Biomimetic anti-icing epoxy coating based on controlled-secreting hydrophobic small molecules in microcapsules through shrinkable gel under low temperature

The design of anti-icing structures is challenging for epoxy coatings, which are widely used in aircraft, wind power generation equipment, and outdoor buildings. Inspired by the principle that bird feathers are not easily frozen, a smart biomimetic anti-icing epoxy coating based on controlled-secreting hydrophobic small molecules in microcapsules was designed in this work. The remarkable feature of these microcapsules is that they can secreting small molecule oil at low temperature, but the release rate is very low at room temperature controlled by restriction of gel in the microcapsules' shell. Optical and SEM morphology showed that microcapsules were globe-shaped particles with compacted shells. FT-IR results indicated that the core material of glycerol trioctanoate was well protected by the shell skeleton of cross-linked methylated melamine-formaldehyde (HMMM) resin. Gelatin was filled in the microporous structure of the shell skeleton structure. AFM results showed that the gel material shrank at low temperatures, producing tiny holes in the shell material. The temperature sensitivity of gelatin was the valve for core release. The controlled-secreting property of microcapsules under various temperatures was measured using high-oil absorbent paper. Pore microstructure appeared on the shell of microcapsules after an alcohol delusion of the gel process. It was found that the secreting rate of the core material from the microcapsule was faster at low temperatures (-10∼ 20 °C) because of the shrinkage of gel material in the skeleton structure. SEM results also indicated that the microcapsules were dispersed homogeneously in the epoxy coating without any accumulation phenomenon. Moreover, the interface between microcapsules and epoxy resin was stable, and no interface separation debonding appeared even under the temperature of −20–40 °C. Surface hydrophobicity tests indicated that the epoxy coating with 3.0 wt% microcapsules had the largest water contact angle of 95°. The core material-secreting traces were observed, which confirmed that the hydrophobic small molecules migrated to the surface of the epoxy coating. Ice shear force values proved that more additive microcapsules provided more hydrophobic small molecules' secreting capacity to the coating's surface under a low temperature of −15 °C. This anti-icing function was sustainable and stable under violent temperature-change cycling, ensuring the coating material had a longer anti-icing service life.