Understanding aggregation and growth in a cross-linked polymer film*

Oil paints, used by celebrated artists such as Rembrandt, Picasso, Dalí and others, are composite materials consisting of pigment nanoparticles and polymerized drying oil. Dissocation of the pigment results in metal ions that react with the oil, yielding an insoluble metal soap. Over time scales of decades to centuries, these metal soaps aggregate, forming visible clusters and thus tainting the original work of art.

Lack of understanding of the aggregation and growth processes that occur in a cross-linked film hinders the conservation efforts aimed at preserving traditional works of art. To understand this degradation process, we propose a theoretical model combining existing models of nucleation and growth, as well as Ostwald ripening, with the elasticity and creep behavior of cross-linked polymers. Our model predicts the growth rates of clusters spanning nanoscopic to macroscopic length scales. The analytical results are supported by Monte Carlo simulations.