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

Abstract

Highly enhanced adhesion can be achieved between surfaces patterned with complementary micro-channel structures. An elastic material, poly(dimethylsiloxane) (PDMS), is used to fabricate such surfaces by molding into a silicon master with micro-channel profi les patterned by photolithography. For each pair of complementary surfaces, dislocation defects are observed in the form of visible striations, where ridges fail to fully insert into the channels, and the rotational misalignment angle was found to be the key factor controlling the dislocation distribution and adhesion strength. Adhesion between complementary interfaces, as measured by energy release rate required to propagate an interfacial crack, can be enhanced by up to 30 times compared to a fl at control depending on the misalignment angle. The ability to control the orientation and periodicity of dislocation patterns by changing misalignment angle makes this system eminently controllable. This system could be a useful experimental tool in assisting research on geometry -controlled adhesion, while providing a test-bed for stability theories of interacting dislocations and crack fronts.

Meso-scale dislocations and friction of shape-complementary soft interfaces

“…With increasing misorientation angle, the density of these patterns also increases. As reported previously [37], for the ridge-channel pair, the dark regions are where ridges on one side of the interface are aligned with, and have entered into, channels on the other side. Lighter regions are where ridges climb over a ridge on the other side to enter the adjacent channel, which can be considered as a screw dislocation with a Burgers vector of magnitude equal to the periodic lattice spacing.…”

“…The foregoing discussion suggests that the dislocation core can be treated as a crack under mixed-mode loading, and that the misorientation and load dependence of friction can perhaps both be explained in terms of partially opened cracks near the dislocation core. This idea is further developed below, generalizing our previous approach to this problem in which we accounted for the mode III component (screw dislocation) but not for dilation or external pressure and shear loading [37,38].…”

“…The structure of the screw dislocations of our experiments is shown schematically in figure 4d royalsocietypublishing.org/journal/rsif J. R. Soc. Interface 18: 20200940 cores; each core occupies a width of 2a [37]. The regions where ridges are completely inserted into channels appear featureless in optical micrographs.…”

“…(Mismatch of periodic spacing results in edge dislocation arrays.) While these dislocations permit surfaces to adhere for small misorientation, they carry elastic energy, the release of which attenuates the adhesion enhancement [37]. The orientation and density of these defects can be accurately described using the geometrical analysis of Moiré patterns [38].…”

Generation of Customizable Micro-wavy Pattern through Grayscale Direct Image Lithography

“…The development of practical and cost-effective methods of producing patterned microstructures is currently of great interest, especially in the field of surface studies 1 , cell adhesion 2 , and microfluidic 3 . The wavy pattern is highly desirable features, as it is eminently useful for biological applications 4 5 and for adjusting surface properties such as adhesion 6 7 , friction 6 , and hydrophobicity 8 . A standard technique to create micro-wavy features is depositing thin metal films onto polydimethylsiloxane (PDMS) substrates with some degree of thermally-induced pre-strain 9 .…”