Experimental study on coupled dynamics of a droplet impacting flexible substrates

In this study, the coupled dynamics of droplet impact on flexible superhydrophobic substrates are experimentally investigated using high-speed imaging and position sensing techniques across a range of Weber numbers (We = 7.06–70.57) and substrate flexibilities (E = 0.45–1.40 MPa). Regarding the droplet impact dynamics, the spreading phase is not significantly influenced by the Weber number or substrate flexibility, as inertial forces dominate during this stage, while the influence of substrate deformation remains relatively minor. In contrast, the receding phase is predominantly governed by the Weber number. With respect to the oscillation dynamics of the flexible substrate, the vibrational deflection increases with higher Weber numbers and lower substrate flexibility, whereas the vibration period is solely determined by the substrate's mechanical properties. The contact time observed on flexible substrates is longer than that on rigid substrates, which can be attributed to the scaling relationship between the oscillation periods of the droplet and the substrate. Based on these observations, a predictive correlation for the contact time of a droplet impacting flexible superhydrophobic substrates has been proposed. These findings provide valuable insights for the design of droplet-flexible substrate systems aimed at controlling contact time, offering a theoretical foundation for predicting system performance through the use of flexible materials.