Study of the Homologous Retention Increment in Flat-Bed Chromatography

Abstract

Relations between the chromatographic retention of various classes of homologous compounds in flat-bed chromatography systems and the thermodynamic properties of the latter were investigated. Provided the retention of solute (i) is due to liquid-liquid partition, the R_Mi is related to the partial molar excess Gibbs free energies of the solute in the mobile and stationary phases, G^E _im and G^E _is , by R_Mi = [(G^E _im - G^E _is )/ 2.3RT] - log A, where R and T are the universal gas constant and the absolute temperature of the system, respectively, and A = d_mM_sφ_m/d_sM_mφ_s, d, M, and φ denoting the densities, molar masses, and cross-sectional areas of the mobile and the stationary phases, m and s, respectively. The difference in the partial molar excess Gibbs free energies per solute methylene group in the mobile and in the stationary phase, related with the R_M increment per methylene group of solute by G^E _m (CH₂) - G^E _s (CH₂) = 2.3RTR_M (CH₂), can be used to characterize the difference in the polarities of the phases.     

Laser light-scattering studies of soluble high performance fluorine-containing polyimides

Two sets of soluble high performance polyimides synthesized from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′-(trifluoromethyl)-4,4′-diaminobiphenyl diamine (PFMB), and from 2,2′-bis(trifluoromethyl)-4,4′,5,5′-biphenyl-tetracarboxylic dianhydride (HFBPDA) and 2,2′-(trifluoromethyl)-4,4′-diaminobiphenyl diamine (PFMB) have been investigated by static and dynamic laser light scattering (LLS) in tetrahydrofuran (THF) at 30°C. The calibrations, for 6FDA-PFMB: <R_g> (nm) = 3.87 × 10^?2 <M_w> ^0.568, <R_h> (nm) = 2.38 × 10^?2 <M_w>^0.560 and <D> (cm²/s) = 2.13 × 10^?4 <M_w>^?0.560; for HFBPDA-PFMB: <R_g> (nm) = 2.24 × 10^?2 <M_w>^0.626, <R_h> (nm) = 1.27 × 10^?2 <M_w>^0.621 and <D> (cm²/s) = 3.99 × 10^?4 <M_w>^?0.621, have been established, where <M₂>, <R_g>, <R_h> and <D> are the weight-average molar mass, the root mean square z-average radius of gyration, the z-average hydrodynamic radius and the z-average translational diffusion coefficient, respectively. A combination of <M_w> and the translational diffusion coefficient distribution G(D) leads to the calibrations of D (cm²/s) = 2.41 × 10^?4M^?0.564 and D (cm²/s) = 6.16 × 10^?4M^?0.656 for 6FDA-PFMB and HFBPDA-PFMB, respectively, where D and M correspond to monodisperse species. With these calibrations, we can convert a translational diffusion coefficient distribution G(D) into a corresponding molar mass distribution f_w(M). On the basis of the Kratky-Porod wormlike chain model, the persistence lengths (q) were found to be ? 3.3 nm and ? 4.5 nm, respectively, for 6FDA-PFMB and HFBPDA-PFMB, which indicates that both polyimide chains have an extended conformation. In addition, <R_g> / <R_h> ? (1.7-1.9) shows that they are in coil conformation. Therefore, we conclude that both polyimides have an extended coil conformation.     

Rheological and thermal properties of saponified cassava starch‐g‐poly(acrylamide) superabsorbent polymers varying in grafting parameters and absorbency

Cassava starch‐graft‐poly(acrylamide) superabsorbent polymers (SAPs) with varying absorbencies were synthesized. Weight average molecular weight (M_w) of the hydrolyzed starch‐graft‐copolymers ranged from 1.6 × 10⁶ to 2.8 × 10⁶ g/mol, the largest being shown by the sample with highest percentage grafting. The storage (G′) and loss modulus (G″) of hydrogels were determined as a function of frequency. G″ was larger than G′ for the hydrogels with higher absorbencies and exhibited a liquid‐like behavior. However, hydrogels with lower absorbencies showed a reverse viscoelastic behavior. The viscosity of hydrogels determined using a Brookfield viscometer at different shear rates was found to be larger for the hydrogels with higher absorbencies. The melting temperature (T_m) and enthalpy change of fusion (ΔH_f) of the SAPs ranged from 149.7 to 177.7°C and 65 to 494.9 J/g, respectively and showed a positive correlation with grafting parameters and M_w. Heavy metal ion removal capacity of hydrogel followed the order Cu²⁺ > Pb²⁺ > Zn²⁺. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40368.     

Study of stability and thermodynamic properties for polychlorinated dihydrophezines by density functional theory

The thermodynamic properties of 76 polychlorinated dihydrophezines (PCDPs) in the gaseous state at 298.15 K and 101.325 kPa, have been calculated using the density functional theory (the BHANDHLYP/6‐31G*) with Gaussian 03 program. Based on these data, the isodesmic reactions were designed to calculate the standard formation heat (Δ_fH^θ), standard Gibbs free energy of formation (Δ_fG^θ) of PCDPs in the gaseous state. The relations of these thermodynamic parameters with the number and position of chlorine substituents (N_PCS) were discussed, and it was found that there exist good correlation between thermodynamic parameters, including heat capacity at constant volume , entropy (S^θ), enthalpy (H^θ), free energy (G^θ), Δ_fH^θ, Δ_fG^θ, and N_PCS. The relative stability order of PCDP congeners was theoretically proposed based on the relative magnitude of their Δ_fG^θ. In addition, the values of molar heat capacity at constant pressure (C_p,m) for PCDP congeners have been calculated.     

Theoretical Study on Thermodynamic and Detonation Properties of Polynitrocubanes

We investigated the heat of formation (Δ_fH) of polynitrocubanes using density functional theory B3LYP and HF methods with 6‐31G*, 6‐311+G**, and cc‐pVDZ basis sets. The results indicate that Δ_fH firstly decreases (nitro number m=0–2) and then increases (m=4–8) with each additional nitro group being introduced to the cubane skeleton. Δ_fH of octanitrocubane is predicted to be 808.08 kJ mol⁻¹ at the B3LYP/6‐311+G** level. The Gibbs free energy of formation (Δ_fG) increases by about 40–60 kJ mol⁻¹ with each nitro group being added to the cubane when the substituent number is fewer than 4, then Δ_fG increases by about 100–110 kJ mol⁻¹ with each additional group being attached to the cubic skeleton. Both the detonation velocity and the pressure for polynitrocubanes increase as the number of substituents increases. Detonation velocity and pressure of octanitrocubane are substantially larger than the famous widely used explosive cyclotetramethylenetetranitramine (HMX).     

Simple Method for Prediction of the Standard Gibbs Free Energy of Formation of Energetic Compounds

A reliable simple method for prediction of the standard Gibbs energy of formation (Δ_fG^θ) of energetic compounds containing nitroaromatic, acyclic, and cyclic nitramine, nitrate ester, and nitroaliphatic compounds is introduced herein. The method is based on the contribution of elemental composition (Δ_fG_elem^θ) and the correcting function for the presence of additive and non‐additive molecular fragments (Δ_fG_corr^θ). In presence of some molecular moieties, Δ_fG_corr^θ may increase or decrease the value of Δ_fG_elem^θ, depending on the intermolecular interactions. The experimental root‐mean‐square error (RMSE) of the novel correlation (22.7 kJ mol⁻¹) is quite good. For some energetic compounds, where the computed values of two complex models of the quantitative structure‐property relationship (QSPR) theory were available, the experimental RMSE developed by the new method is smaller than the values obtained by QSPR method.     

Chain orientation in sheared molten poly(ethylene oxide) fractions by measurement of infrared dichroism

Rheo-infrared spectroscopy was used to study the development of orientation of molten narrow molar mass fractions of poly(ethylene oxide) [molar masses between 18,000 and 120,000 g/mol] during non-Newtonian shear flow at shear rates between 2 and 270 s^?1 and temperatures between 75 and 100°C. The steady state degree of orientation [expressed as the Hermans orientation function (f_ss)] reached a saturation level with increasing shear rate; f_ss increased with increasing molar mass (M) according to f_ss = C₁ ? C₂/M (C₁ and C₂ are coefficients; the latter depended on shear rate and temperature). The coefficient C₁ (f_ss) for a polymer with infinite molar mass took a universal value close to 0.05 for the temperatures and shear rates used. Under large shear stresses, the relationship between stress and orientation deviated markedly from linearity. The time to establish a steady state level of orientation was proportional to M^1/2. The recovery of the isotropic state after the cessation of shear could initially be described by a simple exponential relaxation law: f ∝ e, where τ_ρ is the relaxation time. The latter showed a weak molar mass dependence according to τ_r ∝ M^0.6 and an Arrhenius temperature dependence with an activation energy of ～60 kJ/mol. The relaxation of the shear stress after the cessation of shear was more rapid than the recovery of the isotropic state.     

Mechanisms of electroless metal plating. III. Mixed potential theory and the interdependence of partial reactions

Electroless plating reactions are classified according to four overall reaction schemes in which each partial reaction is either under diffusion control or electrochemical control. The theory of a technique based on the observation of the mixed potential as a function of agitation, concentration of the reducing agent and concentration of metal ions is presented. Using this technique it is shown that in electroless copper plating the copper deposition reaction is diffusion-controlled while the formaldehyde decomposition reaction is activation-controlled. Values of the kinetic and mechanistic parameters for the partial reactions obtained by this method and by other electrochemical methods indicate that the two partial reactions are not independent of each other.Nomenclature a Tafel slope intercept - A electrode area - b _M Tafel slope for cathodic partial reaction - b _R Tafel slope for anodic partial reaction - B _M diffusion parameter for CuEDTA^2– complex - diffusion parameter for dissolved oxygen - B _R diffusion parameter for HCHO - C _M bulk concentration of copper ions - bulk concentration of dissolved oxygen - C _R ^a surface concentration of HCHO - C _R bulk concentration of HCHO - D _R diffusion coefficient of HCHO - E electrode potential - E _M thermodynamic reversible potential for the metal deposition reaction - E _M ⁰ standard electrode potential for copper deposition - E _MP mixed potential - E _R thermodynamic reversible potential for reducing agent reaction - E _R ⁰ standard electrode potential for HCHO - F Faraday constant - i _M current density for metal deposition - i _M total cathodic current density - i _M ^k kinetic controlled current density for metal deposition - i _M ⁰ exchange current density for metal deposition - i _M ^D diffusion-limited current density for metal deposition - i _M ^D diffusion-limited current density for total cathodic reactions - current density for oxygen reduction - i _plat plating current density - i _R current density for HCHO oxidation - i _R ⁰ exchange current density for HCHO oxidation - i _R ^D diffusion-limited current density for HCHO oxidation - n _M number of electrons transferred in metal deposition reaction - n _R number of electrons transferred in the HCHO oxidation reaction - R gas constant - T absolute temperature - stoichiometric number - _M transfer coefficient for metal deposition - _R transfer coefficient for HCHO oxidation - _M symmetry factor - number of steps prior to rate determining step - _M overpotential for metal deposition - _R overpotential for HCHO oxidation - v kinematic viscosity - rotation rate of electrode     

Significance of logarithmic throwing index: a theoretical approach

An expression for the metal distribution ratio in electroplating systems as a function of the primary current density ratioL in the formM=L [W(1–r)/(1+K)] is derived.W,r andK are three dimensionless parameters related to the current efficiency ratio, the concentration polarization and activation polarization during the metal discharge. The function [W(1–r)/1+K] is compared with 1/A, the logarithmic throwing index empirically determined by Chin. The metal distribution ratio calculated by the use of the above formula is compared with the experimentally observed values. The close agreement between the two within an accuracy of 10% proves the validity of the equation derived. The logarithmic throwing power of electroplating systems is thus confirmed on theoretical grounds.Nomenclature A Logarithmic Throwing Index —inverse of the slope of the plot of logM versus logL - b Tafel slope. Slope of the equation =a + b logi - d_n Current efficiency in percent for metal deposition at near cathode - d _f Current efficiency in percent for metal deposition at far cathode - E The overall cell potential - E _n The potential drop in the electrolyte between the anode and near cathode - E _f The potential drop in the electrolyte between the anode and far cathode - e _a Dynamic anode potential - e _n Dynamic potential at the near cathode at a current densityi _n - e _f Dynamic potential at the far cathode at a current densityi _n - f a fraction = - i The average current density (A dm^–2) - i _n The primary current density at the near cathode when there is no polarization(A dm^–2) - i _f The primary current density at the far cathode when there is no polarization(A dm^–2) - i _n The secondary current density at the near cathode (A dm^–2) - i _f The secondary current density at the far cathode (A dm^–2) - i _{H n} The partial cathode current density at the near cathode for parallel cathodic reactions other than metal discharge (A dm^–2) - i _{H f} The partial cathode current density at the far cathode for parallel cathodic reactions other than metal discharge (A dm^–2) - i _{M n} The partial cathode current density for metal discharge at the near cathode - i _{M f} The partial cathode current density for metal discharge at the far cathode - K A dimensionless parameter =b/2.3E _f - l Linear Ratio =l _f/l _n ori _n i _f - l _n Linear distance of the near cathode (cm) - l _f Linear distance of the far cathode (cm) - M Metal distribution ratio - m _n Weight of metal deposited on the near cathode - m _f Weight of metal deposited on the far cathode - R Secondary current distribution ratio=i _n/i_f - r A dimensionless parameter related toK andf and given byf=(1/L) ^r/K - W A dimensionless parameter related current efficiency ratioR ^W–1 =d _n/d_f - Specific resistivity of the electrolyte( cm^–2) - _n The overpotential at the near cathode (V) - _f The overpotential at the far cathode - i ₀ The exchange current density     

A new method for determining aflatoxins in groundnut and groundnut cake using fourier transform infrared spectroscopy with attenuated total reflectance

A new analytical method was developed for the determination of aflatoxins in groundnut and groundnut cakes by Fourier transform infrared (FTIR) spectroscopy using horizontal attenuated total reflectance technique. Groundnut and groundnut cake samples were used in this study. The wave-lengths were selected for the four types of aflatoxins—B₁, B₂, G₁, and G₂—and the standards prepared for earch by spiking some clean sample with the aflatoxins in concentrations of 0–1200 parts per billion. A partial least square regression was used to derive the calibration models for each toxin. The coefficients of determination (R ²) of the calibration model were computed for the FTIR spectroscopy predicted values vs. actual values of aflatoxins in parts per billion. The R ² was found to be 0.9911, 0.9859, 0.9986, and 0.9789 for aflatoxins B₁, B₂, G₁ and G₂, respectively. Standard errors of calibration for groundnut samples were found to be 1.80, 2.03, 1.42, and 2.05 for aflatoxins B₁, B₂, G₁, and G₂, respectively. Calibration models were validated with an independent set of samples. The R ² of validation models were computed. The SD of the difference for repeatability of the FTIR method was found to be better than that of the chemical method. Based on the results obtained, FTIR spectroscopy can be a useful instrumental method for determining aflatoxins in oilseeds and oilseed cakes. With its speed and ease of data manipulation by computer software, it is a possible alternative to the standard wet chemical methods for a rapid and accurate routine determination of aflatoxin levels in food and feed.     

Synthesis and polyelectrolyte behavior of poly(methacrylic acid) star polymers

Poly(tert‐butyl methacrylate) [P(tBMA)] star polymers were synthesized by copolymerization of p(tBMA) macroinitiator with ethylene glycol dimethacrylate via atom transfer radical polymerization method. P(tBMA) stars had a narrow molecular weight distribution (M_w/M_n = 1.06–1.15). The ratio of radius of gyration to hydrodynamic radius R_G/R_H, which indicates inner segment density, was in the range 1.16–1.22 in tetrahydrofuran (THF) (arm number f = 25–142). These stars behaved not as hard spheres but as soft spheres in THF. Poly(methacrylic acid) stars were obtained by the hydrolysis of P(tBMA) arms. We investigated the conformation of star polyelectrolyte as a function of pH and ionic strength by means of dynamic light scattering (DLS). The hydrodynamic diameter increased gradually from 18.8 to 48.3 nm as a function of the solution pH. In addition, we compared experimental results with theoretical models for star polyelectrolytes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Elucidating the Crack Resistance of Alkali‐Activated Slag Mortars Using Coupled Fracture Tests and Image Correlation

The resistance of alkali silicate‐activated slag mortars to crack propagation is explored. With increasing SiO₂‐to‐alkali oxide ratio (M_s) of the activating solution (between 1.0 and 2.0), the flexural strengths, fracture energies, and the strain energy release rates (crack resistance, G_R) are noted to increase. The G_R values, especially of the systems with M_s of 1.5 and 2.0, are higher than that of ordinary portland cement (OPC) mortar. In contrast, the fracture process zone (FPZ) was observed to be smaller for the alkali‐activated slag mortars, with higher localized strains. Similarly, the FPZs also shrink with increasing M_s. These responses are related to the differences in the reaction products in these systems. The fundamental differences in the fracture response of these binder systems are elucidated through tracking the FPZ development. The crack extension‐crack tip opening displacement relations and its relationship with the inelastic strain energy release rates are also used to bring out the differences between the binder systems.     

Is there any contradiction between the stress and energy failure criteria in micromechanical tests? Part III. Experimental observation of crack propagation in the microbond test

A direct observation of crack propagation in the microbond test was carried out for five different fiber/polymer matrix systems. This technique appeared to be a very effective tool for interface characterization. Experimental plots of the force required for further crack propagation as a function of debond length were analyzed using both energy-based and stress-based models of debonding. The fracture mechanics analysis was used to construct families of crack resistance or R-curves which showed the variation of energy release rate, G, with the debond length, and included the effect of interfacial friction in debonded regions. For the first time, analogs of the R-curves were created within the scope of the stress-based model to present the local shear stress near the crack tip, τ, as a function of crack length. In both models, the behavior of the interfacial parameter (G or τ) strongly depends on the assumed value of the interfacial frictional stress (τ_f). However, for each matrix/fiber system there exists such a τ_f value for which the investigated parameter is nearly constant over the whole region of stable crack propagation (70–90% of the embedded length). Moreover, these best-fit τ_f values for each specimen appeared to be practically the same for both energy-based and stress-based approaches. Thus, both interfacial toughness, G _ic, and local interfacial shear strength, τ_d, adequately characterize the strength of a fiber/matrix interface. Extrapolation of R-curves and their analogs to zero crack length allows measurement of the interfacial parameters with good accuracy.     

Frequency and voltage dependence of dielectric properties,complex electric modulus,and electrical conductivity in Au/7% graphene doped‐PVA/n‐Si (MPS) structures

In order to increase the capacitance of Au/n‐Si (MS) structure, 7% graphene doped PVA was coated on n‐Si as an interfacial layer. The measured data of capacitance (C) and conductance (G/ω) of Au/7% graphene doped‐PVA/n‐Si (MPS) structure was utilized for the calculation of real and imaginary parts of complex permittivity (ε^* = ε′ − jε″), loss tangent (tanδ), complex electric modulus (M^* = M′ + jM″), and electrical conductivity (σ). The admittance measurements (C and G/ω) were carried out in the frequency range of 0.5 kHz to 1 MHz at room temperature. Frequency dependence of the dielectric constant (ε′), dielectric loss (ε″) and tanδ shows a dispersive behavior at low frequencies. This behavior was explained by Maxwell–Wagner relaxation. Due to the dipolar and the interfacial polarizations, as well as the surface states (N_ss) and the interfacial PVA layer, the parameters exhibited a strong dependence on frequency and applied bias voltage. The σ versus log(f) plot exhibited both low and high frequency dispersion phenomena such that at low frequencies σ value corresponding to the dc conductivity (σ_dc), but at high frequencies it corresponds to the ac conductivity (σ_ac). M′ and M″, both, have low values in the low frequency region. However, an increase is observed with the increasing frequency due to the short‐range mobility of charge carriers. As a result, the change in dielectric parameters and electric modulus with frequency is the result of relaxation phenomena and surface states. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43827.     

SrLa(R0.5Ti0.5)O4 (R=Mg,Zn) microwave dielectric ceramics with complex K2NiF4‐type layered perovskite structure

Dense SrLa(R_0.5Ti_0.5)O₄ (R=Mg, Zn) ceramics were prepared by a standard solid‐state reaction method. The single phase with complex K₂NiF₄‐type layered perovskite structure and I4/mmm space group was revealed by XRD, and the refined structure was analyzed by Rietveld analysis. Significantly improved dielectric constant was obtained in SrLa(R_0.5Ti_0.5)O₄ ceramics compared to the analogues SrLaAlO₄ and SrLaGaO₄, which is attributed to the increasing normalized bond lengths of Sr/La‐O(1) and Sr/La‐O(2a) bonds and the higher polarizability of (R_0.5Ti_0.5)³⁺ than Al³⁺ and Ga³⁺. In addition, τ_f converts to a positive value with the increase in dielectric constant. The following microwave dielectric properties were obtained in the dense ceramics: ε_r=25.5, Qf=72 000 GHz, τ_f=29 ppm/°C for SrLa(Mg_0.5Ti_0.5)O₄, and ε_r=29.4, Qf=34 000 GHz, τ_f=38 ppm/°C for SrLa(Zn_0.5Ti_0.5)O_4. Furthermore, the stability of K₂NiF₄‐type structure in MLnBO₄ [M=Ca, Sr, Ba; Ln=Y, Sm, Nd, La; B=Al, Ga, (Mg_0.5Ti_0.5), (Zn_0.5Ti_0.5)] compounds was discussed in relation to the tolerance factor of perovskite layer and the radius ratio of M²⁺ and Ln³⁺, based on which near‐zero τ_f values are expected to be obtained in SrLa(R_0.5Ti_0.5)O₄‐SrLaAlO₄ and SrLa(R_0.5Ti_0.5)O₄–SrLaGaO₄ unlimited solid solutions.     

多溴代二苯并呋喃/噻吩热力学性质的定量构效关系

多溴代二苯并呋喃(PBDFs)是剧毒环境污染物,主要来源于溴系阻燃剂的燃烧和高温裂解过程,其性质与其结构有关;多溴代二苯并噻吩(PBDTs)的结构与其非常相似。通过计算多溴代二苯并呋喃和多溴代二苯并噻吩254个分子的原子特征值,利用分子图形学技术获得了一种新的连接性指数——路径指数mP,采用多元回归分析方法建立了PBDFs的分子总能量(ET)、标准焓(H0)、自由能(G0)、标准熵(S0)和恒容热容(c0v)以及PB-DTs的标准焓(H0)、自由能(G0)、标准生成焓(ΔfH0)和标准生成吉布斯自由能(ΔfG0)的定量结构-性质相关模型,相关性良好(r20.995),利用Jackknifed法检验了模型的稳定性和预测能力,Jackknifed检验的相关系数r2均在0.995以上,对标准熵预测的相对平均误差为0.52%,预测结果和文献值基本吻合。     

Primary and secondary distributions after a small-amplitude potential step at disk electrode coated with conducting film

The set of equations and boundary conditions for the “primary potential/current distribution” after a small-amplitude potential step has been analyzed for a film-coated disk electrode in contact with an electrolyte. The solution of these equations provides the overall short-time resistance of this system, R_tot, which is determined by the short-time resistance of the electrolyte solution in contact with the bare disk electrode, R_s, and the short-time film resistance to the current passage in the normal direction, (r_o, disk radius; L_f, film thickness; κ_f, its specific conductivity). The deviation of R_tot from the sum of these resistances, R_s + R_f, originates from a three-dimensional potential/current distribution in solution. Procedures to calculate the film resistance and its specific conductivity on the basis of the measured values of R_tot and R_s have been proposed. Similar analysis has also been carried out for the “secondary potential/current distribution” in the same system. The overall resistance for this regime is related to the short-time solution resistance, R_s, and to the total resistance of the electrode, equal to the sum of the resistance, R_f, and two interfacial resistances, R_m/f and R_f/s. A method to determine the bulk-film parameters, R_f and κ_f, from data for the secondary distribution is discussed. Advantages and restrictions of the proposed route to transport parameters of a film at the electrode surface are analyzed, in comparison with existing methods of their determination.     

Effect of silicon alloying addition on the corrosion behaviour of aluminium in some aqueous media

The corrosion behaviour of three Al–Si alloys was studied after galvanostatic passivation in 0.1 M sodium tartrate, sulfate and borate solutions using EIS techniques. The degree of passivation depends on the anion type, the degree of polarization and the alloy composition. It was also found that increase in pH led to a decrease in polarization resistance R _p. The effect of formation voltage, V _f, on the growth and dissolution kinetics of the oxide grown on the alloys was studied. The polarization resistance value increases as V _f increases up to a certain value; above this the R _p value decreases. This critical V _f depends on the alloy composition and the test solution. The kinetics of oxide layer dissolution in the absence and presence of Cl^– ions was also studied. Increase in immersion time leads to a more severe attack by Cl^– ions as shown by the decrease in the value of R _p. At low Cl^– ion concentration the value of R _p is higher than that in chloride ion free sulfate solutions, because the rate of passive film repair is much higher than that of barrier layer dissolution. However, at high Cl^– ion concentration penetration of Cl^– through defects in the barrier layer leads to formation of an oxyhalide layer.     

The influence of molecular weight of acid dyes on the yield stress of dyed nylon monofilament

The yield stress of nylon filament dyed with several acid dyes has been determined as a function of dye content and the molecular weight of acid dyes. The nylon filament dyes with acid dye has greater yield stress than undyed one. The relation between the increment of the yield stress (f) due to the adsorption of acid dye and the dye content (C) in the filament can be expressed by parameters A and B as log f = A log(C ? _C) + B, where C₀ is the dye content under which no contribution to the yield stress is observed and C₀ depends on the number of sulfonic groups in acid dye. It is found that these parameters A and B are expressed by M (the difference between the molecular weight of acid dye and the weight of SO₃Na groups in it) as A = 1 ? 100/M, B = k₁ M^k2, where k¹ and k² are the constants which depend on the parent chemical structure of dyes. The parameters A and B are expected to give available informations as to the physical state of adsorbed dye on nylon filament.