Dynamic enhancement in adhesion forces of microparticles on substrates

We report a dynamically induced enhancement in interfacial adhesion between microsized particles and substrates under dry and humid conditions. The adhesion force of soft (polystyrene) and hard (SiO2 and Al2O3) microparticles on soft (polystyrene) and hard (fused silica and sapphire) substrates was measured by using an atomic force microscope with retraction (z-piezo) speed ranging over 4 orders of magnitude. The adhesion is strongly enhanced by the dynamic effect. When the retraction speed varies from 0.02 to 156 μm/s, the adhesion force increases by 10% to 50% in dry nitrogen while it increases by 15% to 70% in humid air. Among the material systems tested, the soft-soft contact systems exhibit the smallest dynamic effect while the hard-hard contacts show the largest enhancement. A dynamic model was developed to predict this dynamic effect, which agrees well with the experimental results. The influence of dynamic factors related to the adhesion enhancement, such as particle inertia, viscoelastic deformations, and crack propagation, was discussed to understand the dynamic enhancement mechanisms.