Tuning the wetting properties of Paraloid B72 from hydrophilicity to superamphiphobicity combined with antibacterial properties

Abstract

Paraloid B72 is a methyl acrylate/ethyl methacrylate copolymer which is extensively used as a consolidant, binder, adhesive, protective coating and varnish for the conservation and preservation of cultural heritage buildings and objects. In this study, a one-step method is developed to convert the inherently hydrophilic B72 into a superamphiphobic material, thereby improving its protective performance against both water- and oil-based pollutants. In particular, B72 is blended with silica nanoparticles (Si) and a fluororesin (F) in various concentrations, producing coatings which are initially deposited on glass (reference substrate). The nanoparticles highly affect the surface morphology of the coatings, inducing superhydrophobicity, whereas F lowers its apparent surface energy resulting to superamphiphobicity. A systematic study is conducted to carefully select the relative concentrations of the two additives, Si and F, which are necessary to achieve the desired superamphiphobicity. The interaction of the selected superamphiphobic coating with liquid drops spanning a wide range of surface tensions is examined, while the evaporation process of a water drop on the superamphiphobic surface is shown to be governed by a series of stick-slip events. Furthermore, it is demonstrated that the coating imparts superamphiphobicity to wood, paper, cotton and limestone. The latter is subjected to further investigations, revealing that the treatment has minimal impact on both the colour and breathability of limestone while it enhances the resistance of the treated stone to capillary water absorption. Finally, a key finding is that the liquid-repellent nature of the superamphiphobic coating inhibits the growth of S. aureus.

Keywords Antibacterial; Cultural heritage; Paraloid; Stone; Superamphiphobic; Superhydrophobic; Superoleophobic