Direct force measurement of microscopic droplets pulled along soft surfaces

Abstract

When a droplet is placed on a soft material, surface tension forces from the droplet are able to deform the substrate. This thesis explores the effect of substrate stiffness on energy dissipation as a droplet is slid along a soft material. We find behaviour is characterised by two regimes separated by the lengthscale of the deformation in the substrate. For films approximately the lengthscale of the deformation, dissipation increases with thickness. As the thickness becomes much larger than the size of deformation, there is a plateau in dissipation. This result agrees with the model we use to understand energy dissipation in these systems.