Development and application of superhydrophobic coatings with high thermal conductivity and self-healing properties: Synergistically enhancing condensation heat transfer through surface modification

Abstract

Current superhydrophobic coatings suffer from low thermal conductivity (TC), complex processes, and irreparability, limiting their effectiveness in condensation heat transfer for steam energy recovery, especially with low-grade steam. This study focuses on surface modification to enhance condensation heat transfer and develops superhydrophobic coatings with high TC and self-healing properties for practical applications. We investigated the synergistic effects, and the mechanisms of damage and self-healing processes. By optimizing the formula, we improved the hydrophobicity, TC, and mechanical strength. The “brick-and-mortar” coating was created by the self-assembly of SiO₂ and graphene, the hybrid curing of polydimethylsiloxane (PDMS) and polytetrafluoroethylene (PTFE), and the cross-linking with silane coupling agent. It achieved a water contact angle (CA) of 162.7 ± 2.1°, hardness (ISO 4H), adhesion (ISO Level 1 or ASTM 4B). It exhibited stable superhydrophobicity under mechanical and chemical damage, maintaining dropwise condensation for at least 90 days even after damage. The SiO₂@PDMS structure endows the coating with self-healing properties under light/thermal treatment. Its |Z|_{0.1 Hz} remained at 1.3 × 10^10 Ω cm² after 7 days in the 3.5 wt% NaCl solution. Applied to stainless steel, the coating increased heat conduction by 45.4 % and the heat transfer coefficient for low-grade heat by up to 142.6 %, with a 5:4 contribution from superhydrophobicity and high TC. The outstanding TC, low cost, and self-healing properties of this superhydrophobic coating give it broad application prospects in low-grade steam recovery.