Evaluation of the rate of abiotic degradation of biodegradable polyethylene in various environments

The rate of abiotic degradation of polyethylene (PE) films containing a manganese pro-degradant has been studied in various environments at 60 and 70 °C. The degradation was monitored from the change in molecular weight and the elongation at break after exposure to dry and humid air. It was observed that moisture had a strong accelerating effect on the rate of thermo-oxidation of PE films. However, despite the humidity level in the compost environment being similar to that in humid air, the rate of degradation in compost was much slower. It is proposed that ammonia and/or hydrogen peroxide generated by microorganisms in the compost can be responsible for the deactivating effect, as aqueous solutions of these compounds significantly retard the rate of degradation.     

Contrasting behavior of classical salts versus ionic liquids toward aqueous phase J-aggregate dissociation of a cyanine dye

The effect of addition of ionic liquids (ILs) on the aggregation behavior of a cyanine dye, 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-di(4-sulfobutyl)-benzimidazolocarbocyanine (TDBC), was investigated. In basic aqueous buffer solutions (pH ≥ 10), TDBC preferably exists in its J-aggregated form. Addition of hydrophilic ILs > 5 wt % is observed to disrupt the TDBC J-aggregates, converting them to monomer form most likely because of the interaction between bulky IL cation and the J-aggregates in a time-dependent fashion. This is evidenced by the observed increase in monomer band absorbance at the expense of the absorbance band due to J-aggregates over time. Inorganic salts at similar molar concentrations do not cause this phenomenon but instead induce TDBC precipitation. At low concentrations (<5 wt %), the added IL acts similarly to the inorganic salts, reducing the overall absorbance of TDBC in the solution most likely due to cation exchange causing TDBC precipitation. Addition of a molecular solvent, ethanol, at 15 wt % results in an initial increase in monomer absorbance, albeit to a much lesser extent than for the corresponding molar fraction of IL, which then decreases over time with recovery of J-aggregate absorbance--quite opposite the time-dependent behavior seen for TDBC in PB at pH 12.0 with >5 wt % IL. The unique and dual behavior of ILs as an additive toward affecting cyanine dye aggregation is demonstrated.     

A flotation related X-ray photoelectron spectroscopy study of the oxidation of galena surface

The initial steps of the oxidation of galena (PbS) surface with special attention to the oxidation in an aqueous environment were investigated by the X-ray photoelectron spectroscopy method (XPS). Galena monocrystals from two different sources were cleaved and exposed to either air or an aqueous environment. The results show that the presence of organic contamination at the galena surface may exert a dramatic effect on the course of its surface oxidation. In the case of aerial oxidation, the presence of impurities changes the reaction path, suppressing the oxidation of sulfide sulfur to sulfate like species selectively. In the case of aqueous oxidation, the presence of organic contamination at the surface (this contaminants are supposed to be mainly the carboxylic acids and their salts) inhibits the oxidation. Very little oxidation products were found on the galena surface contacted with aqueous solutions at the spontaneously established potential, in accordance with the congruent dissolution-oxidation mechanism.     

Salt Effects on the Aqueous Two-Phase System of Gemini(12-3-12, 2Br<Superscript>−</Superscript>)/SDS/PEG

The effect of added salts (NaCl, KCl and NaBr) on the aqueous two-phase system (ATPS) formed in mixtures of Gemini(12-3-12, 2Br⁻)/sodium dodecyl sulfate/polyethylene glycol has been investigated. Phase diagrams of the aqueous systems containing Gemini(12-3-12, 2Br⁻), sodium dodecyl sulfate (SDS), polyethylene glycol(PEG) and a salt have been determined experimentally at 313.15 K. The results indicate that the addition of salts not only induces the appearance of ATPS-A (in which anionic surfactant is in excess), shortens the phase separation time, enlarges the regions of ATPS-C (in which cationic surfactant is in excess), and decreases the minimum concentration required for forming an ATPS, but also alters the matching between anionic and cationic surfactants. Extractive experiments also showed that these salts notably enhance the extraction ability of ATPS; the Gemini-rich phase exhibits prominent cohesive action with xylenol orange, regardless of whether or not it is the upper phase or the lower phase.     

Influence of Irradiation and Postradiation Storage on the Adhesion of Polyolefins

High Energy Chemistry - The radiolytic surface oxidation of polyethylene and polypropylene in air and in three-phase dispersed systems including water or an aqueous formic acid solution has been...     

Computational study of ion distributions at the air/liquid methanol interface

Molecular dynamic simulations with polarizable potentials were performed to systematically investigate the distribution of NaCl, NaBr, NaI, and SrCl(2) at the air/liquid methanol interface. The density profiles indicated that there is no substantial enhancement of anions at the interface for the NaX systems, in contrast to what was observed at the air/aqueous interface. The surfactant-like shape of the larger more polarizable halide anions, which is part of the reason they are driven to air/aqueous interfaces, was compensated by the surfactant nature of methanol itself. These halide anions had on average an induced dipole of moderate magnitude in bulk methanol. As a consequence, methanol hydroxy groups donated hydrogen bonds to anions where the negatively charged side of the anion induced dipole pointed, and methyl groups interacted with anions where the positively charged side of the anion-induced dipole pointed. Furthermore, salts were found to disrupt the surface structure of methanol. For the neat air/liquid methanol interface, there is relative enhancement of methyl groups at the outer edge of the air/liquid methanol interface in comparison with hydroxy groups, but with the addition of NaX this enhancement was reduced somewhat. Finally, with the additional of salts to methanol, the computed surface potentials decreased, which is in contrast to what is observed in corresponding aqueous systems, where the surface potential increases with the addition of salts. Both of these trends have been indirectly observed with experiments. The surface potential trends were found to be due to the greater propensity of anions for the air/water interface that is not present at the air/liquid methanol interface.     

Effect of ions on the vibrational relaxation of liquid water

We study the relaxation of the O-H stretch vibration of water in aqueous salt solutions using femtosecond two-color pump-probe spectroscopy. The vibrational lifetimes are measured for a series of salts consisting of the anions Cl(-), Br(-), and I(-) and the cations Li(+), Na(+), and Mg(2+), for a range of concentrations from 0.5 M up to 6 M (chloride salts), 9 M (bromide salts), and 10 M (iodide salts). In addition to the previously found dependence of the vibrational lifetime on the nature of the anion, the lifetime is found to depend on concentration and is observed to show a small but significant dependence on the nature of the cation. We present a model in which all the effects of ions on the vibrational relaxaton of liquid water are accounted for.     

Chemiluminescence of bis(2,4,6-trichlorophenyl) oxalate in aqueous micellar systems

The chemiluminescent reaction of bis(2,4,6-trichlorophenyl) oxalate (TCPO) in aqueous micellar systems is compared with the reaction in a mixture of acetonitrile and aqueous phosphate buffer. The chemiluminescence was studied in batch experiments with perylene as the fluorophore. The oxidation of TCPO produced the same intensity of chemiluminescence in the buffered acetonitrile as in Arkopal N-300 micelles, the best micellar system. The solubility of TCPO in an aqueous micellar system is greater than that in the acetonitrile/aqueous buffer (80:20, v/v), but TCPO is less stable in the former system.     

Estimation of cyanide ion in metal salts and complexes by means of chloramine-T and dichloramine-T

A simple and accurate method for the estimation of cyanide in salts and complexes is based on oxidation with chloramine-T (in pH 4 buffer) or dichloramine-T (in presence of acetic anhydride). The oxidation involves a two-electron change. Halides interfere with the estimation of KCN, but the interference can be eliminated by precipitating and determining zinc cyanide. A method for estimating KCN and KCNS in mixtures is also described.     

Contact probe electrochemical characterization and metal speciation of silver LLDPE nanocomposite films

A contact probe methodology, based on the voltammetry of immobilized microparticle approach, is used for characterizing silver species present in linear low density polyethylene (LLDPE) films with different Ag(I)/Ag(0) ratios and silver nanoparticle features usable as food contact polymers. The films displayed characteristic voltammetric features in contact with aqueous acetate buffer, in particular signals for the stripping oxidation of nanoparticulate Ag systems. Significant differences between the studied films were also observed by means of electrochemical impedance spectroscopy and detected at the nanoscopic scale using electrochemical scanning microscopy. Differences in optical and thermal properties of the studied films are associated with the presence of silver nanoparticles. The silver oxidation state as well as nanoparticle size also had influence on the oxidative resistance of the LLDPE films; indeed, films containing cationic silver showed the lowest oxidation induction time value.     

Electron injection dynamics of Ru polypyridyl complexes on SnO2 nanocrystalline thin films

Ultrafast infrared spectroscopy was utilized to investigate the electron-transfer dynamics from Ru(dcbpy)(2)(X)(2) complexes (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine; X(2) = SCN(-), 2CN(-), and dcbpy; referenced as RuN3, Ru505, and Ru470, respectively) to nanocrystalline SnO(2) films. For both films exposed to air (dry) and submerged in a pH 2 buffer solution, all traces show biphasic dynamics with a small ultrafast component (less than 10%) and nonexponential slow component, indicating that most injection occurs from thermalized excited state of the dye. In the dry film, the injection rate becomes slower, comparing RuN3, Ru505, and Ru470, correlating with decreasing excited-state oxidation potentials in these dyes. However, the variation of injection rate with dye potential is less noticeable at pH 2. The possible reason for the different injection dynamics in these dyes and under different environments are discussed. These injection dynamics are also compared with those on TiO(2) and ZnO.     

Effect of sodium phosphate salts on the thermodynamic properties of aqueous solutions of poly(ethylene oxide) 6000 at different temperatures

Precise density, sound velocity, water activity, and phase diagram measurements have been carried out on polyethylene oxide (PEO) in aqueous solutions of sodium di-hydrogen phosphate, di-sodium hydrogen phosphate, and tri-sodium phosphate over a range of temperatures at atmospheric pressure. The experimental density and sound velocity data are used to calculate the apparent specific volume and isentropic compressibility as a function of temperature and concentration. It was found that both of the apparent specific volume and isentropic compressibility of PEO in aqueous solutions increase by increasing temperature and charge on the anion of electrolytes. The results show that the slope of constant water activity lines increased with increasing the temperature and charge on the anion of electrolytes and the vapour pressure depression for an aqueous (PEO + sodium phosphate) system is more than the sum of those for the corresponding binary solutions. Furthermore, the effect of temperature and type of anion of salt on the salting-out effect of polyethylene oxide by sodium phosphate salts has been studied.     

Micellar electrophoresis using ionic liquids

In this study, ionic liquid based cationic surfactants were evaluated as pseudo-stationary phases in micellar electrokinetic chromatography (MEKC). The aggregation behaviour of long-chain (C(12) and C(14)) alkylimidazolium ionic liquids in water and aqueous phosphate buffer was investigated by spectrophotometry. The critical micelle concentrations of these salts were determined and compared to those of tetradecyl- and dodecyltrimethylammonium chloride, salts commonly used in capillary electrophoresis. The practical utilization of a new type of surfactant in MEKC was evaluated by introducing an ionic liquid into the running aqueous buffer to separate neutral analytes-methylresorcinol isomers and benzene derivatives.     

Direct reversible voltammetry and electrocatalysis with surface-stabilised Fe2O3 redox states

Nanoparticle film voltammetry is employed to explore the presence and reactivity of surface-stabilised iron redox centers at the interface of immobilised Fe₂O₃ nanoparticles of ca. 4 nm diameter and aqueous buffer media. Mesoporous films of Fe₂O₃ nanoparticles on tin-doped indium oxide (ITO) substrates are formed in a layer-by-layer deposition process from aqueous colloidal Fe₂O₃ and aqueous cyclohexyl-hexacarboxylate followed by thermal (500 °C) removal of the organic binder content. Both reversible oxidation and reversible reduction responses for Fe(III) are observed in phosphate and carbonate buffer media in the “underpotential” zone. Higher oxidation states of iron formed anodically (here tentatively assigned to Fe(IV)) are shown to be inert in phosphate buffer media but reactive towards the oxidation of glucose in carbonate buffer media.     

过硫酸铵水溶液对聚乙烯表面作用的研究

本文利用X光电子能谱(XPS)及其它技术对过硫酸铵水溶液处理聚乙烯表面改进粘合性的作用机理进行了研究。结果表明,过硫酸铵的氧化作用使聚乙烯表面引入酮、醛、羧基等含氧基团,使其粘合强度显著提高。高密度聚乙烯表面的氧化深度小于40,低密度聚乙烯的均匀氧化深度在40—90之间。处理后的聚乙烯表面未发现明显的交联产物。     

Release of nortriptyline hydrochloride from oil-water microemulsions

The release of nortritptyline hydrochloride from oil-in-water (o/w) microemulsions (isopropyl myristate as oil, propylene glycol as cosurfactant, polysorbate 80 as surfactant and phosphate buffer, pH 7.4, as the continuous phase) containing increasing concentrations of polyethylene glycol 400, used to facilitate the diffusion of a drug from the inner oily phase of the microemulsion to the outer aqueous phase of such a dispersion system, was studied by determining the permeability constants of the drug through hydrophilic and lipophilic membranes separating the o/w microemulsions from the receiving aqueous phase (phosphate buffer pH 7.4). The permeability of nortriptyline hydrochloride from microemulsions through the lipophilic membrane increased as the concentration of polyethylene glycol 400 in the disperse system increased. The apparent permeability constant for nortriptyline hydrochloride, from the microemulsion without polyethylene glycol, was 1.36 x 10(-3) cm x h(-1), it increased up to 7.80 x 10(-3) cm x h(-1) in the presence of polyethylene glycol at a concentration of 50% (v/v) of the initial volume of the aqueous phase.     

Antioxidant activity of daidzein, a natural antioxidant, and its spectroscopic properties in organic solvents and phosphatidylcholine liposomes

Daidzein, one of major isoflavones found in soybeans, has a wide spectrum of physiological and pharmacological functions. The observed biological effects involve its interactions with lipid bilayers, usually detected by indirect methods. In this study we use the native fluorescence of daidzein to report changes observed during its interactions with organic solvents and in a phosphatidylcholine membrane.We have investigated interactions of daidzein with lipid bilayers of egg phosphatidylcholine (PC) by absorption and fluorescence methods. The data obtained indicate emission arises from the conjugate anion in excited singlet state. The fluorescence is found to increase with the basicity of the solution and the polarity of the solvent. An increase in fluorescence anisotropy in the presence of membranes suggests partial incorporation of daidzein molecules into the bilayer. Two fluorescence lifetime components, 1.5 ns and 3.5 ns, reflects the partition of daidzein between aqueous and membrane environments, respectively. On the basis of the obtained spectroscopic data we conclude that up to 15% of daidzein is located in hydrophilic region of the membrane whereas the rest is distributed in aqueous bulk and aqueous/membrane interface.For studying the antioxidant activity of daidzein against lipid peroxidation initiated by AAPH the molecule of C11-BODIPY581/591 has been used as a fluorescent oxidation indicator. The results show that the presence of daidzein anions in the membrane interface increases the inhibitory effect on lipid peroxidation compared to the neutral form of daidzein.     

DODECYLPYRIDINIUM ALKANOATES STABILIZE DISPERSED CHLOROPHYLL

In the presence of a surfactant that does not ligate Mg, chlorophyll is adsorbed to polyethylene particles swollen with tetradecane principally as the infrared-absorbing, highly polymeric species Chl 740. Examples of such surfactants are quaternary ammonium salts and soaps. However, when surfactants of opposite charge are present together, in this case dodecylpyridinium iodide and Na butyrate or myristate, chlorophyll may exist entirely in a dispersed form absorbing around 666 nm. Absorption and fluorescence spectral data show that much of the dispersed pigment is still associated, but as dimeric and perhaps short oligomeric species. It is concluded from fluorescence lifetime analysis that most of the observed fluorescence comes from a small population of chlorophyll that is probably monomeric and isolated; fluorescence of more highly associated species decays with a wide range of lifetimes. The capacity for photochemical sensitization of these particles with dispersed chlorophyll is similar to that of particles with ligating surfactants examined earlier. Structures are suggested for chlorophyll association in which Mg is ligated by water hydrogen-bonded to a carboxylate group, while the dodecylpyridinium counterion lies near the chlorophyll ring. The effect of the two surfactants is synergistic. Overall, spectra of dispersed chlorophyll adsorbates resemble most closely those of colloidal chlorophyll suspensions prepared by dilution of solutions in polar organic solvents with water.     

Fe(III) complexes of 1,4,8,11-tetraaza[14]annulenes as catalase mimics

The development of enzyme mimics of catalase which decompose hydrogen peroxide to water and molecular oxygen according to the 2:1 stoichiometry of native catalase and in aqueous solution at pH 7 and at micromolar concentrations of the enzyme model and hydrogen peroxide is reported. For this purpose, iron(III) complexes of 1,4,8,11-tetraaza[14]annulenes are prepared by various procedures. Efficacious preparations utilize reaction of the [N4] macrocyles with FeII salts in the presence of triphenylamine, followed by gentle oxidation of the FeII complexes by molecular oxygen or by tris(4-bromophenyl)aminium hexachloroantimonate. The complexes are characterized by SQUID magnetometry and by M?ssbauer, EPR, and UV/vis spectrometry. In the solid state, the iron(III) center of the catalytically active complexes exists in the intermediate (quartet, S = 3/2) spin state. Several of these complexes decompose hydrogen peroxide in aqueous buffer solution at pH 7.2 at room temperature with turnover numbers between 40 and 80. The apparent second-order rate constant for hydrogen peroxide decomposition is in the range of 1400-2400 M(-1) s(-1), about 3 orders of magnitude lower than the value for native catalase. Besides oxygen production, a non-oxygen releasing pathway of hydrogen peroxide decomposition is unveiled.     

Fixation de divers polluants dans des alumines monolithiques poreuses

Fixation of various pollutants in a monolithic porous alumina. Ultraporous monoliths of hydrated alumina, prepared at room temperature by atmospheric air oxidation of aluminium, can fix various gaseous phases, for instance up to 1.25 kg hydrogen chloride per kg. The material porosity remains high after heating at 1200–1300°C. Then, this alumina can be impregnated by aqueous solutions of various salts, which result in oxides after drying and calcination. These oxides are confined within the material. For instance, 1 kg monolith can contain more than 2 kg cerium oxide, which serves as a model for the behaviour of transuranium element oxides (PuO₂, AcO₂) contained in radioactive waste.