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Antifreeze Coatings : Three Different Approaches

Martina Hirayama School of Engineering, Zurich University of Applied Sciences

Ice formation, accretion and ice adhesion on different surfaces can result in severe problems e.g. on power lines, transportation in general, aircraft or power production by wind turbines. We investigate in cooperation with industrial partners three different approaches to obtain antifreeze coatings.

Delay of freezing :
When humid air is blown over a glass surface at -10 °C which is coated with a particular silane, water does not freeze but forms liquid droplets instead. On the uncoated glass, however, ice crystals do appear (see fig. 1). This peculiar effect of delayed freezing is caused by the coating’s ability to stabilize supercooled water.

Fig. 1 Microscopy of a wet, cold (-10 °C) glass slide. The left half is coated and water droplets are visible, whereas the right side is uncoated and covered with ice.

Icephobic properties :
The perfect icephobic surface does not yet exist. In fact, ice sticks to everything and its adhesion is measured by the adhesion reduction factor, ARF. It is estimated that an ARF of at least 100 is necessary to prevent icing. We tested many surfaces and developed special coatings, which fulfill the requirement of an ARF of 100 or bigger.

Delay of condensation :
The third approach addresses a specific problem of icing : The fogging of transparent surfaces. Humid air condenses onto the cold surface rendering it iced and opaque. By the use of special polymer coatings we can inhibit icing of transparent surfaces (see fig. 2).

Fig. 2 Left : Cold glass slide with antifogging coating and clear, right : Untreated, cold glass slide, fogged.