Evaluation of silicone elastomers as structural materials for microstructured adhesives

Abstract

Microstructured (sometimes referred to as gecko-like) adhesives have numerous advantages over flat films, especially for practical applications on non-ideal surfaces that may be uneven or contaminated with dust. However, due to interdependence among material surface and bulk properties, the best material to fabricate such adhesives is still unknown. In this work, we analyzed eleven commercially available silicone elastomers to evaluate their use as flat and microstructured adhesives to address multiple material related questions that may impact the choice of the ‘best’ material for microstructured dry adhesives. To illustrate the applicability of the measured properties to modeling microstructured surfaces, we use stalk-shaped microstructures, whose contact mechanics are well understood. We demonstrate that there is no correlation between the adhesion strength of flat and microstructured adhesives; while bulk dissipation is the most important factor influencing the adhesion strength of flat elastomers, after microstructurization, interface toughness becomes more important. Therefore, microstructured elastomers loaded with high surface energy additives may demonstrate higher adhesion than their flat counterparts. We also compare the adhesion of flat and microstructured silicone elastomers on rough substrates. In this case, we show that while flat elastomer adhesion decreases with increasing substrate roughness, microstructured silicone adhesion actually increases with increasing roughness up to 0.19 m. This is the first time an increase in adhesion strength on rough surfaces is reported for materials stiffer than 1.0 MPa.