Attraction of Meso-Scale Objects on the Surface of a Thin Elastic Film Supported on a Liquid

TL;DR

This study investigates how elastic and adhesive properties of a thin film on liquid influence the attraction and aggregation of particles, revealing the role of hysteresis and hydrogel layers in particle interactions.

Contribution

It introduces a modified model accounting for adhesion hysteresis and demonstrates how hydrogel layers enhance particle attraction and aggregation on elastic films.

Findings

Adhesion hysteresis reduces the energy available for particle attraction.

Hydrogel layers significantly increase the range of particle attraction.

Particles tend to aggregate along defects caused by morphological instabilities.

Abstract

We study the interaction of two parallel rigid cylinders on the surface of a thin elastic film supported on a pool of liquid. The excess energy of the surface due to the curvature of the stretched film induces attraction of the cylinders that can be quantified by the variation of their gravitational potential energies as they descend into the liquid while still floating on the film. Although the experimental results follow the trend predicted from the balance of the gravitational and elastic energies of the system, they are somewhat underestimated. The origin of this discrepancy is the hysteresis of adhesion between the cylinder and the elastic film that does not allow the conversion of the total available energy into gravitational potential energy as some part of it is recovered in stretching the film behind the cylinders while they approach each other. A modification of the model accounting for the effects of adhesion hysteresis improves the agreement between theoretical and experimental results. The contribution of the adhesion hysteresis can be reduced considerably by introducing a thin hydrogel layer atop the elastic film that enhances the range of attraction of the cylinders (as well as rigid spheres) in a dramatic way. Morphological instabilities in the gel project corrugated paths to the motion of small spheres, thus leading to a large numbers of particles to aggregate along their defects. These observations suggest that a thin hydrogel layer supported on a deformable elastic film affords an effective model system to study elasticity and defects mediated interaction of particles on its surface.