Dielectric dispersion study of coexisting phases of aqueous polymeric solution: Poly(vinyl alcohol) + poly(vinyl pyrrolidone) two-phase systems

The complex dielectric constant ?^∗(ω)=?^′−j?^″, electric modulus M^∗(ω)=M^′+jM^″, impedance Z^∗(ω)=Z^′−jZ^″ and ac conductivity dispersion behaviour of 5, 10 and 15 wt% concentration aqueous solutions of poly(vinyl alcohol) (PVA) (14?000 and 77?000 g mol⁻¹) and poly(vinyl pyrrolidone) (PVP) (24?000, 40?000 and 360?000 g mol⁻¹) and their binary mixtures were investigated in the frequency range 20 Hz to 1 MHz at 25 °C. Analysis of dielectric constant values confirms that hydrophilic effect of PVA in aqueous solution increases the real part of dielectric constant ?′, whereas for aqueous PVP solutions the hydrophobic effect masks the hydrophilic effect, which reduces ?′ values below 10 kHz. Low-frequency dielectric constant of these aqueous polymeric systems is sensitive to ionic conduction and electrode polarization. The monotonous change in various electrical properties with change in volume percentage of mixture constituents indicates that individual aqueous polymer system retains their own electrical properties in the aqueous two-phase polymeric system.     

Self-association and microenvironment of random amphiphilic copolymers of sodium N-acryloyl-l-valinate and N-dodecylacrylamide in aqueous solution

The present paper reports on the syntheses and association behavior of two random copolymers of sodium N-acryloyl-l-valinate and N-dodecylacrylamide in buffered (pH 8.0) aqueous solution containing 0.1 M NaCl. Surface tension and viscosity results showed pronounced amphiphilic nature of the copolymers in aqueous solution at pH 8.0. Steady-state fluorescence studies using pyrene and N-phenyl-1-naphthylamine as probe molecules suggested microdomain formation through interpolymer association above a critical concentration called ‘critical aggregation concentration’ (CAC) as low as ca. 10⁻³ g L⁻¹. The local polarity of the hydrophobic domain formed in aqueous solution was estimated from steady-state fluorescence spectra of pyrene. The microviscosity of the domains was evaluated using 1,6-diphenyl-1,3,5-hexatriene as a fluorescent probe using steady-sate fluorescence depolarization and time-resolved fluorescence method. Dynamic light scattering technique was performed over a wide range of concentration to determine hydrodynamic size of the aggregates. It was observed that both copolymers retain rather open conformation in dilute solutions having polymer concentrations less than CAC. However, with increase in concentration the intermolecular association becomes favorable towards the formation of more compact aggregates. The transmission electron microscopic images of both copolymers at a concentration above CAC revealed spherical aggregates of uniform diameter (∼50 nm).     

Interactions of cobalt chloride with saccharose in aqueous solutions at 298.15 K

Mutual diffusion coefficients (interdiffusion coefficients) and molar electrical conductivities have been measured for cobalt chloride aqueous solutions in the absence and the presence of saccharose at different concentrations (from 0.01 to 0.3 mol dm⁻³) and 298.15 K. The diffusion coefficients were measured by using the conductimetric method. For these aqueous solutions, limiting molar conductivity values have been calculated. The value of λ⁰(Co²⁺) = 105.36 × 10⁻⁴ S m² mol⁻¹, obtained at 298.15 K in pure water solution, agrees well with that reported in the literature. The Nernst diffusion coefficient values derived from diffusion (1.301 × 10⁻⁹ m² s⁻¹) and from conductance (1.295 × 10⁻⁹ m² s⁻¹) are also in good agreement.The dependence of diffusion coefficients and electrical conductivity of CoCl₂ on the concentration of saccharose is discussed by considering the effect of the carbohydrate on the electrolyte dehydration, as well as on the ion-pairs and complexes (CoCl₂-saccharose and ions-saccharose) formation.     

Electrochemical behavior of LiCoO2 in a saturated aqueous Li2SO4 solution

The electrochemical behavior of a commercial LiCoO₂ with spherical shape in a saturated Li₂SO₄ aqueous solution was investigated with cyclic voltammetry and electrochemical impedance spectroscopy. Three redox couples at E_SCE = 0.87/0.71, 0.95/0.90 and 1.06/1.01 V corresponding to those found at ELi/Li⁺=4.08/3.83, 4.13/4.03 and 4.21/4.14 V in organic electrolyte solutions were observed. The diffusion coefficient of lithium ions is 1.649 × 10⁻¹⁰ cm² s⁻¹, close to the value in organic electrolyte solutions. The results indicate that the intercalation and deintercalation behavior of lithium ions in the Li₂SO₄ solution is similar to that in the organic electrolyte solutions. However, due to the higher ionic conductivity of the aqueous solution, current response and reversibility of redox behavior in the aqueous solution are better than in the organic electrolyte solutions, suggesting that the aqueous solution is favorable for high rate capability. The charge transfer resistance, the exchange current and the capacitance of the double layer vary with the charge voltage during the deintercalation process. At the peak of the oxidation (0.87 V), the charge transfer resistance is the lowest. These fundamental results provide a good base for exploring new safe power sources for large scale energy storage.     

Characteristics of solubilization and encapsulation of fullerene C60 in non-ionic Triton X-100 micelles

The solubilization and encapsulation of monomeric C₆₀ in Triton X-100 micelles were investigated. Characteristic hydrophobic interactions of the type π-π and CH-π between the Triton X-100 micelle and C₆₀ resulted in stable aqueous dispersions of C₆₀ in the micellar medium, as evidenced from UV-vis, fluorescence emission and micro-Raman spectroscopy. Cyclic voltammetry of C₆₀ encapsulated Triton X-100 in aqueous 5 mM LiClO₄ solution revealed a quasi-reversible one-electron reduction peak with E_1/2 = −0.61 V and a reversible reduction peak at E_1/2 = −1.11 V vs. Ag/AgCl reference electrode at a scan rate of 10 mV s⁻¹, a redox behaviour drifting substantially from that of pure C₆₀. An onset concentration of ∼0.025 mM for C₆₀ aggregation in the micellar core was substantiated from the characteristic absorption spectral broadening and quenching of pyrene fluorescence. The molar solubilization capacity of C₆₀ in aqueous Triton X-100 micellar solution was estimated spectrophotometrically to be 0.22.     

Ionic conductivity of chitosan membranes

Chitosan membranes with various degrees of deacetylation and different molecular weights (MW) were prepared by film casting with aqueous solutions of chitosan and acetic acid. Ultraviolet (UV) spectrometry and infrared (IR) spectrometry were used to determine the degree of deacetylation (DDA) of chitosan. The viscosity-average MW of chitosan was measured in an aqueous solvent system of 0.25 M CH₃COOH/0.25 M CH₃COONa. The intrinsic ionic conductivities of the hydrated chitosan membranes were investigated using impedance spectroscopy. It was found that the intrinsic ionic conductivity was as high as 10⁻⁴ S cm⁻¹ after hydration for 1 h. The tensile strength and breaking elongation of the membranes were evaluated according to standard ASTM methods. The crystallinity and swelling ratio of the membranes were examined. A tentative mechanism for the ionic conductivity of chitosan membranes is also suggested.     

Synthesis and electrical conductivity of La-Sr-X-Mg-O (X = Ti, Zr, Al) perovskite solid solution

Perovskite solid solutions of (La_0.6Sr_0.4)(X_1−yMg_y)O_3−δ (X = Ti, Zr, Al) were prepared by a coprecipitation method using corresponding aqueous solutions and ammonium carbonate solution. The freeze-dried powders were sintered in air at 1000-1500 °C for 1-36 h. Single phase solid solutions were produced in the compositions of (La_0.6Sr_0.4)(Zr_0.6Mg_0.4)O_3−δ and (La_0.6Sr_0.4)(Al_0.9Mg_0.1)O_3−δ where (3 − δ) < 3. For the compositions of X = Ti and Zr for y = 0.1 where (3 − δ) > 3, two phases including perovskite solid solution were produced at 1400-1500 °C. The stability of perovskite solid solution was closely related to the fraction of lattice oxygen atom (3 − δ). A relatively high conductivity was measured for (La_0.6Sr_0.4)(Al_0.9Mg_0.1)O_3−δ (σ = 4.15 × 10⁻⁴ S/cm at 600 °C, activation energy 113.4 kJ/mol). The influence of fraction of oxide ion vacancy on the activation energy was small for δ = 0.1-0.3 of perovskite solid solution.     

Adsorption of Hg(II) ions from aqueous chloride solutions using powdered activated carbons

Activated carbons were developed from Casurina equisetifolia leaves, by chemically treating with sulfuric acid (1:1) or zinc chloride (25%), at low (425 °C) and high (825 °C) temperatures. The resulting powdered activated carbons were applied for removing mercuric ions from aqueous solution at different agitation times and mercuric ion concentrations. The equilibrium data fitted well the Langmuir adsorption isotherm. The Langmuir adsorption capacities were 12.3 and 20.3 mg g⁻¹ for low temperature carbons and 43.9 and 38.5 mg g⁻¹ for high temperature carbons impregnated with H₂SO₄ and ZnCl₂, respectively. Studies of the effects of carbon dosage, NaCl concentrations and solution pH values were carried out for the more effective, high temperature carbons. Increasing NaCl concentration resulted in a significant decrease in the adsorption efficiency. Adsorption was high from solutions with low and neutral pH values and lower for solutions with alkaline pH values for the high temperature carbons.     

The sorption of acid dye onto chitosan nanoparticles

The behavior of chitosan nanoparticles as an adsorbent to remove Acid Green 27 (AG27), an acid dye, from an aqueous solution has been investigated with nanochitosan (particle size = 180 nm; degree of deacetylation = 74%). The dye concentration at equilibrium (Q_e, mg/g) was calculated using the weight of the nanoparticles in the mixed solution (Q_es) and the weight of chitosan in the nanoparticles (Q_ep). The experimental isotherm data were analyzed using the Langmuir equation for each chitosan sample; the Langmuir monolayer adsorption capacity (Q₀) was calculated with Q_es and Q_ep and the results were 1051.8 mg/g and 2103.6 mg/g, respectively, which were significantly higher than that of the micron-sized chitosan.     

Use of a selective extractant-impregnated resin for removal of Pb(II) ion from waters and wastewaters: Kinetics,equilibrium and thermodynamic study

Adsorption of Pb(II) ion by a novel extractant-impregnated resin, EIR, was studied as a function of various experimental parameters using batch adsorption experiments. The new EIR was prepared by impregnating gallocyanine (GCN) onto Amberlite XAD-16 resin beads. The EIR was characterized by nitrogen analysis and SEM micrographs. The new EIR showed excellent selectivity factor values (α) for Pb(II) adsorption respect to other metal ions. The effects of some chemical and physical variables were evaluated and the optimum conditions were found for Pb(II) removal from aqueous solutions. The equilibrium adsorption isotherm was fitted with the Langmuir adsorption model. The maximum adsorption capacity (q_max) of EIR for Pb(II) ions was found to be 367.92 mg g⁻¹. The kinetic studies showed that the intra-particle diffusion is the rate-controlling step. Also, the intra-particle diffusion coefficients, D_ip values, were of the order of 10⁻¹² m² s⁻¹. The values of enthalpy (ΔH°) were positive, which confirms the endothermic nature of adsorption process. Also, the positive entropy changes (ΔS°) were showed that the randomness increased along with the adsorption process. In addition, the obtained negative values of Gibbs free energy (ΔG°) indicated feasible and spontaneous nature of the adsorption process at different temperatures. The new adsorbent was very stable so that it can be successfully used for many consecutive cycles without significant loss in its adsorption capacity.     

Insight into the electroreduction of nitrate ions at a copper electrode, in neutral solution, after determination of their diffusion coefficient by electrochemical impedance spectroscopy

The electrochemical reduction of nitrate ions at a copper electrode in an unbuffered neutral aqueous solution is studied. Using a two compartment electrochemical cell, three stationary cathodic waves, noted P1, P2 and P3, were evidenced by cyclic voltammetry at −0.9, −1.2 and −1.3 V/SCE, respectively. By comparing the electrochemical response of nitrate and nitrite containing solutions, P1 was attributed to the reduction of nitrate to nitrite. In order to assign P2 and P3 features by determining the number of electrons involved at the corresponding potential, rotating disk electrode experiments at various rotation speeds, combined with linear sweep voltammetry, were performed. Current data analysis at a given potential was carried out using Koutecky-Levich treatment taking into account water reduction. Confident values of the diffusion coefficient D of nitrate ions were assessed by electrochemical impedance spectroscopy for nitrate concentrations of 10⁻³, 10⁻² and 10⁻¹ M. For a nitrate concentration of 10⁻² M, D was found to be 1.31 × 10⁻⁵ cm² s⁻¹ allowing the number of electrons to be determined as 6 for P2 and 8 for P3, in accordance with nitrate reduction into hydroxylamine and ammonia, respectively. The formation of hydroxylamine was confirmed by the observation of its reoxidation at a Pt microelectrode present at the Cu electrode/nitrate solution interface.     

Studies on swelling behaviors,mechanical properties,network parameters and thermodynamic interaction of water sorption of 2-hydroxyethyl methacrylate/novolac epoxy vinyl ester resin copolymeric hydrogels

A series of the highly cross-linked hydrogels has been developed by the syntheses of bulk copolymers based on 2-hydroxyethyl methacrylate (HEMA) and novolac epoxy vinyl ester resin (NEVER). The resulting hydrogels were investigated on their equilibrium water content (EWC), swelling behaviors and tensile properties. Dynamic swelling behaviors of copolymeric hydrogels indicate that the swelling process of these polymers follows Fickian behavior. The EWC decreased and volume fraction of polymer in hydrogel (ϕ₂) increased with NEVER content increasing due to its hydrophobicity. The increase of ionic strength of swelling medium or temperature results in a decrease in EWC and an increase in values of ϕ₂. Young’s modulus and tensile strength of hydrogels, as well as effective cross-link density (v_e), increased as NEVER content increased or ionic strength of swelling medium increased, attributing to increasing interaction between hydrophobic groups and polymer–polymer interaction with an increase in NEVER content or in ionic strength. The polymer–solvent interaction parameter χ reflecting thermodynamic interaction was also studied. As NEVER content, ionic strength of swelling medium or temperature increased, the values of χ increased. The values of χ and its two components χ_H and χ_S varied with increasing T. The negative values and trend of the enthalpy and entropy of dilution derived from values of χ_H and χ_S, could be explained on the basis of structuring of water through improved hydrogen bonding and hydrophobic interaction.     

Diffusional mass transfer model for the adsorption of food dyes on chitosan films

The adsorption kinetics of erythrosine B and indigo carmine on chitosan films was studied by a diffusional mass transfer model. The experimental curves were obtained in batch system under different conditions of stirring rate (80–200 rpm) and initial dye concentration (20–100 mg L⁻¹). For the model development, external mass transfer and intraparticle diffusion steps were considered and the specific simplifications were based on the system characteristics. The proposed diffusional mass transfer model agreed very well with the experimental curves, indicating that the surface diffusion was the rate limiting step. The external mass transfer coefficient (k_f) was dependent of the operating conditions and ranged from 1.32 × 10⁻⁴ to 2.17 × 10⁻⁴ m s⁻¹. The values of surface diffusion coefficient (D_s) increased with the initial dye concentration and were in the range from 0.41 × 10⁻¹⁴ to 22.90 × 10⁻¹⁴ m² s⁻¹. The Biot number ranged from 17.0 to 478.5, confirming that the intraparticle diffusion due to surface diffusion was the rate limiting step in the adsorption of erythrosine B and indigo carmine on chitosan films.     

Electrical properties of samaria-doped ceria electrolytes from highly active powders

The correlations of the microstructures and the electrical properties of high reactive Ce_0.8Sm_0.2O_1.9 (SDC) powders, synthesized via an optimal carbonate coprecipitation method, were investigated. Microstructure of the SDC ceramics sintered at 900-1400 °C showed uniform grain and small grain size, compared with those prepared with various methods under similar sintering conditions. These features may be related to high conductivity (σ_600 °C = 0.022 S cm⁻¹) and low activation energy for conduction (0.66 eV). AC impedance spectra were involved to resolve grain interior and grain boundary resistance. Grain boundary contribution to the total resistance showed the values below 1/2 at 200-450 °C, suggesting low grain boundary effect. The motion enthalpy for the grain interior conduction decreased while the association enthalpy increased with sintering temperature up to 1300 °C, which might be possibly originated from the increase in lattice parameters with the sintering temperature.     

Gelation behaviors of cellulose solution dissolved in aqueous NaOH/thiourea at low temperature

Cellulose was dissolved rapidly in 9.5 wt% NaOH/4.5 wt% thiourea aqueous solution pre-cooled to −5 °C, as a result of the formation of an inclusion complex (IC) associated with cellulose, NaOH and thiourea, which could bring cellulose to the aqueous system. To clarify the rheological behaviors of the system dissolved at low temperature, this cellulose solution was investigated by dynamic viscoelastic measurement. The shear storage modulus (G′) and loss modulus (G″) as a function of the angular frequency (ω), concentration (c), temperature (T) and weight-average molecular weight (M_w) were analyzed and discussed. The results revealed that gels could form in the cellulose solution at either high temperature or low temperature, or for longer time. Interestingly, 4 wt% cellulose solution having cellulose M_w of 12.0 × 10⁴ remained at liquid state for longer time (12 days) at the temperature ranging from 0 to 5 °C. The gels already formed at elevated temperature were irreversible, i.e., after cooling to lower temperature including the temperature of cellulose dissolution (−5 °C), they could not be dissolved to become liquid. The Arrhenius analysis of the temperature dependence of viscosity in the cellulose solution indicated that a high apparent activation energy (E_a) occurred at 0 to −5 °C, suggesting the relatively stable IC structure. However, the viscosity of the cellulose solution increased slowly with an increase in the temperature at 0-40 °C, leading to the negative E_a values. The results suggested that the cellulose solution in NaOH/thiourea system is complex to differ from normal polymer systems.     

Estimation of equilibrium parameters using differential evolution in reactive extraction of propionic acid by tri-n-butyl phosphate

The graphical and conventional optimization methods, used for the estimation of equilibrium parameters, do not guarantee the global optimum values. In this study, the equilibrium parameters are estimated using a well proven evolutionary based optimization routine [differential evolution (DE)]. For the estimation of stoichiometry and equilibrium constants, experiments are carried out for the reactive extraction of propionic acid using tri-n-butyl phosphate (TBP) dissolved in n-decane (inert diluent) and 1-decanol (modifier). The number of TBP molecules (n) in the acid:TBP complex and equilibrium extraction constant (K_E) using 1:1 volume ratio of 1-decanol and n-decane as a diluent, are determined through proposed mathematical model using graphical methods as well as the differential evolution algorithm (DE, an optimization routine) and found that the predicted values of distribution coefficient (K_D) using DE are closely matching with the experimental values of K_D. 1:1 complexes between TBP and acid are formed in most of the cases. The enthalpy and entropy of reactive extraction of propionic acid using TBP are also determined and found to be −12.47 kJ mol⁻¹ and −32.42 J mol⁻¹ K⁻¹, respectively. The results of present study will be useful to intensify the recovery of propionic acid from fermentation broth (bio-separation) and aqueous waste stream.     

Swelling behavior of amphiphilic gels based on hydrophobically modified dimethylaminoethyl methacrylate

The amphiphilic gels based on hydrophobically modified dimethylaminoethyl methacrylate with different 1-bromoalkanes (1-C_nH_2n+1Br, n = 2, 4, 6, 8, 12) were synthesized by radiation-induced polymerization and crosslinking. The length of alkyl side chains had significant influence on the swelling behavior of the resulting gels. The swelling degree of the gels decreased with the increase of side chain length, and the gel hardly swelled when n = 12. The effect of temperature and ionic strength on the swelling behavior of the resulting gels revealed that (1) the gels with longer side chains (n ≥ 8) had upper critical solution temperature, while other gels were not thermo-sensitive. (2) Antipolyelectrolyte effect was observed when immersing the gels (n ≥ 8) in NaCl solutions in certain concentration range. The dramatic difference in swelling behavior was attributed to the different gel structures. The gels with short side chains (n ≤ 6) had cellular structure of normal polyelectrolyte gels. The gels (n ≥ 8) had an aggregation gel structure caused by the hydrophobic interaction among alkyl groups and the formation of ion-cluster between tetra-alkyl ammonium cation and Br⁻, which had been analyzed with the aid of SEM, Br⁻-selective electrode and fluorescence molecular probe.     

Electrosynthesis of poly(aniline-co-p-aminophenol) having electrochemical properties in a wide pH range

Copolymerization of aniline and p-aminophenol in aqueous sulfuric acid solutions was electrochemically performed using cyclic voltammetry on platinum electrodes. The monomer concentration ratio can strongly affect the copolymerization rate and electrochemical property of the copolymer. The optimum conditions for the copolymerization are that the potential sweep covers the −0.20 to 0.95 V (vs. SCE) potential range, and that a solution contains 0.18 M aniline, 0.02 M p-aminophenol and 0.50 M H₂SO₄. A resulting copolymer synthesized under the optimum conditions has a good electrochemical activity in 0.50 M solutions of Na₂SO₄ with pH ≤ 10.0. IR and XPS spectra indicate that -OH groups and SO₄²⁻ ions are contained in the resulting copolymer. The SEM images reveal that the microstructure of the copolymer depends on the monomer concentration ratio during the electrolysis.     

Experimental verification on UCST phase diagrams and miscibility in binary blends of isotactic, syndiotactic, and atactic polypropylenes

Issues in blends of polymers of the same chemical repeat unit but with different tacticities were addressed by investigating on the phase behavior and interaction strength of binary blends of three polypropylenes of different tacticities, i.e., isotactic polypropylene (iPP), syndiotactic polypropylene (sPP), and atactic polypropylene (aPP) using polarized optical microscopy (POM) and differential scanning calorimetry (DSC). Although blends of polypropylenes have been widely studied in the past, there are still on-going debates on true phase behavior (miscibility vs. upper critical solution temperature (UCST) or immiscibility). Except for several earlier theoretical predictions based on the Flory-Huggins mean field theories, UCST behavior had not been experimentally proven for blends of sPP/iPP or aPP/sPP, owing to interference from PP crystallinity. In addition, interaction strength of the blends of different tactic polypropylenes is yet to be established. Using the method of equilibrium melting points, the Flory-Huggins interaction parameter of the aPP/iPP blend was shown to possess a significantly negative value (χ₁₂ = −0.21), which proves that the blend is indeed miscible in the melted amorphous as well as semicrystalline states as previously reported in the literature. However, the interaction parameters for the sPP/iPP and aPP/sPP blends were found to be nearly zero (χ₁₂ = −0.02 and −0.0071, respectively, at T = 150-180 °C), indicating that the interactions in two blends are weak and that the corresponding phase behavior for them borders on immiscibility at ambient temperature. This study also utilized novel approaches in constructing UCST phase diagrams by separating the amorphous phase domains from the crystalline spherulites, yielding data plausible for experimentally determining the UCST in iPP/sPP blend vs. aPP/sPP blend.     

Determination of EMC isotherms and appropriate mathematical models for canola

Canola seed needs to be dried to minimize damage during subsequent unit operations. In order to optimize the drying and storage processes of seeds it is necessary to know the equilibrium moisture content at different air equilibrium relative humidities and temperatures. In the present work adsorption equilibrium moisture content isotherms were determined for a specific local canola variety at 25, 40 and 55 °C and seven air relative humidifies within the range of 11-90%. Experimental data were used to model the adsorption isotherm process using non-linear regression analysis. Thirteen available mathematical and semi empirical models were employed to find the best fit isotherm curve model. The Halsey model showed the best results at 25 and 40 °C and the values of coefficient of determination (R²), chi-square (χ²) and root of mean square error (RMSE) were 0.993, 0.122 and 0.295 at 25 °C and 0.994, 0.042 and 0.174 at 40 °C. Another best fit mode was the GAB model at 55 °C which resulted in the values of 0.997, 0.023 and 0.120 for R², χ² and RMSE respectively. The adsorption monolayer moisture content (m₀) was also evaluated using BET equation. The m₀ values at 25 °C, 40 °C and 55 °C were 0.017, 0.016 and 0.015 g H₂O/g solid and the corresponding constant values of the BET equation were found to be −4.733, −5.129 and −10.299 respectively.