Design of anti-icing surfaces assumed significance in aerospace, power systems, marine vessels and automotive sectors. Easy removal of ice from solid surfaces has economic, energy and safety implications. A group of researchers from China and USA have described wettability-dependent ice morphology on the surface of aluminium that had been covered with a hydrophobic, or water-repellent, coating under atmospheric conditions and published their findings recently (Liu et al., Distinct ice patterns on solid surfaces with various wettabilities, www.pnas.org/cgi/doi/10.1073/pnas.1712829114).
The researchers have established a correlation between surface wettability and growth mode of ice crystals and suggested that surface wettabilities dictate the ice growth mode. Accordingly, below a critical value of contact angle, the growth of ice crystals follow along-surface growth mode whereas above this critical value of contact angle, the growth of ice crystals follow off-surface growth mode. It has been demonstrated that the ice crystals grown with off-surface growth mode, having a single point attachment with the surface, can be easily blown away by a breeze whereas those grown with along-surface growth mode, having multiple attachment points, stuck to the solid surface.
The discovery of different ice growth modes on solid surfaces and the feasibility of achieving easy removal of ice crystals grown with off-surface growth mode can be exploited to design better anti-icing surfaces.
The schematic illustrations, snap shots acquired using optical microscopy and video clips will give a better insight about their findings.
Fig. 1 Schematic illustration of the effect of solid surfaces on ice growth; (A) introduction of AgI nanoparticles on solid surfaces to achieve ice nucleation over the entire solid surfaces in the same environment.
Fig. 2 Snapshots acquired at different time periods using an optical microscope coupled with a high-speed camera: (B, D) top-view images; and (C, E) side-view images; (B) growth process of six-leaf clover-like ice on a hydrophobic surface (θ = 107.3°); (C) Off-side growth mode; (D) growth process of sunflower-like ice on a hydrophilic surface (θ = 14.5°); (E) Along-surface growth mode (growth environment: surface temperature is −15 °C; and supersaturation is 5.16)
Video clip demonstrating the growth process of six-leaf clover-like ice on a hydrophobic surface (θ = 107.3°)
http://movie-usa.glencoesoftware.com/video/10.1073/pnas.1712829114/video-1
Video clip demonstrating the growth process of sunflower-like ice on a hydrophilic surface (θ = 14.5°)
http://movie-usa.glencoesoftware.com/video/10.1073/pnas.1712829114/video-2
Fig. 3 Schematic illustration depicting that the ice crystals grown with off-surface growth mode can be easily blown away by a breeze whereas those grown with along-surface growth mode stuck to the solid surface.
T.S.N. Sankara Narayanan
For more information, the reader may kindly refer: Liu et al., Distinct ice patterns on solid surfaces with various wettabilities,
www.pnas.org/cgi/doi/10.1073/pnas.1712829114).
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