Droplet lift-off from hydrophobic surfaces from impact with soft-hydrogel spheres

Abstract Droplet impacts on superhydrophobic surfaces may result in complete bouncing, with the absence of contact hysteresis and viscous dissipation leading droplet to fully rebound off surface. This usually happens retraction phase, when retracts back after reaching a maximum spread diameter. Here, we present experimental evidence bouncing phenomenon where sessile hydrophobic surface bounces its spreading phase soft deformable hydrogel sphere axisymmetrically droplet. We term this as ‘Lift-Off’ propose simple force balance based deformation characteristics explain out-of-plane jump during spreading. observe three different impact regimes, their dependency modified elastic ‘Mach’ number ( M * ) ≈ 0.1 corresponding onset lift-off. also report unique acoustic signatures lift-off cases, associated capture air-bubbles through air-borne retracting rim. These results have potential applications for drainage cleaning, non-stick coating, industrial mixing plant disease