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The ability of superhydrophobic surfaces to stay dry, self-clean and avoid biofouling is attractive for applications in biotechnology, medicine and heat transfer 1 – 10 . Water droplets that contact these surfaces must have large apparent contact angles (greater than 150 degrees) and small roll-off angles (less than 10 degrees). This can be realized for surfaces that have low-surface-energy chemistry and micro- or nanoscale surface roughness, minimizing contact between the liquid and the solid surface 11 – 17 . However, rough surfaces—for which only a small fraction of the overall area is in contact with the liquid—experience high local pressures under mechanical load, making them fragile and highly susceptible to abrasion 18 . Additionally, abrasion exposes underlying materials and may change the local nature of the surface from hydrophobic to hydrophilic 19 , resulting in the pinning of water droplets to the surface. It has therefore been assumed that mechanical robustness and water repellency are mutually exclusive surface properties. Here we show that robust superhydrophobicity can be realized by structuring surfaces at two different length scales, with a nanostructure design to provide water repellency and a microstructure design to provide durability. The microstructure is an interconnected surface frame containing ‘pockets’ that house highly water-repellent and mechanically fragile nanostructures. This surface frame acts as ‘armour’, preventing the removal of the nanostructures by abradants that are larger than the frame size. We apply this strategy to various substrates—including silicon, ceramic, metal and transparent glass—and show that the water repellency of the resulting superhydrophobic surfaces is preserved even after abrasion by sandpaper and by a sharp steel blade. We suggest that this transparent, mechanically robust, self-cleaning glass could help to negate the dust-contamination issue that leads to a loss of efficiency in solar cells. Our design strategy could also guide the development of other materials that need to retain effective self-cleaning, anti-fouling or heat-transfer abilities in harsh operating environments. Water-repellent nanostructures are housed within an interconnected microstructure frame to yield mechanically robust superhydrophobic surfaces.

This study aimed to investigate the impact of different sandpaper sanding meshes on the mechanical and optical properties of microencapsulated Tilia sp. film. An orthogonal experiment revealed that sanding between primers had the most significant effect. Furthermore, an independent experiment implied that increasing the mesh size resulted in decreased surface roughness and decreased color difference, elongation at break, and gloss after liquid resistance. In the aging test, the color difference of the paint film increased with the aging time, and the gloss tended to stabilize. Additionally, the anti-aging gloss of 240 mesh sandpaper used between primers remained relatively stable. The paint film sanded with 240 mesh sandpaper between primers displayed small and regular cracks after temperature and UV aging. Overall, the paint film demonstrated good comprehensive performance when sanded with 240 mesh between primers, 240 mesh between primer/topcoat, and 1000 mesh for topcoat. Self-repairing microcapsules showed better repair efficacy on the coating. This study provides a technical reference for the development of self-repairing coatings.

The tribological performance of tyre–road contacts depends crucially on the contact temperature. This study investigates the reliability and accuracy of acicular grindable thermocouples possessing an original needle-shaped wearable part as applied to measuring temperature at the oscillatory sliding contact between a rubber tyre tread sample and a sandpaper. A linear oscillatory tribometer is used to imitate the sliding phase of tyre–road contact under mild friction conditions. It is shown that the acicular grindable thermocouple measurements are generally test–retest repeatable. Moreover, the thermocouple signal becomes more stable with increasing contact pressure. Compared to the conventional thermocouple technique, the acicular grindable thermocouple overestimates temperature at the rubber friction surface by about 23% due to involvements of its wearable part in friction with the sandpaper. The findings suggest an expansion of the acicular grindable thermocouple technique to full-scale experiments with tyres on the road.

Polypropylene (PP) is widely used in the automotive, packaging, and home appliance industries due to its excellent mechanical properties, chemical stability, and low cost. However, the low surface energy of PP substrates leads to poor adhesion strength between the substrate and polyurethane (PUR) coatings, limiting its potential in applications requiring high adhesion and durable coatings. To enhance the adhesion strength between PP substrates and PUR coatings, methods such as sandpaper abrasion, flame treatment, and surface treatment agents were investigated for their effects on the surface morphology of polypropylene composites. The wettability changes of PP substrate after different treatment methods were studied using a contact angle experiment. The adhesion of the coating on PP substrates was evaluated using the cross-cut test after applying these three surface treatment methods. The results indicated that the effectiveness of the treatments in improving adhesion strength, from strongest to weakest, was as follows: surface treatment agent = flame treatment > sandpaper abrasion.

Recent studies reveal the dramatic impact of seafloor roughness on the dynamics and stability of broad oceanic flows. These findings motivate the development of parameterizations that concisely represent the effects of small-scale bathymetric patterns in theoretical and coarse-resolution numerical circulation models. The previously reported quasi-geostrophic ‘sandpaper’ theory of flow–topography interaction a priori assumes gentle topographic slopes and weak flows with low Rossby numbers. Since such conditions are often violated in the ocean, we now proceed to formulate a more general model based on shallow-water equations. The new version of the sandpaper model is validated by comparing roughness-resolving and parametric simulations of the flow over a corrugated seamount.

Seeds of winter strawberry ( Rubus buergeri Miq.) germinate at a low rate over an extended period due to their hard coat and deep dormancy. This study compared the effects of different physicochemical treatments on the germination rate and duration of the germination period of winter strawberry seeds. Seeds were treated by sandpaper scarification, sulfuric acid (H 2 SO 4 ) scarification, and gibberellic acid (GA 3 ). Of these physicochemical treatments, sandpaper scarification produced the greatest improvement to the germination rate and shortening of the germination period. Treatment with GA 3 also produced positive effects, albeit to a lesser level. By contrast, sulfuric acid scarification decreased the germination rate relative to the control group. Although GA 3 treatment had positive effects on true leaf formation and subsequent growth of seedlings, sandpaper scarification was the most effective method of inducing true leaf formation within a short period and, subsequently, for ensuring normal growth. Sandpaper scarification of seed resulted in > 90% germination, representing an approximately 80% improvement compared with the control group by week 6. Moreover, true leaves emerged in ~ 70% of seedlings within 6 weeks. Sandpaper scarification was thus a very effective seed treatment, not only for improving the germination rate and shortening the germination period of winter strawberry seeds but also for producing healthy seedlings.

The spatio-temporal characteristics of turbulent separations beneath semi-submerged bluff bodies with different undersurface roughness conditions are studied using a time-resolved particle image velocimetry. The Reynolds number based on the free-stream velocity and submergence depth was fixed to 14 400. Three different undersurface conditions – smooth, sandpaper roughness and cube roughness – were examined. The results showed that wall roughness reduces the mean reattachment length, and suppresses the Reynolds stresses in the second half of the mean separation bubble. The Kelvin–Helmholtz instability is observed at the leading edge of the smooth bluff body, but is bypassed in the rough cases. In the first half of the mean separation bubble, the frequencies in the separated shear layer migrate to lower values in a discrete manner through the vortex pairing mechanism. Consequently, multiple vortex shedding motions at different frequencies are nested in the separated shear layer, and the cores of shed vortices are aligned near the isopleth of free-stream velocity. The shed vortex is accompanied with multiple vortices along the edge of mean flow reversal in the upstream locations. These vortices are influenced significantly by wall roughness. A low-frequency flapping motion manifests as enlargement/shrinkage of reverse flow areas in the first half of the mean separation bubble. The frequencies of flapping motion in the smooth and sandpaper cases are similar, but are relatively lower than that in the cube roughness case. This flapping motion is associated with an extremely large vortex shed from the mean reattachment point to the free-stream region.

The Reynolds number dependent flow resistance of heterogeneous rough surfaces is largely unknown at present. The present work provides novel reference data for spanwise-alternating sandpaper strips as one idealised case of a heterogeneous rough surface. Experimental data are presented and analysed in direct comparison with drag measurements of homogeneous sandpaper surfaces and numerical simulations. Based on the homogeneous roughness data, the related challenges and sensitivities for the evaluation of roughness functions from experiments and simulations are discussed. A hydraulic channel height is suggested as an alternative measure for the drag impact of rough surfaces in internal flows. For the investigated heterogeneous roughness, it is found that turbulent flow does not exhibit a fully rough flow behaviour, indicating that the assignment of an equivalent sand grain height as commonly applied for homogeneous roughness is not possible. A prediction of the drag behaviour of rough strips based on an average between rough and smooth drag curves appears promising, but requires further refinement to capture the impact of turbulent secondary flows and spatial transients linking smooth and rough surface parts. While turbulent secondary flow induced by the roughness strips yield significant spanwise variation of the mean velocity profile for the investigated rough strips, we show that the spanwise averaged velocity profiles collapse reasonably well with a smooth or homogeneous rough wall flow. This allows to extract a global roughness function from the spanwise averaged flow field in good agreement with the one deduced from global pressure drop measurements.

A novel recyclable surface-enhanced Raman scattering (SERS)-based immunoassay was demonstrated and exhibited extremely high sensitivity toward prostate specific antigen (PSA). The immunoassay, which possessed a sandwich structure, was constructed of multifunctional Fe3O4@TiO2@Au nanocomposites as immune probe and Ag-coated sandpaper as immune substrate. First, by adjusting the density of outside Au seeds on Fe3O4@TiO2 core-shell nanoparticles (NPs), the structure-dependent SERS and photocatalytic performance of the samples was explored by monitoring and degradating 4-mercaptobenzonic acid (4MBA). Afterwards, the SERS enhancement capability of Ag-coated sandpaper with different meshes was investigated, and a limit of detection (LOD), as low as 0.014 mM, was achieved by utilizing the substrate. Subsequently, the recyclable feasibility of PSA detection was approved by zeta potential measurement, absorption spectra, and SEM images and, particularly, more than 80% of SERS intensity still existed after even six cycles of immunoassay. The ultralow LOD of the recyclable immunoassay was finally calculated to be 1.871 pg/mL. Therefore, the recyclable SERS-based immunoassay exhibits good application prospects for diagnosis of cancer in clinical measurements.

Oceanographic observations have revealed that basin‐scale Rossby waves can travel at speeds systematically exceeding values predicted by linear theory based on the flat‐bottom approximation. Using the recently developed parametric “sandpaper” theory of seafloor roughness, we construct a set of analytical solutions for the vertical structure and dispersion relationship of Rossby waves. We then use simulations to confirm these results and show that baroclinic Rossby waves can be accelerated by irregular small‐scale (3−30km)$(3-30\\,\\text{km})$rough topography by up to a factor of 1.6 relative to their flat‐bottom counterparts. This acceleration is most extreme at high latitudes and wavelengths of approximately 600 km. Our investigation demonstrates the importance of relatively small‐scale processes for the large‐scale flow dynamics in general and baroclinic Rossby waves in particular. Plain Language Summary Rossby waves are planetary waves that operate on spatial scales of up to those of ocean basins and time scales of up to years. They contribute to climate regulation and communicate changes in weather patterns and ocean flows across the globe. These waves have been the subject of continuous interest since their discovery. However, they usually propagate faster than simplified calculations predict. Several hypotheses have been proposed to explain this discrepancy, attributing it, for instance, to the waves riding on background flow and to large vortices masquerading as Rossby waves. This investigation offers an alternative explanation. We explore the effect a rough ocean bottom can have on the speed of the waves and bring theoretical estimates of the wave's structure and speed into agreement with measurements. We demonstrate that a rough bottom exerts significant drag on the lower part of the wave and causes its upper portion to move faster. Using numerical simulations, we show this acceleration is significant for a wide range of oceanographically relevant parameters. Key Points Observed phase speeds of Rossby waves systematically exceed the prediction of standard linear theory Taking into account the small‐scale variability in the bottom relief brings theoretical estimates of speed close to measurements The effect is most pronounced for extra‐tropical waves with low viscosity and relatively short wavelengths