Characterization of methyl functionalized silica nanosprings for superhydrophobic and defrosting coatings.

Thin non-PFA superhydrophobic coatings are desirable for heat exchangers due to their lower thermal resistance, and reduced environmental concerns. Coatings requirements must also include robustness and longevity and facilitate high defrosting rates in refrigeration applications to warrant their adoption and use. Methyl functionalized silica nanosprings (SN) possess water droplet static contact angles above 160° with contact angle hysteresis values as low as 6.9° for a submicron thick coating. The methyl functional groups render the silica surface hydrophobic, while the geometrical and topographical characteristics of the nanosprings make it superhydrophobic. Results show that SN are capable of removing 95% of the frost from the surface at a lower temperature than the base aluminum substrate. The submicron SN coating also decreases the time to defrost by ~1.5 times and can withstand more than 20 frosting-defrosting cycles in a high humidity environment akin to real working conditions for heat exchangers.