Rose petals may involve high water contact angles together with drop adhesion which are antagonistic wetting properties. Petal surfaces have a cuticle which is generally considered a continuous, hydrophobic lipid coating. The peculiar properties of rose petals are not fully understood and have been associated with high surface roughness at different scales. Here, the chemical and structural features of natural upper and lower petal surfaces are analyzed by atomic force microscopy (AFM). Both rose petal surfaces are statistically equivalent and have very high roughness at all scales from 5 nm to 10 μm. At the nanoscale, surfaces are fractal‐like with an extreme fractal dimension close to df = 2.5. A major nanoscale variability is also observed which leads to large (nanoscale) wettability changes. To model the effect of roughness and chemical variability on wetting properties, a single wetting parameter is introduced. This approach enables to explain the Rose petal effect using a conceptually simple scheme. The described fundamental mechanisms leading to high contact angles together with drop adhesion can be applied to any natural and synthetic surface. Apart from introducing a new approach for characterizing a biological surface, these results can trigger new developments on nanoscale wetting and bio‐inspired functional surfaces.
In this article, the authors developed a topographic image processing procedure based on polynomial interpolating functions for studying growth of thin films at nanoscale. Using the topographic atomic force microscopy images as input for the proposed procedure, the authors obtained the surface slope distributions at different thicknesses (2–60nm) for evaporated Au(111) films as well as the thickness dependence of the mean slope. The scaling exponents [namely, the growth exponent β=0.70±0.02 and the dynamic one 1∕z=0.004±0.013 that determine the thickness dependence of the roughness (σ) and the size of the surface features (ξ) as σ∼thicknessβ and ξ∼thickness1∕z, respectively] that result from our analysis indicate that the growth front of the Au films is formed by mound-shaped surface features that grow preferentially in height (i.e., without lateral coarsening). These results, together with the evolution of the mean slope toward a saturation value, suggest that the morphology evolution of the Au films corresponds to early stages of a growth regime characterized by the formation of steep mounds with selected slopes. Plausibly, such mounds would be responsible for the columnar structure observed in thicker Au films by microscopy.
Several mechanisms have been revised to explain the aggregation of metal adsorbates on a 7ϫ7 reconstructed Si͑111͒ surface. Some of them are based on the high mobility of incident particles, while others collect the nonlocal weak or moderate interactions among adsorbates. The adsorbate aggregation, which has been characterized via the temporal evolution of the surface occupation and monomer to cluster density ratios, has been studied for each mechanism through kinetic Monte Carlo simulations as well as by approaches to the corresponding rate equations. The cooperative diffusion is revealed as the unique mechanism that is able to fit fairly the existing data related to the adsorption of metals on the Si(111)7ϫ7 surface.
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