Anti-frost coatings containing carbon nanotube composite with reliable thermal cyclic property

Abstract

One of the most important applications for superhydrophobic coatings is anti-frosting for safety and energy conservation. Safety concerns are especially critical in cold-climate regions where the daily temperature fluctuation is large. However, superhydrophobic coatings have not been studied in terms of their thermomechanical reliability. In this study, wetting characteristics and stress relaxation behavior were quantitatively investigated with multi-walled carbon nanotube (MWNT)–silicone composite films under thermal cycling conditions. It is concluded that an open structure with numerous nanopores among the fillers, constituting air pockets described as the “Cassie structure,” is of great importance not only for developing a film's superhydrophobic nature but also for accommodation of thermal stress that results from a difference in coefficient of thermal expansion between the coating and the substrate. The amount of stress relaxation for a 30 vol% MWNT–silicone composite film with open structure reaches ∼80% of the value for its counterpart with a closed structure and no pores. A superhydrophobic MWNT–silicone composite film that can endure over 4000 thermal cycles (−30 °C to room temperature) is fabricated by controlling the composition and microstructure of the composite. In addition, the importance of the size and shape of the nanofillers in delaying nucleation and growth of frost on superhydrophobic coatings is also discussed.