Detrended fluctuation analysis of UV degradation in a polyurethane coating

Changes in the intrinsic structure of paint surfaces resulting from extended UV exposure can significantly alter the appearance of paint due to a breakdown in the resin that binds the pigments and flattening agents. In this study, the coating structure of a solvent-based poly-urethane was analyzed to establish correlations between the intrinsic spatial scaling properties of the coating and UV exposure time. Atomic force microscopy and laser scanning confocal microscopy were employed to map surface structures over a range of scales from 80 nm to 80 εm. The roughness of the polyurethane surface was characterized in terms of scaling exponents using detrended fluctuation analysis to identify long-range, power law relations, and to correct for inhomogeneities in the surface structure. The time-dependence of the roughening process was also determined and correlated with changes in gloss. AMSTA-AR-CCB-TA, Watervliet, NY 12189-4050. Email: majohn@pica.army.mil and pcote@pica.army.mil