Graphene oxide (GO) nanofillers have been incorporated into polymeric coatings and composites to improve the mechanical, barrier, and thermal properties of the system. This study aims to develop methods for investigating and assessing surface morphological changes of waterborne polyurethane (WBPU) coatings containing GO additives under different UV exposure conditions to understand how the GO nanofillers affect the integrity of coatings surface and eventually the long-term performance of the coatings. Morphological changes are important to track because they can alter a protective coatings appearance as well as barrier, scratch, and crack-resistance properties. Specimens of GO/WBPU coatings with different GO mass loadings were exposed to high intensity ultraviolet (UV) light using the NIST SPHERE device at 55 ºC and two relative humidity (RH) levels (≈ 0 % and 75 %). Laser scanning confocal microscopy (LSCM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the surface morphological changes at different UV exposure times and conditions. General approach was to use LSCM optical method to quickly screen the surface morphological changes of samples in multiscale, then zoom into a smaller scanning area to identify GO particles versus polymer features on the UV-degraded surfaces using AFM and SEM. In addition, AFM in Peak Force QNM mode (quantitative nanomechanical property) mapping was used to measure the increase of surface modulus to validate the presence of GO particles at the surface that accompanied the surface morphological changes. Overall, a combination of microscopy methods was found useful to assess the change in surface morphology of GO/WBPU coatings, to understand the effect of GO particles on degradation behavior under different exposure conditions. This approach can be employed for other polymer coatings that incorporate graphene-family nanomaterials.
April 8-10, 2019
AFM, Coatings, Graphene oxide, Laser scanning confocal microscopy, nanofiller, waterborne polyurethane, UV