Curvature induced hierarchical wrinkling patterns in soft bilayers

Abstract

Sinusoidal wrinkling will occur in a planar film-substrate bilayer when the uniaxial compressive strain imposed to the system exceeds a critical value. However, when a core-shell soft cylinder is subjected to axial compression, surface wrinkling patterns may evolve from the sinusoidal mode to the diamond-like mode, depending on the modular ratio and the curvature of the system. Inspired by this phenomenon, we here propose a simple yet robust strategy to fabricate hierarchical wrinkling patterns by controlling the curvature of a film-substrate system. To quantitatively understand the experimental results, a three-dimensional finite element model has been built to track the wrinkling pattern evolution. Furthermore, a phase diagram is provided based on the theoretical analysis and finite element simulations, which may guide the experimental design. In addition, the wetting properties of the surface with hierarchical micropatterns fabricated using the proposed method are investigated. The results show that the hierarchical surface wrinkles lead to anisotropic wetting behavior, which can be tuned by controlling the imposed compressive strain. The tunable anisotropic wetting surface fabricated here may find a broad range of applications such as in the development of sensors, fluidic devices, micro-reactors and biomedical devices.

Transient instabilities in the swelling dynamics of a hydrogel sphere

“…Whereas the surface instabilities which may characterise the steady state of hydrogels being constrained in space and undergoing large volume variations have been largely studied [17][18][19], the same is not true in the case of transient surface instabilities. An especially interesting transient phenomenon observed during the free swelling of hydrogels is the protrusion of surface patterns on the surface.…”

Bioinspired Multiscale Wrinkling Patterns on Curved Substrates: An Overview

“…4, methods using to obtain core-shell structures include chemical approaches such as surface treatment of oxygen plasma (UV and UVO) [177][178][179][180], surface chemical oxidation [132], chemical vapor deposition [58,181], as well as physical approaches such as metal sputtering [59,182], dip coating [54,55,61], and mechanical wrapping [53,60,64]. The formation of wrinkling patterns on curved substrates can be induced by applying various external stimuli such as heating/cooling [58,59], stretching/releasing [53,60,183], inflation/deflation [54,55,61], and swelling/deswelling [177,179]. For core-shell cylinders, axial compression is important for fabricating ring-patterned fibers for diverse applications [53,60] (Fig.…”

Surface Instability of Bilayer Hydrogel Subjected to Both Compression and Solvent Absorption

“…The pre-stretched substrate not only showed substantial shifts in the critical strain for the onset of post-wrinkling bifurcation, but also exhibited qualitatively different modes of surface instability, such as tripling. Shao et al [50] analyzed the curvature-induced hierarchical wrinkling patterns in soft bilayers. These theoretical analyses are limited to elastomeric soft solids such as PDMS and silicone rubber.…”