The Influence of Backing Layer Thickness on the Adhesion and Detachment Behavior of Micropillar-Arrayed Surfaces

Significant progress has been made in the study of adhesion behavior on bioinspired fibrillar surfaces. Most studies mainly focus on the influence of fibril materials and geometry on adhesion. Several experiments found that the thickness of the backing layer of the fibrillar surface also greatly affects its adhesion performance, but the mechanical mechanism is still unclear. In the present article, a theoretical model for adhesive contact of a micropillar-arrayed surface with a finite thickness backing layer is established. The influence of the backing layer thickness on the interfacial adhesion and debonding behavior under a uniform vertical displacement is studied. The relationship between the adhesion force at the tip of every single pillar, the deformation of the pillar and the backing layer, and the total adhesion force, is analytically obtained. It is found that the thinner the backing layer, the more uniform the adhesion force of the micropillars and the greater the total adhesion force of the micropillar-arrayed surface will be, consistent with the existing experimental results. Another new phenomenon is that as the backing layer thickness decreases, the initial debonding of the micropillar-arrayed surface will shift from the peripheral micropillars to the central micropillars. The mechanical mechanisms that cause these phenomena are theoretically revealed, which are mainly due to the coordinated deformation of micropillars and the backing layer. Further finite element calculations and adhesion experiments validate the theoretical predictions. All the findings can provide theoretical guidance for the design of fibrillar adhesives with excellent adhesion properties.