The colorimetric properties of three, leuco dye-based thermochromic inks at 31
°C activation temperature were studied. The inks had similar pigment particle size distribution and comparably thick ...microcapsule shells with similar stability against oxygen plasma etching. The colour of the inks was dependent on temperature as well as the thermal history of the sample, which gives rise to colour hysteresis. The area of the observed hysteresis loop in CIELAB colour space determines how different colours appear on the sample when decolourisation and colourisation processes are compared. The largest colour difference achieved for the same sample that arose because of different thermal history and temperature were determined. Four characteristic temperatures were ascribed to the two chemical reactions causing colour hysteresis. The stability of the decolourised state at cooling <activation temperature was confirmed as >10
h. The reversibility of the thermochromic effect diminished approximately linearly with the highest heating temperature.
Thermochromic composites of benzofluoran dye, bisphenol A developer and octadecanol solvent were investigated to analyse how different molar ratios of developer influences the structural, optical and ...thermal properties. Increasing the amount of developer gives stronger absorption in the visible region and larger colour contrast between coloured and discoloured states. The colour clearing temperature of all studied composites is well below their melting point and the phase transitions are influenced only little by the content of the developer. The crystalline structure is fully controlled by the solvent; it changes from the γ phase to the liquid at heating and returns through the rotator phase into the γ phase at cooling. Crystallinity of the composites diminishes with the content of the developer, causing increased scattering of light. The dye: developer molar ratio equal to 1:3 was determined to be large enough to open lactone ring in all dye molecules. Colour hysteresis of such composites shrinks to practically single sigmoidal curve whereas the colour contrast still increases with higher amount of the developer. This effect could be attributed to developer – solvent interactions in a composite with lower crystallinity.
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•The colour of thermochromic composite changes well below its melting temperature.•The two solid state phases of solvent resolve during cooling.•Dye: developer molar ratio of at least 1:3 is required to open all lactone rings.•Higher amount of developer give larger colour contrast and narrower hysteresis.•Lower crystallinity of composites may affect protonation efficiency of the dye.
Particulate matter (PM) pollution is one of the major threats to cultural heritage outdoors. It has been recently implied that organic aerosols will prevail over inorganic carbon particulates in the ...future, changing the main mechanisms of damage caused by poor air quality to calcareous heritage in particular. We studied fresh particulate deposits on marble and limestone surfaces exposed to urban air in sheltered and unsheltered configurations. Due to different air pollution sources in different seasons, the amount and composition of surface deposits varied throughout the year. The main and most constant contributor to PM2.5 (particles smaller than 2.5 μm) were primary traffic emissions (30 %), followed by secondary formation of acidic inorganic aerosols, such as sulphate in summer and nitrate in winter (33 % altogether), and seasonal biomass-burning emissions (14 %). Although biomass burning is the major source of primary organic aerosols including the light-absorbing fraction that prevailed over black carbon (BC) in colder months (up to 60 % carbonaceous aerosol mass), we show that surface darkening causing the soiling effect is still governed by the minor BC fraction of atmospheric aerosols, which remained below 20 % of the carbonaceous aerosol mass throughout the year. This, however, can change in remote environments affected by biomass-burning emissions, such as winter resorts, or by rigorous BC mitigation measures in the future. In the short run, sheltered positions were less affected by different removal processes, but we show that surface deposits are not simply additive when considering longer periods of time. This must be taken into account when extrapolating surface accumulation to longer time scales.
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•Interaction between heritage materials and airborne particles is poorly understood.•Fresh deposits are characterized to be able to study aging after the deposition.•PM source apportionment is correlated with surface reflectance and chemistry.•Surface deposits resemble main PM sources but do not sum up on long time-scales.•Light absorption by black carbon causing soiling still exceeds that of brown carbon.
The properties of carbon black surfaces which might affect their influence on the conductivity of dispersions in polar and non-polar media were analysed. Low-structured furnace black, high-structured ...gas black and extremely high-structured extra-conductive carbon black were studied. The size distribution of aggregates was measured. Raman spectroscopy provides relative amounts of disordered, graphitic and amorphous phases, and the lateral size of crystallites. X-ray photoelectron spectroscopy gives the oxygen content and the nature of functional groups on particle surfaces. The chemical nature of surface functional groups was analysed with infrared spectroscopy. All samples are disordered carbon blacks with different amounts of oxygen on their surfaces. The carbonyl-based surface groups were obtained on the acidic sample and other oxygen groups on the alkaline ones. A negligible amount of oxygen combined with a high amount of the graphitic phase and alkaline nature gives high conductivity of carbon black in polar and non-polar solvents. The conductivity of dispersion also increases with a higher structure, i.e. larger aggregates with a wide size distribution.
► Disordered phase highly prevails over the graphitic and amorphous ones. ► Branching of primary particles gives larger aggregates and wider size distribution. ► Highly graphitic and alkaline particles without oxygen give conductive dispersions. ► The structure and particle size distribution of aggregates promotes conductivity.
Many applications use gonioapparent targets whose appearance depends on irradiation and viewing angles; the strongest effects are provided by light diffraction. These targets, optically variable ...devices (OVDs), are used in both security and authentication applications. This study introduces a bidirectional spectrometer, which enables to analyze samples with most complex angular and spectral properties. In our work, the spectrometer is evaluated with samples having very different types of reflection, concerning spectral and angular distributions. Furthermore, an OVD containing several different grating patches is evaluated. The device uses automatically adjusting exposure time to provide maximum signal dynamics and is capable of doing steps as small as 0.01°. However, even 2° steps for the detector movement showed that this device is more than capable of characterizing even the most complex reflecting surfaces. This study presents sRGB visualizations, discussion of bidirectional reflection, and accurate grating period calculations for all of the grating samples used.
Scandium (Sc) is known to be one of the most effective alloying elements of aluminum alloys. The only drawback is its high price, but that could change quickly due to the promising results of recent ...research on its extraction. However, the data on how it affects anodic oxidation are very scarce. In this research, we analyzed how a micro-addition of Sc to the AlMg alloy affects the growth mechanism and properties of the protective aluminium oxide layer depending on the anodization parameters. For comparison, alloy AA5083 with a similar magnesium content was also anodized with the same anodizing parameters. In all experiments, sulfuric acid (VI) with concentrations of 1.72 M or 2.2 M at temperatures of 21 °C or 35 °C was used as the electrolyte. Potentiostatic (18 V) and galvanostatic (20 mA/cm2) anodizing methods were applied. The results (SED-EDS) show that scandium is uniformly intercalated in the matrix of the oxide layer and decreases its resistivity, which increases the oxide growth rate during potentiostatic anodizing and decreases the pore density and pore diameters during galvanostatic anodizing. Moreover, it increases the mobility of cations through the oxide layer, thus accelerating the oxidation reaction in concentrated sulfuric acid electrolytes. On the other hand, the increased cation mobility considerably increases the sensitivity to the temperature of the electrolyte, which can change the growth mechanism of the oxide layer and thus its morphology.
Since the world’s energy demands are growing rapidly, there is a constant need for new energy systems. One of the cleanest, most abundant, and renewable natural resources available is solar energy; ...therefore, the development of surfaces with high absorption of solar radiation is increasing. To achieve the best efficiency, such surfaces are coated with spectrally selective coatings, which are strongly influenced by the pigments and resin binders. Spectrally selective paints have a very specific formulation, and since the applied dry coatings should exhibit high spectral selectivity, i.e., high solar absorptivity and low thermal emissivity, the rheological properties of liquid paints are of great importance. In the present work, we studied the effect of the rheological properties of liquid thickness-insensitive spectrally selective (TISS) paints on the spectral selectivity and adhesion of dry coatings on a polymeric substrate. The results showed that the functional and adhesion properties of dry coating on polymeric substrates is strongly dependent on the rheological properties of the binder and catalyst used for the preparation of the liquid paints. It was shown that the paints with good spectral selective properties (thermal emissivity eT < 0.36 and solar absorptivity aS > 0.92) and good adhesion (5B) can be prepared for polymer substrates.
•Substituting a pigment with another one requires testing of the entire coating.•The most important effect comes from the shielding of pigments against UV radiation.•The coating base plays the ...central role in stability against accelerated weathering.•Preparation of pigment paste has certain role but pigment chemistry only a minor one.•Most colour change occurs in the first 200h of accelerated weathering.
The shades of decorative coatings for façades are currently changing from white and pale to more chromatic ones. This also imposes a phase-out of heavy-metal pigments based on cadmium and lead, which cover the full range of yellow, orange, and red shades, and show excellent performance. The substitute pigments have many limitations regarding heat stability, colour strength, opacity, light fastness, or dispersibility. While all components of the final coating contribute to these properties, we have studied here the stability of four orange pigments suitable to replace the pigments with heavy metals in water-based coatings for outdoor applications in a different binder system (acrylate styrene with different amount of silicone resin, vinyl acetate versatate and acrylate based polymer). The accelerated weathering tests show that the stability of all samples strongly depends on the applied coating base and is systematically higher in white coating bases, especially when combined with pigment pastes prepared without a binder. The pigment chemistry, being inorganic, hybrid, or organic plays a role, but the stability of the coating gradually depends on the other components.
The human reception of light includes image-forming and non-image-forming effects which are triggered by spectral distribution and intensity of light. Ideal lighting is similar to daylight, which ...could be evaluated by spectral or chromaticity match. LED-based and CFL-based lighting were analyzed here, proposed according to spectral and chromaticity match, respectively. The photobiological effects were expressed by effectiveness for blue light hazard, cirtopic activity, and photopic vision. Good spectral match provides light with more similar effects to those obtained by the chromaticity match. The new parameters are useful for better evaluation of complex human responses caused by lighting.
Reversible colour change of leuco dye-based composites is in general closely related to their phase change, thus the two phenomena should occur at around the same temperature and should be influenced ...similarly. However, spatial confinement of the analysed sample affects the change in colour differently compared to its phase transition and the most pronounced effects can be observed during cooling. The bulk composite is coloured while still liquid and the colour hysteresis does not exhibit a loop. In an open-porous medium the colouration coincides well with the crystallization and the colour hysteresis widens to about 4 °C. Microencapsulated composite exhibits two crystallization processes, one of them taking place at the bulk crystallization temperature and the other one at about 20 °C lower. Under such conditions the composite is coloured just before the onset of the second crystallization, i.e. about 15 °C below crystallization in the bulk, and the corresponding colour hysteresis widens to 18 °C. The two crystallization forms are thermally independent and have the same crystalline structure. These effects should be taken into account when designing future applications where the phase-changing materials are implemented.
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