How Science Can Contribute to the Remedial Conservation of Cultural Heritage

Colloid science is contributing solutions to counteract the degradation of artifacts, favoring their transfer to future generations. Advanced materials such as nanoparticles, coatings, gels and microemulsions have been assessed in conservation, spanning from archeological sites to modern and contemporary art. We give an overview of the fundamental milestones and latest innovations in conservation science, targeting solutions and tools for remedial conservation based on green nanomaterials and hybrid systems. Future perspectives and outstanding challenges in this exciting field are then outlined.     

The degradation of wall paintings and stone: Specific ion effects

Salts are ubiquitous both on the surface and in the porous network of works of art such as wall paintings and stone. Cyclic solubilization and crystallization takes place with fluctuating environmental conditions, inducing mechanical stress in the pores and the flaking of the artistic surface. The preventive conservation of precious cultural heritage would thus benefit from models able to describe quantitatively the behavior of electrolyte solutions. Besides the pore size distribution of the wall, cyclic crystallization depends on relative humidity and temperature. Whereas the behavior of single salts' solutions is known, that of mixed solutions (commonly found on artifacts) is still an open issue, owing to the specific interactions of counterions and coions. Classical theories of electrolytes need many fitting parameters to provide predictive and quantitative information, and research focuses on matching phenomenological set of rules with models that take into account quantum mechanical dispersion forces. Classical models have been used so far to describe the behavior of some mixed salts' solutions commonly found on murals and stone, in terms of their RH_eq, which is the relative humidity of air in equilibrium with the saturated solution. Results indicate that environmental conditions deemed safe in the presence of single salts, represent indeed a threat to artifacts in the presence of mixed solutions, with other deviations due to the fact that the crystallization of salts takes place within mesoporous networks. We hope that the reviewed results might contribute a stimulus for further reanalysis of the degradation of works of art, where the synergistic effect of counterions and coions are taken into account. Such interpretation of the artifacts' degradation has been so far overlooked in preservation studies.     

Traditional and non-traditional,innovative and ephemeral materials and techniques in today’s cultural heritage

When working with products of contemporary art, one must consider traditional, innovative, and ephemeral materials, depending on the artist’s intentions, to which concepts of originality and authenticity do not always apply. Case studies are discussed to compare the conservation and restoration procedures of works of art from different periods. The importance of involving historical-technical experts, authors, and manufacturers of materials used in artifacts is highlighted. Conservation procedures cannot be the same for all works of contemporary art. One must employ a methodology based on the critical study of not only the materials used, but also the philosophy and creative conceptual intentions of the artist.     

The use of surfactants in the cleaning of works of art

Surfactants have been historically used for cleaning artifacts, but it was only in the last decades that serendipitous approaches were replaced by research in the field of soft matter and colloid science. Surfactants are components of nanostructured fluids, which were assessed for the removal of soil and aged coatings from paintings and are fundamental in processes that range from the inclusion of grime in micelles to the swelling and dewetting of polymer layers. Intriguing aspects involve the synthesis and use of biodegradable and self-cleavable surfactants, and the confinement of nanostructured fluids in gels, which boost the selectiveness of cleaning interventions. The performances of these advanced systems surpass those of traditional cleaning materials such as solvent blends and thickeners. The most important results are here reviewed and future perspectives given. Besides granting the transfer of cultural heritage to future generations, advanced cleaning materials are relevant to transversal fields, such as detergency, cosmetics, and drug delivery.     

Advances in the Cathode Materials for Lithium Rechargeable Batteries

The accelerating development of technologies requires a significant energy consumption, and consequently the demand for advanced energy storage devices is increasing at a high rate. In the last two decades, lithium‐ion batteries have been the most robust technology, supplying high energy and power density. Improving cathode materials is one of the ways to satisfy the need for even better batteries. Therefore developing new types of positive electrode materials by increasing cell voltage and capacity with stability is the best way towards the next‐generation Li rechargeable batteries. To achieve this goal, understanding the principles of the materials and recognizing the problems confronting the state‐of‐the‐art cathode materials are essential prerequisites. This Review presents various high‐energy cathode materials which can be used to build next‐generation lithium‐ion batteries. It includes nickel and lithium‐rich layered oxide materials, high voltage spinel oxides, polyanion, cation disordered rock‐salt oxides and conversion materials. Particular emphasis is given to the general reaction and degradation mechanisms during the operation as well as the main challenges and strategies to overcome the drawbacks of these materials.     

Spectroscopic evaluation of painted layer structural changes induced by gamma radiation in experimental models

The degradation of cultural heritage objects by insects and microorganisms is an important issue for conservators, art specialists and humankind in general. Gamma irradiation is an efficient method of polychrome wooden artifacts disinfestation. Color changes and other modifications in the physical chemical properties of materials induced by gamma irradiation are feared by cultural heritage responsible committees and they have to be evaluated objectively and precisely. In this paper FTIR and FT-Raman spectroscopy methods were used to investigate the structural changes in some experimental models of tempera paint layers on wood following 11 kGy gamma irradiation at two dose rates. Radiation chemistry depends on the particular pigment, matrix formed by protein, resin (in case of varnished samples) and water presence. For the majority of painted layer in experimental models very small spectral variations were observed. Small changes in the FTIR spectra were observed for the raw sienna experimental model: for the higher dose rate the egg yolk protein oxidation peaks and the CH stretching bands due to lipids degradation products increased.     

Characterization of green copper phase pigments in Egyptian artifacts with X-ray absorption spectroscopy and principal components analysis

The characterization of materials in historical artifacts can contribute significantly to their preservation and understanding; however, sampling and characterization are ideally performed using non-destructive approaches. The analysis of green pigments from Egyptian artifacts presents a further challenge as responses to laboratory based techniques have proven unsuccessful in many cases. An alternative approach is the use of non-destructive X-ray absorption near-edge structure spectroscopy, which was performed on a reference set of copper-containing green minerals and other compounds. Data projection using principal component analysis was used to explore the spectral data structures and to illustrate the relationship between the spectra and copper speciation, resulting in a calibration or training set of the reference materials used. Data from the training set were compared with samples from Egyptian artifacts. The combination of X-ray absorption spectroscopy with principal components analysis provides a novel approach in archeometry and the characterization of objects of cultural heritage.     

Simple methods for characterization of metals in historical textile threads

Characterization of metal threads on historical textile materials is important for preservation of valuable cultural heritage. Obtained results dictate decisions on cleaning, conservation and restoration steps. The most important part of characterization is chemical analysis of originally applied materials, since this enables understanding the nature of chemical and physical degradation and determines the cleaning methods. Methods applied should be non-destructive and sensitive enough to detect trace elements in small sample amounts. The goal of this research was to describe the most useful procedures for fast and simple determination of specific metals of interest. Therefore we propose application of scanning electron microscopy equipped with EDS detector (SEM-EDS) for sample surface analysis and inductively coupled plasma-optical emission spectroscopy (ICP-OES) for chemical analysis of metals threads. For quality insurance reasons, a comparative method applied for chemical analysis was atomic absorption spectrometry (AAS). This combination of methods has proven to be very useful in analysis of historical samples, since SEM-EDS was a simple and non-destructive method which provided information on chemical composition of sample surfaces, while ICP-OES and AAS enabled the full insight into the average chemical composition of samples. Nevertheless, both ICP-OES and AAS were destructive methods which demanded dissolving of samples prior to the analysis. In this work nine different metal fibers collected from historical textile materials were characterized. Proposed methods enabled obtaining information on sample constitution, morphology, topology and chemical composition.     

Literature review on superhydrophobic self‐cleaning surfaces produced by electrospinning

Self‐cleaning surface is potentially a very useful addition for many commercial products due to economic, aesthetic, and environmental reasons. Super‐hydrophobic self‐cleaning, also called Lotus effect, utilizes right combination of surface chemistry and roughness to force water droplets to form high contact angle on a surface, easily roll off a surface and pick up dirt particles on its way. Electrospinning is a promising technique for creation of superhydrophobic self‐cleaning surfaces owing to a wide set of parameters that allow effectively controlling roughness of resulted webs. This article gives a brief introduction to the theory of super‐hydrophobic self‐cleaning and basic principles of the electrospinning process and reviews the scientific literature where electrospinning was used to create superhydrophobic surfaces. The article reviewed are categorized into several groups and their results are compared in terms of superhydrophobic properties. Several issues with current state of the art and highlights of important areas for future research are discussed in the conclusion. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Smart photoactive soft materials for environmental cleaning and energy production through incorporation of nanophotocatalyst on polymers and textiles

Energy and environment are key issues for the sustainable development of human beings and are also the current and long‐term focuses of scientific research. New energy and environmental technologies in combination with polymer and textile science work to create many additional functions for conventional polymers and fabrics. Therefore, some novel technical polymers and textiles, such as photovoltaic and photocatalytic polymers and textiles, have begun to emerge. Generally, light‐activated chemicals, materials, or processes that are produced or enabled by light and the agent absorbing light starting a photochemical alteration in the system is nominated as photocatalyst. This review firstly introduces the different photoactive materials, their classifications, and degradation mechanism. Then, inorganic semiconductor nanoparticles were selected as the best candidate for the application in soft materials. Finally, a detailed study was provided on both preparations of photoactive soft materials using metal oxide semiconductors and their advantages and applications. This paper will be more helpful for the scientists working in the field of photoactive soft materials.     

The mystery of the discolored flints. New molecules turn prehistoric lithic artifacts blue

Prehistoric artifacts turning blue in the store rooms of the Natural History Museum in Verona, Italy recently raised serious issues for heritage materials conservation. Our analytical investigation showed that the unusual discoloration process of the flint tools is caused by the surface presence of at least three previously unknown pigmenting molecules of the triphenylmetane dyes class: 6-(bis(2,2,4-trimethyl-1,2-dihydroquinolin-6-yl)methylene)-2,2,4-trimethyl-2,6-dihydroquinolinium and its hydrogenated derivatives 2,2,4-trimethyl-6-((2,2,4-trimethyl-1,2,3,4-tetrahydroquinolin-6-yl)(2,2,4-trimethyl-1,2-dihydroquinolin-6-yl)methylene)-2,6-dihydroquinolinium and 6-(bis(2,2,4-trimethyl-1,2,3,4-tetrahydroquinolin-6-yl)methylene)-2,2,4-trimethyl-2,6-dihydroquinolinium. The peculiar formation of the molecules is possibly catalyzed within the silica pore surface starting from a well-known rubber stabilizer 2,2,4-trimethyl-1,2-dihydroquinoline released by the plastic pads flooring the storing cabinets. The investigated reaction and its surprising blue product represent a case study of the application of modern materials science to conservation and a serious warning towards the unpredictable challenges faced in the preservation of our cultural heritage.     

Surface Modification on Nickel Rich Cathode Materials for Lithium-Ion Cells: A Mini Review

Nickel-rich (Ni-rich) layered oxides are considered as the most promising cathode candidates for lithium-ion cells owing to their high theoretical specific capacity. However, the higher nickel content endows structural deformation through unwanted phase transitions and parasitic side reactions that lead to capacity fading upon prolonged cycling. Hence, a deep understanding of the chemistry and structural behaviour is essential for developing Ni-rich Lithium Nickel Cobalt Manganese oxide (NCM) cathode-based high-energy batteries. The present review focuses on the different challenges associated with Ni-rich NCM materials and surface modification as a strategy to solve the issues associated with NCM materials, assessment of several coating materials, and the recent developments in the surface modification of Ni-rich NCMs, with an in-depth discussion on the impact of coating on the degradation mechanism.     

Phase transitions in calcium nitrate thin films

Calcium carbonate is a ubiquitous mineral and its reactivity with indoor and outdoor air pollutants will contribute to the deterioration of these materials through the formation of salts that deliquesce at low relative humidity (RH). As shown here for calcium nitrate thin films, deliquescence occurs at even lower relative humidity than expected from bulk thermodynamics and lower than the recommended humidity for the preservation of artifacts and antiques.     

Novel Macromolecular Antioxidants for Industrial Applications in Multiple Sectors

Antioxidants are used to protect organic materials from degradation during exposure to heat and/or light in the presence of oxygen. Novel macromolecular antioxidants have been developed which provide superior resistance to oxidative degradation to plastics, lubricants, and cooking oils vs. state‐of‐the‐art commercial antioxidants.     

Monitoring of the degradation dynamics of agricultural films by IR thermography

The high consumption of plastic materials for use in agriculture is generating serious problems regarding environmental impact. Biodegradable materials are at present the only solution to this type of problems. Research in material science is daily proposing different materials with this requirement for application in various sectors. One of the problems is to analyse the degradation states of the films before their application in order to know the time and the modality of degradation. Here we propose a novel method based on thermography vs time which allows the degradation dynamics of agricultural films to be evaluated.In our experiment we put some biodegradable materials of our interest on soil in an open field. The main characteristic of these materials is that they are originally liquid and they are sprayed on soil and immediately cross-link into a film state. Through an IR thermal camera we monitored the state of the films day by day and analysed the thermal images in order to detect the continuous changing of their physical properties.     

Electrochemistry for conservation science

Voltammetry of microparticles, an electrochemical methodology based on the record of the voltammetric response of sparingly soluble solids mechanically transferred to the surface of inert electrodes in contact with suitable electrolytes, is able to provide significant analytical information in the fields of conservation and restoration of cultural goods. Using this methodology, identification, speciation, and relative and absolute quantification of analytes from works of art samples can be achieved. Applications to the analysis of organic and inorganic pigments in paints, fibbers, ceramic materials as well as alteration compounds in paintings and metallic artifacts are reviewed.     

Voltammetric methods applied to identification, speciation, and quantification of analytes from works of art: an overview

Voltammetry of microparticles, an electrochemical methodology based on the record of the voltammetric response of sparingly soluble solids mechanically transferred to the surface of inert electrodes in contact with suitable electrolytes, is able to provide significant analytical information in the fields of conservation and restoration of cultural goods. Using this methodology, identification, speciation, and relative and absolute quantification of analytes from works of art samples can be achieved. Applications to the analysis of organic and inorganic pigments in paints, fibbers, ceramic materials as well as alteration compounds in paintings and metallic artifacts are reviewed.     

Germanium‐Based Nanomaterials for Rechargeable Batteries

Germanium‐based nanomaterials have emerged as important candidates for next‐generation energy‐storage devices owing to their unique chemical and physical properties. In this Review, we provide a review of the current state‐of‐the‐art in germanium‐based materials design, synthesis, processing, and application in battery technology. The most recent advances in the area of Ge‐based nanocomposite electrode materials and electrolytes for solid‐state batteries are summarized. The limitations of Ge‐based materials for energy‐storage applications are discussed, and potential research directions are also presented with an emphasis on commercial products and theoretical investigations.     

Combinatorial and high-throughput materials science

There is increasing acceptance of high-throughput technologies for the discovery, development, and optimization of materials and catalysts in industry. Over the years, the relative synchronous development of technologies for parallel synthesis and characterization has been accompanied by developments in associated software and information technologies. This Review aims to provide a comprehensive overview on the state of the art of the field by selected examples. Technologies developed to aid research on complex materials are covered as well as databases, design of experiment, data-mining technologies, modeling approaches, and evolutionary strategies for development. Different methods for parallel synthesis provide single sample libraries, gradient libraries for electronic or optical materials, similar to polymers and catalysts, and products produced through formulation strategies. Many examples illustrate the variety of isolated solutions and document the barely recognized variety of new methods for the synthesis and analysis of almost any material. The Review ends with a summary of success stories and statements on still-present problems and future tasks.     

Design Strategies of Si/C Composite Anode for Lithium-Ion Batteries

Silicon-based materials that have higher theoretical specific capacity than other conventional anodes, such as carbon materials, Li₂TiO₃ materials and Sn-based materials, become a hot topic in research of lithium-ion battery (LIB). However, the low conductivity and large volume expansion of silicon-based materials hinders the commercialization of silicon-based materials. Until recent years, these issues are alleviated by the combination of carbon-based materials. In this review, the preparation of Si/C materials by different synthetic methods in the past decade is reviewed along with their respective advantages and disadvantages. In addition, Si/C materials formed by silicon and different carbon-based materials is summarized, where the influences of carbons on the electrochemical performance of silicon are emphasized. Lastly, future research direction in the material design and optimization of Si/C materials is proposed to fill the current gap in the development of efficient Si/C anode for LIBs.