Adhesion of Microchannel-Based Complementary Surfaces

Abstract

We show that highly enhanced and selective adhesion can be achieved between surfaces patterned with complementary microchannel structures. An elastic material, poly(dimethylsiloxane) (PDMS), was used to fabricate such surfaces by molding into a silicon master with microchannel profiles patterned by photolithography. We carried out adhesion tests on both complementary and mismatched microchannel/micropillar surfaces. Adhesion, as measured by the energy release rate required to propagate an interfacial crack, can be enhanced by up to 40 times by complementary interfaces, compared to a flat control, and slightly enhanced for some special noncomplementary samples, despite the nearly negligible adhesion for other mismatched surfaces. For each complementary surface, we observe defects in the form of visible striations, where pillars fail to insert fully into the channels. The adhesion between complementary microchannel surfaces is enhanced by a combination of a crack-trapping mechanism and friction between a pillar and channel and is attenuated by the presence of defects.

Structure and Energetics of Dislocations at Micro‐Structured Complementary Interfaces Govern Adhesion

“…The width of the dislocation region a , the width of the core region b , and the fraction of dislocation area in one sample, as a function of interchannel spacing c (when θ < 2°), are presented in Figure 4. It shows that the fraction of area covered by defects in one sample is approximately proportional to c , consistent with our previous study 13. It also shows that the widths of the dislocation and its core regions both increase with increasing inter‐channel spacing, c .…”

“…It can be seen that crack propagation on structured interfaces behaves quite differently from that on flat interfaces. For structured interfaces, there are two distinct fronts, one where the ridges have partially debonded from their complementary channels, and a second one behind which the ridges are fully extracted from their channels, consistent with observations from the previous study 13. For structured samples, the shape of the debonded region is always close to circular, but never perfectly so, with or without the influence of dislocations.…”

“…It is well known that the energy release rate at the tip of a kinked crack can be significantly less than its value prior to kinking. For example, the energy release rate at the tip of kinked crack, where the kink angle is 90° from the initial crack plane, is only 25% of the energy release rate that would exist if the crack had advanced straight ahead 13, 23. Therefore, even in dislocation‐free zones, the directionally patterned heterogeneous interface does not simply unzip in a continuous manner.…”

“…Various types of complementarity have been widely observed in nature, e.g., shape, charge, magnetic, and hydrogen‐bonding 1–12. The recent study by Singh et al13 provides a comprehensive list of references, both theoretical and experimental. Although the physical principles of complementarity in nature are quite well understood, the deliberate control of adhesion selectivity of material surfaces by complementarity has not been studied much as yet 14.…”

“…It is more difficult simultaneously to achieve selective adhesion and the basic question is whether and how the inevitably present small mismatches, either in the dimensions of the pattern or in alignment of the two sides of the interface, will be accommodated over length scales much larger than that of the repeating pattern. Singh et al13 investigated the adhesion enhancement between complementary surfaces with micro‐channel structures in a rectangular‐toothed pattern, and observed an interesting phenomenon: the appearance of defects in the form of visible striations.…”