Dielectric relaxation in some polyacrylate solutions

The dielectric constant ?′ and loss factor ?″ of poly(butyl acrylate), poly(butyl methacrylate), and poly(isobutyl methacrylate) solutions are reported in the frequency region of 1 kHz to 24.42 GHz at four different temperatures of 27, 40, 50, and 60°C. Cole–Cole plots are plotted to obtain the distribution parameter and relaxation time. The activation energies are evaluated assuming dielectric relaxation to be a rate process in these solutions. A possible relaxation mechanism is discussed.     

Magnetic resonance in amorphous FexNi80-xP14B6: I. Ferromagnetic and reentrant alloys

We present a study of ferromagnetic resonance in amorphous Fe_xNi_80-xP₁₄B₆ for Fe concentrations down to that required for ferromagnetism. The resonance was studied at microwave frequencies between 10 and 35 GHz and at temperatures between 2 and 300 K. We find i) in accord with previous data on amorphous ferromagnets, each alloy investigated is magnetically inhomogeneous even in its ferromagnetic state, ii) the intrinsic relaxation parameter λ / Mγ for each alloy falls between the value for pure Fe and the value for pure Ni, iii) a low temperature linewidth rise which is frequency independent and follows an empirical form suggested earlier, iv) frequency dependent linewidth maxima at low T which do not correspond to low field spin freezing temperatures, and v) anisotropy fields intruding at low temperatures. The corresponding anisotropy energy is similar to that proposed for spin glasses as are the temperature and frequency dependences of the anisotropy constant. With part II of this paper, this represents the most complete resonance study to date of the evolution of spin glass behavior in Fe based alloys.     

Reentrant magnetism - a low field study

We report low field dc magnetization measurements on (Fe_xMn_1?x)₇₅P₁₆B₆Al₃ alloys at 4 ? T ? 300 K. Reentrant magnetic behavior is observed for x = 0.65, 0.7 and 0.8. By comparing field cooled and zero-field cooled states at low T we separate out the reversible and irreversible contributions to the magnetization M and identify the (field-dependent) temperature for the onset of irreversibility. It is shown that the reversible part of the magnetization can be described by the usual scaling laws for critical behavior in magnetic systems not only at the transition from the paramagnetic to the ferromagnetic phase but also when the latter transforms to a spin glass. We identify the irreversible part of M with a spin glass order parameter.     

Unified description for the effect of spin freezing on ESR linewidth

We have shown that, for a number of systems which undergo a spin glass type transition, the temperature dependence of the ESR linewidth (above the freezing temperature) exhibits a single simplified form which can be roughly understood on the basis of elementary assumptions. Remarkably, the linewidth of ferromagnetic resonance observed in the surface layer of a?Y_1?xFe_x alloys exhibits the same dependence on temperature.     

On quick oscillations in functional equations with deviating arguments

For the functional equation L_ny(t) + H(t,y(g(t)) = f(t), n ? 2, where $\text{L}{}_{\mathrm{n}}\text{=}\text{1}\text{p}{}_{\mathrm{n}}\text{(t)}\text{d}\text{dt}\text{1}\text{P}{}_{\mathrm{n\; ?\; 1}}\text{(t)}\text{d}\text{dt}\text{…}\text{d}\text{dt}\text{1}\text{P}{}_1\text{(t)}\text{d}\text{dt}\text{·}\text{P}{}_0\text{(t)}$ sufficient conditions have been found to ensure that a solution is either quickly oscillating or else it is nonoscillatory. Both canonical and noncanonical forms of L_n have been studied.     

Dual-activation protocol for tandem cross-aldol condensation: An easy and highly efficient synthesis of α,α′-bis(aryl/alkylmethylidene)ketones

Commercially available lithium hydroxide monohydrate (LiOH·H₂O) was found to be a novel ‘dual activation’ catalyst for tandem cross-aldol condensation between cyclic/acyclic ketones and aromatic/heteroaromatic/styryl/alkyl aldehydes leading to an efficient and easy synthesis of α,α′-bis(aryl/alkylmethylidene)ketones at r.t. in short times. The reaction of aryl, heteroaryl, styryl and alkyl aldehydes with acyclic and five/six-membered cyclic ketones afforded excellent yields after 2 min to 1.25 h. The reaction conditions were compatible with various electron withdrawing and electron donating substituents, e.g. Cl, F, NO₂, OMe and NMe₂. The rate of the cross-aldol condensation was influenced by the nature of the ketone and electronic and steric factors associated with the aldehyde. The reaction took place at a faster rate for acyclic ketone (e.g., acetone) than that for cyclic ketone (e.g., cyclohexanone). In case of cycloalkanones, the rate of the reaction was dependent on the size of the ring of the cycloalkanone. The cross-aldol condensation of cyclopentanone was faster than that of cyclohexanone for a common aldehyde. In case of reactions involving aliphatic aldehyde having α-hydrogen atom no self-aldol condensation of the aldehyde took place.     

Molecular iodine selective membrane for iodate determination in salt samples: chemical amplification and preconcentration

A molecular iodine selective membrane has been used for preconcentration of I₂ generated in situ by iodometric reaction of with excess I⁻ in acidic medium (pH 1–2). This iodometric reaction amplifies the iodine content six times resulting in enhancement of analytical response ranging from three times for molecular methods to six times for elemental methods. The chemical conditions of this iodometric reaction were optimized for quantitative generation and subsequent sorption of I₂ in the membrane samples (96 ± 3%). The homogeneous transparent membrane was prepared by immobilizing I₂-complexing polyvinylpyrrolidone (PVP) in the plasticized cellulose triacetate matrix. Four different analytical methods were examined for quantitative determination of in iodized salt samples by preconcentrating it as I₂ in the membrane matrix. These methods were: (1) spectrophotometry of the PVP-I₂ complex formed in the membrane matrix, (2) a radiotracer method using I⁻ tagged with ¹³¹I radiotracer, (3) instrumental neutron activation analysis (INAA), and (4) energy-dispersive X-ray fluorescence (EDXRF) analysis. The contents thus determined in the iodized salt samples by the membrane-based radiotracer method were compared with the total iodine determined in salt samples by epithermal instrumental neutron activation analysis (EINAA). The membrane-based method for iodate determination in salt samples has advantages over conventional analytical methods, for example preconcentration and chemical amplification, and is free from interference from anions. Figure A molecular iodine selective membrane was used for the quantitative preconcentration of I₂ generated in situ by iodometric reaction of with excess I^aˆ’ in acidic medium, which amplifies iodine content six times     

Radical Chain Breaking Bis(ortho-organoselenium) Substituted Phenolic Antioxidants

The presence of a chalcogen atom at the ortho-position of phenols enhances their radical chain-breaking activity. Here, a copper(I)-catalyzed reaction of 2,6-dibromo- and 2,6-diiodophenols with diorganodiselenides has been studied for the introduction of two organoselenium substituents at both ortho-positions of the phenolic radical chain-breaking antioxidants, which afforded 2,6-diorganoseleno-substituted phenols in 80–92% yields having electron-donating CH₃, and electron-withdrawing CN and CHO functionalities. Additionally, 2,6-diiodophenols with electron-withdrawing CHO and CN groups also afforded novel 5,5′-selenobis(4-hydroxy-3-(phenylselanyl)benzaldehyde) and 5,5′-selenobis(4-hydroxy-3-(phenylselanyl)benzonitrile) consisting of three selenium and two phenolic moieties along with 2,6-diorganoseleno-substituted phenols has been synthesized. The electron-withdrawing CHO group has been reduced by sodium borohydride to the electron-donating alcohol CH₂OH group, which is desirable for efficient radical quenching activity of phenols. The developed copper-catalyzed reaction conditions enable the installation of two-arylselenium group ortho to phenolic radical chain-breaking antioxidants, which may not be possible by conventional organolithium-bromine exchange methods due to the sluggish reactivity of trianions (dicarba and phenoxide anion), which are generated by the reaction of organolithium with 2,6-dibromophenols, with diorganodiselenides. The antioxidant activities of the synthesized bis and tris selenophenols have been accessed by DPPH, thiol peroxides, and singlet oxygen quenching assay. The radical quenching antioxidant activity has been studied for the synthesized compounds by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. The bis-selenophenols show comparable radical deactivating activity, while tris seleno-bisphenols show higher radical deactivating activity than α-tocopherol. Furthermore, the tris seleno-bisphenol shows comparable peroxide decomposing activity with ebselen molecules.     

Rapid synthesis of water-glass based aerogels by in situ surface modification of the hydrogels

The objective of the present research was to reduce the processing time of water-glass based aerogels synthesized via an ambient pressure drying. For this purpose we employed a co-precursor method for the surface modification in hydrogels using trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDS). The surface modification resulted in the displacement of pore water from the hydrogels and thereby absolutely avoiding the time-consuming solvent exchange step. The attachment of trymethylsilyl (Si(CH₃)₃) groups to the silica surface was confirmed by the presence of SiCH₃ peaks at 2900, 1400, 1255 and 845 cm⁻¹ in the Fourier Transform Infrared (FTIR) spectra. The differential thermal analysis (DTA) revealed that the aerogels maintain their hydrophobic behavior up to a maximum temperature of 500 °C above which they become hydrophilic. The physical and textural properties of the silica aerogels have been reported and the results have been discussed by taking into account the surface modification and the amounts of the pore water displaced out from the hydrogels.