Many organisms in
nature have evolved superhydrophobic surfaces
that leverage water droplets to clean themselves. While this ubiquitous
self-cleaning process has substantial industrial promise, experiments
have so far been unable to comprehend the underlying physics. With
the aid of molecular simulations, here we rationalize and theoretically
explain self-cleaning mechanisms by resolving the complex interplay
between particle–droplet and particle–surface interactions,
which originate at the nanoscale. We present a universal phase diagram
that consolidates (a) observations from previous surface self-cleaning
experiments conducted at micro-to-millimeter length scales and (b)
our nanoscale particle–droplet simulations. Counterintuitively,
our analysis shows that an upper limit for the radius of the droplet
exists to remove contaminants of a particular size. We are now able
to predict when and how particles of varying scale (from nano-to-micrometer)
and adhesive strengths are removed from superhydrophobic surfaces.