Steel reinforced concrete is often used in buildings, roads and bridges, however, freeze–thaw damage and steel corrosion pose threats to the strength of concrete. Furthermore, ice formation on concrete road-surfaces greatly increases injury and fatality rates. Superhydrophobic materials are promising candidates to alleviate these problems due to their anti-corrosion and anti-icing properties. However, the weak mechanical robustness of superhydrophobic surfaces makes them difficult to apply to concrete surfaces. Here we report a facile route to fabricate superhydrophobic concrete (S-concrete) via metal mesh covering and fluoroalkylsilane modification. Comparative robustness tests, including sandpaper abrasion, knife scratch and hammer beat, were performed on commercial superhydrophobic paint + adhesive coatings and our S-concrete, which indicated that our S-concrete had far superior surface mechanical durability. To illustrate the practical prospects, we performed further tests on the S-concrete, including artificial cold rain, freeze–thaw, and corrosion under applied voltage in corrosive solution. The S-concrete showed remarkable anti-icing, anti-freeze–thaw, and anti-corrosion properties, and mechanical robustness.

Reducing the contact time between impacting droplets and superhydrophobic surfaces has attracted much attention in recent years due to the importance of controlling heat and mass transfer. Previous researchers have proposed several methods, such as lifting the droplets before the retraction, accelerating the retraction process, or splashing the droplets. One example includes symmetry-breaking surfaces, which were used to accelerate the droplet retraction to realize the fast detachment. However, the dependence of the contact time on impact velocity and surface structure scale remains unclear. Here, we experimentally study the droplet impact dynamics on cross-scale cylindrical superhydrophobic surfaces. The reduction of the contact time is achieved on the surfaces with a ridge smaller or larger than the droplets, spanning different bouncing regimes. We describe the droplet behaviors and propose theoretical models from the view of retraction speed to explain the contact time variations. The maximum reduction is observed to occur when the ridge diameter is close to that of the droplets, which is also predicted by the models.

How to improve stent mechanical properties is a key issue for designing biodegradable polymeric stents (BPSs). In this study, a new design method of BPS was proposed based on the force analysis of supporting rings and bridges during stent implantation, and a novel BPS called open C-shaped stent (OCS) with superior comprehensive mechanical properties was developed accordingly. The key mechanical properties including radial force, radial recoil, and axial foreshortening of the OCS have been comprehensively studied and compared with those of the Abbott BVS using finite element analysis (FEA). In addition, the effects of the stent geometries on these mechanical properties have also been discussed in detail. Besides, in vitro mechanical tests including stent expansion and planar compression experiments have been performed to verify the simulation results. Based on the FEA results, it is found that the radial force and radial recoil of the designed OCS are 30% higher and 24% lower than those of the BVS, respectively. Meanwhile, the OCS is not shortened during expansion. Radial force and radial recoil are mainly dependent on the supporting ring structure, and the utilization of designed unequal-height supporting ring (UHSR) can effectively improve these two properties. Axial foreshortening is mainly determined by the bridge geometry as well as the connecting position of the bridge with the adjacent supporting rings. It is feasible to improve the axial foreshortening by using the bridges with a curved structure and locating the connecting position in the middle of the straight section of the supporting elements. The rationality of the proposed OCS and the effectiveness of the finite element method have been verified by in vitro experiments.

The extrusion of polymer profile products with complex microcross section is difficult due to the extrudate deformation, especially for the profile with multihollow lumens and inner ribs. In order to investigate the effect of die lip geometry on extrudate deformations, three-dimensional simulations have been undertaken for typical small profile extrusions both inside and outside the die using finite-element method (FEM). The Carreau model was used to describe the shear-thinning behavior of polymer melt. The systematic definitions of the die lip geometric parameters and evaluations of the extrudate deformations were proposed. It was found that the thickness and profile deformations happen asynchronously, and the existence of the inner rib changes the global deformation, which cannot be predicted by a deformation combination of the basic geometries. Among the investigated die lip geometric parameters, the wall thickness ratio has the most pronounced effect on both thickness and external profile deformations of the extrudates, with the maximum variation of more than 80%. The decrease of the hollow ratio significantly reduces the extrudate deformation extent, especially the extrudate external profile and the extrudate thickness of the thin-wall region. Even with uniform thickness, the location and shape of the inner rib also generate extrudate deformations not only on the inner rib but also on the thickness of the outer ring at the region not connected with it, by a minor variation level of 5–25%. Comprehensive understandings on the mechanism of extrudate deformations and effects of die lip geometry were obtained. Some hints for small profile die design were provided accordingly. Numerical results showed qualitative and quantitative agreement with the experiments.

The riblet structures of shark skin have a significant biological function for drag reduction, which has been verified. However, it is difficult to fabricate large‐scale bionic shark skin surface with high precision and low cost. The real shark skin micro‐riblets were first measured and approximately simplified to obtain shark‐skin‐inspired micro‐riblets. Numerical simulations were performed to explore the drag‐reduction effect of the micro‐riblets surface. According to the simplified micro‐riblets, a nickel mould with negative micro‐structures was manufactured by Ultra‐Violet Lithographie, Galvanoformung and Abformung technique. Roller embossing process was adopted to replicate shark‐skin‐inspired micro‐riblets, capable of transferring the micro‐riblets to polyvinyl chloride (PVC) and polyethylene terephthalate (PET) films. After embossing experiments, the effect of process parameters on roller embossing qualities including mould temperature, rolling pressure and rolling speed, evaluated by the depths of riblets embossed on the polymer films, were investigated. The results showed that the roller embossing process is a feasible and effective method to continuously replicate shark‐skin‐inspired micro‐riblets on polymer substrates. Moreover, the optimal process parameters were determined, including mould temperatures of 70°C (for PVC) and 60°C (for PET), compression ratios of 1.22 (for PVC) and 1.53 (for PET) and rolling speed of 1 r/min.