Dynamics of sphere impact on a suspended film with glycerol and surfactant

Understanding the dynamics and inherent mechanisms of sphere impact on suspended films is important for improving sphere-film separation techniques. In this study, we conducted experiments to investigate the dynamics of sphere impact on suspended films and examine typical phenomena. We revealed the effects of dynamic viscosity and surface tension of films by altering the glycerol content (G) and the relative surfactant concentration (C*) and elucidated the characteristics of film deformation, sphere trajectory (hs), and contact time (tc). Moreover, we obtained the influences of sphere and film properties on bubble volume (Vbub) by analyzing force balance. The results indicate that three modes are observed and divided using the dimensionless energy parameter E* = Ek0/(ΔEfs + Evis) based on energy analysis, considering the sphere kinetic energy (Ek0), film surface energy increment (ΔEfs), and viscous dissipation (Evis): satisfying E* < 1, retention occurs; satisfying 1 < E* < 127.7(Ds/Df)2 (where Ds is the sphere diameter, Df is the film diameter), bubble entrainment passing appears; satisfying E* > 127.7(Ds/Df)2, non-bubble entrainment passing emerges. During retention, increasing G and C* causes film surface elasticity and hs to present a trend of first rising and then falling. For passing, the increase in G reduces deformability, leading hs to decrease, while increasing C* makes the film more susceptible to deformation, causing hs to increase. In addition, a film vibration period (τf) is introduced to measure tc, satisfying tc > 2τf for retention, while satisfying tc < τf/3 for passing. Inspection of the relationship between film deformation and falling height indicates that Vbub enlarges with increasing Ds and C* but shrinks with increasing G and release height Hs0.