqueous alcohol solutions are investigated, with particular focus on the transition from the initial acceleration to the steady-state motion. By combining surface tension measurements using quasi-elastic laser scattering (QELS) and tracer particle visualization, we quantitatively analyze the relationship between interfacial forces and flow fields. In steady-state constant-speed motion, both measurements demonstrate that the propulsion is primarily driven by the surface tension difference between the front and rear sides of the liquid marbles. In contrast, during the initial acceleration phase, the forward Marangoni flow was found to exceed the propulsion velocity, indicating a significantly increased contribution of the forward flow to self-propulsion. The comparison between the propulsion velocity and the surrounding flow velocity reveals that the dominant driving mechanism switches from flow-driven propulsion in the acceleration regime to surface tension-driven propulsion in the steady and deceleration regimes. This work provides experimental evidence of a temporal transition in propulsion mechanisms and offers new insights into how self-propelled systems reach steady-state motion.