This paper investigates the impact behavior between water drops with different velocities and cylindrical superhydrophobic surfaces with various diameters and presents two possible outcomes of drop impact, which are asymmetric rebound and stretched breakup. Due to the special cylindrical topology of the surface, drops undergo an asymmetric spreading and retracting process in the azimuthal and the axial direction, which results in three types of asymmetric rebound, including jug-like rebound, wing-like rebound, and rebound breakup. The stretched breakup is observed in the collision of drops with higher impact velocities and smaller cylinder diameters. The diameter ratio D* and Weber number We are found to be the determinants of the bouncing patterns. With the decrease in the diameter ratio D* or the increase in the Weber number We, the bouncing patterns transformed from jug-like rebound through wing-like rebound and finally to stretched breakup. We put forward a modification form of the Weber number (α = We/D*) affected by the diameter ratio D*, indicating the ratio between the inertia force and the surface tension, as the criterion to distinguish the upward rebound from the downward stretch, which helps obtain the linear relation of critical We_cr and D*_cr. Furthermore, asymmetric rebound and stretched breakup could effectively shorten the contact time between drops and substrates. The contact time is found to be mainly determined by the dimensionless parameter α. The correlation between the dimensionless contact time and the dimensionless parameter α is demonstrated to be τ_c ∝ αⁿ.

To improve polishing performance and reduce the environmental pollution of chemical mechanical polishing (CMP) tests, mesoporous shell/core silica abrasives were prepared, and a novel green CMP slurry was developed, including sorbitol, hydrogen peroxide and sodium carbonate. Prior to CMP, fused silica was roughly polished with ceria slurry. Using developed mesoporous abrasives, surface roughness S_a is reduced from 0.347 to 0.253 nm for a scanning area of 200 × 200 μm², and the material removal rate (MRR) is increased from 70 to 127 nm min⁻¹, compared with traditional solid abrasives. Based on molecular dynamics (MD) simulations, a novel atomic removal model is proposed for mesoporous abrasives through the immediate elastic recovery of atoms. MD simulations suggest that the formation of convex peaks and pits was inhibited by the mesoporous structure, promoting uniform distribution of surface atoms and atomic removal. This is different from a conventional simple increase of polishing times. In addition, more bridge bonds of Si–O–Si and a lower average Si–O bond order are produced in fused silica samples due to their mesoporous structure, contributing to a higher MRR.

The influence of liquid viscosity on the splashing behavior of a drop impacting a smooth surface is investigated. It is found that the liquid viscosity plays a reversed role on the drop splash, and the liquid viscosity promotes the drop splash in the low-viscosity cases but suppresses the drop splash in the high-viscosity cases. Here, we focus on the dynamics of the lifting lamella during the splashing behavior and demonstrate that the increase in liquid viscosity could contribute to the lower splashing angle α_s. Furthermore, an empirical relationship of the splashing angle is obtained according to the experimental results. The reversed role of liquid viscosity is reflected in the positive effect both on the aerodynamic force and viscous force. For low-Oh cases, the increase in aerodynamic force predominates and promotes the drop splash. For high-Oh cases, the increase in viscous force predominates and suppresses the drop splash. We eventually put forward a splash criterion on smooth surfaces, which could successfully characterize the splashing behavior in this work and previous studies, and indicate the reversed role of liquid viscosity on drop splash.

This work presents an experimental study on the splashing behaviors of drops impinging on rough solid surfaces. Most prior studies have shown the increase in surface roughness can promote the occurrence of a drop splash. Interestingly, we found two opposite effects of surface roughness on the drop splash that the increase in surface roughness can promote splash of low-viscosity drops but suppress splash of high-viscosity drops. According to the wetting state of the spreading lamella on rough surfaces, the splash regime can be classified into two modes: corona splash and prompt splash. It is found that the increase in surface roughness can promote the prompt splash but suppress the corona splash. The increase in surface roughness could provide wide channels for air to escape and suppress the corona splash. Meanwhile, the larger surface roughness could also disrupt the expanding lamella and promote the prompt splash. The dimensionless parameter Oh_r can be used to distinguish two splash regimes, and the critical value Oh_rc is obtained from experimental results, at which the splash regime changes from the prompt to corona splash. Emphatically, we obtain the splash criteria in two regions, which could reflect the opposite effects of surface roughness on the drop splash and successfully characterize the splashing behaviors in this work and previous studies. The results of this work are expected to provide valuable insights to control the drop splash in industrial applications.

With the continuous expansion of Unmanned Aerial Vehicle (UAV) applications, the threat of icing on UAV flights has garnered increased attention. Understanding the icing principles and developing anti-icing technologies for unmanned aircraft is a crucial step in mitigating the icing threat. However, existing research indicates that changes in Reynolds numbers have a significant impact on the physics of ice accretion. Icing studies on aircraft operating at high Reynolds numbers cannot be directly applied to unmanned aircraft, and mature anti-icing/deicing techniques for manned aircraft cannot be directly utilized for UAVs. This paper firstly provides a comprehensive overview of research on icing for fixed-wing UAVs, including various methods to study unmanned aircraft icing and the identified characteristics of icing on unmanned aircraft. Secondly, this paper focuses on discussing UAV anti-icing/deicing techniques, including those currently applied and under development, and examines the advantages and disadvantages of these techniques. Finally, the paper presents some recommendations regarding UAV icing research and the development of anti-icing/deicing techniques.

In the present study, we carried out an experimental investigation of the impinging and freezing processes of a supercooled large water droplet on an ice surface. One high speed camera was used to measure the dynamic motions of the water droplet while two charge coupled device (CCD) cameras were adopted to obtain the images of the freezing process and the freezing morphologies, respectively. The effects of the water droplet temperature and the ice surface temperature on the impact and freezing processes of the water droplet were carefully evaluated. The results showed that the subcooling degree of the water droplet had an apparent influence not only on the spreading process but on the freezing morphology as well. When the subcooling temperature of the water droplet was high (e.g., T_w= –3.0 °C), a triangle cross-section profile formed. However, once the subcooling temperature of the water droplet was relatively low (e.g., T_w= –9.0 °C), the final ice morphology consisted of two parts: one part was a cone-like bead in the center while the other part was an ice ring at the periphery. Moreover, at the same water droplet temperature, raising the ice surface temperature led to an increase in the maximum spreading factor.