Mechanistic study of cationic dye interactions with clay‐polymer dispersions via metachromatic effect,aggregation, and surface charge

Interactions for a series of aqueous dispersions of a clay, Laponite, and nonionic difunctional triblock copolymer, Pluronic L62, with two cationic dyes, crystal violet and brilliant green, are studied using UV–vis spectroscopy, dynamic light scattering (DLS), and electrophoretic mobility (EPM) to better understand the adsorption mechanisms. Different concentrations for clay, 0.1–2.0 g/L, mixed with polymer, 0.125–0.5 g/L to produce an organoclay, were tested with a fixed dye concentration, 2.0 × 10^?5 mol/L. The aggregation states of the cationic dyes interacting with the clay–polymer dispersions were characterized by UV–vis absorbance. The dyes changed aggregation states from monomer to dimer and higher aggregate states upon addition to varying Laponite–polymer dispersion concentrations. DLS was used to understand the adsorbed polymer and dye interactions on the clay particle showing longer relaxation times for the largest aggregates observed from UV–vis absorbance. The EPM was used to characterize the surface charge of the clay relative to the polymer–dye interactions, which showed that the surface charge approached zero as the dyes interacted with clay–polymer dispersions. The most significant changes occurred with a reduction in light scattering intensity and longer relaxation decay at 0.1 g/L Laponite and 0.5 g/L Pluronic L62 concentrations in the presence of cationic dyes. The study of the clay–polymer–dye interactions help to better understand and design chemical templates for removal of contaminates in waste‐water treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40141.     

Effect of nanoclays on the dyeability of polypropylene nanocomposite fibres

Polypropylene clay fibres loaded with different alkylammonium-modified montmorillonite were prepared using a melt spinning technique and relationships between the structure and properties of the nanopolypropylene fibres are discussed. Experiments carried out using transmission electron microscopy showed that the chemical structure of the organic modifier and the interlayer spacing of the clay induced different dispersions of the clay, thus improving accessibility of the nano fibre. It is known that nanoclays are effective and efficient sorbents for dyes. Therefore, the dyeing behaviour of the nano polypropylene fibres with two distinct acid dyes and a disperse dye was studied and the build-up of dyes, measured as colour yield, reported. The best results were obtained when the clay was well dispersed in nanopolypropylene fibres; that is, when maleated polypropylene was added as a compatibiliser and when disperse dye was used. Good wash fastness was then obtained.     

染料通用性的研究进展

每一类型染料由于自身结构和性质特点决定它只能对与它具有亲和力的纤维进行染色，否则无法获得良好的染色效果。如果能用同一只染料对不同类型的纤维进行染色将有重要的现实意义，称之为染料的通用性。本文回顾了实现染料通用性的两种可能途径的研究进展，包括对纤维的改性和对染料的改性。研究涉及新型染料分子结构的设计和合成，该染料分子具有在染浴之外不需进行其它的化学反应就对所有的纤维具有亲和力的特性，因此能在同一染浴中对不同结构类型的纤维进行染色，本文称该新型染料为通用染料。同时还提出通用染料分子的设计原则和需要解决的关键问题。     

Synthesis,stability and printing properties of a novel 2‐sulphophenoxy‐4‐chloro‐s‐triazine reactive dye for ink‐jet printing of wool

We report here the synthesis and characterisation of a new medium‐reactivity reactive dye containing 2‐sulphophenoxy‐4‐chloro‐s‐triazine, having enhanced the activity of the chlorine atom for further substitution by the functional groups carried by wool fibre. In addition, a dichloro‐s‐triazine dye was also synthesised for the purpose of comparison. The progress of synthesis reactions and purity of the dyes were determined using capillary electrophoresis and thin layer chromatography. The molecular structure and the chemical compositions of the synthesised dyes were confirmed using Fourier Transform–infrared spectral data and elemental analyses. The inks containing the synthesised dyes were formulated and ink‐jet‐printed onto wool fabrics and then the printed fabrics were steamed at 102°C. Compared with the dichloro‐s‐triazine dye, superior performance in terms of ink stability, K/S and dye fixation was observed for the new 2‐sulphophenoxy‐4‐chloro‐s‐triazine dye. In addition, the light fastness of the fabric printed with the inks containing the new dye was 0.5‐grade greater than that of the fabric printed with the inks containing the dichloro‐s‐triazine dye, and no changes in shade and staining were observed following wash fastness tests of the fabrics printed with the inks containing the new dye.     

Solid-State Chemistry of Cyanine-Type Dyes and the Effect of Two Novel Counterions on Their Crystal Properties

Organic dyes undergo a variety of solid-state chemical processes, including intra- and intermolecular reactions, gas-solid reactions, and polymorphic transformations. The properties of dye solids are markedly affected by this chemistry. This paper reviews solid state dye chemistry from the literature and reports in detail the chemistry of two novel cyanine dye salts whose properties are controlled by the nature of their counterions. In cyanine-oxonol salts, the oxonol counterion is a large planar dye which forms crystalline dye aggregates with cyanine ions. There is a multiplicity of polymorphic forms of these mixed dyes reflecting multiple favorable dye aggregate geometries. The cyanine-borate salts undergo intermolecular solid-state reactions. In either large single crystals or dispersions of the latter salts in polymer binders, alkyl transfer from the anion to the chromophore can be induced thermally or photochemically.     

The Photofading of Mixtures of Azo Dyes and Mixtures of an Azo Dye and Oxygen in Aquous Solutions Containing d,l-Mandelic Acid

The reactions of the reducing species formed on photo-excitation of d, l-mandelic acid in aqueous solutions with azo dyes, oxygen, mixtures of azo dyes, and mixtures of azo dyes and oxygen have been investigated. The results indicate that all reactions can be described as reductions of the oxidising agents (azo dyes and/or oxygen) by the photochemically formed reducing species. The azo dyes used can be arranged in a sequence according to their electron affinities. The higher the electron affinity the more susceptible a dye is to reduction in d, l-mandelic acid on ultraviolet irradiation. The inhibition of the photoreduction of azo dyes in solution by oxygen is mainly caused by a competition of the azo dye present and oxygen for the reducing species. However, the rates of fading of the dyes in aerobic solutions are only partly determined by the electron affinities of dye and oxygen. Other factors, such as the relative rates of intermediate reactions and the occurrence of as yet unidentified side-reactions, determine to an important extent the sequence of stability of the azo dyes during irradiation in aerobic solutions.     

Kinetic and Calorimetric Studies of Reactive Dye Hydrolysis and Alcoholysis Reactions

Kinetic and calorimetric studies have been carried out to determine rate constants and enthalpy changes for the hydrolysis and alcoholysis reactions as a function of pH, for some reactive dyes at a given temperature, in the temperature range 25–35°C. The alcoholysis reactions were carried out in homogeneous media using glucose, sorbitol, methanol, r–propyl alcohol and ho–propyl alcohol respectively. The calorimetric data have been obtained using a sensitive rating–period calorimeter. The results indicate that, irrespective of whether the rate constants k“–or k”AO–are independent of pH or not, the heat of hydrolysis HH which is exothermic, increases with pH, whereas the heat of alcoholysis HA which is also exothermic, decreases with increase in pH for glucose and sorbitol for all the dyes studied. For the reaction with methanol, on the other hand, while k“AO– decreases with increase in pH, HA increases for the two dyes studied, namely, Procion Brilliant Red MX–2B (ICI) and Procion Red MX–G (ICI). The HA values, using n–propyl and iso–propyl alcohol, indicate that the interaction of these reactive dyes with secondary alcohol groups leads to a lowering of HA. Studies on HH in buffered and unbuffered solutions of the dyes indicate that the presence of buffer decreases the heat of hydrolysis. Taking into cons/deration both the kinetic and thermodynamic data, it is suggested that, for the hydrolysis reaction, the changes in reactivity and heat of reaction with pH are Influenced by the changes in the solvent environment at different pH values. In the case of alcoholysis reactions using glucose and sorbitol, the decrease in HA with increase in pH could be attributed to an Increase in the interaction of the dye with secondary alcohol groups. Other factors which could influence the heats of such reactions are steric factors associated with the dye and carbohydrate molecule, changes in the structure of water around these molecules and changes in activity coefficients.     

Dependence of the dyeability of modified cotton on the substituents and the nature of the dye

Cotton cellulose was chemically modified by introducing acrylamide, acrylonitrile and carboxyalkyl moieties in the form of groups or polymers. In carbamylethylated, cyanoethylated and carboxymethylated cotton, these moieties are in monomeric groups, whereas, in graft copolymers of cotton cellulose with acrylamide, acrylonitrile or acrylic acid, the moieties are in polymeric forms. These substrates were dyed independently using direct, acid, basic or reactive dyes. Results showed that at roughly equal nitrogen content, polyacrylamide–cotton graft copolymer exhibited a much higher colour strength than carbamylethylated cotton when the two substrates were dyed using basic dye. The opposite is the case for direct and reactive dyes. The acid dye produced comparable colour strengths. Similar trends were observed when the other samples were dyed with these four dyes. The results were explained in terms of microstructural changes in the physical and chemical structure of cotton caused by the etherification and grafting reactions.     

Photostability of Anthraquinone and Azo Dyes in N-Ethylacetamide (Nylon Model)

Measurements of the quantum yields of photodegradation of anthraquinone and azo dyes in N-ethylacetamide (nylon model) and triplet sensitisation of dye fading showed that the photochemical reactions are initiated by an upper excited n-π* triplet state. The primary photochemical reaction with both anthraquinone and azo dyes involves hydrogen abstraction from the amide so/vent. In some cases oxygen retards dye fading by reoxidation of the reduced structures. In other cases oxygen accelerates the photochemical reaction via free-radical initiated oxidation reactions. The quantum yields of dye fading are strongly wavelength dependent. On exposure to a simulated sunlight spectrum photodegradation is mostly caused by radiation in the region 300–400 nm. While unsubstituted anthraquinone is very photoreactive, amino-substituted anthraquinones are much more photostable in N-ethylacetam/de. Photostability of mono- and di-substituted anthraquinone derivatives increases with the electron-donating power of substituent groups. Azo dyes with increased conjugation such as diazo and naphthazo structures are more photostable than simple azobenzene derivatives. Certain electron-withdrawing substituents, which do not affect dye colour, improve the ‘oxidative’ photostability of both anthraquinone and azo dyes. A cobalt premetallised azo dye (C.I. Acid Red 182) is very photostable in N-ethylacetamide, showing the effect of metal chelates on photostability. The low values of quantum yields for the dye solutions are comparable with those of acid and disperse dyes in nylon films, indicating that N-ethylacetamide is a suitable nylon model for mechanistic studies of dye fading.     

Photodegradation of Cotton Cellulose

The relation between the fading and phototendering behaviour of Caledon Yellow GN, 5GK and 4G on cotton cellulose has been examined. A distinction is drawn between the reactions promoted by visible light and those promoted by ultraviolet radiation. Caledon Yellow 5GK is the most efficient phototenderer in visible light and production of the leuco dye accompanies this process. Phototendering by this mechanism can also be identified with Caledon Yellow GN, although to a much smaller extent than with 5GK, and production of the leuco form is accompanied by formation of free radicals. Regeneration of the original dye is best promoted by an atmosphere of moist oxygen. Excitation by short-ultraviolet radiation leads to irreversible chemical changes in the dyes and degradation of the cellulose. The most efficient phototenderer in visible light (Caledon Yellow 5GK) markedly inhibits the degradation of cotton by ultraviolet radiation, whereas the poor phototenderers in visible light (Caledon Yellow 4G and GN) exert no such marked protection. The mechanisms of these reactions are discussed. Hydrogen abstraction by the excited non-aggregated dye is the most probable path to the leuco dye and photodegradation in visible light, and the mechanism is thus comparable with the mechanisms elucidated for anthraquinone compounds in solution and on cellulose. Electronic-energy transfer to the cellulose, in competition with the abstraction process, would be favoured during ultraviolet irradiation, and is the mechanism suggested for the degradation of cellulose under these conditions. The influence of dye aggregation on the reactions and the mechanism of the irreversible chemical changes in the dyes are also discussed.     

Photostabilization of Beauveria bassiana conidia using anionic dyes

Microbial biocontrol agents, which are selective and non-polluting measures for controlling insect pests, are sensitive to environmental factors, notably solar UV radiation. To overcome the constraint of photoinstability and provide adequate field performance, the photostabilizing potential of organo-clay matrices was studied. The clay mineral surfaces were modified by adsorption of chitosan, a polycationic biopolymer. The positively charged clay–chitosan complexes served for adsorption of potent photoprotective anionic dyes. A variety of clay–chitosan–dye matrices were prepared and examined as to their potential to photostabilize UV-irradiated fungal conidia of the entomopathogen Beauveria bassiana. The matrices were composed of palygorskite, montmorillonite, bentonite and kaolinite and of 6 anionic dyes: Acid Yellow 25 (AY), Chrysophenine G (Chrys.), Direct Yellow 50 (DY), Mordant Blue (MB), Fast Green (FG) and Naphthol Yellow S (NYS). The adsorption isotherms of dyes and their level of adsorption to the organo-clays were established. Clay–chitosan complexes per se were able to bestow significant measures of photoprotection, apparently due to their UV light scattering property. High and relatively consistent levels of photostabilization were observed with clay–chitosan matrices containing Chrys., AY, NYS and DY following prolonged irradiation. Depending on the clay-based matrix, MB and FG provided less persistent photostabilization levels. In contrast to the other clay–chitosan complexes, the high photoprotection bestowed by kaolinite–chitosan per se obscured to a great extent any contribution of the anionic dyes. Apparently, the photostabilization of the clay-based matrices is a combination of UV light scattering capacity of clay minerals and the UV screening effect due to the adsorbed dyes.     

DIFFERENTIAL THERMAL ANALYSES OF SOME MISSOURI FIRE CLAYS*

Differential thermal analyses were made of a large number of fire clays representative of Missouri production. Flint clays gave typical kaolinite curves. The curves of plastic and semiplastic clays were similar to that of kaolinite. Staining with aniline dyes, petrographic determination, and ceramic behavior indicate that clay minerals other than kaolinite are present in Missouri semiplastic clays but these (other clay minerals) were not revealed by the differential thermal method. High-alumina hurley clays showed variously endothermic peaks of diaspore, boehmite, and kaolinite, but no exothermic peak which is characteristic of kaolinite.     

Studies on the dyeability and dyeing mechanism of polyurethane/clay nanocomposite filaments with acid,basic and reactive dyes

Polyurethane/clay nanocomposite (PUCN) filaments were spun by the dry‐jet‐wet spinning method. To prepare the PUCN filaments, 0.25, 0.50 and 1% of nanoclay on the weight of polyurethane were incorporated in the polyurethane dope. The interaction between clay and polyurethane was analysed by attenuated total reflectance–Fourier Transform‐infrared (ATR‐FTIR) spectroscopy. The structure and morphology of the PUCN filaments were analysed by wide‐angle X‐ray diffraction (WAXD) and transmission electron microscopy (TEM). Both the neat polyurethane and the PUCN filaments were dyed with different acid, basic and reactive dyes. The neat polyurethane filaments exhibited poor dyeability with all three classes of dyes. By contrast, the PUCN filaments showed a significantly higher dye uptake with all of the dyes used. Furthermore, the dye uptake increased significantly as the percentage of clay in the filaments increased, as indicated by the increase in the K/S values of the dyed filaments. The dyeing mechanism with all three dyes, as well as the increased dyeability of the PUNC filaments in comparison to those of the neat polyurethane filaments, was discussed.     

Some properties of dual fluorescence of methine dyes

Studies of the dependence of methine dye absorption and fluorescence properties on the molecular composition of the dyes, on solvent polarity and on the temperature of the sample were made. The results have confirmed our recent suggestion that the emission band of methine dyes in polar solvents is composed of molecular and excimer fluorescence. The spectral properties of different types of molecular composition of methine dyes indicated the centre in the dye molecule involved in excimer formation. On the basis of a liquid nitrogen temperature spectrum and the lifetimes of fluorescence it is suggested that this type of methine dye which can form the excimers has a strong tendency to aggregate in the ground states. These aggregates are able to quench the molecular fluorescence. An increase of solvent polarity causes disaggregation of dye molecules giving an increase of molecular fluorescence and an increased probability of excimer formation. Thus, in polar solvents the long-wavelength emission band arises.     

Adsorption of alizarinate–micelle complexes on Na-montmorillonite

The adsorption on Na-montmorillonite of the monovalent anion alizarinate and its complexes with micelles of cationic surfactants was investigated. Micelles were prepared from octadecyltrimethylammonium (ODTMA) and benzyldimethylhexadecyl-ammonium (BDMHDA). Alizarinate–micelle complexes are much more efficient for the adsorption of the dye than alizarinate alone, e.g., from 0.05 mM alizarinate solution 12.5 mmol per 100 g clay was adsorbed in the presence of micelles, whereas only 4 mmol per 100 g clay was adsorbed in their absence. However, unlike the adsorption of alizarinate on the clay, where its adsorbed fraction increased with the concentration of the clay, in the presence of micelles, the concentration of the clay should be optimized for achieving maximal adsorption of alizarinate. This effect is due to monomer adsorption on excessive clay sites, which leads to the decomposition of micelles, and consequently, the adsorption of alizarinate is reduced.Visible spectra of alizarinate–micelle complexes in water and adsorbed on montmorillonite were recorded. The absorption band of alizarinate in aqueous solutions at 522 nm was red-shifted in the presence of ODTMA and BDMHDA micelles due to the effect of the micelle microenvironment. Further shifts were observed in the presence of montmorillonite indicating that the alizarinate–micelle complexes were adsorbed on the clay. Significant spectroscopic changes were observed after the adsorption of alizarinate–BDMHDA-micelle complex on the clay indicating that the adsorption leads to changes in the micelle. This observation suggests that the dye may serve as a probe in visible-spectroscopy study of the adsorption of micelles on clay minerals.     

Kinetic aspects of dye addition in continuous integration dyeing

Following on from previous papers by the authors concerning the integration dyeing method, this paper studies the kinetic behaviour of the dye when integrated continuously in an isothermal solution over a period of 60 min. The dyeing systems selected were acid dyes on wool and cationic dyes on Leacril 16 fibre. Curves of the kinetics of dye absorption by the fibres were similar to those of the addition of dye to the dyebath. At low exhaustion the systems followed an Arrhenius law, contrary to the behaviour at high exhaustion where the dye absorption was almost independent from temperature. A mathematical method is described to assess the total amount of the dye to be added in relation with the desired temperature and exhaustion.     

Fundamental and applied research on clay minerals: From climate and environment to nanotechnology

This brief overview comments on recent trends in scientific research and development of clay minerals and was stimulated by the compilation of papers for this special issue to pay tribute to the 34th International Geological Congress held in 2012. The essentially geological context of the conference was a reminder that increased understanding of the genesis and evolution of clays and clay minerals provides insights that have applications in mining, environmental management, paleoclimate, Earth and extraterrestrial sciences. The requirement for multidisciplinary knowledge, including geology, mineralogy, chemistry and materials science, and modern instrumentation and analysis of clay minerals, is essential to a full understanding of the genesis, role and potential new uses for these fine-grained industrial minerals. Latest studies are typically focused on processing and modifying of clay minerals as adsorbents, catalysts, and biomaterials. The emphasis for future work is on advanced clay-based nanomaterials for use in new approaches to sustainable energy, green environment, and human health.     

Poly(acrylamide/laponite) nanocomposite hydrogels: Swelling and cationic dye adsorption properties

Super adsorbent polyacrylamide (PAAm)/nanoclay (laponite, Lap) hydrogels were prepared by in situ free radical polymerization of AAm in an aqueous solution with clay as a crosslinker. The swelling properties and water‐soluble cationic dye adsorption behaviors of the PAAm/laponite (PAAm/Lap) nanocomposite (NC) hydrogels were investigated. The parameters of swelling and diffusion of water in dye solutions were evaluated for the PAAm/Lap NC hydrogels. The adsorption behavior of the monovalent cationic dyes such as Basic Blue 12 (BB 12), Basic Blue 9 (BB 9), and Basic Violet 1 (BV 1), were studied on the NC hydrogels. The effects of the clay content of the hydrogel on its cationic dye uptake behavior were studied. The adsorption studies indicated that the rates of dye uptake by the NC hydrogels increased in the following order: BB 9 > BB 12 > BV 1. This order is similar to the swelling results of the PAAm/Lap NC hydrogel in the dye solutions. The equilibrium uptakes of the different dyes by the PAAm/Lap NC hydrogel were nearly the same. In the dye absorption studies, S‐type adsorption in the Giles classification system was found for the BB 12 and BV 1 dyes, whereas L ‐type was observed for the BB 9 dye. After the heat treatment of PAAm/Lap, the rate of dye uptake and equilibrium dye uptake were increased. The NC hydrogels may be considered as a good candidate for environmental applications to retain more water and to remove dyes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Luminescence and laser action of coumarin dyes doped in silicate and aluminosilicate glasses prepared by the sol-gel technique

Coumarin dyes are encapsulated in silicate and aluminosilicate polymeric glasses synthesized by the sol-gel technique. The coumarin dyes retain their luminescent properties in all of the aged gels and in many of the dried gels (xerogels). The luminescence spectra of the new optical materials are reported. The luminescence of coumarin 4 provides a probe at the molecular level of the changes which occur during the gelation and drying. The spectral changes are studied and discussed in detail. Gels and xerogels doped with coumarin 460, 480, and 540A exhibit optical gain and laser action. The laser properties of these new solid-state dye laser materials are reported and discussed.     

A spectroscopic approach for structural characterization of polypropylene/clay nanocomposite

This study focuses on the degree of dispersion and structural development of organomodified MMT clay (OMMT) during processing of polypropylene clay nanocomposites using both conventional and nonconventional characterization techniques. PP‐g‐MA and Cloisite 15A were melt blended with three different grades of PP separately in a micro‐twin screw compounder at selected screw speed and temperature. The clay was modified with fluorescent dyes and the adsorbed dye content in the clay gallery was estimated by using UV‐spectrophotometric method. The effects of residence time and molecular weight of the PP matrix on the clay dispersion were studied. The extent of dispersion and exfoliation of the clay in polymer matrix determined from the torque versus time data obtained from microcompounder. It was further supported by XRD, SEM, TEM, and DSC analysis. Offline dielectric and fluorescence spectrophotometric studies were also carried out. Changes in dielectric constant and dielectric loss with both frequency and temperature yielded quantitative information about the extent of clay exfoliation and intercalation in the polymer matrix. It was observed that with an increase in MFI (decrease in molecular weight) and mixing time, the extent of clay dispersion and exfoliation were also improved due to easy diffusion of polymer chains inside clay gallery. POLYM. COMPOS., 31:2007–2016, 2010. © 2010 Society of Plastics Engineers