The low surface energy characteristics and hydrophobicity of silicone coatings are the core functional foundations. The two are interrelated and jointly determine the anti-fouling and self-cleaning properties of the coating. The following is an analysis from three aspects: molecular mechanism, performance and application correlation:

1. Molecular mechanism of low surface energy characteristics
‌Chemical structure root‌
Silicone coatings are based on ‌Si-O-Si‌ as the main chain and low polar groups (such as methyl and phenyl) as the side chains. The Si-O bond has high bond energy (121 kcal/g molecule), which gives the molecular chain flexibility and stability; while the outward-arranged methyl groups reduce the surface energy to ‌20-25 mN/m‌ (much lower than 72 mN/m of water), forming a hydrophobic barrier.
‌Modification improvement‌: The introduction of fluoroalkyl groups (such as -CF₃) can further reduce the surface energy to ‌6.7 mN/m‌, and the contact angle reaches 115°.

‌Surface molecular orientation‌
Heat treatment (350-400℃) causes the siloxane dipoles to be oriented, and the methyl groups densely cover the surface, minimizing the surface energy. The surface energy of the untreated coating is about 30 mN/m, and the contact angle increases from 60° to 100-110° after heat treatment.

2. Mechanism of hydrophobicity
‌Static hydrophobic effect‌
Low surface energy makes the water contact angle ‌≥90°‌, showing obvious hydrophobicity. Typical data:

Contact angle of pure silicone coating: ‌101°‌ (methyl-dominated)
Contact angle of fluorosilicone modified coating: ‌≥110°‌ (lotus effect level)
‌Dynamic self-cleaning function‌
When the surface energy of the coating is ≤25 mN/m, rainwater can wash away more than 90% of the dust. The mechanism is:

‌Low adhesion‌: Water rolling angle <10°, dirt is easily peeled off by water flow
‌Micro-nano rough structure‌: Add nano-SiO₂ and other materials to construct a papillary structure, trap air to form an air cushion, and the contact angle can reach 150-161.5° (super hydrophobic)

3. Performance correlation and application performance
‌Characteristic correlation‌ ‌Application performance‌
‌Low surface energy + high flexibility‌ Ship antifouling: When the surface energy is <25 mJ/m², the adhesion strength of marine organisms is reduced by 70%
‌Hydrophobicity + breathability‌ Building protection: Allow water vapor to pass through (0.5-2.0 g/m²·h), while blocking liquid water from penetrating
‌Chemical inertness + low surface energy‌ Metallic art paint finish: Anti-fingerprint (contact angle 110°), oil stains are not easy to adhere
‌Limitations‌ Pure silicone has low mechanical strength and needs to be modified (such as silicon-epoxy composite) to improve adhesion.

4. Progress in modification technology
‌Nano hybrid enhancement‌
Aminopropyl-modified SiO₂ nanoparticles (particle size 55-230nm) are grafted with silicone polymers to make the contact angle of cotton fabric reach 158.5°, and it is still >140° after 20 washes.
‌Fluorosilicone synergistic effect‌
Perfluoroalkyl + siloxane network structure, the contact angle rises to 161.5°, and the rolling angle is only 9° (close to the super hydrophobic limit).
‌Environmentally friendly water-based‌
The dynamic surface tension of water-based silicone wetting agent (polyether modified silicone oil) is ≤25 mN/m, which solves the problem of substrate shrinkage.
‌Application tips‌: In extreme environments (such as strong acids/solvents), fluorosilicone modification or composite coatings are required to avoid failure due to Si-O bond hydrolysis (strong acid) or swelling (oils).