Substituent effects on the photofading of disperse azo dyes on poly(ethylene terephthalate) substrate

The relationships between the chemical structures and oxidative fading of the disperse azo dyes, p‐nitrophenylazo‐ and benzothiazoleazo‐anilines, on poly(ethylene terephthalate) substrate are discussed in terms of the parameters k_0,i (rate constants of reaction towards ¹O₂) and f_i (photosensitivity), the molecular parameters of molecular orbital theory and substituents in the diazo and coupling components, on the assumption that the initial rates of oxidative fading are proportional to the product of k_0,i and f_i. 2‐Methoxy‐5‐acetylamino‐N‐substituted aniline couplers exhibited large f_i values. 2‐Chloro and 4‐nitro substituents of aniline diazo components exhibited small f_i values or high quantum yields of internal conversion, while 4‐nitro substituent did not. A close correlation between N‐substituents and light fastness, proposed by Müller and supplemented by Dawson, demonstrates the applicability of frontier orbital theory, through the highest occupied molecular orbital (HOMO) energy of the dyes, to the analysis of oxidative fading. Dyes with N‐2‐cyanoethyl substituents, which gave a lower HOMO energy, also exhibited superior light fastness compared with N‐2‐hydroxyethyl substituents.     

Modelling the charring behaviour of structural lumber

Charring rates for large‐section timber based on experimental data have been generally established. The established rates may not be appropriately used for the prediction of failure times of lumber members which are small by comparison. It is questionable whether a constant rate can be safely assumed for lumber members since the rate is likely to increase once the centre‐point temperature of the members starts to rise. This paper presents an empirically based model of charring rates for Spruce‐Pine‐Fir (SPF) Machine‐Stress‐Rated (MSR) 2×4 lumber subjected to a constant‐temperature exposure of 500°C, on the basis of test results on 55 specimens. In order that the model can be used with reliability analysis, one of the two model parameters was treated as a Lognormal random variable to explain variations observed in the charring rates. Furthermore, the model has been extended to permit evaluations for other lumber sizes and under exposures such as ASTM E119 fire conditions. The model was compared with existing models and used to predict char data found in the literature. Copyright © 1999 John Wiley & Sons, Ltd.     

Fluorescence assay of glucosylceramide glucosidase using NBD-Cerebroside

A sensitive fluorometric assay for glucocerebroside β-glucosidase [Dinur, T., Grabowski, G.A., Desnick, R.J., and Gatt, S. (1984)Anal. Biochem. 136, 223–234] has been reexamined. It was found that the lipids containing the NBD moiety (12-[N-methyl-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)] used for standardization of the assay are light-sensitive and that the yield of fluorescent light is very sensitive to the composition of the solvent used in the fluorometric measurement. Some protection against fading could be obtained by adding a free-radical trapping agent, Slow Fade. The fading of the free NBD-acid, when used for standardization, could be prevented by adding ethanol to the solvent, but this reduced the fluorescence yield. It is recommended that some of the fluorescent substrate be enzymatically hydrolyzed completely to NBD-ceramide, which can be utilized as the standard without the need to add ethanol. A warning about enzyme reaction rate stability with time is given, with a suggestion for ensuring constancy of activity.     

Thermoresponsive microhydrogels: preparation,properties and applications

A microgel is a fascinating type of soft matter. Among the various microgels, great interest has been shown in microhydrogels because their functions are realized in water, which is the most benign liquid to humans. The microhydrogel‐composing polymers have their own delicate hydrophilic ? hydrophobic balance, which is sensitive to environmental conditions such as temperature, pH, ionic strength, light and specific (bio)molecules, in many cases. This review describes the methodology for the preparation of such microhydrogels, their properties, and finally their applications in physicochemical, biological and biomedical, optical and photonic, and chemical fields. The main material cited is a representative temperature‐sensitive polymer, poly(N‐isopropyl acrylamide), but some other environment‐friendly polymers such as cellulose derivatives are also reported. © 2013 Society of Chemical Industry     

Polydopamine‐coated silk yarn for improving the light fastness of natural dyes

One of the problems occasionally associated with the use of natural dyes in the dyeing of silk is the susceptibility of the dyed yarn to fading in light. While a number of approaches have been used to address this problem, the use of polydopamine (PDA), a known agent with photo‐protective properties, has not been assessed previously. In this study, silk was pretreated with nano‐particulate PDA formed in situ by oxidation of a dopamine solution, then dyed with lac dye or annatto dye as model natural dyes. Photofading rates were significantly reduced in the case of annatto‐dyed, PDA‐coated silk relative to uncoated silk, while wash fastness was unaffected and remained only moderately good. In contrast, no significant change was seen in photofading rates with treated or untreated lac‐dyed silk, and wash fastness was also unaffected. The PDA did not adversely affect resultant colour values if the concentration of the dopamine precursor was kept low. When this was done, acceptable colours were obtained in the dyed silk. Further investigation is warranted of PDA as a photofading protectant and mordant with other natural dyes on silk and other fibres.     

Photochemical Mechanism of an Atypical Algal Phytochrome

Phytochromes are bilin‐containing photoreceptors that are typically sensitive to the red/far‐red region of the visible spectrum. Recently, phytochromes from certain eukaryotic algae have become attractive targets for optogenetic applications because of their unique ability to respond to multiple wavelengths of light. Herein, a combination of time‐resolved spectroscopy and structural approaches across picosecond to second timescales have been used to map photochemical mechanisms and structural changes in this atypical group of phytochromes. The photochemistry of an orange/far‐red light‐sensitive algal phytochrome from Dolihomastix tenuilepis has been investigated by using a combination of visible, IR and X‐ray scattering probes. The entire photocycle, correlated with accompanying structural changes in the cofactor/protein, are reported. This study identifies a complex photocycle for this atypical phytochrome. It also highlights a need to combine outcomes from a range of biophysical approaches to unravel complex photochemical and macromolecular processes in multi‐domain photoreceptor proteins that are the basis of biological light‐mediated signalling.     

Quiescent crystallization of poly(lactic acid) studied by optical microscopy and light‐scattering techniques

The crystallization behavior of poly(lactic acid) (PLA) has been studied extensively, and this has resulted in different reported values for the nucleation densities (Ns) and crystal growth rates (Gs) for similar grades. These inconsistencies may be magnified when they are used in subsequent modeling studies. Therefore, the quiescent crystallization behaviors of three PLA grades were studied with polarized optical microscopy and small‐angle light‐scattering experiments. The Gs and Ns were determined at several isothermal crystallization temperatures with a device that provided near‐instantaneous cooling to the isothermal crystallization temperature. Two growth rate regimes, which were attributed to α and α′ crystallization with a transition around 120 °C, were observed. Avrami analysis revealed that the poly(l ‐lactic acid) homopolymer crystal growth was three‐dimensional and was unaffected by the presence of stereocomplex PLA. The PLA copolymer crystals had a transition from an initial sheaflike conformation to three‐dimensional growth. Furthermore, the lamellar twisting of the homopolymer was observed at the isothermal crystallization temperature around 144 °C. These findings can be used for future modeling studies to predict material behavior in various industrial processes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44566.     

Eco‐friendly pretreatment of silk fabric for dyeing with Delonix regia extract

The flowers of Delonix regia have been evaluated for the natural dyeing of silk using a biomordant and enzymes. This is an eco‐friendly textile pretreatment that does not utilise metal mordanting. The aqueous extract obtained from the dried red flowers was used for the dyeing of silk fabrics. A bright reddish‐brown hue colour was observed when 30% owf Delonix extract was used on the pretreated silk material. The silk fabric was treated with either an enzyme or biomordant. The resulting dyed fabric showed resistance to fading. Finally, all dyed specimens were tested for wash and light fastness properties, making Delonix a viable alternative to synthetic red dyes. Through desorption studies, the order of reactivity of enzymes towards dye uptake in the one‐step process was found to be lipase > diasterase > protease–amylase = Pyrus(biomordant). For the two‐step process, the order of reactivity of enzymes was found to be protease–amylase > lipase > Pyrus (biomordant) > diasterase. Overall, it can be concluded that, treatments, the two‐step process was better in terms of larger colour yield values, fastness properties and both dye adherence ability.     

Study on micellization of poly(N‐isopropylacrylamide‐butyl acrylate) macromonomers in aqueous solution

A kind of thermo‐sensitive macromonomer, styrene‐terminated poly(N‐isopropylacrylamide‐butyl acrylate) [P(NIPAm‐BA)] has been synthesized in this work. With the help of ultraviolet spectrum (UV), proton nuclear magnetic resonance (¹H‐NMR), potentiometric titration and dynamic light scattering (DLS), the molecular structure, thermo‐sensitive characteristics, and micellization behaviors of this kind of macromonomer have been investigated. The obtained results demonstrate that, the molecular structure of thermo‐sensitive macromonomer, including the content of comonomer unit on the backbones and the variety of terminal groups, has great influence on its low critical solution temperature (LCST) and critical micelle concentration (CMC). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermomechanical processing environment and morphology development of a thermotropic polymer liquid crystal

We have studied a longitudinal polymer liquid crystal consisting of poly(ethylene terephthalate) (PET) and p‐hydroxybenzoic acid, namely PET/0.6PHB, where 0.6 is the mole fraction of the second component. The material was injection molded with systematic variations of the melt and mold temperatures and injection flow rate using design of experiments based on a Taguchi orthogonal array. Thermomechanical environment defined by local melt temperatures and shear rates and stresses imposed during processing was estimated by computer simulations of the mold‐filling phase. The morphology of the moldings was characterized by optical and scanning electronic microscopy, wide‐ and small‐angle X‐ray scattering, and differential scanning calorimetry. An analysis of variance approach identified the significant processing variables and their contributions to variations of morphological parameters. The processing environment affects strongly the melt viscosity, and there is a strong thermo‐mechanical coupling. The result is a complex multilaminated and hierarchical microstructure, whose morphological features are very sensitive to the processing conditions. Relationships between local thermomechanical variables (rather than global ones) and the morphological parameters are established. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Palladium Nanoparticles in Suzuki Cross‐Couplings: Tapping into the Potential of Tris‐Imidazolium Salts for Nanoparticle Stabilization

Inspired by the proclivity of various palladium sources to form nanoparticles in imidazolium‐based ionic liquids, we now report that tris‐imidazolium salts bearing hexadecyl chains and a bridging mesitylene moiety are potent stabilizers of palladium nanoparticles efficiently prepared via a Chaudret‐type hydrogenation of the bis(dibenzylideneacetone)palladium(0). The palladium nanoparticles have been isolated in pure form and characterized by ¹H nuclear magnetic resonance, transmission electron microscopy, electron diffraction and dynamic light scattering. The new materials proved effective in Suzuki cross‐coupling at a loading of 0.2% palladium. Thus, using a tris‐imidazolium iodide‐palladium material, a series of biaryl products has been prepared starting from aryl bromides and some activated chlorides. The possibility that this catalytic activity might be due to the formation of palladium N‐heterocyclic carbenes has been addressed through solid state ¹³C NMR and the synthesis of an imidazolium analogue in which the acidic 2‐H was replaced with a methyl group.     

Design and study of a color sensitivity function

If we study color reproduction, such as computer color matching or the appraisal of metametric index, we wish to understand the characteristic of color differences that are caused by the object spectral reflectivity change at each wavelength. If we simulate the light source, we wish to know the characteristics of color differences that are caused by change in relative power distribution of the light source at each wavelength; if we simulate a human eye instrument, we wish to know the characteristics of color differences that are caused by change in visual sense of human eyes at each wavelength. So, we define the color‐sensitivity functions of an object, a light source, and human eyes. According to the chromatic theory, the color‐sensitive functions of an object, a light source, and human eyes are defined in the widely used CIE1976 (L*a*b*) color space and color difference.¹ Their mathematical formulae are deduced. The three kinds of color‐sensitive functions are studied systematically and comprehensively in the whole color space. The characteristics of the color‐sensitive functions are summarized, and the mathematical models of the three kinds of color‐sensitive functions can be utilized in some fields such as computer color matching, simulation of a standard light source, and humans viewing a colorimeter. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 118–124, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20089     

The assessment of scattered light in ophthalmic materials

The assessment of scattered light in lenses, sunglasses and eye protection has been carried out in various ways. Wide‐angle scatter (haze) is used in the United States, Australia and New Zealand. Small‐angle scatter (light diffusion) is specified in Europe. Little is known of the relationships within and between the methods. In an international standard, a single method is generally required. The measurement of wide‐angle scatter (haze) (two variations of a method) and small‐angle scatter (light diffusion) (three variations of a method) were carried out on 12 samples, 4 abraded, 4 with inclusion defects and 4 with surface coating defects, in an international inter‐laboratory comparison. The consensus means and confidence limits were used to compare two haze methods: the “Basic” light diffusion method and two variations of the “Simplified” light diffusion method. For abraded samples, haze and light diffusion measures are linearly related. For the remaining samples, the haze method was a much more sensitive detector of low levels of light scatter. The three measures of light diffusion are highly linearly correlated. Haze is the more sensitive measure for lower levels of light scatter when due to smaller scattering elements. The Basic and Simplified methods are highly linearly correlated. The red laser Simplified method returns a value 10% lower than that of the Basic method, and the green laser Simplified method returns a value 12% higher than that of the Basic method. These can be accounted for by a calibration factor or different acceptance values. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 416–423, 2016     

Synthesis and characterization of fast responsive thermo‐ and pH‐sensitive poly[(N,N‐diethylacrylamide)‐co‐(acrylic acid)] hydrogels

BACKGROUND: A considerable amount of research has been focused on smart hydrogels that can respond to external environmental stimuli, especially temperature and pH. In this study, fast responsive thermo‐ and pH‐sensitive poly[(N,N‐diethylacrylamide)‐co‐(acrylic acid)] hydrogels were prepared by free radical copolymerization in aqueous solution using poly(ethylene glycol) (PEG) as a pore‐forming agent. RESULTS: Swelling studies showed that the hydrogels produced had both temperature and pH sensitivity. The deswelling kinetics at high temperature demonstrated that the shrinking rates were influenced by the addition of the pore‐forming agent and the amount of acrylic acid in the initial total monomers. The deswelling curves in low‐buffer solutions had two stages. Pulsatile swelling studies indicated that the PEG‐modified hydrogels were superior to the normal ones. These different swelling properties were further confirmed by the results of scanning electron microscopy. CONCLUSION: Such fast responsive thermo‐ and pH‐sensitive hydrogels are expected to be useful in biomedical fields for stimuli‐responsive drug delivery systems. Copyright © 2008 Society of Chemical Industry     

Digital color reconstructions of cultural heritage using color‐managed imaging and small‐aperture spectrophotometry

There are many examples of cultural heritage having optical properties that have changed with the passage of time. Examples include the yellowing, darkening, and fading of paints and varnishes caused by light exposure and atmospheric pollution. When it is infeasible to treat an object, an image simulation can provide a view to the past, known as a color reconstruction. A technique is described that relies on a color‐managed image, spectral reflectance factor measurements of the object, an optical model of colorant mixing, an optical database of artist materials, spreadsheet software, and image editing software. Spectral calculations are used to create adjustment curves where segmented portions of an object's image are translated in color. This approach has been used to produce color reconstructions of paintings by Vincent van Gogh and Georges Seurat. This colorimetric translation methodology is described and an example shown for the Chicago version of Vincent van Gogh's Bedroom. The methodology is compared with pixel‐based processing.     

The light fading mechanism of dyes derived from rhubarb extract

The effect of relative humidity and mordanting on the fading kinetics and colour change of dyes derived from rhubarb extract on wool and silk has been investigated. Wool samples showed negligible change in colour even after 100 h of exposure, whereas silk samples became significantly darker. Relative humidity in the range of 10–45% and mordanting did not appear to affect the rate of fading on both the fibres. However, the rate and extent of change in colour (ΔE) on exposure was different for different mordants. The high resistance of the dye to light fading indicates that the dye is present in a highly aggregated form in silk and wool.     

Toward the accurate modeling of amorphous nonlinear materials—polymer stress relaxation (I)

We expand our analytical modeling strategy for polymer non‐linear stress relaxation (A) to specify the remaining steps to accurately deal with the nonaffine nature of the materials’ local strains and stresses relative to their average overall values, and (B) to make it consistent with a new cooperative theory of amorphous materials dynamics, providing a model of tunable fragility that sheds light to most aspects of the behavior, including the glass transition. The stress relaxation models (1) describe a nonlinear (strain‐dependent) behavior that becomes linear at very low strains, (2) quantify the effect of temperature, (3) may quantify the effects of changes in free volume, and (4) ensure very fast computations of the materials’ response irrespective of the experimental time scale. The models are sensitive to the influence of different initial states of the material, as may result from varying degrees of molecular orientation and aging levels, and are able to predict from experimental stress relaxation moduli (for a poly (methylmethacrylate)—PMMA and a bis‐phenol‐A polycarbonate—PC) the values of the crossover frequency, ν_c, crossover temperature, T_c, and the minimum activation energy, in addition to the initial and long‐time plateau moduli, in agreement with independently measured values. POLYM. ENG. SCI., 56:348–360, 2016. © 2016 Society of Plastics Engineers     

Effect of thermomechanical history on the crystallization of poly(ether‐block‐amide)

The quiescent and flow‐induced crystallization of a poly(ether‐block‐amide) is studied by means of rheo‐optical methods. Both optical microscopy and small angle light scattering have been used. The multiblock copolymer has a microphase‐separated structure with an order–disorder transition at 180–185°C, as measured with rheometry and SAXS. The number of nuclei, spherulitic growth rates, and the characteristic time scale for crystallization are compared with that of a polyamide of similar molar mass. For the poly(ether‐block‐amide)—containing a majority of amide segments—the growth rates of the spherulites during quiescent crystallization are similar for the block copolymer and the homopolymer, even if the spherulitic structures are not the same. When flow is applied, the two materials behave differently. The flow increased the nucleation density in the homopolymer but not in the block copolymer. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Effect of Solids Loading on Resonant Mixed Al‐Bi2O3 Nanothermite Powders

Sensitive nanoenergetic powders, such as nanothermites, have traditionally been processed by ultrasonic mixing of very low solids loaded suspensions in organic solvents, which has restricted their use and application due to high solvent content and associated handling issues. In this work, we report on the performance and mixing quality of nanothermite mixtures prepared in a LabRAM resonant mixer at high solids loadings as compared to ultrasonic mixing. Specifically, the aluminum‐bismuth(III) oxide (Al/Bi₂O₃) system processed in the polar solvent N,N‐dimethylformamide (DMF) was investigated. It was found that the performance and overall quality of mixing was strongly correlated to the volumetric solids loading during processing; increasing volumetric solids loading decreases separation of particles, leading to more particle interaction and more intimate mixing. The measured performance of this system processed at 30 vol‐% was similar to traditionally ultrasonicated mixtures. Increasing the solids loading above 30 vol‐% yielded diminishing returns in performance and may introduce additional safety concerns since dry powders are very sensitive to electrostatic discharge. This mixing approach uses significantly less solvent than traditional ultrasonic mixing, results in a higher density final material, and is amenable to scaling. In addition, solvent wetted nanothermite mixed at 30 vol‐% solids loading can be mixed and deposited from a single applicator and was observed to be over five orders of magnitude less sensitive to electrostatic discharge than dry powders. This relative insensitivity enables the safe deposition of high density nanothermite ink onto devices.