  There is a huge interest in developing super-repellent surfaces for
anti-fouling and heat transfer applications. To characterize the wetting
properties of such surfaces, the most common approach is to place a
millimetric-sized droplet and measure its contact angles. The adhesion and
friction forces can then be indirectly inferred from the Furmidge's relation.
While easy to implement, contact angle measurements are semi-quantitative and
cannot resolve wetting variations on a surface. Here, we attach a
micrometric-sized droplet to an Atomic Force Microscope cantilever to directly
measure adhesion and friction forces with nanonewton force resolutions. We
spatially map the micron-scale wetting properties of superhydrophobic surfaces
and observe the time-resolved pinning-depinning dynamics as a droplet detaches
from or moves across the surface.
