Emiliano Carretti

Structural Behavior of Highly Concentrated Hyaluronan

When investigated under high concentration conditions, hyaluronan (HA) solutions in physiological saline are shown to generate stable superstructures. An abrupt change in the rheological properties observed on increasing the temperature suggests the breaking of certain cooperative bonds. The thermal disruption of the HA superstructure is accompanied by a sharp transition from a long- to a restricted-connectivity water structuring, which is interpreted as a concurrent transition from a stable to a temporary polymer network. The intermolecular associations are considered to be originated by hydrophobic interactions between the nonpolar groups of the polymer backbones.

Nanomaterials in art conservation

Tackling the degradation of cultural heritage requires a global effort. We call on all material scientists to develop new nanomaterials and methods for the preservation of artwork.

Nanoscience for Art Conservation: Oil‐in‐Water Microemulsions Embedded in a Polymeric Network for the Cleaning of Works of Art

parent, and the cleaning action can be monitored visually and controlled during the application. The idea that underpinned this study was to produce a complex system in which the structure and superior performance of the microemulsion were preserved, and the diffusion of its droplets was controlled by the mesh size and viscosity of the polymeric network. With this view, we analyzed possible changes induced by hmHEC in the nanostructure of the o/w mE and studied the interactions between the microemulsion embedded in the hmHEC network (M1/ hmHEC) and the organic materials to be removed from the

D-Sorbitol, a structurally simple, low molecular-mass gelator

A comprehensive examination of the ethanol gels produced with D-sorbitol, one of the simplest and lowest mass organogelator molecules known, is reported. Data from several spectroscopic and structural experiments reveal that the nature of the self-assembled fibrillar assemblies, spherulites for the most part, depends acutely on the manner in which the sol phase is treated. The critical concentration to form a gel at room temperature is ca. 1.5 wt% and a plateau value for melting the gels, ca. 50 °C, is reached near 3.5 wt%. Ostwald ripening, whose rate, again, depends on the history of the preparation, was also observed.

Surfactant-Based Photorheological Fluids: Effect of the Surfactant Structure

The effect of the surfactant structure on the mechanical and structural properties of surfactant based photorheological fluids are presented in this paper. Cetyltrimethylammonium bromide (CTABr) mixed with trans-o-methoxycinnamic acid in a basic environment can form photosensitive systems. The driving force is the ability of surfactant molecules to form wormlike micelles in the presence of the anionic photosensitive additive. Taking into account that slight changes in the surfactant monomers structure can induce drastic modifications of the micellar aggregate features, the role the of the nature of the counterion (in the CTAX type surfactants) or the headgroup size (CTRABr type surfactants) and its influence on the mechanical properties of surfactant based photorheological fluids using trans-o-methoxycinnamic acid (trans-OMCA) as additive were investigated. Rheological studies reported in this paper show that the viscosity of these systems drastically varies only by changing the nature of the surfactant counterion. Moreover, by increasing the bulk simply by replacing the three methyl groups with three ethyl groups in the surfactant headgroup moiety, the viscosity drastically decreases. Highly photosensitive PR fluids can be further obtained using cetyltrimethylammonium trans-o-methoxycinnamate (CTAOMC) as surfactant at neutral pH. In addition to the complete rheological characterization carried out by means of the application of both a steady shear and a dynamic shear stress, a 1H NMR and NOESY study was also performed.

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.

Acrylamide-Based Magnetic Nanosponges: A New Smart Nanocomposite Material

Nanocomposite materials consisting of CoFe2O4 magnetic nanoparticles and a polyethylene glycol-acrylamide gel matrix have been synthesized. The structure of such materials was studied by means of small-angle scattering of X-rays and polarized neutrons, showing that the CoFe2O4 nanoparticles were successfully and homogeneously embedded in the gel structure. Magnetic, viscoelastic, and water retention properties of the nanocomposite gel confirm that the properties of both nanoparticles and gel are combined in the resulting nanomagnetic gel. Scanning electron microscopy highlights the nanocomposite nature of the material, showing the presence of a gel structure with different pore size distributions (pores with micron and nano-size distributions) that can be used as active sponge-like nanomagnetic container for water-based formulations as oil-in-water microemulsions.

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).

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.

Gels for the conservation of cultural heritage.

Gels are becoming one of the most important tools for the conservation of cultural heritage. They are very versatile systems and can be easily adapted to the cleaning and consolidation of works of art. This perspective reviews the major achievements in the field and suggests possible future developments.