Tuning of microcapsule adhesion by varying the capsule-wall thickness.

The adhesion area and topology of spherical hollow polyelectrolyte shells adhering to flat glass or polyelectrolyte-covered glass surfaces are studied. Strong adhesion is found for anionic poly(sodium 4-styrenesulfonate)-terminated shells on cationic poly(ethylene imine)-covered glass, while no adhesion of those shells on uncoated glass is found. The adhering shells are deformed and obtain a truncated sphere topology with a circular adhesion disk. The radius of the adhesion disks can reach up to 50% of the shell radius for shells of several tens of microns. The dependency of the size of adhesion areas on the capsule radius and capsule wall thickness is also investigated. Remarkably, the size of the adhesion areas is found to depend strongly on the wall thickness, which offers interesting perspectives for controlling capsule adhesion properties. A model based on the energy balance of deformation and wetting energies is presented that explains the observed trends.