Surface Wrinkling on Polydimethylsiloxane Microspheres via Wet Surface Chemical Oxidation

Abstract

Here we introduce a simple low-cost yet robust method to realize spontaneously wrinkled morphologies on spherical surfaces. It is based on surface chemical oxidation of aqueous-phase-synthesized polydimethylsiloxane (PDMS) microspheres in the mixed H2SO4/HNO3/H2O solution. Consequently, curvature and overstress-sensitive wrinkles including dimples and labyrinth patterns are successfully induced on the resulting oxidized PDMS microspheres. A power-law dependence of the wrinkling wavelength on the microsphere radius exists. The effects of experimental parameters on these tunable spherical wrinkles have been systematically investigated, when the microspheres are pre-deposited on a substrate. These parameters include the radius and modulus of microspheres, the mixed acid solution composition, the oxidation duration, and the water washing post-treatment. Meanwhile, the complicated chemical oxidation process has also been well studied by in-situ optical observation via the microsphere system, which represents an intractable issue in a planar system. Furthermore, we realize surface wrinkled topographies on the whole microspheres at a large scale, when microspheres are directly dispersed in the mixed acid solution for surface oxidation. These results indicate that the introduced wet surface chemical oxidation has the great potential to apply to other complicated curved surfaces for large-scale generation of well-defined wrinkling patterns, which endow the solids with desired physical properties.

Curvature-induced symmetry breaking determines elastic surface patterns

“…The GSH model implies that analogous transitions occur when the compressive stress in the film is increased. This prediction is in agreement with recent microscale experiments 28,34 (Fig. 1g-i), suggesting that the theory is universally applicable to both microscopic and macroscopic systems.…”

“…2 for additional examples with spatially varying curvature). The observation of similar pattern transitions in systems ranging from a few micrometres 26,28,34 to several centimetres 20,27 , combined with the fact that curvature-induced pattern selection can now be understood in terms of a symmetry breaking in the effective field equations, suggests that such processes form common universality classes. The generic differential-geometric framework developed here enables a systematic classification of wrinkling phenomena in complex geometries, by examining the symmetry properties of effective higher-order differential operators built from the surface metric and film-substrate coupling forces.…”

“…The additional (Γ 1 , Γ 2 ) terms will prove crucial below when matching theory and experiments. The generalization of equation (1) for arbitrary surfaces is given in Supplementary Equation (34).…”

One‐Step Spontaneous Formation of Dual Wrinkling on Uniform‐Sized Microparticles Induced by Surface

“…Considering the materials for wrinkled microparticle fabrication, poly(dimethyl siloxane) (PDMS) and elastomeric crosslinked polymer that are stable for the adapting technique (e.g., UV irradiation) have been prepared into wrinkled microparticles. However, biocompatible polymers based on aliphatic polyesters have poorer mechanical and thermal stability compared to PDMS.…”

Self-Supported Crack-Free Conducting Polymer Films with Stabilized Wrinkling Patterns and Their Applications

“…As a typically non-lithographic micro/nano-fabrication method, surface wrinkling has attracted intense interest owing to its simplicity, universality, low cost and so on891011. This instability-driven patterning usually occurs on a film/substrate bilayer system with a rigid film bound to a compliant substrate (e.g., polydimethylsiloxane (PDMS)), once the driving force exceeds the bilayer material-defined critical value.…”