Luigi Dei

Spectroscopic techniques in cultural heritage conservation: A survey

Abstract This review describes the application of selected spectroscopic techniques to the world of cultural heritage conservation. In recent times, science and technology have been applied to the world of cultural heritage, conservation and preservation. In this field, spectroscopic techniques represent one of the most powerful tools to investigate the structure of all the materials constituting the “cultural object.” In particular, this survey will consider the “status of art” in the field of some important spectroscopic techniques for the characterization of the following works of art: easel paintings, paper and ink artifacts, stone monuments and wall paintings, and archaeological ceramics. The spectroscopic techniques that have been used and will be reviewed are Fourier transform infrared spectroscopy and also coupled with the microscope, X‐ray fluorescence spectroscopy, proton‐induced X‐ray emission spectroscopy, ultraviolet, visible and fluorescence spectroscopy, Raman spectroscopy, and Mossbauer spectroscopy.

Chitosan Films Doped with Gold Nanorods as Laser-Activatable Hybrid Bioadhesives

Chitosan is a linear chain polysaccharide comprising glucosamine and N -acetyl glucosamine residues joined together by β -1,4-glycosidic bonds. It is derived as an acids-soluble material by deacetylation of chitin, which is commonly found in the outer skeleton of crustaceans and in the cell walls of fungi. A variety of fundamental properties such as excellent biocompatibility and biodegradability make chitosan a very attractive material for biomedical applications including wound dressing, tissue engineering and drug delivery. [ 1 , 2 ] The peculiar tendency of chitosan to form films with high mechanical strength, good elasticity and rather slow biodegradation is among the principal reasons why this material is gaining a primary role in medical technology. [ 2–4 ] Examples of applications of chitosan films are the localized chemotherapy based on the local delivery and sustained release of antineoplastic agents after cancer removal [ 5 ] and the tissue repair by closing chronic, accidental, and surgical wounds. [ 4 , 6 ] In order to enable these applications, the chitosan films need to be secured to the target, which may be achieved by suturing. [ 7 ] However, in many cases, suturing may be hardly feasible such as for poorly accessible or delicate body regions (e.g., intracranial, myocardial, etc.). In addition metals and synthetic materials in use for implantation can interfere with the functional rehabilitation of the site due to foreign-body reactions, causing infl ammation and abnormal wound healing. [ 8 ]

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.

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.

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.

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).

Bidimensional state conformation of poly-γ-methyl-l-glutamate. II. Collapse mechanism of α and β conformations

Abstract The mechanism of the collapse process of the α and β conformations of poly-γ-methyl- l -glutamate at the water-air interface was studied. It is shown that the collapse process occurs in two stage for both conformations. The first is attributable to a process of nucleation and the second to the growth of the nuclei formed. The enthalpies, entropies, and free energies of activation were determined for the two conformations. The entropic and enthalpic contributions for the first stage of the collapse process are identical for the two conformations, while in the second stage the values of Δ S ‡ and Δ H ‡ differ widely, though the Δ G ‡ are identical. Ellipsometric measurements and scanning electron microscopy support the proposed nucleation mechanisms.

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.