Optical Properties Of Pigments Research Articles

Extraction of Optical Characteristics of Diffuse Particles for Modelling a Dispersed Medium

Currently, virtual prototyping, i.e. preliminary modelling of processes on a computer has become ubiquitous. It is also applied to modern automobile paints in order to correctly reproduce the colour of the paint. The most practically important task is colour matching: calculation of the paint composition necessary to obtain a given colour. The complexity of modelling the propagation of light in paint is due to its complex structure and the wide variety of pigments, including diffuse ones. This problem can be solved by simulation of the light scattering by the dispersed pigment particles. To do this we need the optical properties of pigments, which are often unknown. In this paper, we propose several different methods for extraction of the pigment properties by measuring the light scattering of specially prepared samples. All methods are based on minimizing the difference between measured and calculated scattering values as a function of pigment properties. The methods differ in the types of paint samples that must be prepared and measured to obtain the pigment data. We describe the operation of the methods and test their robustness. As a result, one method has proven to be much more robust to the measurement errors. The colour of the real sample was also compared with the calculated colour of the paint, in the modelling of which the obtained properties of the pigments were used.

Liquid Crystal Cellulose Nanocrystal/ Polyvinylpyrrolidone Pigments Engineered from Agro‐Waste Sugarcane Bagasse

AbstractBio‐inspired iridescent materials can possibly replace organic dyes and pigments, however, fabricating materials that resemble the appearance of absorbing pigments is challenging. Extracting cellulose nanocrystals (CNCs) from waste biomass is a sustainable practice in light of socio‐economic and environmental concerns. In an attempt, CNCs from sugarcane bagasse are isolated through acid hyrdolysis. Stable anisotropic dispersions of CNCs are doped with polyvinylpyrrolidone (PVP). Iridescent composite films are cast from these suspensions through evaporation–induced self‐assembly approach (EISA). The physicochemical properties of the films are studied at different loadings of PVP. These iridescent CNC/PVP composite films are then ball‐milled to produce iridescent red and blue tone color pigments. The morphology and optical properties of pigments are studied through Field emission scanning electron microscopy (FE‐SEM) and Hot‐stage Polarized Optical Microscopy (POM). These pigments are then re‐dispersed in a transparent polar polymer matrix to visually observe the color induced by them using solvent casting approach.

The Integrative Biology of Pigment Organelles, a Quantum Chemical Approach.

Coloration is a complex phenotypic trait involving both physical and chemical processes at a multiscale level, from molecules to tissues. Pigments, whose main property is to absorb specific wavelengths of visible light, are usually deposited in specialized organelles or complex matrices comprising proteins, metals, ions, and redox compounds, among others. By modulating electronic properties and stability, interactions between pigments and these molecular actors can lead to color tuning. Furthermore, pigments are not only important for visual effects but also provide other critical functions, such as detoxification and antiradical activity. Hence, integrative studies of pigment organelles are required to understand how pigments interact with their cellular environment. In this review, we show how quantum chemistry, a computational method that models the molecular and optical properties of pigments, has provided key insights into the mechanisms by which pigment properties, from color to reactivity, are modulated by their organellar environment. These results allow us to rationalize and predict the way pigments behave in supramolecular complexes, up to the complete modeling of pigment organelles. We also discuss the main limitations of quantum chemistry, emphasizing the need for carrying experimental work with identical vigor. We finally suggest that taking into account the ecology of pigments (i.e., how they interact with these various other cellular components and at higher organizational levels) will lead to a greater understanding of how and why animals are vividly and variably colored, two fundamental questions in organismal biology.

An Alternative Phase-Sensitive THz Imaging Technique for Art Conservation: History and New Developments at the ENEA Center of Frascati

In recent years, THz imaging techniques have been used in several fields of application. At the beginning of the century, the low availability of powerful THz sources was one of the limiting factors to the advancement of THz technology. At the ENEA center in Frascati, two Free Electron Lasers (FELs) operating in the THz spectral region were available at that time, making it possible to exploit all the features of THz imaging. In this paper, we will describe an alternative THz imaging technique, developed over 15 years of studies at the ENEA center of Frascati, and its application in the art conservation field, reporting the latest results of such studies on the optical properties of pigments in the GHz-THz region of the spectrum, on the possibility of detecting biological weeds under mosaic tiles and on the THz analysis of ancient leather wallpapers. This alternative technique was first developed in the framework of a bilateral collaboration between Japan and Italy, the THz-ARTE Project, which involved NICT (Tokyo), NNRICP (Nara), ENEA (Frascati) and IFAC-CNR (Florence). Most of the THz imaging techniques at that time were based on THz-Time Domain (THz-TD) devices. In the paper will be described how this alternative technique is able to measure the phase of the reflected radiation, thus providing information on the optical properties of the materials under study, such as mural paintings and mosaics. This makes it possible to detect the presence of hidden artworks, additional elements under paint layers, and dielectric materials. To describe the potential and the limits of this alternative imaging technique we will start from a description of the first THz imaging setup at the ENEA center of Frascati, based upon a THz Free Electron Laser. A description of the theoretical principle underlying this technique will be given. The first results in the field of art conservation are summarized, while the new results of a systematic study on the optical properties of pigments are reported and the realization of a portable THz imaging device, and its application “on site” for the analysis of frescoes are shown. The success of this prototype lead to the identification of different types of artworks as possible targets to be studied. New results about the ability of detecting water, and possibly the water content of biological weeds, under mosaic tiles are described, while new experimental measurements on Leather Wallpapers, both “in situ” and in a laboratory environment, are discussed later. A final analysis on the pro and the cons of this alternative imaging technique and on its possible utilization with the developed prototype is carried out together with the considerations on possible future developments and its potential use as an extension of other imaging techniques.

The Use of Sentinel-3 Imagery to Monitor Cyanobacterial Blooms

Cyanobacterial harmful algal blooms (CHABs) have been a concern for aquatic systems, especially those used for water supply and recreation. Thus, the monitoring of CHABs is essential for the establishment of water governance policies. Recently, remote sensing has been used as a tool to monitor CHABs worldwide. Remote monitoring of CHABs relies on the optical properties of pigments, especially the phycocyanin (PC) and chlorophyll-a (chl-a). The goal of this study is to evaluate the potential of recent launch the Ocean and Land Color Instrument (OLCI) on-board the Sentinel-3 satellite to identify PC and chl-a. To do this, OLCI images were collected over the Western part of Lake Erie (U.S.A.) during the summer of 2016, 2017, and 2018. When comparing the use of traditional remote sensing algorithms to estimate PC and chl-a, none was able to accurately estimate both pigments. However, when single and band ratios were used to estimate these pigments, stronger correlations were found. These results indicate that spectral band selection should be re-evaluated for the development of new algorithms for OLCI images. Overall, Sentinel 3/OLCI has the potential to be used to identify PC and chl-a. However, algorithm development is needed.

Combustion Synthesis of Ultrafine Powders of Co3O4 for Selective Surfaces of Solar Collectors

Solar selective paints, with the addition of Co3O4 as a pigment, are used to improve energetic efficiency in solar collectors. Although Co3O4has been obtained by different methods, references about combustion synthesis are scarce. Co3O4 powders have been synthesized by stoichiometric and non-stoichiometric routes using aspartic acid (Asp) or tri-hydroxi-methyl-aminomethane (Tris) as fuels. The samples were calcined in air at 500°C. They were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectrum and the specific surface area of the samples was determined by means of the Brunauer–Emmett–Teller technique. The optical properties of pigments were assessed by means of a spectrophotometer. In all cases, powders exhibited the crystalline structure of Co3O4. A minimum crystallite average size of 29nm was observed for powders obtained by the “stoichiometric/Asp” combustion route, while a maximum value of 41nm was stated for powders obtained by the “non-stoichiometric/Asp” combustion process. The average particle size ranged between 50 and 100nm. The powders obtained by the“stoichiometric/Asp” method were selected to study their optical properties; their solar absorption value was 86%. Solar selective surfaces composed by Co3O4 pigments and an alkyd resin were obtained and applied over copper or aluminum substrates. In both cases, solar absorptance was of 93% and comparable with similar solar selective surfaces, but the thermal emittance value was higher than 90%, as a consequence of the large width of the films.

The effects of particle size distribution on the optical properties of titanium dioxide rutile pigments and their applications in cool non-white coatings

The particle size distributions of three commercially available titanium dioxide pigments were measured, and their effects on the optical properties of the pigments were investigated. The Altiris 550 and 800 pigments possess larger median particle size and wider size distributions than those of the conventional titanium dioxide rutile. The visible (VIS) reflectance, the solar reflectance and the lightness of the films and coatings singly pigmented with any of these three pigments decrease as the pigment particle size increases. The VIS transmittance and near-infrared (NIR) reflectance both increase as the pigment particle size increases. The main reflection band of the coatings shifts farther into the NIR region with increasing pigment particle size. The partially VIS-transmitting Altiris pigments enable the NIR and the solar reflectance of cool non-white coatings to be improved, thereby yielding metameric matches to the desired colors.

Influence of particle size distribution of calcium carbonate pigments on coated paper whiteness

The optical properties of pigments used for paper coating are linked to their morphology. The light scattering through coated layers depends upon the size and the size distribution of the pigments and their packing behavior. In this report the effect of particle packing of various calcium carbonate pigments on the whiteness of the final coated paper is studied. Different grades of calcium carbonate pigments of different particle size distribution and optics were used for coating applications on base papers. Base papers of different optics were also selected. The entire study was carried out at different coat weights. It was observed that the overall scattering from the coated sheet depends upon the light scattering from the base paper as well as through the coated layer. Higher light scattering through the coated layer will lower the effect of the base paper, whether it is dark or bright. So high bright and white pigments are not only the criteria for an enhancement in the optical properties of coated paper; the particle size and size distribution should also be considered before introducing any pigment into a coating formulation. The base optics should also be chosen on the bases of the pigments’ optics and their morphology.

Photopyroelectric technique for the measurement of thermal and optical properties of pigments in liquid solution

The analytical solution for the one-dimensional heat diffusion problem for a two-layer system, in the Beer-Lambert model for light absorption, is shown to be useful for the implementation of a novel photopyroelectric (PPE) methodology, for the measurement of thermal and optical properties for pigments in liquid solution. The PPE signal, as a function of the sample's thickness, is used for this goal. Exponential decay for the PPE amplitude, followed by a constant PPE phase, for solutions at low dye concentration and an exponential decay for the PPE amplitude but a linear PPE phase behavior for the higher concentrated ones are shown and are, respectively, used for the measurement of the optical absorption coefficient and thermal diffusivity for liquid samples. These PPE phase behaviors also provide a criterion to decide on the corresponding limit for optical and thermal properties measurement. This PPE methodology was tested by measuring the optical absorption coefficient (at 658 nm) and thermal diffusivity for solution of methylene blue and copper sulfate in distilled water at various concentrations. Independent measurements of optical properties, using a commercial spectrometer, were done to compare with the corresponding ones obtained with this PPE methodology, finding very good agreement to each other.

Optical characterization and modeling of black pigments used in thickness-sensitive solar-selective absorbing paints

The performance of black pigments used in thickness-sensitive solar-selective absorbing paints for solar thermal collectors depends on the optical properties of the pigments. Knowledge of the intrinsic optical properties of most paint pigments is very limited. Pellets made from either FeMnCuO x or black carbon dispersed in KBr matrix have been used to determine the effective optical coefficients of the pigments. Scattering and absorption cross-sections were derived from reflectance and transmittance measurements at near normal angle of incidence in the wavelength range 0.3 to 2.5 μm. Volume concentrations of the pigments that gave linear dependencies for the coefficients were found to be between 0.053 and 0.53% (FeMnCuO x ) and 0.076 and 0.31% (black carbon). Subsequently, a four-flux model has been used for calculation of reflectance for thickness-sensitive spectrally-selective paints. The paints were obtained from the FeMnCuO x and black carbon pigments embedded in silicone and phenoxy resin, respectively. We have used the experimentally determined scattering and absorption cross-sections of the pigments as input to the four-flux theory and the calculations have been performed for different thicknesses and/or pigment volume fraction of the paints. The calculated reflectances were compared with experiments and the results for thick films fit well.

Non‐destructive Determination of Leaf Chlorophyll Content in Four Crop Species1

AbstractA recent non‐destructive technique allows estimation of leaf chlorophyll content using the portable SPAD‐502 chlorophyll meter. Measurements were taken on four species (winter wheat, maize, soyabean and tobacco) subjected to different nitrogen regimes or senescence status and the: non‐destructive readings were compared with analytical results obtained by solvent extraction. In general, the relationship between the SPAD measurement and the analytical result was not linear and species was a factor in three out of four crops. Linear, quadratic and exponential curve fitting are presented; only die interpolation with a polynomial exponential function adequately descries the whole data set. The presence of statistically non‐significant differences between the estimated values of wheat and maize on the one hand and significant: points of difference between those of tobacco and soyabean on the other suggests distinct behaviour patterns far monocots and cicots. This type of response maybe explained by differences, in the optical properties of pigments with differing sparial distributions (sieve effect) and therefore by in vivo and in vitro different procedures and the structural diversity of leaves belonging to the two subclasses.

顔料の光学的性質とその応用

顔料の光学的性質とその応用

Advanced methods of testing the optical properties of pigments

Advanced methods of testing the optical properties of pigments