Curvature‐Controlled Wrinkling Surfaces for Friction

Abstract

Topographical patterns endow material surfaces with unique and intriguing physical and chemical properties. Spontaneously formed wrinkling has been harnessed to generate surface topography for various functionalities. Despite promising applications in biomedical devices and robot engineering, the friction behavior of wrinkling on curved surfaces remains unclear. Herein, wrinkled surfaces are induced by sputtering metals on soft polymer microspheres. The wrinkle morphologies and length scales can be controlled precisely by tailoring the microsphere radius (substrate curvature) and film thickness. The wrinkled surfaces exhibit controlled friction property, depending on the wrinkling patterns and length scales. An increase in friction force with increasing surface roughness is generally found for dimple patterns and labyrinth patterns. The dimple patterns show the lowest friction due to strong curvature constraint. The herringbone patterns exhibit apparent friction anisotropy with respect to topographic orientation. These results will guide future design of wrinkled surfaces for friction by harnessing substrate curvature.

Harnessing Heterogeneous Wrinkles in Metal/Polydimethylsiloxane Film System by Combination of Mechanical Loading and Heat Treatment

“…It is well known that the friction property is dependent on the surface roughness, especially for isotropic wrinkle surfaces. [ 41 ] In our experiment, however, the surface roughness is not the main factor in influencing the friction anisotropy. As shown in Figure S6, Supporting Information, the measured surface roughness is almost constant for θ > 15°, while it decreases quickly for θ < 15° (especially at θ = 0°) because the scan line has no obvious height contrast.…”

“…The friction anisotropy is more than 200% (decreasing from ≈12 to ≈5.5 mV) in this work, much larger than the previous study based on herringbone patterns. [ 41 ]…”

“…The friction force tends to increase with increasing local slope of contact surface. [ 41,42 ] By comparing the profile lines 2 and 3 as shown in Figure 4c, the effective wavelength increases greatly while the amplitude remains unchanged as θ decreases. The elongated wavelength can be expressed as λ′ = λ/sin θ, where λ is the wavelength at θ = 90°.…”

Dynamic wrinkling pattern exhibiting tunable fluorescence for anticounterfeiting applications

“…In addition, wrinkles could also serve as graphical tags since the graphical images formed by wrinkles could be identified by naked eyes due to the light scattering caused by wrinkling pattern. Owing to the randomness, 3D topography, and nondeterministic process and unpredictability of the formation, wrinkling patterns caused by a surface mechanical instability [26][27][28][29][30][31][32] can realize a higher level of security in anticounterfeiting. Combining both responsive fluorescent behavior and the dynamic wrinkling pattern [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] into the same anticounterfeiting tag will undoubtedly enhance the information capacity and security.…”

Bioinspired Multiscale Wrinkling Patterns on Curved Substrates: An Overview

“…9 [49]: Equation 9 suggests that σ 0 is affected by the substrate curvature, mismatch strain, and the modulus ratio. Mismatch strain between the shell and the core can be induced by inhomogeneous expansion or shrinking induced by external stimuli such as thermal shrinkage [58,59], solvent-induced swelling [52,131,132], and volumetric growth [2,10,14]. The mismatch strain can be calculated by the expansion coefficient of the shell and the core, denoted as α shell and α core , respectively.…”