Bio-inspired surface from Northwestern University contains nanoscale peaks and valleys that help deter frost formation.
Benefits
- Chemical-free
- Reduced cost
Applications
- Aviation
- Commercial & residential buildings
- Applicances
UN Sustainable Development Goals Addressed
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Goal 9: Industry Innovation & Infrastructure
The Challenge
Frost is a common problem that can occur on a variety of surfaces. In the airline industry, flights can be grounded by even the slightest layer of frost on the windshield or wings of the aircraft. Frost on airplane wings can create drag, making flight dangerous or even impossible. Reduced frost formation would result in fewer cancelled flights and less use of strong deicing chemicals.
Innovation Details
The frost-reduction effect can be achieved by tweaking the texture of any material’s surface by adding millimeter tall peaks and valleys with small (40-60 degree) angles in between, similar to those found on the surfaces of mint leaves. Condensation is enhanced on the peaks and suppressed in the valleys of wavy surfaces. The small amount of condensed water in the valleys then evaporates, resulting in a frost-free area. Even on a surface material that attracts water, the water still evaporated from the valleys when below the freezing point. These surfaces reduced frost formation by 60%, and could theoretically reduce it up to 80%. Although a thin line of frost still forms on the peaks of the surface topography, it can be defrosted with considerably less energy. It also bypasses the need for using liquids with lower frosting points or surface coatings, which can be easily scratched.
Frost forming on a 3D-printed maple leaf. Photo: Ken Park/Northwestern University.
Biological Model
Mint leaves have uneven surfaces, consisting of convex (surface) and concave (veined) regions. Frost forms when humid air vapor or condensation makes contact with a surface that is below freezing temperature. On the concave regions there is much less frost, which is controlled by the geometry of the leaf, not the surface texture. When condensation forms on a leaf, the condensed droplets in the valley evaporate due to the lower vapor pressure of ice compared with water, resulting in a frost-free zone in the valley, which resists frost propagation even on superhydrophilic surfaces.
