Fig 2. Average nanoscale surface roughness of pure polyester and 4.5% and 9% SiO₂NPs polyester composite coatings on steel substrata as a function of exposure time from year 0 to year 5, under tropical (left) and sub-tropical (right) conditions.

Data is presented as mean ± standard deviation. Insets: change in average roughness values as a function of time.