Effects of Stiff Film Pattern Geometry on Surface Buckling Instabilities of Elastic Bilayers

Abstract

Buckling instabilities-such as wrinkling and creasing-of micropatterned elastic surfaces play important roles in applications, including flexible electronics and microfluidics. In many cases, the spatial dimensions associated with the imposed pattern can compete with the natural length scale of the surface instabilities (e.g., the wrinkle wavelength), leading to a rich array of surface buckling behaviors. In this paper, we consider elastic bilayers consisting of a spatially patterned stiff film supported on a continuous and planar soft substrate. Through a combination of experimental and computational analyses, we find that three surface instability modes-wrinkling, Euler buckling, and rigid rotation-are observed for the stiff material patterns, depending on the in-plane dimensions of the film compared to the natural wrinkle wavelength, while the intervening soft regions undergo a creasing instability. The interplay between these instabilities leads to a variety of surface structures as a function of the pattern geometry and applied compressive strain, in many cases yielding contact between neighboring stiff material elements because of the formation of creases in the gaps between them.

Programmable microscale stiffness pattern of flat polymeric substrates by temperature-memory technology

“…Polymeric substrates comprising local mechanical stiffness pattern or nanostructural features are intensively investigated in the context of applications such as haptic displays (touchpads), stretchable electronics, mechanical and optical data storage devices, [1][2][3][4][5][6][7][8] or as instructive cell substrates guiding mechanosensitive (stem) cells. [9][10][11][12][13][14][15] While individual cells can react to structural features of few nanometers in size and mechanical differences in the Pascal (Pa) range, [9,14] the tactile sensitivity of a human finger is only capable of detecting structural features above 10 nm and local mechanics in the kPa regime.…”

Bioinspired Multiscale Wrinkling Patterns on Curved Substrates: An Overview

“…Beyond the wrinkling of large-size uniform film bonded on elastic substrate, recently, a series of studies have revealed differently post-wrinkle morphologies in systems composed of patterned stiff films on soft substrates [111][112][113][114][115][116][117][118][119]. When the length scale of the pattern is comparable to the wavelength of wrinkles, stress localization near the pattern arises under compression.…”

“…When the length scale of the pattern is comparable to the wavelength of wrinkles, stress localization near the pattern arises under compression. The feature size, geometry, and spacing are all demonstrated to have important effect on the wrinkling and post-wrinkle morphologies of patterned films [ 111 , 114 , 116 , 118 ]. For example, the preformed pattern can act as novel boundary to direct surface wrinkling for controllable fabrication of hierarchical wrinkling patterns with precise orientation [ 113 , 119 ].…”

“…For example, Wang et al demonstrated that the critical strains for initializing the wrinkle-to-crease transition at the edge of lattice hole are much lower than the typical critical strain value [ 116 ]. By considering both the imposed stiff patterns and the soft bare substrate, Ouchi et al [ 118 ] studied the morphology evolution of a non-continuous patterned stiff film bonded on a soft substrate under uniaxial compressive stress. Depending on the ratio of stripe length to wrinkle wavelength and gap size, they observed a set of surface morphologies including wrinkling, period-doubling, Euler buckling, zigzag, and sawtooth patterns.…”

Instantaneous micropatterning of a double-network hydrogel surface triggered by mechanical force

“…Several creative approaches have been demonstrated for creating patterns on soft materials 4,5 , particularly photolithography 6,7 , buckling instabilities [8][9][10] , printing 11,12 , and moulding 13,14 . Photolithography is one of the most common methods for the chemical patterning of soft material surfaces owing to its high resolution and possibility of on-demand patterning.…”