The Salvinia Paradox: how the hydrophilic patches help keeping the plant’s surface dry

Simone MELONI, DIMA Sapienza University of Rome

Plants and animals have developed very diverse strategies to prevent the wetting by water and other liquids. Very interesting is the case of Salvinia Molesta, which leaves are decorates with hydrophobic eggbeater-like hairs. What makes special this case is the fact that these hairs feature hydrophilic patches at their top. One question to address is how these hydrophilic patches help keeping non-wet the surface of this plant. We investigated this problem by combining atomistic simulations and continuum models. Focusing on a simplified system, we show that this combination of hydrophobic and hydrophilic domains improves the stability of the contact between the liquid/air interface and the top of the hairs. This is achieved through a modification of the free energy profile of the wetting/cavitation process from the hydrophilic patches. In practice, the liquid/air interface stays pinned at the hydrophilic patches, which helps plants resisting to changes of thermodynamic and mechanical conditions, such as local changes of temperature and pressure, or the action of external forces, which can trigger the wetting of the surface. A continuum theory interpreting atomistic results is used to design surfaces of even improved stability. Our findings suggest possible routes to design surfaces of interest for technological applications requiring non-wettable submerged surfaces: energy related applications, marine applications, medical application, and many others.

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