Multiscale Soft Surface Instabilities for Adhesion Enhancement

Soft systems due to their innate aspects (low elastic moduli and exorbitant response to external stimuli) are susceptible to buckling induced surface instabilities. Surface instabilities in soft materials are fascinating to study upon due to their potential to be developed into functional materials, to model real-life biological tissues, etc.

Polydimethylsiloxane (PDMS) with its distinctive properties is a favorable material in this regard, to drive instabilities and enhance a multitude of properties. Here, we have demonstrated an easy and cheap method to create crease instabilities on ultra-soft PDMS (modulus ~ few kPa) by the constrained swelling in Toluene. The developed instabilities were further investigated using optical microscopy, 3D optical profiler, and texture analyzer. The surface features, with sizes varying over three orders of magnitude, have the potential to increase the adhesion. In addition, the variation in adhesion energy has been examined quantitatively.  The flexibility and adaptability of this ultra-soft material, along with the easy procedure to generate permanent surface patterns make this work promising towards adhesive as well as other engineering applications.