Wilhelm Barthlott

W. Barthlott, or Wilhelm Barthlott, investigated the structure and function of plant surfaces using scanning electron microscopy. His group connected microscopic surface features with water repellency and self-cleaning, giving the lotus effect an experimental basis and motivating technical surface designs.^[ref]

With C. Neinhuis, Barthlott compared plant surfaces after adding particles and applying controlled artificial rinsing. The measured function was particle removal by rolling droplets, interpreted together with surface microrelief and water repellency.^[ref] The later team interview describes how botanical observations motivated materials research rather than beginning from an already specified industrial design.^[ref]

An original force-balance illustration explains why easy rolling matters. Model a droplet of mass $m$ on an inclined surface as having a fixed retention force $F_r$. Downhill motion can begin when $mg\sin \alpha >F_r$, where $\alpha$ is the tilt. For stipulated $m=10\mathrm{mg}$, $g=9.81\mathrm{m}{\mathrm{s}}^{-2}$ and $F_r=20\mu \mathrm{N}$, the threshold isThis simplified threshold is not a measured value for a lotus leaf. It shows that droplet mass and retention both affect motion; a high static contact angle alone does not supply the needed force balance. Real retention also depends on surface defects, droplet geometry and wetting history.