Flexible hydrogels connecting adhesion and wetting

TL;DR

This paper investigates the transition between adhesion and wetting phenomena using hydrogels and soft PDMS, revealing new behaviors and a model bridging classical theories, with implications for cleaning applications.

Contribution

It introduces a novel experimental and theoretical framework that connects adhesion and wetting through soft-on-soft interactions with intermediate material properties.

Findings

Discovered a smooth transition between adhesion and wetting regimes.

Developed a theoretical model bridging classical adhesion and wetting theories.

Identified hydrogels as potential cleaning agents for sticky PDMS surfaces.

Abstract

Raindrops falling on window panes spread upon contact, whereas hail can cause dents or scratches on the same glass window upon contact. While the former phenomenon resembles classical wetting, the latter is dictated by contact and adhesion theories. The classical Young-Dupre law applies to the wetting of pure liquids on rigid solids, whereas conventional contact mechanics theories account for rigid-on-soft or soft-on-rigid contacts with small deformations in the elastic limit. However, the crossover between adhesion and wetting is yet to be fully resolved. The key lies in the study of soft-on-soft interactions with material properties intermediate between liquids and solids. In this work, we translate from adhesion to wetting by experimentally probing the static signature of hydrogels in contact with soft PDMS of varying elasticity of both the components. Consequently, we probe this transition across six orders of magnitude in terms of the characteristic elasto-adhesive parameter of the system. In doing so, we reveal previously unknown phenomenology and a theoretical model which smoothly bridges adhesion of glass spheres with total wetting of pure liquids on any given substrate. Lastly, we highlight how solid like hydrogels can be treated as potential candidates for cleaning impurities from conventionally sticky PDMS substrates.