Synthesis,characterization, and water sorption properties of new aromatic polyamides containing benzimidazole and ethylene oxide moieties

New polyamides, containing a benzimidazole side group and ethylene oxide moieties in the structural repeat unit, were synthesized by low‐temperature polycondensation. The aim of this design was to obtain polyamides that were more soluble in common organic solvents and hence had better processability than benzimidazole polyamides while maintaining the water sorption properties characteristic of the latter. The results showed that the number of ether linkages of the repeat unit played an important role in the glass‐transition temperature and in the water sorption properties, the polyamides with one or two ethylene oxide units being more hydrophilic than benzimidazole polyamides. However, the length of the ethylene oxide chain played a minor role in the solubility because the second member of the series, with two ether linkages (i.e., one ethylene oxide unit), reached the same level of solubility as those polyamides with more ethylene oxide moieties. No crystallinity was observed by X‐ray and calorimetric measurements for the new polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 112–121, 2005     

The improved nuclear parton distributions

In this paper we propose an improvement of the EKS nuclear parton distributions for the small x region of high energy processes, where the perturbative high parton density effects cannot be disregarded. We analyze the behavior of the ratios and and verify that at small x they are strongly modified when compared to the EKS predictions. The implications of our results for heavy ion collisions in RHIC and LHC are discussed. Received: 18 January 2001 / Revised version: 6 March 2001 / Published online: 3 May 2001     

Spin and temperature dependence of the magnetic hyperfine field of Cd in the rare earth-aluminum Lavesphase compounds RAl2

Perturbed angular correlation spectroscopy has been used to investigate the combined magnetic and electric hyperfine interaction of the probe nucleus ¹¹¹Cd in ferromagnetically ordered rare earth (R)-dialuminides RAl₂ as a function of temperature for the rare earth constituents R=Pr, Nd, Sm, Eu, Tb, Dy, Ho and Er. In compounds with two magnetically non-equivalent Al sites (R=Sm, Tb, Ho, Er), the magnetic hyperfine field was found to be strongly anisotropic. This anisotropy is much greater than the anisotropic dipolar fields, suggesting a contribution of the anisotropic 4f-electron density to magnetic hyperfine field at the closed-shell probe nucleus. The spin dependence of the magnetic hyperfine field reflects a decrease of the effective exchange parameter of the indirect coupling with increasing R atomic number. For the compounds with the R constituents R=Pr, Nd, Tb, Dy and Ho the parameters B₄, B₆ of the interaction of the crystal field interaction have been determined from the temperature dependence of the magnetic hyperfine field. The ¹¹¹Cd PAC spectrum of EuAl₂ at 9 K confirms the antiferromagnetic structure of this compound.     

Thermodynamics of high-pressure ice polymorphs: ices III and V

Thermodynamic properties of high-pressure ice polymorphs, ices III and V, are studied theoretically. The results of TIP4P molecular dynamics simulations in the NPT ensemble are used to calculate the temperature dependence of the specific volume of ices III and V at pressures 0.25 and 0.5 GPa, respectively. New P-V-T equations of state of ices III and V are derived using a method generalizing the one proposed by Fei et al. [J. Chem. Phys. 99 (1993) 5369], and new results concerning the equilibrium phase transitions ice III-water and ice V-water are presented.     

Sequence of structural phase transitions of CsInF4 crystal

In this work we employ calorimetric and dielectric techniques to study the sequence of structural phase transitions (SPTs) of CsInF₄ crystal in the temperature range from 450 to 250 K. Our results show three first-order SPTs. Based on these results and on direct interferometric observation of the domain patterns, we discuss the elastic state of CsInF₄ phases.     

Hyperfine interactions in cubic perovskites

ABO₃ perovskites display several physical properties determined by the characteristics of A and B cations. These compounds have cubic structure at high temperature. Lower symmetry cells that are distorted cubes are found at low temperature. Defects modify the properties of these compounds. Under standard conditions oxygen vacancies are produced. Cation substitution also alters the characteristics of perovskites. These materials have been studied by Perturbed Angular Correlation (PAC) spectroscopy and other hyperfine techniques. In this way abundant information is available to determine charge distributions close to probes. In the cubic phase perturbations were detected that are produced by the interaction of probes with defects. To show up these effects we analyze the quadrupole interaction at ¹⁸¹Ta in several compounds: ABO₃ with A=Ca, Sr and Ba, BaTi_1−x Hf _x O₃ and PbZr_1−x Ti _x O₃ for 0⩽x⩽1. Three different quadrupole interactions were found and are interpreted in terms of distinct probe-oxygen vacancy configurations. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Comparative Study of the Photosensitizer Penetration into Artificial Caries Lesions in Dentin Measured by the Confocal Raman Microscopy

This study utilized the confocal Raman microspectroscopy (CRM) technique for the first time to investigate the degree of the penetration of toluidine blue‐orto (TBO) in artificial caries lesions produced by two distinct caries‐inducing models. The dentin specimens (n = 10) were divided into three groups: control, in vitro and in situ. Thereafter, the lesion depth and the demineralization level were evaluated by cross‐sectional microhardness (CSMH). CRM mapping across the dentin surface was assessed after the dye application. The CSMH and CRM data were analyzed by t‐test and ANOVA, respectively (P < 0.05). The values of the lesion depth and the demineralization areas were higher for in situ samples (P < 0.05). The TBO penetration values (μm) for the control, in vitro and in situ groups were 44.8 ± 5.6, 46.1 ± 4.5 and 51.2 ± 8.5, respectively. There were no statistically significant differences among the groups (P > 0.05). The rate of TBO penetration was detected up to about <50 μm and the demineralization level did not influence the results. These results have showed promising parameters to develop new protocols for deep caries lesions management using photodynamic antimicrobial chemotherapy.     

Utilization of an ionic liquid in situ preconcentration method for the determination of the 15 + 1 European Union polycyclic aromatic hydrocarbons in drinking water and fruit‐tea infusions

An ionic liquid (IL) in situ preconcentration method was optimized and applied to the monitoring of the 15 + 1 European Union polycyclic aromatic hydrocarbons in water and fruit‐tea infusions. The optimized method utilizes 10 mL of water (or infusion) containing 38 μL of the IL 1‐butyl‐3‐methylimidazolium chloride and a content of 36.1 g/L NaCl, which are mixed with Li‐NTf₂ (340 μL, 0.2 g/mL), followed by vortex (4 min) and centrifugation (5 min). The obtained microdroplet containing hydrocarbons is diluted with acetonitrile and injected into an HPLC with UV/Vis and fluorescence detection. The method presented average enrichment factors of 127 for water (tap water and bottled water) and 27 for two fruit‐tea infusions; with average relative recoveries of 86.7 and 106% for water and fruit‐tea infusions, respectively. The method was sensitive, with detection limits ranging from 0.001 to 0.050 ng/mL in water, and from 0.010 to 0.600 ng/mL in fruit‐tea infusions, for the fluorescent hydrocarbons. Real extraction efficiencies ranged from 12.7 to 58.7% for water, and from 20.2 to 117% for the infusions. The method was also fast (～12 min) and free of organic solvents in the extraction step.     

Monitoring chlorophenols in industrial effluents by solid-phase microextraction–gas chromatography–mass spectrometry

A method for the determination of 19 chlorophenols in industrial effluents samples using solid-phase microextraction (SPME) coupled to gas chromatography–mass spectrometry has been developed. Four kinds of different SPME fibres have been studied. Among them, the polyacrylate and carbowax®-divinylbenzene fibres were the most adequate. The extraction process was optimized by means of the experimental design, which allows the study of a large number of factors with a reasonable number of experiments. The optimized method allows the determination of the studied chlorophenols in complex matrices with a high organic content with detection limits down to 0.07?ng?mL^?1 and RSD ranging from 4.4% to 13.8%. The recovery studies with spiked real effluent samples at low levels of chlorophenols ranged from 59.8% to 142.1% for the lowest level (0.5?ng?mL^?1) and from 79.6% to 115.8% for the highest spiked level (2?ng?mL^?1). These results show the suitability of the proposed method to monitor chlorophenols in complex samples. 2,4,5-TCP was detected at concentrations close to its limits of detection in effluents coming from an oil refinery.     

Micellar Extraction of Polycyclic Aromatic Hydrocarbons from Certified Marine Sediment

Abstract

In the present study the extraction of polycyclic aromatic hydrocarbons from a certified marine sediment (SRM 1941a) with a micellar medium of polyoxyethylene 10 lauryl ether by micro-wave- and ultrasound-assisted method has been evaluated. The analysis of extracts has been carried out by HPLC with fluorimetric detection and wavelength programming. Hydrocarbons with more than three rings gave average recoveries of 77.4% and 86.5%, by microwave- and ultrasound-assisted methods respectively, with a mean relative standard deviation better than 6.2%.