Nanostructured Surfactant-Based Systems for the Removal of Polymers from Wall Paintings: A Small-Angle Neutron Scattering Study

Abstract

Nanostructured soft matter systems represent effective and long-lasting solutions with respect to traditional and often obsolete methodologies for the conservation of works of art. In particular, complex fluids such as micelles and microemulsions are the most performing media for the removal of organic materials from porous supports, like wall paintings or stones. In this Article, we report on the characterization of two systems, EAPC and XYL, which have shown good to optimal performances in the removal of organic polymers from wall paintings. EAPC is a five-components fluid composed of water, sodium dodecylsulfate (SDS), 1-pentanol (PeOH), propylene carbonate (PC), and ethyl acetate (EA), while XYL is a "classical" o/w microemulsion, where p-xylene droplets are stabilized in water by SDS and PeOH. Small-angle neutron scattering (SANS) with contrast variation is used to infer a detailed picture of the structure of these complex fluids, with a particular focus on the partition of the components between the bulk phase and the nanocompartments. We found that, differently from XYL, the EAPC system is neither a microemulsion nor a simple micellar solution, with the cosolvents partitioned between the dispersing phase and the disperse droplets. These different structural features play a key role in defining the cleaning effectiveness and specifically the kinetics of interaction between the nanofluid and the polymeric coating to be removed, which is of paramount importance for the application in the field. Both of these nanofluids are effective in polymer removal, but EAPC is considerably more efficient and versatile. The composition and the structure at the nanoscale determine the capability of removing a broad range of different polymer coatings from porous materials. A representative case study is here described, addressing a particularly challenging conservative issue, which is the removal of a multilayered aged coating that was irreversibly damaging the pictorial layer of the Annunciation Basilica in Nazareth.

Practical applications of small-angle neutron scattering

“…35,36 For self-assembling organic species in solution, SANS is particularly useful because of the afforded high contrast between a 1 H-rich material and a 2 D-rich solvent. Consequently, one of the more common uses of SANS is for the characterisation of aggregate structures of surfactants, [37][38][39][40][41] 33,52,53 are also investigated, for a variety of purposes including mustard gas decontamination, 50 art restoration, 51 and drug delivery. 33 In this case, selective deuteration of the different components is frequently used to obtain a more detailed structural picture, as highlighted in Fig.…”

Mikroemulsionen, Micellen und funktionelle Gele: Erhaltung von Kunstwerken mit Kolloiden und weicher Materie

“…The reported effectiveness of nanostructured fluids prompted studies both on their structure and reactivity when they are applied for the cleaning of artefacts. A relevant study provided fundamental information on two o/w systems, selected based on the following rationale: [13] 1) One fluid, named XYL, contained a solvent insoluble in water (p-xylene), while the second, named EAPC, was a multi-component fluid containing two solvents partially soluble in water, i.e. ethyl acetate (EA) and propylene carbonate (PC); both fluids used SDS (sodium dodecyl sulfate) and 1-PeOH (1-Pentanol).…”

“…[19] For cleaning purposes it is fundamental that the structure of the micelles is not significantly altered by confinement in the gels, which was confirmed by SAXS analysis. [13,17,20] Advanced semi-IPNs gels showed outperforming properties for highly sensitive substrates such as dyed paper and paintings with low amounts of binders (e.g. Tang-ka paintings, see Figure 4).…”

Innovative Nanomaterials: Principles, Availability and Scopes

“…• In several practical applications, nanostructured fluids can remove effectively detrimental coatings that can not be dissolved by conventional solvents (e.g. acetone, benzyl alcohols and xylenes), or that would require the use of aggressive and toxic solvents (Carretti et al 2007;Baglioni et al 2012). This is due to the structure and chemical composition of the surfactant-based fluids, and to the mechanisms through which they interact with organic coatings (the interaction will be further described in Sect.…”