Microemulsion Encapsulated into Halloysite Nanotubes and their Applications for Cleaning of a Marble Surface

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.