Dynamics of diffusion, evaporation, and retention of organic solvents in paints by unilateral NMR and HR-MAS NMR spectroscopy

Abstract

Transport of organic solvents in polymeric matrices plays a central role in many processes of interest to the coatings industry. Previous studies have focused on individual processes taking place in the solvent-paint system. In the present study, we report results on the molecular dynamics in a solvent/paint system during the entire sequence of absorption, diffusion, swelling, and evaporation processes, obtained non-invasively, in situ, and in real time using unilateral NMR relaxometry. The associated chemical structures were investigated using HR-MAS NMR spectroscopy. Four distinct ranges of molecular motion in the solvent/paint film were identified based on proton NMR transverse relaxation time (T2) data. The fast motion of the freely moving solvent molecules was discriminated from the slower motion of the so-called bound phase of the solvent molecules physically and chemically interacting with the cross-linked polymer network. In addition, two distinct domains of the cross-linked and mobile phases of the polymerized oil were observed, allowing the study of both the dynamics of the swelling-contraction process of the polymer and of the solubilization process. Such non-invasive analyses provide significant information on transport phenomena of the solvent in the paint film, as well as on the effects of various solvents applied to oil paintings.