Surface Color Change Research Articles

Evaluation of color changes in PV modules using reflectance measurements

The main objective of this paper is to investigate the possibility of evaluating the color changes in real photovoltaic modules from reflectance measurements. To accomplish this main objective, the work has been organized into three main axis: (1). Exploring the possibility of using simplified instrumentation and techniques for the measurement of color parameters in solar cells. (2). Identifying a simple parameter as an indicator of solar module color appearance and (3). Exploring the possibility of correlating that parameter with solar module degradation. It is explored the use of reflectance and related magnitude Yellowness Index (YI) as an indicator of photovoltaic (PV) solar module surface color change and degradation. While spectrometric quantities as transmittance have been used as a measurement of separated encapsulant and backsheet characteristics, in the present paper reflectance of the surface of real PV solar mono and polycrystalline modules are analyzed. With the objective of verifying the applicability of such measurements in real PV installations, the correctness of using simplified measurement geometries and portable spectrometers is tested. It is found that 45°/45° and hemispheric reflectance supply similar results. Consequently portable fiber optic spectrometers and simple fiber optic probes with their holders can be used. We found that 45°/45° and hemispheric reflectance with their associated Yellowness Index can be used indistinctly in the cases analyzed as a good indicator of superficial color changes. We have also concluded that Yellowness Index is a good indicator of changes in appearance in PV modules. It is observed an increase of Yellowness Index with ultraviolet dose supplied to a solar module and a reduction in its maximum power.

The impact of drying and steaming processes on surface color changes of tension and normal beech wood

Beech wood has a high frequency of defects such as red heartwood, reaction wood (tension wood). For the experimental measurements four logs without visible defects like red heartwood, which can noticeably affects the measurements' results were qualified. The drying medium temperature in the first phase of the process before the moisture content of the specimens fell below the FSP was maintained at 45 °C. Then, the temperature was gradually increased to the maximum value 65 °C. The results showed that different initial wood moisture content does not affect to final value of tension and normal wood. The colorimetric parameter L* was much higher for tension wood. After steaming, there were greater differences in the colorimetric parameters, respectively, a* and b*. After drying the difference of all colorimetric parameters between tension and normal wood was significantly less. The color changes were only noticed in the surface layers of specimens. Differences were small, and thus, the impact of the tension wood on the color changes was not confirmed. However, since the lightness of tension wood plays a key role for its visual detection, it may be adequate to only measure the lightness parameter (L*).

The Evaluation of Color and Surface Roughness Changes in Resin based Restorative Materials with Different Contents After Waiting in Various Liquids: An SEM and AFM study.

The aim of the study was to evaluate of surface roughness and color changes of the resin-based five restorative dental materials after aging in liquids at different pH values. Totally 250 specimens were prepared, including 50 specimens for the each material group from five different restorative materials (G1[Filtek Z550], G2[Beautifil II], G3[Vertise Flow], G4[Dyract XP], G5[GCFujiIILC]), using the 10-mm diameter and 2-mm thickness molds. A total of 50 specimens in the each group, were divided into five subgroups (n = 10) to be immerse into five liquids at different pH. After initial color and roughness measurements, samples were stored in the same liquids for 7 and 14 days and all of the measurements were repeated on the 7th and 14th days. scanning electron microscopy and atomic force microscopy analyses were performed in the all groups. When the color change(ΔE) results are examined statistically; most of the ΔE is in Fuji II LC; and at least in Filtek Z550, it was determined that cola and gastric acid had the greatest effect on ΔE averages and showed significant differences (p < .05). When the average roughness values(Ra) are analyzed statistically, the highest values were found in Fuji II LC and the lowest values were found in Filtek Z550 (p < .05). The liquids which had the highest roughness average (ΔRa) were statistically significant and gastric acid and orange juice were the most effective ones (p < .05). Asidic beverages significantly increased the surface roughness and discoloration of dental restorative materials. RESEARCH HIGHLIGHTS: The results of this research showed that dental restorative materials, which are resin-based, affected both the color and surface roughness after waiting in the low pH value beverages. These results are supported with the scanning electron microscopy and atomic force microscopy images in our research. Clinically, this situation will create esthetic and functional problems in the dental filling restorations. For this reason, the results of this study seem to be important and we think that this article could be contribute to the literature.

Vacuum pretreatment coupled to ultrasound assisted osmotic dehydration as a novel method for garlic slices dehydration

This study investigated the effects of multi-frequency mode ultrasound and vacuum technology on the water loss (WL) of garlic slices during osmotic dehydration (OD), and their effects on the microstructure of garlic. A new method of OD for garlic slices was proposed – Vacuum pretreatment coupled to ultrasound assisted osmotic dehydration (VUOD). The results indicated that the WL of the garlic slices treated with VUOD (21.12%) was significantly (p < 0.05) higher than slices treated with normally OD (NOD) (10.67%), vacuum pretreatment OD (VOD) (14.18%), and multi-frequency mode ultrasound assisted OD (UOD) (11.20–13.56%). A mass transfer mechanism of VUOD was proposed. Low-field nuclear magnetic resonance results quantified the moisture migration in the vacuole, cytoplasm and intercellular space, and the cell wall of garlic cells. The quality properties (allicin content, surface color change and firmness) of VUOD treated garlic slices are predominately better than NOD, VOD and UOD treated samples.

Surface properties and color stability of dental flowable composites influenced by simulated toothbrushing

This study evaluated surface gloss, roughness and color change of six current flowable composites after simulated toothbrushing, including four traditional flowable composites (i.e. GrandioSO Flow, Arabesk Flow, Kerr Revolution Formula 2 and Gradia Direct LoFlo), one self-adhering flowable composite (Kerr Vertise Flow) and one universal injectable composite (G-ænial Universal Flo). Forty-eight dimensionally standardized specimens (n=8/group) were made from six composites. Before and after 1 h toothbrushing simulation, surface gloss was measured with a glossmeter, and surface roughness was evaluated with a profilometer, and color was measured with a spectrophotometer. In this study, G-ænial Universal Flo, termed as universal injectable composite by the manufacturer, presented excellent surface properties after toothbrush abrasion; Gradia Direct LoFlo showed excellent color stablity after toothbrush abrasion; color alteration of composites caused by toothbrush abrasion was acceptable on the premise that 3.3∆E units were considered as acceptable threshold values.

UV sensor based on polyurethane foam

Ultraviolet light (UV) present in solar radiation has an important effect on the health of human skin. For that reason, we developed a disposable and easy-to-manufacture UV light sensor based on surface color change of a polyurethane (PU) film and examined its performance against radiation received from a lamp or from the sun. The chemical modification after UV exposition and the consequent color variation from light yellow to brown in PU sensor were studied by using RGB image analysis and a reflectance prototype containing an Arduino board. It was found that the photochemical modification of PU films increases absorption of visible radiation in the blue spectrum range. Furthermore, PU surface was more sensitive to UV (<390) than that found in visible light when exposed to sunlight, which was associated with the presence of a chromophore in the material modified. In addition, it was found that the extract obtained from irradiated PU showed its maximum absorption at 309 nm. Hence, the use of this economical light radiation sensor seems to be a very promising tool to determine exposure to UV light from the solar spectrum.

Facile preparation of novel layer-by-layer surface ion-imprinted composite membrane for separation of Cu2+ from aqueous solution

A novel surface ion-imprinted composite membrane was fabricated using layer-by-layer technology for selective adsorption separation of copper ion. The ion-imprinted multilayer was introduced on modified polyethersulfone substrates by electrostatic interaction. Photocrosslinking was initiated by adding 4,4′-diazostilbene-2,2′-disulfonic acid disodium salt and template ions were eluted by HAc solution. Effects of preparation and adsorption conditions, such as cationic polyelectrolyte species, crosslinking agent concentration, assembly layer number, pH and initial Cu(II) concentration, on adsorption behaviors were investigated. Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscope and X-ray photoelectric spectroscopy were used for the characterization of the copper ion-imprinted membrane (Cu-IIM). Batch adsorption experiments for studies of adsorption kinetics, adsorption selectivity and stability were conducted. The maximum adsorption capacity reached up to 48.0 mg·g−1 when 3.5 bilayers were deposited on the surface of membrane under specific experimental conditions (C0 = 200 mg·L−1, pH 6.0, 400 mL, 25 °C). The Cu-IIM exhibited a higher selectivity for copper ions when competitive ions were present. In addition, the Cu-IIM showed good stability. Moreover, according to the observation of the surface color change of the Cu-IIM during the adsorption process, the membrane could be used for qualitative concentration detection of copper ions in aqueous solution.

The effect of organic salts on the browning of dried squid products processed by air-drying

To control discoloration of dried Japanese common squid (Todarodes pacificus) product, influence of 0–1% organic salts, including sodium gluconate (Na-gluconate), sodium citrate (Na-citrate), sodium phytate (Na-phytate), sodium benzoate (Na-benzoate) and sodium tartrate (Na-tartrate), on Maillard browning in the squid meat during air-drying was investigated. Changes in surface color of the dried squid were mitigated by the addition of organic salts. Organic salts also showed inhibitory effects on autolysis and generation of free amino acids (FAAs), especially arginine, in both the dried squid meat and the model solution. Moreover, Maillard reaction degree of the dried squid was decreased by using organic salts. The addition of 1% Na-citrate or 1% Na-phytate well suppressed the browning of the dried squid (p < 0.05). The results indicated that organic salts having strong chelating ability, including Na-citrate and Na-phytate, can prevent the browning of the dried squid product by inhibiting the generation of FAAs.

Effect of catalytic infrared dry-blanching on the processing and quality characteristics of garlic slices

This study investigates the effects of catalytic infrared (CIR) dry-blanching (CIRDB) on the processing and quality of garlic slices. CIRDB processing parameters of CIR processing temperature, slice thickness and processing time were studied versus the processing characteristics of internal temperature, peroxidase (POD) activity and moisture reduction. Blanched garlic quality characteristics of surface color change (ΔE), allicin retention rate, vitamin C retention rate and microbial content were determined. Hot water blanching (WB) was used as a comparison. The results indicated that increasing CIR processing temperature and/or reducing the slice thickness accelerated internal temperature rise and POD inactivation and moisture reduction. To achieve 90% inactivation of POD, the CIRDB treatment resulted in moisture reductions of 15.87–40.37%, microbial reductions of 1.76–3.91-log, ΔE between 2.03 and 10.01, retention rate of allicin between 10.63 and 33.31%, and retention rate of vitamin C between 55.00 and 81.13%. CIRDB achieved the high-quality garlic products compared with WB.

Effect of thickness on non-fried potato chips subjected to infrared radiation blanching and drying

This study investigated the effect of thickness (0.6, 0.8, 1.0 and 1.3 mm) on non-fried potato chips that were treated with a sequential infrared (IR) radiation blanching and drying method. The process characteristics such as the residual polyphenol oxidase (PPO) activity, moisture content reduction and drying rate of IR-treated potato slices were studied. The quality characteristics, including color and texture, were also determined. The residual PPO activity decreased with the increase in sample thickness, in a range of 2.13–8.81% after IR-blanching. The first-order kinetics fitted well for the PPO inactivation curve. The final moisture content (MC) of samples with various thicknesses reached a range of 3.85–4.51% (w.b.) after IR-treatment. The thinner sample had a faster drying rate than the thicker slices. The drying behavior can be described well using the Midilli model. Surface color changes of potato chips with different thickness were expressed by a 0.12-fold decrease in the L* value, and a 4.72-fold and 0.57-fold increase in the a* and b* values, respectively, after IR-treatment. The values of hardness increased by 0.96-fold with the increase in sample thickness from 0.6 to 1.3 mm. In addition, the sensory evaluation revealed that consumers preferred the sample with a thickness of 0.8 mm based on the overall degree of liking.

The analysis of thermal and anodic oxide layers on selected biocompatible titanium alloys

In the case of titanium alloys, the oxide layers on their surfaces strongly influence biocompatibility and corrosion resistance. To improve these characteristics, properties of oxide layers prepared by various methods on different base materials were examined. In this work, samples of widely used biomaterials, CP titanium grade 2 and alloy Ti6Al4V, were compared with recently developed β‐titanium alloy Ti‐39 wt% Nb. On the samples from these materials, the thermal (600°C/8 hr/atmospheric air) and anodic (1‐M H2SO4/100 V/1 hr) oxide layers were prepared. The change of surface color was observed. The surface topography of oxidized samples was observed using scanning electron microscopy. The thickness of oxide layers was measured and observed on the cross‐sectional samples. The further analysis of oxide layers surfaces was conducted using X‐ray photoelectron spectroscopy and atomic force microscopy. The growth of hydroxyapatite for further comparison of oxide layers was realized in Hank' balanced salt solution.

Effects of modified atmosphere packaging conditions on quality preservation of powdered infant formula

The effect of different modified atmospheres (100% N2, 100% CO2, 70% N2/30% CO2, 50% N2/50% CO2, and air) on the quality preservation of powdered infant formula was investigated by a storage test at 30°C. Metal can packages of 400 g per unit were stored for 493 days with periodic measurements of package gas composition and product quality attributes, which included peroxide value (POV), pH, titratable acidity, bifidobacteria count, hydroxymethylfurfural content, surface colour, and solubility. In the air package, POV as an oxidative quality index increased highly along with oxygen concentration decrease, reaching a maximum of 58.7 meq/kg lipid at 350 days. Compared with the air package, POV increase of the product was significantly lower, with all the O2‐excluded modified atmosphere packages showing a maximum of 28.5 to 29.3 meq/kg at 350 days. Packages of high CO2 concentration experienced a pH decrease and an acidity increase of the stored product caused by dissolution of CO2. The count of bifidobacteria in the product was maintained higher after 119 days in the package of 100% CO2 than in the other packages. Hydroxymethylfurfural content showed a slight increase after an initial period of slight decrease, with little difference among the package treatments. There were no significant changes in product solubility and surface colour during storage. Considering that the high CO2 atmosphere helps the survival of bifidobacteria and protects the product from oxidation without negative effects on the other quality attributes, it is suggested for use in packaging of powdered infant formula.

Condensation mode transition and condensation heat transfer performance variations of nitrogen ion-implanted aluminum surfaces

Aluminum substrate specimens are irradiated with nitrogen ions at various ion dose and ion energy levels in order to realize dropwise condensation on the specimen surfaces. Dropwise steam condensation initially occurs on these specimens, but the condensation mode changes into filmwise condensation. When the condensation mode changes to filmwise condensation, the heat transfer coefficient is measured to be approximately 40% lower than that predicted using the Nusselt theory; in addition, the color of the surface changes from yellow-brown to silver-white. This surface color change is the result of the hydrolysis reaction between the condensate and the nitrogen ion-implanted aluminum surface. Non-condensable gas is generated by the hydrolysis reaction, and this non-condensable gas diminishes the heat transfer coefficient. In addition, the material composition of the specimen’s surface changes and causes the transition of the condensation mode.

Smart textile framework: Photochromic and fluorescent cellulosic fabric printed by strontium aluminate pigment

Smart clothing can be defined as textiles that respond to a certain stimulus accompanied by a change in their properties. A specific class herein is the photochromic and fluorescent textiles that change color with light. A photochromic and fluorescent cotton fabric based on pigment printing is obtained. Such fabric is prepared by aqueous-based pigment-binder printing formulation containing inorganic pigment phosphor characterized by good photo- and thermal stability. It exhibits optimal excitation wavelength (365 nm) results in color and fluorescence change of the fabric surface. To prepare the transparent pigment-binder composite film, the phosphor pigment must be well-dispersed via physical immobilization without their aggregation. The pigment-binder paste is applied successfully onto cotton fabric using screen printing technique followed by thermal fixation. After screen-printing, a homogenous photochromic film is assembled on a cotton substrate surface, which represents substantial greenish-yellow color development as indicated by CIE Lab color space measurements under ultraviolet light, even at a pigment concentration of 0.08 wt% of the printing paste. The photochromic cotton fabric exhibit three excitation peaks at 272, 325 and 365 nm and three emission peaks at 418, 495 and 520 nm. The fluorescent optical microscope, scanning electron microscope, elemental mapping, energy dispersive X-ray spectroscopy, fluorescence emission and UV/Vis absorption spectroscopic data of the printed cotton fabric are described. The printed fabric showed a reversible and rapid photochromic response during ultra-violet excitation without fatigue. The fastness properties including washing, crocking, perspiration, sublimation/heat, and light are described.

Effects of TiO2 nanoparticles on the photodegradation of poly(lactic acid)

ABSTRACTPhotodegradable poly(lactic acid) (PLA)/titanium dioxide (TiO2) nanocomposites could be utilized as an eco‐friendly material. The photocatalytic degradation was investigated under accelerating artificial ultraviolet irradiation conditions for the period up to 100 days according to GB/T16422.3/ISO 4892.4. The change of surface color, gloss loss, morphology, weight loss, intrinsic viscosity, chemical structure, mechanical properties at different irradiation times were verified via solid reflection spectrophotometer, scanning electron microscopy, Ubbelohde viscometer, Fourier transform infrared spectrometer, and tensile test. The structural change accompanied by the degradation of the irradiated samples clearly showed that the photodegradation of PLA/TiO2 nanocomposites process was via a bulk erosion mechanism. The photodegradability of PLA/TiO2 samples was higher than that of pure PLA and benefitted a lot from a good dispersion of TiO2 nanoparticles. The present study suggests that the photodegradation of PLA could be controlled by loading dispersed g‐TiO2 nanoparticles. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46509.

Determinative Surface-Wrinkling Microstructures on Polypyrrole Films by Laser Writing

We report a simple and efficient laser-writing strategy to fabricate hierarchical nested wrinkling microstructures on conductive polypyrrole (PPy) films, which enables us to develop advanced functional surfaces with diverse applications. The present strategy adopts the photothermal effect of PPy films to mimick the formation of hierarchical nested wrinkles observed in nature and design controlled microscale wrinkling patterns. Here, the PPy film is grown on a poly(dimethylsiloxane) (PDMS) substrate via oxidation polymerization of pyrrole in an acidic solution, accompanied by in situ self-wrinkling with wavelengths of two different scales (i.e., λ1 and λ2). Subsequent laser exposure of the PPy/PDMS bilayer induces a new surface wrinkling with a larger wavelength (i.e., λ3). Owing to the retention of the initial λ1 wrinkles, we obtain hierarchical nested wrinkles with the smaller λ1 wrinkles nested in the larger λ3 ones. Importantly, we realize the large-scale path-determinative fabrication of complex oriented wrinkling microstructures by controlling the relative motion between the bilayer and the laser. Combined with the induced changes in surface color, surface-wrinkling microstructures, and conductivity in the PPy films, the laser-writing strategy can find broad applications, for example, in modulation of surface wetting properties and fabrication of microcircuits, as demonstrated in this work.

Evaluation of surface roughness and color change of bovine enamel after immersion in dye solution

Aim: The aim of this in vitro study was to evaluate the influence of dye solution on enamel color change after bleaching protocols and the effectiveness in maintaining the color of these agents.Material and Methods: The buccal surfaces of sixty-five bovine incisors were cleaned and polished, and the enamel specimens were divided into thirteen groups: G1 to G6: treated with 6% hydrogen peroxide using different surface agents; G7 to G12: treated with 15% hydrogen peroxide using different surface agents; G13: control. After 24 hours, the groups treated were immersed in black tea solution; the control group was stored in artificial saliva. The color was evaluated prior to bleaching, 24 hours later and after immersion in the dye solution; the roughness was measured immediately after bleaching, 24 hours later and 7 days after immersion in the dye solution. The data was analyzed using the Kruskal-Wallis test, followed by the Miller test for roughness analysis, and the Duncan test for color change analysis. It was used 5% significant level with p&lt;0.05.Results: The data found in the evaluation of surface roughness after bleaching indicated a reduction of roughness in all the groups. The surface agent Bifluoride, when applied, showed an increase in roughness after its application and it decreases after immersion in dye solution; the surface agent Desensibilize and the XP Bond adhesive showed greater color alteration after immersion in dye solution.Conclusions: All the groups studied, under different whitening technique, were effective in promoting whitening.

Moisture barrier properties of single-layer graphene deposited on Cu films for Cu metallization

The moisture barrier properties of large-grain single-layer graphene (SLG) deposited on a Cu(111)/sapphire substrate are demonstrated by comparing with the bare Cu(111) surface under an accelerated degradation test (ADT) at 85 °C and 85% relative humidity (RH) for various durations. The change in surface color and the formation of Cu oxide are investigated by optical microscopy (OM) and X-ray photoelectron spectroscopy (XPS), respectively. First-principle simulation is performed to understand the mechanisms underlying the barrier properties of SLG against O diffusion. The correlation between Cu oxide thickness and SLG quality are also analyzed by spectroscopic ellipsometry (SE) measured on a non-uniform SLG film. SLG with large grains shows high performance in preventing the Cu oxidation due to moisture during ADT.

Effects of water and microbial-based aging on the performance of three dental restorative materials.

The objective of this study was to evaluate the performance changes of three restorative materials before and after three different aging treatments: storage in distilled water, Streptococcus mutans (S. mutans) and oral salivary microbes suspensions for one month. Resin composite (RC), giomer and glass ionomer cement (GIC) were chosen for aging procedures. Surface morphology, roughness average (Ra), color changes and mechanical properties were all determined before and after aging respectively. Biomass and metabolism difference of early attached biofilm on the material surface were tested through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and lactic acid measurement. The results showed that after S. mutans or salivary microbes aging treatments, GIC group displayed significant morphology changes, with Ra value significantly higher than that before aging (p < .001). Color changes of giomer and GIC group after S. mutans aging were not clinically acceptable. All materials after two microbial-based aging treatments had higher flexural strength than that before aging (p < .05). Giomer after salivary microbes aging had higher elastic modulus than the initial values (p < .05). Additionally, early attached biofilm biomass and lactic acid production in GIC group after S. mutans or salivary microbes aging were higher than that before aging (p < .05). While one-month water aging showed less influences on material performance to some extent. In conclusion, to better simulate the harsh oral environment, in vitro microbial-based aging models showed more advantages in evaluating dental restorative materials' degradation over time.

Modeling and predicting of the color changes of wood surface during CO2 laser modification

Abstract To adopt a greener approach, a novel thermal treatment for wood was proposed. Poplar wood surface was treated by CO2 laser and the surface color changes were evaluated by CIELAB color space. The treated and untreated surface were scanned by Epson scanner to measure lightness difference (ΔL*), red-green index difference (Δa*) and yellow-blue index difference (Δb*), then the total color difference (ΔE*) was calculated. The laser energy load on wood surface caused characteristic changes in the chemical component, which were determined by means of Fourier infrared spectrometer (FTIR). Response surface methodology (RSM) was used for modelling and to establish a relationship between color changes and laser modification parameters. The results showed that the feed speed, sweep width and laser power had significant effects on color changes of wood surface. The ΔE* increased with the increasing of laser power, however it decreased with increasing of feed speed and sweep width, because of the amount of heat transferring decreased with the increasing of feed speed and sweep width. The results of FTIR revealed chemical structure in the wood components, which is one of the reasons to the color changes of the wood surfaces. The established quadratic mathematical model applied to describe the relationship between color changes and laser modification parameters had a good prediction. It will be useful for selecting appropriate modification parameters to achieve desired color changes.