Enhanced self-cleaning performance of bio-inspired micropillar-arrayed surface by shear.

Inspired by the sliding behavior of gecko feet during climbing, the contribution of the shear effect to the self-cleaning performance of a bio-inspired micropillar-arrayed surface is studied through a load-shear-pull contact process. It is found that self-cleaning efficiency can be enhanced significantly by shear. The efficiency also depends on microparticle size. For the case of relatively large and small microparticles, self-cleaning efficiency increases first and then almost keeps a constant with the increase of shear distance at different preloads. For medium microparticles, shear can effectively improve self-cleaning efficiency only when the preload is small. The mechanical mechanism under such enhancement is mainly due to the varying contact states between microparticles and micropillars with the shear distance. When the shear distance is large enough, the final self-cleaning efficiency is not sensitive to shear distance anymore because the contact state reaches dynamic equilibrium. Based on such a self-cleaning mechanism of large microparticles, a simple and effective manipulator that can efficiently transfer solid particles is further proposed.

Self-Cleaning Performance of the Micropillar-Arrayed Surface and Its Micro-Scale Mechanical Mechanism.

The exceptional adhesive ability of geckos remains almost uninfluenced by contaminated surfaces, showing that the adhesion system of geckos has self-cleaning properties. Although there have been several studies on the self-cleaning performance of geckos and gecko-inspired synthetic adhesives, the microscale mechanical mechanism of self-cleaning is still unclear. In the present study, a micropillar-arrayed surface is fabricated using a template molding method to investigate its self-cleaning performance in a load-pull contact process. The effects of preload, microparticle size on self-cleaning properties are studied. The self-cleaning efficiency of the micropillar-arrayed surface is found to increase with an increase in the microparticle size. For large and small microparticles, self-cleaning efficiency increases with an increase in the preload. For medium microparticles, self-cleaning efficiency first increases and then decreases as the preload increases. The mechanical mechanism underlying such self-cleaning performance is further elucidated; it is mainly attributed to the competition among the elastic energy stored in the micropillars induced by the bending deformation, the interfacial adhesion energy between the microparticles and the deformed micropillars, and the interfacial adhesion energy between the microparticles and substrate, as well as the varying contact states between the microparticles and the deformed micropillars. The preload can not only change the contact states between the microparticles and the micropillar-arrayed surface but also influence the bending elastic energy stored in the micropillars. The results obtained in the present study can help deeply understand the self-cleaning mechanism of micropillar-arrayed surfaces as well as provide a guideline for designing functional surfaces with high self-cleaning efficiency.