ADHESIVE PROPERTIES OF TOPOGRAPHICALLY PATTERNED AND MECHANICALLY DEFORMED SURFACES

Adhesives are becoming more widely used for applications that previously relied on mechanical methods to secure the interface of two materials due to their cost effectiveness, lower weight, and ease of use. Examples of these new adhesive spaces include functional adhesives for robotic or manufacturing applications, composite materials in automotives and aircrafts, and wearable medical devices. As adhesives continue to push into new spaces, new methods must be developed to control their adhesive properties. Furthermore, understanding how the adhesive properties of these materials change due to deformation is critical in order to select or design new adhesives for specific applications. 

In this work we develop a material with pressure tunable adhesion by utilizing surface patterning. A simple and scalable fabrication method, polymer thin film dewetting, is used to pattern the surface of a soft elastomer with stiff, microscopic, and axisymmetric asperities. Patterning of the surface with these asperities leads to pressure tunable adhesion where adhesion strength increases with increasing applied pressure. Additionally, it is shown that changes to the relationship between adhesion strength and applied pressure by altering the pattern geometry are investigated.

The surface properties of amorphous elastomers have long been assumed to be independent of deformation. However, experimental studies within the last 15 years have shown this to be false for very soft solids and gels with moduli on the order of 10s-100s KPa when deformation of the material is below a critical length scale. The surface stress of these materials differs from the bulk and are dependent on the degree of deformation of the solid. Theoretical works have also shown this to be true for stiffer materials, however it is difficult to use the same experimental techniques to probe the surface stress of elastomers with moduli on the order of MPa. In this work, a new experimental technique is proposed to investigate the deformation dependent surface properties of elastomers. Additionally, this same technique allows us to probe the deformation-dependent adhesion properties of elastomers. We show that the shape of contact between a uniaxially stretched elastomer and rigid spherical probe provides insight into changes in surface stress. Furthermore, our results indicate that material composition, specifically filler composition and loading, affects the adhesion hysteresis of these elastomers.