Nanomechanical degradation of a waterborne acrylate coating due to accelerated weathering revealed by atomic force microscopy

Waterborne polymer coatings are increasingly used as sustainable alternatives to solvent-borne systems, but their long-term durability remains a challenge. Elucidating their degradation mechanism at the nanoscale, where damage first emerges, is essential for delivering more durable waterborne coatings. Here, we use intermodulation atomic force microscopy (ImAFM) to investigate the nanoscale origins of degradation in an accelerated weathered waterborne acrylate coating. Our measurements reveal a progressive, three-stage degradation pathway induced by accelerated weathering. In the first stage, the coating stiffens as a result of physical aging and (photo-)chemically induced degradation. Subsequently, former acrylate particles re-emerge and become surrounded by regions of increased damping and reduced stiffness. Continued weathering eventually gives rise to pronounced viscoelastic heterogeneity. To support these observations, we performed both bulk and nanoscale dynamic mechanical analysis measurements on accelerated weathered samples. These measurements reveal increased storage modulus and damping, consistent with the nanoscale evolution observed by ImAFM. Together, these results identify the mechanical changes that precede macroscopic embrittlement and demonstrate that durability limitations in waterborne acrylate coatings are strongly linked to the development of localized viscoelastic heterogeneity at the nanoscale.