Abstract
Halloysite nanotubes were used to incorporate anionic surfactant micelles and an organic solvent to generate a cleaning system to be applied in Cultural Heritage restoration. The targeted adsorption is driven by electrostatic interactions based on the nanotubes peculiar charge separation. Namely anionic species are driven to the positively charged inner surface while being prevented from interacting with the halloysite outer surface that possesses a positive charge density. The hybrid organic/inorganic emulsion was characterized by dynamic light scattering. Analysis of the autocorrelation function allowed us to define the presence of surfactant aggregates inside/outside the nanotube lumen as a function of the nanotube/surfactant ratio in an aqueous mixture. The application of this prepared emulsion for the controlled cleaning of a marble artifact is demonstrated. To this purpose, a membrane of nanofibrous polyacrylonitrile was prepared by electrospinning and was applied between the work of art and the cleaning agent to avoid the release of residues on the marble surface. This work represents a further step toward the opportunity to extend the use of emulsions for cleaning protocols for stone-based artifacts or in technological applications where surfactant separation is required by a simple centrifugation/sedimentation method.
Highlights
Microemulsions have largely attracted attention in cleaning for Cultural Heritage restoration, replacing conventional methods that are difficult to control
The oil in water emulsions were characterized by Dynamic light scattering (DLS) to identify the best conditions to prepare oil droplet sizes for loading into the halloysite nanotubes (HNTs) lumen
The ζ potential for the microemulsions provided a negative value of ~−12 mV. These findings suggest the presence of a negative charge at the micelle/water interface, which guarantees the suggest the electrostatic presence ofinteraction a negativewith charge atpositive the micelle/water interface, which guarantees the selective selective electrostatic interaction with HNT positive inner surface
Summary
Microemulsions have largely attracted attention in cleaning for Cultural Heritage restoration, replacing conventional methods that are difficult to control. The commonly used organic solvents or gels are often toxic and high evaporation rates can represent a risk for the operators. Restoration of the Renaissance paintings by Masaccio, Masolino, and Lippi in the Brancacci Chapel in Florence (1984–1990) represents the first case study reporting the use of microemulsions for conservation purposes [2,3]. Amphiphile-based systems were intensively studied by Piero Baglioni to remove synthetic materials (acrylic and vinyl polymers) from painted surfaces [4]. These results show that the designed nanostructures improved the traditional methods while both minimizing the environmental impact and the optimizing cleaning performance [4]. Disadvantages for the use of colloidal systems are related to the high wettability of the treated surface and to spreading within the substrate porosity
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