Cleaning acrylic paints: mineral spirits-based microemulsions and the question of residues

This paper presents a summary of some research into the evaluation of mineral spirits-based microemulsions as wet surface cleaning systems for artists’ acrylic emulsion paint films. Examples from four different mineral spirits-based microemulsion systems were evaluated, each having a different primary surfactant component. Particular attention is given here to determination, using surface-sensitive analytical techniques (ATR-FTIR, XPS and ToF-SIMS), of possible microemulsion surfactant residues remaining on paint films after wet cleaning treatment. Three different test paint films were subjected to simulated cleaning treatments: Golden Heavy Body Acrylic PY3 (azo yellow); Liquitex Heavy Body Artist Acrylic PY3 (azo yellow); and Liquitex Heavy Body Artist Acrylic PW6 (titanium white). In comparison with untreated controls, samples were analysed by the above methods at two stages: after treatment with cleaning liquid but without any clearance step, and again after clearance of any residue with hydrocarbon solvent. These investigations have shown that only trace amounts of surfactant residues may remain on paint surfaces. Indications of the presence of residual surfactant naturally depends on the respective sensitivities of the different analytical techniques: the detection limit for ATR-FTIR is lower than XPS and ToF-SIMS. As has been shown to be the case for aqueous treatments, levels of intrinsic surfactant in acrylic paint films and migrated surfactant located at paint surfaces can also be affected by these cleaning treatments

Conservation of artists' acrylic emulsion paints: XPS, NEXAFS and ATR-FTIR studies of wet cleaning methods

Works of art prepared with acrylic emulsion paints became commercially available in the 1960s. It is increasingly necessary to undertake and optimise cleaning and preventative conservation treatments to ensure their longevity. Model artists' acrylic paint films covered with artificial soiling were thus prepared on a canvas support and exposed to a variety of wet cleaning treatments based on aqueous or hydrocarbon solvent systems. This included somewith additives such as chelating agents and/or surfactants, and microemulsion systems made specifically for conservation practice. The impact of cleaning (soiling removal) on the paint film surface was examined visually and correlated with results of attenuated total reflection Fourier transform infrared, XPS and near-edge X-ray absorption fine structure analyses - three spectroscopic techniques with increasing surface sensitivity ranging from approximately - 1000, 10 and 5 nm, respectively. Visual analysis established the relative cleaning efficacy of the wet cleaning treatments in line with previous results. X-ray spectroscopy analysis provided significant additional findings, including evidence for (i) surfactant extraction following aqueous swabbing, (ii) modifications to pigment following cleaning and (iii) cleaning system residues

Evidence and use of metal-chromophore interactions: luminescence dichroism of terthiophene-coated gold nanoparticles in polyethylene oriented films

Nanocomposites with unusual and anisotropic optical properties have been obtained through the dispersion of gold nanoparticles and gold-binding chromophores in a stretched polymer matrix (Ultra High Molecular Weight PolyEthylene, UHMWPE). Strongly dichroic terthiophene-based chromophores, previously used in anisotropic UHMWPE dispersions, were modified with a thiol group and used for the preparation of gold nanoparticles. We demonstrate that the electronic systems of the chromophores are coupled with the gold nanoparticles. For the first time, evidence is reported that the polarization of the absorbed radiation can be preserved during energy transfer between a chromophore and a metal particle.14243495350

Proton Transfer on the Edge of the Salt/Co-Crystal Continuum: X-ray Photoelectron Spectroscopy (XPS) of Three Isonicotinamide Salts

X-ray photoelectron spectroscopy (XPS) has emerged as a technique that allows for characterization and classification of hydrogen bonding and proton transfer interactions in organic crystal structures, in a way that is complementary to crystallography by X-ray or neutron diffraction. Here, we analyze the nitrogen 1s core-level binding energies (BEs) of isonicotinamide (IN) systems with proton transfer between donor and acceptor groups at short distances. We show how a careful calibration of the BE scale places these salt systems correctly on the edge of the so-called salt–cocrystal continuum. We show how performing a fitting analysis of the data that is consistent with elemental analysis, expected stoichiometry, and quantification of adventitious carbon contamination facilitates the determination of absolute BEs with accuracy and reproducibility within ±0.1 eV. The determined N 1s core-level BEs of the protonated IN acceptors suggest that the local geometric arrangements of the donor, acceptor, and proton can influence the N 1s core-level BE significantly

X-ray Raman scattering: a new in situ probe of molecular structure during nucleation and crystallization from liquid solutions

X-ray Raman scattering (XRS) has been used for in situ probing of solute molecule speciation in solution during cooling crystallization. The C and N K-edges of aqueous imidazole were measured as a function of temperature to monitor the transition from the undersaturated state through supersaturation to crystallization. A new jacketed-vessel crystallizer with internal flow was used, which enables thermal control and minimizes radiation damage. We have demonstrated that the C and N K-edges of imidazole are sensitive to changes in local bonding. In line with this, an abrupt change in the N K-edge fine structure indicates the onset of desolvation and crystallization from the supersaturated solution. In contrast, negligible changes are observed in the C and N K-edge spectra acquired during cooling, indicating that the average solvation structure around imidazole molecules does not change significantly while traversing the thermodynamically metastable supersaturated zone. To the best of our knowledge this is the first time X-ray Raman scattering has been used for studying molecular speciation in organic aqueous solutions during crystallization. Time-dependent density functional theory (TD-DFT) calculations of the near-edge spectra were performed using implicit, explicit and combined solvation models to elucidate the likely binding sites of the water molecules. An explicit solvation model with one water molecule coordinating each nitrogen moiety in the imidazole ring accurately reproduces the peak positions and intensities of the XRS spectra of aqueous imidazole solution