Fig 1. Surface nanotopography of pure polyester and 4.5% and 9% SiO₂NPs polyester composite coatings on steel substrata under sub-tropical and tropical climate from year 0 to year 5.

Atomic force micrographs, over a scanning areas of 1 × 1 μm², showing the change in surface nanotopography of (A) 0% SiO₂NPs, (B) 4.5% SiO₂NPs, and (C) 9% SiO₂NPs after the 5-year exposure to subtropical and tropical climates.