Surface-Active Ionic-Liquid-Based Coatings as Anti-Biofilms for Stone: An Evaluation of Their Physical Properties

The biodeterioration of stone surfaces can be a threat to the conservation of built heritage. Much effort has been put into finding treatments and processes to mitigate biocolonization and its effects, both in terrestrial and underwater environments. Recently, the use of surfactant ionic liquids has been shown to have biocidal and antifouling effects on stone. However, little information is currently available on the morphological and physical properties of such coatings. In this paper, we report on the physical characterization of coatings based on an ionic liquid (IL) consisting of N-(2-hydroxyethyl)-N,N-dimethyl-1-do-decanaminium cation and a combination of bromide and dodecylbenzenesulfonate (DBS) anions in a molar ratio of 3:1, respectively. Nanosilica and tetraethyl orthosilicate were used as binders to promote the adhesion of the ionic liquid to the stone surface. The coatings were applied on Carrara marble samples and analyzed using Scanning Electronic Microscopy (SEM), static contact angles, colorimetric measurements and capillary water absorption. The resistance to UV radiation and seawater was also investigated. The results show that the IL behaves differently depending on the binder. The latter influences the arrangement of the IL and its wettability, which decreases in the case of NanoEstel, whereas this parameter increases in the case of Estel. In addition, the coatings show good resistance to the degradation agents.