Lamella evolution of glycerol–water droplets on a rotating surface

The study presents an experimental investigation of droplet impact on a rotating smooth stainless-steel surface. High-speed imaging was used to quantify the time-resolved lamella area for water and glycerol–water solutions over rotational speeds from 0 to 10 000 rpm and impact velocities from 1.2 to 1.8 m s−1. The results show that for water droplets, a four-stage lamella evolution is identified at intermediate rotational speeds, consisting of inertia-driven spreading, capillary-driven receding, rotation-induced secondary spreading, and a capillary–centrifugal annular expansion stage. At sufficiently high rotational speeds, capillary-driven receding is fully suppressed, and the lamella expands continuously under rotation-dominated conditions. Increasing viscosity reduces the maximum lamella area and slows capillary-driven recession, while also stabilizing the lamella against rapid thinning. A distinct transition time τtr is identified from the reversal of viscosity ordering in the lamella area: before τtr, more viscous liquids spread less, whereas after τtr, they retain a larger lamella. This reversal is enhanced by rotation but originates from late-time viscous–capillary dynamics rather than from the regime-map transition itself. The normalized transition time remains of order unity relative to the inertial-capillary time, confirming that inertial-capillary relaxation controls the timing of the reversal, while rotation primarily governs the strength of the post-transition reorganization. A regime map and rotational Bond number analysis further distinguish between temporal control of the transition and centrifugal dominance after transition.