Non-Aqueous Poly(dimethylsiloxane) Organogel Sponges for Controlled Solvent Release: Synthesis, Characterization, and Application in the Cleaning of Artworks.

Polydimethylsiloxane (PDMS) organogel sponges were prepared and studied in order to understand the role of pore size in an elastomeric network on the ability to uptake and release organic solvents. PDMS organogel sponges have been produced according to sugar leaching techniques by adding two sugar templates of different forms and grain sizes (a sugar cube template and a powdered sugar template), in order to obtain materials differing in porosity, pore size distribution, and solvent absorption and liquid retention capability. These materials were compared to PDMS organogel slabs that do not contain pores. The sponges were characterized by Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) and compared with PDMS slabs that do not contain pores. Scanning electron microscopy (SEM) provided information about their morphology. X-ray micro-tomography (XMT) allowed us to ascertain how the form of the sugar templating agent influences the porosity of the systems: when templated with sugar cubes, the porosity was 77% and the mean size of the pores was ca. 300 µm; when templated with powdered sugar, the porosity decreased to ca. 10% and the mean pore size was reduced to ca. 75 µm. These materials, porous organic polymers (POPs), can absorb many solvents in different proportions as a function of their polarity. Absorption capacity, as measured by swelling with eight solvents covering a wide range of polarities, was investigated. Rheology data established that solvent absorption did not have an appreciable impact on the gel-like properties of the sponges, suggesting their potential for applications in cultural heritage conservation. Application tests were conducted on the surfaces of two different lab mock-ups that simulate real painted works of art. They demonstrated further that PDMS sponges are a potential innovative support for controlled and selective cleaning of works of art surfaces.

Performance of innovative nanomaterials for bone remains consolidation and effect on 14C dating and on palaeogenetic analysis.

An innovative protocol for the consolidation of ancient bone remains based on the use of nanometric HydroxyAPatite (HAP) was set up and tested through a multidisciplinary approach. A new protocol for the synthesis of HAP nanoparticles was developed, and the composition of the obtained nanomaterial was investigated through Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD); sizes, shape and morphology of the synthesized particles were studied by Scanning Electron Microscopy (SEM). The consolidation performance was evaluated by testing the new nanomaterial on degraded ancient bone findings. An increase of the mineral density and of the micro-hardness of the bone were observed. The new consolidation method was also tested to assess possible effects on the palaeogenetic analysis and radiocarbon dating on the treated bones. The consolidation treatment does not introduce any contaminations that could affect radiocarbon dating and has no general detrimental impact on the genetic characterization of the skeletal remains. This consolidation procedure represents a more compatible conservation tool with respect to traditional procedures: it has been shown that the treatment is effective, easily-applicable and compatible with post-consolidation analysis.

Indoor levels of volatile organic compounds at Florentine museum environments in Italy.

Indoor Air Quality monitoring in cultural institutions is of particular concern to protect these places and the cultural heritage content. An indoor monitoring campaign was performed in three museums in Florence (Italy) to determine the occurrence and levels of volatile organic compounds (VOCs). VOCs of interest included BTEX (benzene, toluene, ethylbenzene, xylenes), terpenes, aldehydes, organic acids, and cyclic volatile methyl siloxanes (cVMS). The most abundant VOCs in all samples analyzed were BTEX, which were strictly related to the traffic source, followed by siloxanes and terpenes. Among BTEX, toluene was always the most abundant followed by xylenes, ethylbenzene, and benzene. cVMS in exhibition rooms with the presence of visitors showed higher values compared to samples collected when the museums were closed. Terpenes showed not only the influence of vegetation-biogenic sources surrounding a museum but could also be related to the wood used for the construction of showcases and furniture and the use of cleaning products. Data obtained also showed the presence of organic acids and aldehydes whose source can be traced back to exhibits themselves and wood-based furniture. Assessing the levels of organic acids in museums is important because, over time, it can cause deterioration of the artifacts.

First evidence of microplastic ingestion by fishes from the Amazon River estuary.

This study investigated occurrence of microplastic particles in digestive tracts of fishes from the Amazon River estuary. A total of 189 fish specimens representing 46 species from 22 families was sampled from bycatch of the shrimp fishery. Microplastic particles removed from fish gastrointestinal tracts were identified using Attenuated Total Reflectance - Fourier Transform Infrared (ATR-FTIR). In total, 228 microplastic particles were removed from gastrointestinal tracts of 26 specimens representing 14 species (30% of those examined). Microplastic particles were categorized as pellets (97.4%), sheets (1.3%), fragments (0.4%) and threads (0.9%), with size ranging from 0.38 to 4.16 mm. There was a positive correlation between fish standard length and number of particles found in gastrointestinal tracts. The main polymers identified by ATR-FTIR were polyamide, rayon and polyethylene. These findings provide the first evidence of microplastic contamination of biota from the Amazon estuary and northern coast of Brazil.

Structural, rheological and dynamics insights of hydroxypropyl guar gel-like systems.

A dynamic, rheological, and structural characterization of aqueous gel-like systems containing hydroxypropyl guar gum (HPG), borax and glycerol is presented in this paper. The role of glycerol, which is introduced as a plasticizer in the formulation, is investigated by means of 11B NMR and 1H NMR PGSTE measurements in order to clarify its contribution to the gel network formation and its interaction with borax, with whom it forms a complex. The effect of gels components on the rheological behaviour and on the activation energy related to the relaxation process of the system was assessed by means of rheology. The results obtained suggest that the mechanical properties of these gels can be tuned and controlled by modulating the formulation in a wide range of compositions. Moreover, a structural characterisation has been also carried out by means of Small Angle X-ray Scattering (SAXS) to highlight the role of the various components on the mesh size of the network. The structural and mechanical characteristics of these systems suggest their potential use for applicative purposes. In this regard, one of the gel set up has been successfully tested as cleaning agent on the surface of a XIX stucco fragment coming from the La Fenice theatre (Venice, Italy) for the removal of a dirt layer composed by dust and particulated matter originated during a fire in 1996.

Specific Anion Effects on the Kinetics of Iodination of Acetone.

Specific ion effects on the kinetics of iodination of acetone in an acidic medium are investigated by UV/Vis spectrophotometry as a function of nature of the acid and temperature. The results indicate that the order of the reaction with respect to acetone is practically unaffected by the composition of the acid while the value of the mixed constant k1 K increases according to the sequence HBr

Structure and rheology of gel nanostructures from a vitamin C-based surfactant.

The structure and rheology behaviour of gels produced by water dispersions of a vitamin C-derived surfactant (ascorbyl-6-O-dodecanoate) were investigated by means of SAXS and rheology experiments for the first time. The gel state is formed upon heating and is due to an anisotropic expansion of the tightly compact lamellar structure. The phase transition involves primarily the melting of the alkyl chains and a significant increment in the interlamellar water layer. In particular, our results show that in the gel the hydrophobic chains are in a liquid-like state, as in the core of a micelle, while the head groups release their acidic proton, become negatively charged and determine the onset of strong electrostatic interactions between facing lamellae. The full hydration of the anionic head groups and the uptake of a significant amount of water increase the interlamellar thickness and stabilise the gel structure. Rheology and SAXS measurements together provide an updated picture for the gel state. Moreover, for the first time we show the presence of a concentration threshold, above which the self-assembled aggregates interact more strongly and deplete some of the water that is retained in the interlamellar region.

Controlled graphene oxide assembly on silver nanocube monolayers for SERS detection: dependence on nanocube packing procedure.

Hybrid graphene oxide/silver nanocubes (GO/AgNCs) arrays for surface-enhanced Raman spectroscopy (SERS) applications were prepared by means of two procedures differing for the method used in the assembly of the silver nanocubes onto the surface: Langmuir-Blodgett (LB) transfer and direct sequential physisorption of silver nanocubes (AgNCs). Adsorption of graphene oxide (GO) flakes on the AgNC assemblies obtained with both procedures was monitored by quartz crystal microbalance (QCM) technique as a function of GO bulk concentration. The experiment provided values of the adsorbed GO mass on the AgNC array and the GO saturation limit as well as the thickness and the viscoelastic properties of the GO film. Atomic force microscopy (AFM) measurements of the resulting samples revealed that a similar surface coverage was achieved with both procedures but with a different distribution of silver nanoparticles. In the GO covered LB film, the AgNC distribution is characterized by densely packed regions alternating with empty surface areas. On the other hand, AgNCs are more homogeneously dispersed over the entire sensor surface when the nanocubes spontaneously adsorb from solution. In this case, the assembly results in less-packed silver nanostructures with higher inter-cube distance. For the two assembled substrates, AFM of silver nanocubes layers fully covered with GO revealed the presence of a homogeneous, flexible and smooth GO sheet folding over the silver nanocubes and extending onto the bare surface. Preliminary SERS experiments on adenine showed a higher SERS enhancement factor for GO on Langmuir-Blodgett films of AgNCs with respect to bare AgNC systems. Conversely, poor SERS enhancement for adenine resulted for GO-covered AgNCs obtained by spontaneous adsorption. This indicated that the assembly and packing of AgNCs obtained in this way, although more homogeneous over the substrate surface, is not as effective for SERS analysis.

Hofmeister effect of anions on calcium translocation by sarcoplasmic reticulum Ca(2+)-ATPase.

The occurrence of Hofmeister (specific ion) effects in various membrane-related physiological processes is well documented. For example the effect of anions on the transport activity of the ion pump Na(+), K(+)-ATPase has been investigated. Here we report on specific anion effects on the ATP-dependent Ca(2+) translocation by the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA). Current measurements following ATP concentration jumps on SERCA-containing vesicles adsorbed on solid supported membranes were carried out in the presence of different potassium salts. We found that monovalent anions strongly interfere with ATP-induced Ca(2+) translocation by SERCA, according to their increasing chaotropicity in the Hofmeister series. On the contrary, a significant increase in Ca(2+) translocation was observed in the presence of sulphate. We suggest that the anions can affect the conformational transition between the phosphorylated intermediates E1P and E2P of the SERCA cycle. In particular, the stabilization of the E1P conformation by chaotropic anions seems to be related to their adsorption at the enzyme/water and/or at the membrane/water interface, while the more kosmotropic species affect SERCA conformation and functionality by modifying the hydration layers of the enzyme.

Synergy of Cobalt and Silver Microparticles Electrodeposited on Glassy Carbon for the Electrocatalysis of the Oxygen Reduction Reaction: An Electrochemical Investigation.

The combination of two different metals, each of them acting on different steps of the oxygen reduction reaction (ORR), yields synergic catalytic effects. In this respect, the electrocatalytic effect of silver is enhanced by the addition of cobalt, which is able to break the O-O bond of molecular oxygen, thus accelerating the first step of the reduction mechanism. At the same time, research is to further reduce the catalyst's cost, reducing the amount of Ag, which, even though being much less expensive than Pt, is still a noble metal. From this point of view, using a small amount of Ag together with an inexpensive material, such as graphite, represents a good compromise. The aim of this work was to verify if the synergic effects are still operating when very small amounts of cobalt (2-10 µg·cm(-2)) are added to the microparticles of silver electrodeposited on glassy carbon, described in a preceding paper from us. To better stress the different behaviour observed when cobalt and silver are contemporarily present in the deposit, the catalytic properties of cobalt alone were investigated. The analysis was completed by the Levich plots to evaluate the number of electrons involved and by Tafel plots to show the effects on the reaction mechanism.

Specific anion effects in Artemia salina.

The specific anion effect on the vitality of Artemia salina was investigated by measuring the Lethal Time LT50 of the crustaceans in the presence of different sodium salts solutions at room temperature and at the same ionic strength as natural seawater. Fluoride, thiocyanate and perchlorate are the most toxic agents, while chloride, bromide and sulfate are well tolerated. The rates of oxygen consumption of brine shrimps were recorded in mixed NaCl+NaF or NaCl+NaSCN solutions as a function of time. The results are discussed in terms of the Hofmeister series, and suggest that, besides the biochemical processes that involve F(-), SCN(-) and ClO4(-), the different physico-chemical properties of the strong kosmotropic and chaotropic anions may contribute in determining their strong toxicity for A. salina.

Aragonite crystals grown on bones by reaction of CO2 with nanostructured Ca(OH)2 in the presence of collagen. Implications in archaeology and paleontology.

The loss of mechanical properties affecting archeological or paleontological bones is often caused by demineralization processes that are similar to those driving the mechanisms leading to osteoporosis. One simple way to harden and to strengthen demineralized bone remains could be the in situ growth of CaCO3 crystals in the aragonite polymorph - metastable at atmospheric pressure -which is known to have very strong mechanical strength in comparison with the stable calcite. In the present study the controlled growth of aragonite crystals was achieved by reaction between atmospheric CO2 and calcium hydroxide nanoparticles in the presence of collagen within the deteriorated bones. In a few days the carbonation of Ca(OH)2 particles led to a mixture of calcite and aragonite, increasing the strength of the mineral network of the bone. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) and Fourier transform infrared (FT-IR) spectrometry showed that aragonite crystallization was achieved. The effect of the aragonite crystal formation on the mechanical properties of the deteriorated bones was investigated by means of X-rays microtomography, helium porosimetry, atomic force microscopy (AFM), and Vickers microhardness techniques. All these data enabled to conclude that the strength of the bones increased of a factor of 50-70% with respect to the untreated bone. These results could have immediate impact for preserving archeological and paleontological bone remains.

Micelle, microemulsions, and gels for the conservation of cultural heritage.

Past restorations performed with acrylic and vinyl polymers showed detrimental effects to wall paintings that lead to the complete disfiguration of the painted surfaces. The removal of these materials performed with the traditional solvent-based methodology represents a real challenge to conservators and usually achieves very poor results. This review reports on the new palette, nowadays available to restorers, based on microemulsions, micellar systems, physical and chemical gels specifically formulated for the cleaning of cultural heritage artefacts. These systems have been developed in the last twenty years within the cultural framework of colloids and surface science.

Interactions between nanostructured calcium hydroxide and acrylate copolymers: implications in cultural heritage conservation.

The interactions between an acrylic copolymer, poly ethylmethacrylate/methylacrylate (70:30) (Poly(EMA/MA), and Ca(OH)2 nanoparticles were investigated in order to establish the reciprocal influence of these two compounds on their peculiar properties. The carbonation kinetics of Ca(OH)2 nanoparticles by atmospheric CO2 was investigated by FTIR and SEM measurements and compared to that of a nanocomposite film. CaCO3 formation occurred even in the presence of the copolymer, but only after an induction period of ca. 200 h and with a lower reaction rate. Some implications in cultural heritage conservation dealing with application of nanolime on artifacts previously treated with acrylic copolymers were discussed. Contact angle measurements, mechanical cohesion properties, and water vapor permeability allowed us to conclude that the optimum behavior of nanolime with respect to transpiration was not compromised by the presence of the copolymer, and the behavior in terms of mechanical properties recovery by the application of Ca(OH)2 nanoparticles remained excellent even in the presence of poly(EMA/MA).

Analysis of egg-based model wall paintings by use of an innovative combined dot-ELISA and UPLC-based approach.

The chemical analysis of egg-based wall paintings-the mezzo fresco technique-is an interesting topic in the characterisation of organic binders. A revised procedure for a dot-enzyme-linked immunosorbent assay (dot-ELISA) able to detect protein components of egg-based wall paintings is reported. In the new dot-ELISA procedure we succeeded in maximizing the staining colour by adjusting the temperature during the staining reaction. Quantification of the colour intensity by visible reflectance spectroscopy resulted in a straight line plot of protein concentration against reflectance in the wavelength range 380-780 nm. The modified dot-ELISA procedure is proposed as a semi-quantitative analytical method for characterisation of protein binders in egg-based paintings. To evaluate its performance, the method was first applied to standard samples (ovalbumin, whole egg, egg white), then to model specimens, and finally to real samples (Giotto's wall paintings). Moreover, amino acid analysis performed by innovative ultra-performance liquid chromatography was applied both to standards and to model samples and the results were compared with those from the dot-ELISA tests. In particular, after protein hydrolysis (24 h, 114 °C, 6 mol L(-1) HCl) of the samples, amino acid derivatization by use of 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate enabled reproducible analysis of amino acids. This UPLC amino acid analysis was rapid and reproducible and was applied for the first time to egg-based paintings. Because the painting technique involved the use of egg-based tempera on fresh lime-based mortar, the study enabled investigation of the effect of the alkaline environment on egg-protein detection by both methods.

Light-responsive nanocomposite sponges for on demand chemical release with high spatial and dosage control.

We present a biocompatible device for on demand chemical release in the form of a light-activated sponge-like nanocomposite scaffold, which ensures excellent control over the principal parameters of chemical release and dosage in order to sustain effective therapeutic action. The sponge consists of a porous biopolymer scaffold containing a dispersion of gold nanorods, which acts as an absorber of the incoming laser light, and of thermosensitive micelles, which serve as a reservoir for the drug molecules to be released. The photothermal response of the nanoparticles contained inside the sponge triggers a contraction in proximal micelles, thus promoting the expulsion of the drug that in turn is released from the sponge to the external environment. The peculiar physiochemical and structural properties of the nanocomposite sponges impart a number of interesting features to the proposed drug release system, including the possibility of spatially confining the therapeutic treatment as well as precise control of the amount of released drug as a function of duration and power of the excitation light.

Cosolvent gel-like materials from partially hydrolyzed poly(vinyl acetate)s and borax.

A gel-like, high-viscosity polymeric dispersion (HVPD) based on cross-linked borate, partially hydrolyzed poly(vinyl acetate) (xPVAc, where x is the percent hydrolysis) is described. Unlike hydro-HVPDs prepared from poly(vinyl alcohol) (PVA) and borate, the liquid portion of these materials can be composed of up to 75% of an organic cosolvent because of the influence of residual acetate groups on the polymer backbone. The effects of the degree of hydrolysis, molecular weight, polymer and cross-linker concentrations, and type and amount of organic cosolvent on the rheological and structural properties of the materials are investigated. The stability of the systems is explored through rheological and melting-range studies. (11)B NMR and small-angle neutron scattering (SANS) are used to probe the structure of the dispersions. The addition of an organic liquid to the xPVAc-borate HVPDs results in a drastic increase in the number of cross-linked borate species as well as the agglomeration of the polymer into bundles. These effects result in an increase in the relaxation time and thermal stability of the networks. The ability to make xPVAc-borate HVPDs with very large amounts of and rather different organic liquids, with very different rheological properties that can be controlled easily, opens new possibilities for applications of PVAc-based dispersions.

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 (11)B 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 (11)B 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.

New frontiers in materials science for art conservation: responsive gels and beyond.

The works of art and artifacts that constitute our cultural heritage are subject to deterioration, both from internal and from external factors. Surfaces that interact with the environment are the most prone to aging and decay; accordingly, soiling is a prime factor in the degradation of surfaces and the attendant disfigurement of a piece. Coatings that were originally intended to protect or contribute aesthetically to an artwork should be removed if they begin to have a destructive impact on its appearance or surface chemistry. Since the mid-19th century, organic solvents have been the method of choice for cleaning painted surfaces and removing degraded coatings. Care must be taken to choose a solvent mixture that minimizes swelling of or leaching from the original paint films, which would damage and compromise the physical integrity of all the layers of paint. The use of gels and poultices, first advocated in the 1980s, helps by localizing the solvent and, in some cases, by reducing solvent permeation into underlying paint layers. Unfortunately, it is not always easy to remove gels and their residues from a paint surface. In this Account, we address the removal problem by examining the properties of three classes of innovative gels for use on artwork--rheoreversible gels, magnetic gels, and "peelable" gels. Their rheological properties and efficacies for treating the surfaces of works have been studied, demonstrating uniquely useful characteristics in each class: (1) Rheoreversible gels become free-flowing on application of a chemical or thermal "switch". For art conservation, a chemical trigger is preferred. Stable gels formed by bubbling CO(2) through solutions of polyallylamine or polyethylenimines (thereby producing ammonium carbamates, which act as chain cross-links) can be prepared with a wide range of solvent mixtures. After solubilization of varnish and dirt, addition of a weak acid (mineral or organic) displaces the CO(2), and the resulting free-flowing liquid can be removed gently. (2) Incorporation of magnetic, coated-ferrite nanoparticles into polyacrylamide gels adds functionality to a versatile system comprising oil-in-water microemulsions, aqueous micellar solutions, or xerogels that act as sponges. The ferrite particles allow the use of magnets both to place the gels precisely on a surface and to lift them from it after cleaning. (3) Novel formulations of poly(vinyl alcohol)-borate gels, which accept a range of organic cosolvents, show promise for swelling and dissolving organic coatings. This family of gels can be quite stiff but can be spread. They are non-sticky and have sufficient strength to be removed by peeling or lifting them from a sensitive surface. These three classes of gels are potentially very important soft materials to augment and improve the range of options available for conserving cultural heritage, and their interesting chemical-physical properties open a rich area for future scientific investigation.