A Theoretical Model of Enhanced Adhesion of Bioinspired Micropillar Arrayed Surfaces

To achieve better adhesion, micropillar arrayed surfaces inspired by the gecko adhesion system have gained significant attention. However, debate continues on whether micropillar arrayed surfaces actually enhance interfacial adhesion compared to smooth surfaces. To clearly understand the factors influencing the adhesion force of micropillar arrayed surfaces and provide a criterion for achieving enhanced adhesion of such the surfaces, a theoretical model of a micropillar arrayed surface containing an elastic backing layer is established. Under a vertically uniform displacement load, the micropillars will detach from the rigid substrate. The adhesion behavior of each micropillar and the variation pattern of the entire adhesion force influenced by the geometry of the micropillars, materials of the micropillars and backing layer during the detaching process are analyzed. A load sharing efficiency is defined, and is found to increase with an increase in the micropillar aspect ratio, Young's modulus ratio of the backing layer to the micropillars, and separation distance between neighboring micropillars, but decrease with an increase in sample size. The entire adhesion force of a micropillar arrayed surface can be quantified, which is larger than that of a smooth surface if the micropillar aspect ratio, Young's modulus ratio of the backing layer to the micropillars and separation distance between neighboring micropillars are appropriate. Detailed diagrams are respectively provided for the load sharing efficiency of all the micropillars and the comparison of the adhesion forces between micropillar arrayed and smooth surfaces with different geometric and material parameters, from which the design strategies of approaching equal load sharing regime and stronger adhesion force of the micropillar arrayed surface than that of the smooth one can be clearly found. The obtained results can not only deepen the understanding of the adhesion behavior of fibrillar surfaces but also provide theoretical guidance for achieving robust adhesion of the micropillar arrayed surfaces.