Multiscale Effect of Hierarchical Self-Assembled Nanostructures
on Superhydrophobic Surface
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Abstract
In
this work, we describe self-assembled surfaces with a peculiar
multiscale organization, from the nanoscale to the microscale, exhibiting
the Cassie–Baxter wetting regime with extremely low water adhesion:
floating drops regime with roll-off angles < 5°. These surfaces
comprise bundles of hierarchical, quasi-one-dimensional (1D) TiO<sub>2</sub> nanostructures functionalized with a fluorinated molecule
(PFNA). While the hierarchical nanostructures are the result of a
gas-phase self-assembly process, their bundles are the result of the
capillary forces acting between them when the PFNA solvent evaporates.
Nanometric features are found to influence the hydrophobic behavior
of the surface, which is enhanced by the micrometric structures up
to the achievement of the superhydrophobic Cassie–Baxter state
(contact angle (CA) ≫ 150°). Thanks to their high total
and diffuse transmittance and their self-cleaning properties, these
surfaces could be interesting for several applications such as smart
windows and photovoltaics where light management and surface cleanliness
play a crucial role. Moreover, the multiscale analysis performed in
this work contributes to the understanding of the basic mechanisms
behind extreme wetting behaviors