Effect of the Alkyl Chains and of the Headgroups on the Thermal Behavior of Ascorbic Acid Surfactants Mixtures

The role of the alkyl chain length and of the headgroup on the thermal behavior of mixtures of ASC8 (ascorbyl octanoate) and ASC16 (ascorbyl hexadecanoate) was investigated through differential scanning calorimetry, small- and wide-angle X-ray scattering, and Fourier transform infrared spectroscopy experiments. The formation of two eutectics and of a peritectic point was found from the phase diagram, and their structural properties were studied. The results were compared by investigating the thermal behavior of mixtures of octanoic acid and hexadecanoic acid. The findings provide insights into the role of the ascorbyl headgroups on the intermolecular interactions that determine the phase behavior of the two ascorbic acid based surfactants in the solid state

Complex Fluids Confined into Semi-interpenetrated Chemical Hydrogels for the Cleaning of Classic Art: A Rheological and SAXS Study

The removal of aged varnishes from the surface of easel paintings using the common conservation practice (i.e., by means of organic solvents) often causes pigment leaching, paint loss, and varnish redeposition. Recently, we proposed an innovative cleaning system based on semi-interpenetrated polymer networks (SIPNs), where a covalently cross-linked poly­(hydroxyethyl methacrylate), pHEMA, network is interpenetrated by linear chains of poly­(vinylpyrrolidone), PVP. This chemical gel, simply loaded with water, was designed to safely remove surface dirt from water-sensitive artifacts. Here, we modified the SIPN to confine complex cleaning fluids, able to remove aged varnishes. These complex fluids are 5-component water-based nanostructured systems, where organic solvents are partially dispersed as nanosized droplets in a continuous aqueous phase, using surfactants. The rheological behavior of the SIPN and the nanostructure of the fluids loaded into the gel were investigated, and the mechanical behavior of the gel was optimized by varying both the cross-linking density and the polymer concentration. Once loaded with the complex fluids, the hydrogels maintained their structural and mechanical features, while the complex fluids showed a decrease in the size of the dispersed solvent droplets. Two challenging case studies have been selected to evaluate the applicability of the SIPN hydrogels loaded with the complex fluids. The first case study concerns the removal of a surface layer composed by an aged brown resinous patina from a wood panel, the second case study concerns the removal of a homogeneous layer of yellowed varnish from a watercolor on paper. The results show that the confinement of complex fluids into gels allowed unprecedented removal of varnishes from artifacts overcoming the limitations of traditional cleaning methods

Structural and Mechanical Properties of “Peelable” Organoaqueous Dispersions with Partially Hydrolyzed Poly(vinyl acetate)-Borate Networks: Applications to Cleaning Painted Surfaces

The preparation and structural characterization of a family of viscoelastic dispersions of borate cross-linked, 80% hydrolyzed poly(vinyl acetate) (80PVAc) in aqueous–organic liquids are presented. Correlations between mechanical properties (from rheological measurements) and the degree and nature of cross-linking (from ¹¹B NMR spectroscopy) are reported, and the results are used to assess their potential as low-impact cleaning agents for the surfaces of paintings. Because the dispersions can be prepared at room temperature by simple procedures from readily available materials and can contain up to 50% (w/w) of an organic liquid, they offer important advantages over previously described cleaning agents that are based on fully hydrolyzed PVAc (i.e., poly(vinyl alcohol). The mechanical properties of the various aqueous–organic dispersions, as determined quantitatively by rheological investigations and qualitatively by their ease of removal from a solid surface (i.e., the so-called “peel-off” ability) have been tuned systematically by varying the amount of organic liquid, its structure, and the concentrations of borax and 80PVAc. The ¹¹B NMR studies demonstrate that the concentration of borate ions actively participating in cross-linking increases significantly with the amount of organic liquid in the mixture. The degree of cross-linking remains constant when the 80PVAc and borax concentrations are varied, as long as their ratios are kept constant. Some of the 80PVAc–borax dispersions have been tested successfully as cleaning agents on the surface of a 16th–17th century oil-on-wood painting by Lodovico Cardi, “Il Cigoli”, that was covered by a brown patina and on the surface of a Renaissance wall painting by Vecchietta in Santa Maria della Scala, Siena, Italy, that had a degraded polyacrylate coating from a previous conservation treatment