Abstract
Surface modification of polymers and paints is a popular and effective way to enhance the properties of these materials. This can be achieved by introducing a thin coating that preserves the bulk properties of the material, while protecting it from environmental exposure. Suitable materials for such coating technologies are inorganic oxides, such as alumina, titania and silica; however, the fate of these materials during long-term environmental exposure is an open question. In this study, polymer coatings that had been enhanced with the addition of silica nanoparticles (SiO2NPs) and subsequently subjected to environmental exposure, were characterized both before and after the exposure to determine any structural changes resulting from the exposure. High-resolution synchrotron macro ATR-FTIR microspectroscopy and surface topographic techniques, including optical profilometry and atomic force microscopy (AFM), were used to determine the long-term effect of the environment on these dual protection layers after 3 years of exposure to tropical and sub-tropical climates in Singapore and Queensland (Australia). Principal component analysis (PCA) based on the synchrotron macro ATR-FTIR spectral data revealed that, for the 9% (w/w) SiO2NP/polymer coating, a clear discrimination was observed between the control group (no environmental exposure) and those samples subjected to three years of environmental exposure in both Singapore and Queensland. The PCA loading plots indicated that, over the three year exposure period, a major change occurred in the triazine ring vibration in the melamine resins. This can be attributed to the triazine ring being very sensitive to hydrolysis under the high humidity conditions in tropical/sub-tropical environments. This work provides the first direct molecular evidence, acquired using a high-resolution mapping technique, of the climate-induced chemical evolution of a polyester coating. The observed changes in the surface topography of the coating are consistent with the changes in chemical composition.
Highlights
The surface modification of polymers and paints used to coat substrate surfaces is an attractive method for enhancing the properties of these materials [1,2,3,4]
The water contact angles were found to be slightly lower than 90 ̊ for all of the substrate coatings prior to exposure, indicating that they were exhibiting marginally hydrophobic behavior, as would be expected for a surface comprised of polyester
The results obtained using this combined technique provided evidence of changes occurred as a result of environmental exposure, in the molecular structure of the polymer
Summary
The surface modification of polymers and paints used to coat substrate surfaces is an attractive method for enhancing the properties of these materials [1,2,3,4]. Materials typically used for these applications are inorganic oxides, such as alumina, titania and silica [2,3,4] These materials are often combined or derivatized in various ways; one example is via the absorption of functional agents throughout mesoporous networks. These coatings may be applied through solution based processes or via vapor deposition technologies. Given that the substrate surfaces being coated may be unstable in the environment, the fate of the coating materials and their ability to retain their protective and mechanical properties during long-term environmental exposure is of paramount importance. The long-term effect of environmental exposure upon these dual protection layers on steel surfaces has, not been studied
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