NMR determination of crystallinity for poly(?-l-lysine)

Crystallinity of poly(?-l-lysine) (?-PL) was discussed by analyzing the differences in the ¹H spin-spin relaxation times (T₂^H), the ¹³C spin-lattice relaxation times (T₁^C), and the ¹³C NMR signal shapes between the crystalline and the non-crystalline phases. The observed ¹H relaxation curve (free induction decay followed by solid-echo method) showed the sum of Gaussian and exponential decays. Similarly, the observed ¹³C relaxation curves obtained from the Torchia method were double-exponential. The ¹³C NMR spectrum of ?-PL was divided into the narrow and the broad lines by utilizing the intrinsic differences in the ¹H spin-lattice relaxation times in the rotating-frame between them, which are attributed to the crystalline and the non-crystalline phases, respectively. Even though the crystallinity is obtained from the identical NMR measurements, the estimated values are different with each other. The crystallinity estimated from the T₂^H differences was 75.8 ± 0.1% at 333 K and 60.7 ± 0.4% at 353 K. From the T₁^C differences, the value was estimated to be 62 ± 11%. Furthermore, the value estimated from the NMR signal separation was 54 ± 5%. In this study we have explained these discrepancies by the difference in susceptibility among the experiments for the inter-phase, which exists in-between the crystalline and the amorphous phases. Furthermore, the estimated crystallinity was ascertained by the X-ray diffraction experiment.     

Monitoring the chemical crosslinking of propylene polymers through rheology

The chemical crosslinking of propylene polymers is described; the reaction has been performed under dynamic conditions, using a peroxide and a furan or bis-maleimide-based coagent as crosslinking promoter; the reaction mechanisms have been investigated through FT-IR spectrometry. Crosslinking experiments have been carried out while keeping constant the amount and the nature of peroxide and increasing the coagent concentration; four different coagents have been used. The samples have been studied, in the molten state, by measuring the melt flow rates (MFR) and the values of G′ (storage modulus), G″ (loss modulus), Tg(δ) (ratio G″/G′), and η^∗ (complex viscosity), in the frequency range 10⁻²-10² rad s⁻¹. Another set of measurements has been performed on the same materials, collecting for each sample the values of η⁰ (zero shear viscosity) and J_e⁰ (steady state creep compliance) by creep-creep recovery experiments. The effects of crosslinking degree estimated by gel content and through rheological measurements allows one to evaluate the efficiency of the coagent both in terms of prevention of β-scission and promotion of the crosslinking reactions. These results are discussed with reference to the selection of proper conditions of the crosslinking process in order to achieve a material having desired MFR, rheological behavior and melt elasticity for selected application.     

Controlling floc sizes in a pipe between pump and membrane inlet

Cake resistance is influenced by floc size deposited on membrane surface. Enlarging floc size can reduce cake resistance. The small particles are enlarged by coagulation and flocculation processes in conventional mixing tank at membrane filtration system. Fully-grown flocs for reducing the cake resistance, however, are ruptured while passing through a pump. In light of this fact, this study aims to experimentally look at the reaggregation phenomenon through control of G-values in pipe from pump to inlet of membrane. In addition, reaggregation phenomenon of the mixing system is compared with first-aggregation in-line injection system in which coagulant is injected just before a pump. These results suggest that first-aggregation of in-line injection system is better than reaggregation of mixing system for G-value above 3100 s^− 1. G-values in pipe of real world membrane filtration system are usually much larger than 3100 s^− 1. Due to reason, in-line injection system is expected to perform better than mixing tank as proved in this study.     

A 13C-n.m.r. study of radiation-induced racemization in isotactic polypropylene

Unexpectedly large changes in the stereochemistry of isotactic polypropylene have been observed by ¹³C-n.m.r. following γ-irradiation at 25°C up to 250 kGy. The observed G-value of 64 for the loss of isotactic triads is much higher than previously reported G-values for scission, crosslinking or hydrogen formation in irradiated polypropylene. A mechanism of initial chain scission, racemization and subsequent recombination is indicated. The pattern of pentad sequences is inconsistent with the occurrence of isolated random racemization events; this suggests that the energy released on recombination promotes a second racemization within a range of 1–3 monomer units.     

Separation of isotope C using high-performance structured packing

A special high-performance structured packing, PACK-¹³C, with the surface area high as 1135 m² m⁻³ was developed, and the first stable isotope ¹³C pilot-scale plant using structured packing was designed and constructed by carbon monoxide cryogenic distillation, which has run smoothly over 6 months. The height and inner diameter of the distillation column were respectively, 20 m and 45 mm and the height of packing bed was 18 m. The column was well insulated by vacuum multilayer insulation and the total heat leakage of the column was less than 30 W. When the F-factor changes from 0.18 to 0.90 ms⁻¹ (kg m⁻³)^1/2, the numbers of theoretical plates per meter decreases from 30 to 20, the pressure drop is less than 25 Pa for each theoretical plate, the dynamic liquid holdup is between 11% and 21%, and the pilot-scale plant produces 2.1 g 15% isotope ¹³C each day. The fluid mechanical and mass transfer empirical equations were developed according to the experimental data of PACK-¹³C. The PACK-¹³C structured packing exhibits very high performances in isotope separation efficiency and operational flexibility, which is far superior to the traditional random packing. PACK-¹³C is a perfect packing to serve in ¹³C separation to increase productivity and reduce consumption.     

Synthesis and characterization of the LDH hydrotalcite-pyroaurite solid-solution series

A layered double hydroxide (LDH) hydrotalcite-pyroaurite solid-solution series Mg₃(Al_xFe_1 − x)(CO₃)_0.5(OH)₈ with 1 − x = 0.0, 0.1……1.0 was prepared by co-precipitation at 23 ± 2 °C and pH = 11.40 ± 0.03. The compositions of the solids and the reaction solutions were determined using ICP-OES (Mg, Al, Fe, and Na) and TGA techniques (CO₃²⁻, OH⁻, and H₂O). Powder X-ray diffraction was employed for phase identification and determination of the unit cell parameters a_o and c_o from peak profile analysis. The parameter a_o = b_o was found to be a linear function of the composition. This dependency confirms Vegard's law and indicates the presence of a continuous solid-solution series in the hydrotalcite-pyroaurite system. TGA data show that the temperatures at which interlayer H₂O molecules and CO₃²⁻ anions are lost, and at which dehydroxylation of the layers occurs, all decrease with increasing mole fraction of iron within the hydroxide layers.Features of the Raman spectra also depend on the iron content. The absence of Raman bands for Fe-rich members (x_Fe > 0.5) is attributed to possible fluorescence phenomena.Based on chemical analysis of both the solids and the reaction solutions after synthesis, preliminary Gibbs free energies of formation have been estimated. Values of ΔG°_f(hydrotalcite) = − 3773.3 ± 51.4 kJ/mol and ΔG°_f(pyroaurite) = − 3294.5 ± 95.8 kJ/mol were found at 296.15 K. The formal uncertainties of these formations constants are very high. Derivation of more precise values would require carefully designed solubility experiments and improved analytical techniques.     

Determination of the elastic constants of portlandite by Brillouin spectroscopy

The single crystal elastic constants C_ij and the shear and adiabatic bulk modulus of a natural portlandite (Ca(OH)₂) crystal were determined by Brillouin spectroscopy at ambient conditions. The elastic constants, expressed in GPa, are: C₁₁ = 102.0(± 2.0), C₁₂ = 32.1(± 1.0), C₁₃ = 8.4(± 0.4), C₁₄ = 4.5(± 0.2), C₃₃ = 33.6(± 0.7), C₄₄ = 12.0(± 0.3), C₆₆ = (C₁₁-C₁₂)/2 = 35.0(± 1.1), where the numbers in parentheses are 1σ standard deviations. The Reuss bounds of the adiabatic bulk and shear moduli are K_0S = 26.0(± 0.3) GPa and G₀ = 17.5(± 0.4) GPa, respectively, while the Voigt bounds of these moduli are K_0S = 37.3(± 0.4) GPa and G₀ = 24.4(± 0.3) GPa. The Reuss and Voigt bounds for the aggregate Young's modulus are 42.8(± 1.0) GPa and 60.0(± 0.8) GPa respectively, while the aggregate Poisson's ratio is equal to 0.23(± 0.01). Portlandite exhibits both large compressional elastic anisotropy with C₁₁/C₃₃ = 3.03(± 0.09) equivalent to that of the isostructural hydroxide brucite (Mg(OH)₂), and large shear anisotropy with C₆₆/C₄₄ = 2.92(± 0.12) which is 11% larger than brucite. The comparison between the bulk modulus of portlandite and that of lime (CaO) confirms a systematic linear relationship between the bulk moduli of brucite-type simple hydroxides and the corresponding NaCl-type oxides.     

Perovskite and A2MO4-type oxides as new cathode materials for protonic solid oxide fuel cells

Solid state ionic devices based on high-temperature proton conductors can be used for various applications, especially in a new class of fuel cells, the Protonic Ceramic Fuel Cell (SOFC-H⁺). These systems are currently operating at intermediate temperatures (500-600 °C) and one of the major problems is the overpotential at the cathode side. In this context, various perovskite oxides AMO_3 − δ (A = La, Ba, Sr; M = Mn; Fe, Co, Ni) and A₂MO₄-type compounds (A = La, Nd, Pr or Sr; M = Ni) have been investigated. Their properties under moist cathodic atmosphere have been studied. Actually, they are stable and exhibit high electrical conductivity (σ > 100 S cm⁻¹) as well as good electrocatalytic properties towards oxygen reduction.The electrochemical properties of these oxides deposited on the protonic electrolyte BaCe_0.9Y_0.1O_3 − δ have been studied and the Area Specific Resistances have been measured under air/H₂O (3%) atmosphere. The obtained values at 600 °C, especially for Ba_0.5Sr_0.5Fe_0.8Co_0.2O_3 − δ and Pr₂NiO_4 + δ show to be promising cathode materials for Protonic Ceramic Fuel Cell applications.     

An in situ Raman study of the intercalation of supercapacitor-type electrolyte into microcrystalline graphite

An initial Raman study on the effects of intercalation for aprotic electrolyte-based electrochemical double-layer capacitors (EDLCs) is reported. In situ Raman microscopy is employed in the study of the electrochemical intercalation of tetraethylammonium (Et₄N⁺) and tetrafluoroborate (BF₄⁻) into and out of microcrystalline graphite. During cyclic voltammetry experiments, the insertion of Et₄N⁺ into graphite for the negative electrode occurs at an onset potential of +1.0 V versus Li/Li⁺. For the positive electrode, BF₄⁻ was shown to intercalate above +4.3 V versus Li/Li⁺. The characteristic G-band doublet peak (E_2g2(i) (1578 cm⁻¹) and E_2g2(b) (1600 cm⁻¹)) showed that various staged compounds were formed in both cases and the return of the single G-band (1578 cm⁻¹) demonstrates that intercalation was fully reversible. The disappearance of the D-band (1329 cm⁻¹) in intercalated graphite is also noted and when the intercalant is removed a more intense D-band reappears, indicating possible lattice damage. For cation intercalation, such irreversible changes of the graphite structure are confirmed by scanning electron microscopy (SEM).     

Influence of precursor Bi/Fe ion concentration on hydrothermal synthesis of BiFeO3 crystallites

In this study we investigated the effect of precursor Bi³⁺/Fe³⁺ ion concentration on the hydrothermal synthesis of BiFeO₃ crystallites. It is demonstrated that the phase-purity and morphology of the products is highly dependent on the metal ion concentration. Phase-pure BiFeO₃ crystals can be prepared at the Bi³⁺/Fe³⁺ ion concentration ranging from 0.025 to 0.0625 M. The samples prepared at n(Bi³⁺/Fe³⁺)=0.025, 0.0375, 0.05, and 0.0625 M, are composed, respectively, of cuboid-like particles (100–200 nm), regular spherical agglomerates (30–40 μm) made up of irregular grains with size about several hundred nanometers, irregular flower-like clusters formed from irregular grains of several hundred nanometers in size, and octahedron-shaped particles (500–600 nm). These samples have a similar bandgap energy of 2.20 eV and exhibit a typical antiferromagnetic behavior at room temperature.     

Correlations between SARA fractions and physicochemical properties with H NMR spectra of vacuum residues from Colombian crude oils

Areas of resonance signals present in 12 frequency bins of the ¹H NMR spectra of the vacuum residues of five Colombian crudes and a blend were correlated with their SARA components and some physicochemical properties. The residues studied were obtained from light paraffinic to heavy aromatic Colombian crudes. Correlations between the NMR spectra and properties were obtained with partial least square PLS and multiple linear regression MLR. Prediction models for SARA obtained by PLS had R² > 0.97 while CV − q² was between 0.92 and 0.99. Models obtained with MLR for SARA showed a high for the first three components and a lower one for asphaltene. The R² of the prediction models for density, API Gravity, S, N, Ni ppm and wax %m content plus nC5- and -C7 insolubles were >0.988 while CV − q² was between 0.87 and 0.99. The proposed correlation methods are fast and less costly than the conventional ones.     

Radiolysis of Tributyl Phosphate by Particles of High Linear Energy Transfer

Tributyl Phosphate (TBP), used in chemical separation processes for used nuclear fuel, is susceptible to radiolysis causing losses in process performance. We have studied its degradation by exposing dry 1M TBP/n-dodecane solutions to gamma radiation from a cesium-137 source and in a mix of low and high linear energy transfer (LET) radiation by irradiating samples in the UC Irvine TRIGA^® reactor and utilizing the ¹⁰B(n,α)⁷Li reaction. In a 1 M solution of TBP in n-dodecane the degradation of TBP (G^?_TBP) was found to be 0.36 and 0.14 μmol/J for low and high LET radiation, respectively. The formation of dibutyl phosphoric acid, DBP, (G⁺_DBP) in this solution was found to be 0.18 and 0.047 μmol/J for low and high LET radiation, respectively. In samples exposed to low LET as well as a mix of low and high LET a variety of TBP degradation products containing phosphorus were observed indicating that other degradation products than DBP and the monobutyl diacid (MBP) were formed. Our results for both low and high LET radiation compare well with previous studies on these systems indicating that high LET degrades TBP to a lesser extent than gamma radiation. Available data for high LET is not as abundant as for low LET making such comparisons challenging. Nevertheless, our method yields a value for G⁺_DBP that agrees well with previous alpha radiolysis studies indicating that our method shows promise for studying high LET radiolysis in liquid-liquid extraction systems.     

Novel thermo-responsive membranes composed of interpenetrated polymer networks of alginate-Ca and poly(N-isopropylacrylamide)

In this work, interpenetrated polymer networks (IPN) composed of alginate-Ca²⁺ and poly(N-isopropylacrylamide), PNIPAAm, were synthesized and their water uptake capability was measured at temperatures from 25 to 40 °C and compared to that of pure alginate-Ca²⁺ hydrogels without PNIPAAm. A sharp decrease of WU was observed when IPN hydrogels are heated above 32-33 °C. The phenomenon is associated to a drastic shrinking of hydrogels. At temperatures above 32 °C the PNIPAAm chains collapse, contracting their network and pulling back the alginate-Ca²⁺ network. The rate of shrinking depends of the heating rate. The phenomenon is more effective and faster in IPN containing lower amount of alginate-Ca²⁺. The shrunken IPN hydrogels can be re-swollen but the expansion is slower than the shrinking. The diffusion of Orange II dye through the membrane of IPN hydrogels decreases if the temperature is raised up to 35 °C. The shrinking results in a decrease of the average pores size that makes more difficult the diffusion of Orange II. The average pore size was evaluated in several stages by analysis of SEM micrographs of freeze dried samples: 102.0±14.3 μm at 25 °C, 15.7±5.4 μm at 33 °C and 0.4±0.3 μm at 40 °C. Below the LCST of PNIPAAm, the IPN hydrogels exhibit a morphology characterized by open pores but above the LCST their surface becomes more regular and compact. As a consequence, an increase of the apparent activation energy for permeability, , of Orange II is measured.     

Electrochemical study of the interaction between Eu and ciliate Euplotes octocarinatus centrin

A new species was formed when protein P₂₃ (one segment of ciliate Euplotes octocarinatus centrin) was added to a solution of Eu³⁺. The interaction between P₂₃ and Eu³⁺ was investigated by cyclic voltammetry, pulse voltammetry and electrochemical impedance spectroscopy in 10 mM N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid (HEPES) buffer (pH 7.4) using a pyrolytic graphite electrode. The formal potential (E^o′) of Eu³⁺ shifted from −0.61 to −0.84 V (versus saturated calomel electrode) after P₂₃ was added to the Eu³⁺ solution. The diffusion coefficient (D), the charge-transfer coefficient (α) and the electron transfer standard rate constant (k_s) were obtained in the absence and the presence of P₂₃. The affinity constant of Eu³⁺ and P₂₃ was determined to be (1.89 ± 0.51) × 10⁴ M⁻¹. The electrochemical investigation of europium bound to the protein provided useful data for the studies of calcium-binding proteins.     

Effects of gamma radiation on two aromatic polysulfones

Two aromatic polysulfones, poly(oxy-1,4-phenylenesulfonyl-1,4-phenyleneoxy-1,4-phenyleneisopropylidene-1,4-phenylene) (I) and poly (oxy-1,4-phenylenesulfonyl-1,4-phenylene) (II), undergo crosslinking and chain scission at 30°C during γ-irradiation, the former being predominant in vacuum and the latter in air. Both processes occurred more readily in I, which contains isopropylidene linkages. Gel measurements gave G(crosslink) = 0.051, G(scission) = 0.012 for this polymer at 30°C in vacuum. Increased irradiation temperatures resulted in higher crosslinking and gas yields, especially above the glass transition temperature. The tensile strength, flexural strength, and modulus of I were unaffected by γ-irradiation up to about 50 Mrad in air, but the strength decreased markedly at higher doses. The elongation at break decreased progressively with dose. For both polymers, G(gas) = 0.04 at 30°C with the main products being SO₂, H₂, CO₂, CH₄, and H₂O.     

Spherulite growth of l-lactide copolymers: Effects of tacticity and comonomers

The spherulite growth behavior and mechanism of l-lactide copolymers, poly(l-lactide-co-d-lactide) [P(LLA-DLA)], poly(l-lactide-co-glycolide) [P(LLA-GA)], and poly(l-lactide-co-ε-caprolactone) [P(LLA-CL)] have been studied using polarization optical microscopy in comparison with poly(l-lactide) (PLLA) having different molecular weights to elucidate the effects of incorporated comonomer units. The incorporation of comonomer units reduced the radius growth rate of spherulites (G) and increased the induction period of spherulite formation (t_i), irrespective of the kind of comonomer unit. Such effects became remarkable with the content of comonomers. At a crystallization temperature (T_c) of 130 °C, the disturbance effects of comonomers on the spherulite growth decreased in the following order: d-lactide>glycolide>ε-caprolactone, when compared at the same comonomer unit or reciprocal of averaged l-lactyl unit sequence length (l_l). The t_i estimation indicated that the glycolide units have the lowest disturbance effects on the formation of spherulite (crystallite) nuclei. The PLLA having the number-average molecular weight (M_n) exceeding 3.1×10⁴ g mol⁻¹ showed the transition from regime II to regime III at T_c=120 °C, whereas PLLA with the lowest M_n of 9.2×10³ g mol⁻¹ crystallized solely in regime III kinetics and the copolymers excluding P(LLA-DLA) with 3% of d-lactide units crystallized solely according to regime II kinetics. The nucleation and front constant for regime II and III [K_g(II), K_g(III), G₀(II), and G₀(III), respectively] estimated with each (not with a fixed for high-molecular-weight PLLA) decreased with increasing the amount of defects per unit mass of the polymer for crystallization, i.e. with increasing the comonomer content and the density of terminal group through decreasing the molecular weight.     

Synthesis and characterization of ZnxMg1 − xGa2O4:Co fabricated by low-temperature burning method

A series of Zn_xMg_1 − xGa₂O₄:Co²⁺ spinels (x = 0, 0.25, 0.5, 0.75, and 1.0) was successfully produced through low-temperature burning method by using Mg(NO₃)₂·4H₂O, Zn(NO₃)₂·6H₂O, Ga(NO₃)₃·6H₂O, CO(NH₂)₂, NH₄NO₃, and Co(NO₃)₂·6H₂O as raw materials. The product was characterized by X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The product was not merely a simple mixture of MgGa₂O₄ and ZnGa₂O₄; rather, it formed a solid solution. The lattice constant of Zn_xMg_1 − xGa₂O₄:Co²⁺ (0 ≤ x ≤ 1.0) crystals has a good linear relationship with the doping density, x. The synthesized products have high crystallinities with neat arrays. Based on an analysis of the form and position of the emission spectrum, the strong emission peak around the visible region (670 nm) can be attributed to the energy level transition [⁴T₁(⁴P) → ⁴A₂(⁴F)] of Co²⁺ in the tetrahedron. The weak emission peak in the near-infrared region can be attributed to the energy level transition [⁴T₁(⁴P) → ⁴T₂(⁴F)] of Co²⁺ in the tetrahedron.     

Synthesis and transport properties in La2−xAxMo2O9−δ (A = Ca, Sr, Ba, K) series

The La_2−xA_xMo₂O_9−δ (A = Ca²⁺, Sr²⁺, Ba²⁺ and K⁺) series has been synthesised as nanocrystalline materials via a modification of the freeze-drying method. The resulting materials have been characterised by X-ray diffraction (XRD), thermal analysis (TG/DTA, DSC), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The high-temperature β-polymorph is stabilised for dopant content x > 0.01. The nanocrystalline powders were used to obtain dense ceramic materials with optimised microstructure and relative density >95%. The overall conductivity determined by impedance spectroscopy depends on both the ionic radius and dopant content. The conductivity decreases slightly as the dopant content increases in addition a maximum conductivity value was found for Sr²⁺ substitution, which show an ionic radii slightly higher than La³⁺ (e.g. 0.08 S cm⁻¹ for La₂Mo₂O₉ and 0.06 S cm⁻¹ for La_1.9Sr_0.1Mo₂O_9−δ at 973 K). The creation of extrinsic vacancies upon substitution results in a wider stability range under reducing conditions and prevents amorphisation, although the stability is not enhanced significantly when compared to samples with higher tungsten content. These materials present high thermal expansion coefficients in the range of (13-16) × 10⁻⁶ K⁻¹ between room temperature and 753 K and (18-20) × 10⁻⁶ K⁻¹ above 823 K. The ionic transport numbers determined by a modified emf method remain above 0.98 under an oxygen partial pressure gradient of O₂/air and decreases substantially under wet 5% H₂-Ar/air when approaching to the degradation temperature above 973 K due to an increase of the electronic contribution to the overall conductivity.     

A reddish orange stoichiometric phosphor LiEu(PO3)4 for white light-emitting diodes

Stoichiometric phosphors LiGd_1−xEu_x(PO₃)₄(x=0, 0.2, 0.4, 0.6, 0.8, 1.0) were synthesized via traditional solid state reactions. The X-ray powder diffraction measurements show that all prepared samples are isostructural with LiNd(PO₃)₄. Eu³⁺ doped phosphors can emit intense reddish orange light under the excitation of near ultraviolet light from 370 to 410 nm. The strongest two at 591 and 613 nm can be attributed to the transitions from excited state ⁵D₀ to ground states ⁷F₁ and ⁷F₂, respectively. The typical chromaticity coordinates (x=0.620, y=0.368) of Eu³⁺ doped phosphors are in red area. The recorded absorbance spectra indicate that there is effective absorbance in the near UV region for all Eu³⁺ doped samples. Present research indicates that LiGd_1–xEu_x(PO₃)₄ is a promising phosphor for white light-emitting diodes.     

Reinforcement of model filled elastomers: characterization of the cross-linking density at the filler-elastomer interface by H NMR measurements

The cross-linking density at the filler-elastomer interface is analyzed by ¹H NMR measurements in model reinforced elastomers composed by grafted nanosilica particles and cross-linked ethylacrylate chains. We have focused our attention on the effect of introducing fillers on the relaxation of the bulk polymer matrix which is observed at long times (t>100 μs). Measurements performed at high temperature (T>T_g+120 K) have revealed that its relaxation is affected by the topological constraints existing at the particle surface. We deduce that the effect of particles in the bulk matrix can be interpreted as that of an homogeneous additional constraint density which increases proportionally to the surface area introduced in the matrix.