Stability of fluid ultrathin polymer films in contact with solvent-loaded gels for cultural heritage

Abstract

The removal of ultrathin amorphous polymer films in contact with an aqueous gelled solution containing small amounts of good solvent is addressed by means of specular and off-specular neutron reflectometry. The distribution of heavy water and benzyl alcohol is revealed inside Laropal A81, often employed as a protective varnish layer for Culture Heritage in the restoration of easel paintings. The swelling kinetics, interface roughness, and film morphologies were recorded as a function of temperature and increasing benzyl alcohol concentration in the dispersion of Pemulen TR-2, a hydrophobically modified acrylic acid copolymer. The addition of small amounts of good solvent results in the appearance of water-filled cavities inside the varnish, which grow with time. It is shown that while increasing the solvent concentration greatly enhances the hole growth kinetics, an increase in temperature above the glass transition temperature does not have such a big effect on the kinetics.