Determination of bicomponent dye solutions by means of zero‐crossing‐point derivative spectrophotometry

In this study, a new spectrophotometric method was developed for the determination of some textile dyes with different types of overlapping spectra. The binary mixtures of five dyes with yellow, scarlet, red, blue, and navy blue colors were analyzed by zero‐crossing‐point first‐derivative spectrophotometry. The absorption spectra of the mixtures prepared in different ratios were recorded between 400 and 700 nm. First derivative amplitudes at appropriate zero‐crossing wavelengths were selected for the determination of dyes in the mixtures. The proposed method was successfully applied to the determination of dyes with overlapping spectra in their bicomponent mixtures. The proposed derivative method is simple, rapid, and suitable for quantitative analysis of bicomponent dye solutions. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 307–311, 2008.     

主成分回归-分光光度法同时测定食品中的钙、镁

在pH值为10.5的NH4Cl-NH3.H2O缓冲溶液中,以4-甲基偶氮胂-TB为显色剂进行试验,发现Ca和Mg分别与4-甲基偶氮胂-T形成的配合物的吸收光谱有比较严重的重叠,不能利用光度法进行单一组分的测定,本文对同时测定Ca、Mg含量进行了研究,利用主成分回归建立了校正模型,利用该模型对合成试样进行了预报,合成样品中Ca、Mg的平均回收率分别为100.36%和99.27%,利用该方法测定食品中Ca、Mg的含量,试验结果令人满意。     

Absorption of radiation by substances at “high” concentrations: A new equation and process monitoring applications

Beer-Lambert's law has a wide range of applications, spanning the fields of pure sciences and engineering, and is commonly used for the determination of the concentration of an optically sensitive compound, at “low” concentrations. In this report it is shown that a log-log expression, log(T/T₀) = K log(C/C₀), accurately models experimental data (±3%) for four different absorbing species, at “high” concentrations. The dimensionless constant K is shown to be only a characteristic of the absorbing species, and independent of the spectrophotometer/cuvette system used. The new equation is used for on-line monitoring of dynamic biomass concentration in a continuous bioreactor (CSTBR) for a step change in dilution rate.     

Dye binary mixture formulation by means of derivative ratio spectra of the Kubelka–Munk function

In this study, a new method is introduced for the determination of dye concentration in fabrics dyed with bicomponent dye mixtures. The reflectance spectra of the samples dyed with different binary mixtures of dyes were recorded between 400 and 700 nm. The obtained spectra were divided by a standard spectrum of each of the components in the mixtures and the derivative spectra were calculated. The amounts of dyes were determined by measurements in suitably selected wavelengths in the acquired derivative ratio spectra. The obtained results indicate that the developed derivative ratio spectra method is more accurate than the normal Kubelka–Munk method. The proposed derivative method is simple, accurate, and suitable for quantitative analysis of samples dyed with binary mixed shades. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010     

Solid solution synthesis of tantalum carbide‐hafnium carbide by spark plasma sintering

Solid solutions of Tantalum carbide (TaC) and Hafnium carbide (HfC) were synthesized by spark plasma sintering. Five different compositions (pure HfC, HfC‐20 vol% TaC, HfC‐ 50 vol% TaC, HfC‐ 80 vol% TaC, and pure TaC) were sintered at 1850°C, 60 MPa pressure and a holding time of 10 min without any sintering aids. Near‐full density was achieved for all samples, especially in the HfC‐contained samples. The porosity in pure TaC samples was caused by the oxygen contamination (Ta₂O₅) on the starting powder surface. The addition of HfC increased the overall densification by transferring the oxygen contamination from TaC surface and forming ultrafine HfO₂ and Hf‐O‐C grains. With the increasing HfC concentration, the overall grain size was reduced by 50% from HfC‐ 80 vol% TaC to HfC‐20 vol% TaC sample. The solid solution formation required extra energy, which restricted the grain growth. The lattice parameters for the solid solution samples were obtained using X‐ray diffraction which had an excellent match with the theoretical values computed using Vegard's Law. The mechanical properties of the solid solution samples outperformed the pure TaC and HfC carbides samples due to the increased densification and smaller grain size.     

Ultraviolet‐induced crosslinking of poly(vinyl alcohol) evaluated by principal component analysis of FTIR spectra

The crosslinking of poly(vinyl alcohol) (PVA) films under ultraviolet irradiation for between 1 and 4 h was studied in air at 25 °C in the presence of sodium benzoate by Fourier‐transform infrared spectroscopy (FTIR) using the attenuated total reflectance technique (ATR). Principal component analysis (PCA) is a mathematical procedure that allows treatment of the entire infrared spectrum and is very appropriate for analysing the chemical modifications initiated by sodium benzoate which occur in PVA upon UV irradiation. By PCA it was possible to clarify the mechanism of crosslinking of PVA. From this FTIR–PCA study, it is suggested that a free radical arising from the photolysis of sensitizer would abstract a tertiary hydrogen atom from the polymer chain to yield a polymeric radical. This radical reacts with O? H groups, leading to the formation of ether bonds between the polymeric chains and hence to crosslinking and insolubilization of the PVA. © 2001 Society of Chemical Industry     

Swelling mechanism of porous P(VP‐co‐MAA)/PNIPAM semi‐IPN hydrogels with various pore sizes prepared by a freeze treatment

BACKGROUND: The objective of the work reported was to investigate the effect of gel microstructure on the swelling mechanism. A series of porous gels with various pore sizes were prepared by freeze‐treating a conventional hydrogel that contained various amounts of water at ? 20 °C. Scanning electron microscopy and differential scanning calorimetry were used to characterize the microstructure of the porous gels. RESULTS: The experimental results showed that the water content during freezing was the key factor controlling the microstructure. Measurement of swelling kinetics showed that a greater amount of water during the freezing process would lead to a rapid swelling rate. The apparent diffusion coefficients (D_p) at all times during the swelling process were obtained by fitting the experimental data to the diffusion equation. The values of D_p suggested that the swelling mechanism of the gels depends on the pore size. The diffusion exponent (n) obtained by fitting the fractional mass change (M_t/M_∞) to equation of Fick's law further confirmed that the swelling mechanism of the gels is determined by the pore size. CONCLUSION: The swelling mechanism of the gels is determined by the microstructure related to the pore size and the thickness of struts. The microstructure can be controlled by adjusting the water content of the hydrogels by changing the pH of the swelling medium prior to freezing. Copyright © 2008 Society of Chemical Industry     

Spontaneous imbibition of liquids in glass‐fiber wicks. Part I: Usefulness of a sharp‐front approach

Spontaneous imbibition of a liquid into glass‐fiber wicks is modeled using the single‐phase Darcy's law after assuming a sharp flow‐front marked by full saturation behind the front occurring in a transversely isotropic porous medium. An analytical expression for the height of the wicking flow‐front as a function of time is tested through comprehensive experiments involving using eight different wicks and one oil as the wicking liquid. A good fit with experimental data is obtained without using any fitting parameter. The contact‐angle is observed to be important for the success of the model—lower contact angle cases marked by higher capillary pressures were predicted the best. The proposed model provides a nice upper bound for all the wicks, thereby establishing its potential as a good tool to predict liquid absorption in glass‐fiber wicks. However, the sharp‐front model is unable to explain region of partial saturation, thereby necessitating the development of part II of this article series (Zarandi and Pillai, Spontaneous Imbibition of Liquid in Glass fiber wicks. Part II: Validation of a Diffuse‐Front Model. AIChE J, 64: 306–315, 2018) using Richard's equation. © 2017 American Institute of Chemical Engineers AIChE J, 63: 294–305, 2018     

Absorption of ethylene from ethylene‐ethane gaseous mixture by AgNO3 solution in a semi‐continuous process

Ethylene absorption from an ethylene–ethane gaseous mixture in the silver nitrate solution is studied at different temperatures and concentrations. Unlike the previous studies, in which the absorption was studied by batch processes, a semi‐continuous process is applied in the present research. The results show that increase in temperature reduces the amount of absorbed ethylene and absorption time. The amount of absorbed ethylene is increased in solutions with higher concentrations of AgNO₃, whereas the mole ratio of absorbed ethylene per silver nitrate is decreased by increasing the AgNO₃ concentration. Total absorption is modelled as a function of the temperature and concentration of absorbing solution. The estimated values from the model are in good agreement with the experimental data.     

pH effects on the conformational preferences of amyloid beta-peptide (1-40) in HFIP aqueous solution by NMR spectroscopy

The structure and aggregation state of amyloid beta-peptide (Abeta) in membrane-like environments are important determinants of pathological events in Alzheimer's disease. In fact, the neurotoxic nature of amyloid-forming peptides and proteins is associated with specific conformational transitions proximal to the membrane. Under certain conditions, the Abeta peptide undergoes a conformational change that brings the peptide in solution to a "competent state" for aggregation. Conversion can be obtained at medium pH (5.0-6.0), and in vivo this appears to take place in the endocytic pathway. The combined use of (1)H NMR spectroscopy and molecular dynamics-simulated annealing calculations in aqueous hexafluoroisopropanol simulating the membrane environment, at different pH conditions, enabled us to get some insights into the aggregation process of Abeta, confirming our previous hypotheses of a relationship between conformational flexibility and aggregation propensity. The conformational space of the peptide was explored by means of an innovative use of principal component analysis as applied to residue-by-residue root-mean-square deviations values from a reference structure. This procedure allowed us to identify the aggregation-prone regions of the peptide.     

On‐line opto‐viscoelastic analysis of polypropylene fibres using multiple‐beam Fizeau fringes in transmission and a modified creep device

A creep device attached to an automated multiple‐beam Fizeau system in transmission was modified with a designed digital ruler. This device allows on‐line measurements of fibre length during creep experiments in terms of an analogue voltage value. The influence of sustained stress values on creep deformation and optical properties (n^||, n^? and Δn) for polypropylene (PP) fibres was studied interferometrically. The opto‐viscoelastic properties of PP fibres were determined for three different values of constant applied stress of 11.536, 18.717 and 25.905 MPa, at room temperature. Also, the variations of the cross‐sectional area and Poisson's ratio were studied during creep extensions. The compliance curves were obtained as a function of both time and applied stresses. Empirical formulae are suggested to describe the creep compliance curves for PP fibres, and the constants of these formulae were determined and described at each applied stress. A Kelvin chain was used to model the mechanical behaviour of the PP fibres under study. The effect of strain on the mean refractive indices, orientation function density and crystallinity was investigated as a result of the recorded data. Microinterferograms are given for illustration. The modified creep device with the designed digital ruler enables one to obtain instantaneous automatic accurate recording of fibre length values during creep experiments. Calculation of refractive indices, orientation function and crystallinity shows a difference in material behaviour at small stresses from that at higher stresses which may be attributed to different strain rates caused by different stresses. Copyright © 2010 Society of Chemical Industry