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Graphical abstract Abstract Hypothesis Hydrophobic spheres may exhibit three impact modes after impacting the liquid surface. For the impact of common non-spherical particles in practical processes, particle shape affects the flow of surrounding fluid and forces acting on them, thus the impact behaviors of non-spherical particles may differ from those of spherical particles and remain to be revealed. Simulation The impact of hydrophobic micron ellipsoidal particles is numerically studied by solving the coupled equations of particle motion and surrounding fluid flow combining VOF method and dynamic meshing technique. The motion characteristics of the ellipsoids and fluids, and the main forces acting on the ellipsoids during impact are analyzed. Findings The increase in the axis ratio (AR) of ellipsoid decreases the surface tension and fluid force, resulting in a smaller total force acting on the ellipsoid. Correspondingly, the ellipsoid’s impact behavior changes. An impact-mode phase diagram is presented for the studied ellipsoids. Three impact modes, namely, submergence, rebound, and oscillation, exist when AR > 0.8, while only submergence and oscillation exist when AR ≤ 0.8. The critical velocities decrease with the increase in AR , which is well illustrated by the analysis of energy conversion under critical conditions. [ABSTRACT FROM AUTHOR]

Particle impaction on a droplet surface directly affects the particle capture by the droplet, and this phenomenon is the basic process of wet scrubbing and wet deposition. The experimental system is established to in-situ observe the behavior of micron particles impacting on the liquid surface. 50–200 μm hydrophobic PMMA and PS particles were used. The particles showed two types of motion behavior, namely, submergence and oscillation, after impaction onto the liquid surface. During particle sinking, the advancing contact angle remained constant. The shape of the liquid surface met the Young–Laplace equation under the quasi-static assumption. After the angle of the three-phase line reached the critical value, the liquid surface was closed, and the particle submerged. A small bubble formed, adhering to the particle trailing surface. If the particle velocity decreases to zero before the angle of the three-phase lines reaches the critical value, the particle will reverse the direction of its motion. When the particle moves to the horizontal liquid surface, the movement ceases. Reciprocating oscillation behavior was not observed. During particle reversion, the receding contact angle gradually decreased and then remained unchanged. The large contact angle hysteresis is the main cause of failure observation in rebound motion mode in the experiment. The changing rule of the critical submergence/oscillation velocity with the particle diameter and surface tension coefficient was studied. As the particle diameter increases, the critical submergence/oscillation velocity decreases. As the surface tension coefficient increases, the critical submergence/oscillation velocity increases. The observed critical submergence/oscillation velocity in this experiment demonstrated the accuracy of the proposed model. [ABSTRACT FROM AUTHOR]

Efficiently mixing highly viscous liquids in microfluidic systems is appealing for green chemistry such as chemical synthesis and catalysis, but it is a long-standing challenge owing to the unfavorable diffusion kinetics. In this work, a new strategy is explored for mixing viscous droplets by harnessing a peculiar Leidenfrost state, where the substrate temperature is above the boiling point of the liquid without apparent liquid evaporation. Compared to the control experiment where the droplet stays at a similar temperature but in the contact boiling regime, the mixing time can be reduced significantly. Moreover, it is demonstrated that the liquid mixing originates from the chaotic convection flow in the Leidenfrost droplet, characterized by the internal vortex motion evidenced by the microscale visualization. A correlation between mixing time and droplet volume is also proposed, showing a good agreement with experimental results. It is further shown that Leidenfrost droplets can be used to synthesize nanoparticles of the desired morphology, and it is anticipated that this simple and scalable fabrication approach will find applications in the biological, pharmaceutical, and chemical industries., (© 2024 Wiley‐VCH GmbH.)

Bubble bursting at liquid surfaces is ubiquitous and plays a key role for the mass transfer across interfaces, impacting global climate and human health. Here, we document an unexpected phenomenon that when a bubble bursts at a viscoelastic surface of a bovine serum albumin solution, a secondary (daughter) bubble is entrapped with no subsequent jet drop ejection, contrary to the counterpart experimentally observed at a Newtonian surface. We show that the strong surface dilatational elastic stress from the viscoelastic surface retards the cavity collapse and efficiently damps out the precursor waves, thus facilitating the dominant wave focusing above the cavity nadir. The onset of daughter bubble entrainment is well predicted by an interfacial elastocapillary number comparing the effects of surface dilatational elasticity and surface tension. Our Letter highlights the important role of surface rheology on free surface flows and may find important implications in bubble dynamics with a contaminated interface exhibiting complex surface rheology.