卤化银乳剂制备中的新型掺杂剂

本文综述了近年来乳剂制备中常用的新型掺杂剂 ,较详细地介绍了两种能提高光电子利用效率的掺杂剂 ,即过渡金属络合物浅电子陷阱掺杂剂和羧酸盐(酯 )有机空穴陷阱掺杂剂 ,总结了掺杂剂的选择原则 ,并举例说明了掺杂剂对乳剂感光度的影响 .     

Electron trapping model of u.v. induced thermoluminescence in polyethylene

An electron trapping model is proposed to explain the previously observed thermoluminescence output from polyethylene exposed to ultraviolet radiation. Ionization of luminescent molecules by a double excitation mechanism is assumed to be followed by competition for the ejected electrons between shallow traps and radiation-produced alkyl radicals, with electrons in shallow traps also being untrapped by the incident radiation. It is shown that this model not only explains all the available data on thermoluminescence induced by ultraviolet radiation but also correlates well with the very different data on thermoluminescence and alkyl radical production induced by true ionizing radiation.     

Natural and artificial aging of polypropylene–polyethylene copolymers

The degradation of polypropylene–polyethylene copolymers (which were used to make the seats for the Olympic stadium in Barcelona, Spain), in response to natural aging for 2.5 years and artificial aging for 5000 h in a xenon lamp chamber, was studied. The extent of the various photoreactions, including the formation of carbonyl groups, the scission of hydrocarbonated chains, the formation of free radicals in tertiary carbons, and the formation of nonsaturated bonds followed by branching and crosslinking, was analyzed by Fourier transform infrared spectrophotometry. Melting and thermal decomposition were studied by differential scanning calorimetry. In all cases, aging led to a loss of crystallinity. By scanning electron microscopy, it was possible to detect the formation of a porous material after melting crystallization, as well as the presence of micelle orientation. Finally, a comparison between natural and artificial aging effects showed differences, the samples exposed to weathering being modified to a greater extent than the artificially aged ones. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1685–1692, 2003     

Effect of Br gassing after Ar plasma treatment of polyolefins

For simulation and acceleration of artificial polymer ageing, polyolefin foils were exposed to low-pressure Ar plasma. Plasma particle bombardment and irradiation induce C–C and C–H bond scissions by σ?→?σ ^? excitations on the surface and in near-surface layers. Consequently, radicals are generated. They react by recombination, cross-linking, metastable trapping of the radical site or formation of olefinic double bonds. The long-living and metastable trapped C-radicals as well as double bonds in polyolefins were immediately exposed to bromine vapour without breaking the vacuum after switching-off the plasma. These reactive sites rapidly react with the molecular bromine under formation of C–Br bonds. For 5?min of argon plasma exposure, the elemental concentration of bromine was 13% for polyethylene and 22% Br/C for polypropylene as analysed by X-ray photoelectron spectroscopy. Nevertheless, not all C radical sites have reacted with bromine. Later on, when the polyolefins brought in contact with ambient air, an additional post-plasma reaction of the remaining trapped radicals with oxygen was observed. The oxygen concentrations were lower after bromine gassing, thus repressing partially the post-plasma oxidation in the analysed layer (ca. 6?nm) by radical quenching. Such bromination took place either at the surface or in near-surface layers because the Attenuated Total Reflectance (ATR)-FTIR spectra (sampling depth ca. 2500?nm) did not show significant changes for argon plasma-treated PE foils with and without bromine vapour exposure. Further addition of bromine may also occur on C=C double bonds.     

Solution-polymerized rubbers with superior breakdown properties

Natural rubber breaks down readily during mechanical mixing, and rubber processors have traditionally made good use of this property. Emulsion SBR rubber breaks down with greater difficulty and some polybutadiene rubbers, not at all. This paper describes a new class of solution elastomers, both polybutadiene and butadiene–styrene copolymers, designed to undergo controlled breakdown during processing. They can be made by reacting active polymer lithium molecules with tin compounds to produce star-shaped molecules containing a central tin atom connected by tin–carbon bonds. When such a product is mixed with an organic (stearic) acid, some of the tin bonds are ruptured and the desired breakdown occurs. The extent of breakdown can be controlled by the mixing conditions and the amount of organic acid employed. There are numerous applications in which these rubbers process more easily and display better properties than conventional rubbers. Data on breakdown under various conditions and physical properties of the compounds are presented in this paper. In addition to the superior processing characteristics, these products introduce a new concept of elastomer breakdown. The breaking of a polymer chain at a carbon–tin bond by a chemical agent eliminates the need for breaking carbon–carbon bonds by mechanical energy or oxidative degradation. Accomplishing polymer breakdown by a controlled reaction, rather than by conventional means, has long been an unsolved problem of the rubber industry.     

Photodegradation of teflon AF1600 during XPS analysis

Teflon AF1600, containing perfluorinated dioxole rings, was found to be particularly susceptible to X-ray degradation, such as that occurring during X-ray photoelectron spectroscopy. Because of the presence of O, the degradation mechanism is substantially different from those of fluoropolymers containing only C and F. Each atom of a given element was found to have the same susceptibility to attack, irrespective of its position in the repeat unit, with O at least twice as susceptible as F. At any dose between 60 W* X-ray source power/5 min and 240 W/40 min, O was lost at an amount equal to that of F, which necessitated the breaking of two C—O bonds; O also degraded by breaking only one bond, in which case the oxygen was not lost but formed a free radical. The free radicals produced by the homolytic scission of C—C bonds participated in reactions leading to degradation and crosslinking. *The product of X-ray filament emission current and the potential difference between it and the X-ray anode. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1201–1207, 1998     

Oxidation of gamma‐irradiated ultrahigh molecular weight polyethylene

Ultrahigh molecular weight polyethylene (UHMWPE), the current polymer of choice in orthopedic prosthetic devices, is typically sterilized by exposure to Co‐60 gamma irradiation prior to packaging for long‐term storage. However, the exposure to Co‐60 irradiation generates free radicals along the polymer chain that can participate in a series of reactions commencing with the oxidation of the free radicals to form reactive peroxy radicals. This study was undertaken to identify the role of hydroperoxide species in shelf‐aged and accelerated aged UHMWPE samples by using a nitric oxide derivatization technique. It is shown that the concentration of hydroperoxides did not change appreciably with shelf aging. However, during accelerated aging the hydroperoxide concentration increased to a plateau and then decreased, suggesting its role as an intermediate in the process. By contrast, the concentrations of carbonyl species continued to increase during shelf aging and accelerated aging. The effects of several packaging materials on the oxidation characteristics were also investigated. A vacuum foil package is shown to be effective in preventing oxidation to a significant extent during accelerated aging. However, accelerated aging after removal from the foil pack resulted in oxidative degradation. Extended vacuum to remove dissolved oxygen and a 5‐week room‐temperature healing process in the foil pack were shown to be ineffective in reducing oxidative degradation. It also was shown that increased moisture content in the aging environment did not affect the degradation process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2525–2542, 2000     

基于Py-GC/MS研究热解反应中自由基的捕获反应

在500℃下对类煤模型化合物1-萘甲醇与同位素示踪剂的共热解进行了机理研究。利用Py-GC/MS进行快速产物检测,同时联合自由基捕获剂来推断自由基的反应过程。结果表明,在500℃和0.2 min的条件下,1-萘甲醇的热解产物相对单一,但是自由基反应的引发、交换和湮灭极其快速,现有检测方法是对某一时间节点的平衡反应结果的分析。通过D₂O和H₂¹⁸O同位素示踪,成功捕获到了自由基交换后的D取代产物和¹⁸O取代产物。揭示了1-萘甲醇经过1-萘甲基自由基转化为1-萘甲醛的转化过程,发现萘环上的取代基在1-萘甲醇的热解过程中起着重要作用。同时对自由基及产物进行了定性和半定量分析,发现在加入自由基捕获剂后产物的丰度较之前降低了一个数量级,说明了自由基捕获剂抑制了产物的生成。     

Improved Controlled-Release Formulations for a New Trap Design for Male Mediterranean Fruit Flies: The C&C Trap

The Mediterranean fruit fly, Ceratitis capitata, is a major pest of fruits and vegetables in the world. With the help of an extensive trapping program, the continental United States has remained free of established medfly populations. In an effort to increase trapping efficiency, controlled-release polymeric panels with trimedlure and ceralure were developed in conjunction with the development of a new trap, the C&C trap. This study contrasts the effectiveness of different panel formulations with the standard trimedlure polymeric plug and describes the use of the panels in the C&C trap. Field tests in Hawaii using released sterile flies showed consistently higher male medfly catches with panels in C&C traps than with the standard trimedlure polymeric plug in Jackson traps.     

Investigation in thermal endurance of polyesterimide used in electrical machines

The purpose of this investigation is to evaluate thermal lifetime of polyesterimide using Weibull statistics. Thermal aging was performed on twisted pair specimens of copper wire insulated by a polyesterimide layer. The study shows that breakdown voltage varies versus aging time. Its increase is allotted to a crosslinking inducing a diminution of mean‐free path of charge carriers leading thereby to a mobility decrease, whereas its decrease is attributed to the viscosity diminution expressing a weakening of molecular bonds and a mobility increase of charge carriers. Shape parameter changes in function of aging time. Its increase is ascribed to an arrangement of the molecular structure, whereas its decrease is due to an augmentation in the size of defects. The thermal endurance graph is a straight line indicating that the degradation is governed by a first‐order chemical reaction. Activation energy and temperature index were determined. The degradation is governed by the dissolution of copper into the polymer and accelerates its degradation occurring at the polyesterimide–copper interface. Oxygen can diffuse into the insulation and attack copper resulting in the formation of copper oxide. The degradation is caused by the scission of imide and ester bonds. The process is followed by a change in color and a presence of cracks. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Comparison of local molecular motions at chain end and inside of the polymer chain by use of spin trapping method

The spin trapping method was applied to the study of local molecular motion in polyethylene. Spin trapping reagent, 2,4,6-tri-t-butyl nitrosobenzene, was mixed with polyethylene and the free radicals produced by γ-irradiation and thermal degradation were stably trapped by spin trapping reagent. Temperature dependences of e.s.r. spectra of the stable nitroxide radicals trapped were observed and widths of extrema separation and correlation times at various temperatures were compared for the local motions at inside of chain and at chain end. Less mobile character of the molecular motion at inside of the molecular chain was confirmed. Diluent effects to the molecular motions were also studied.     

Oxidizing purification of water using thermal plasma

The generation of atoms and radicals by the equilibrium thermal dissociation of oxygen and the same process involving water vapor are similar in terms of the reactive-species yield and energy consumption. The energy input into the generation of atoms and radicals is the smallest at 4500 K; about 70% of the energy is spent directly for the breaking of chemical bonds. From the calculations of the kinetics of oxygen atom recombination, it follows that cooling at a rate higher than 10⁷ K/s makes it possible to achieve considerable deviations from the equilibrium atom concentration. The lifetime of atoms in cooling thermal plasma is estimated at 10^?5 s. It has been established experimentally that a thermal plasma jet plunging into the water bulk generates hydrogen peroxide. The totality of factors affecting the hydrogen peroxide accumulation rate can be represented in as a generalized parameter, specifically, the atomic oxygen feed rate.     

Structural aspects of sub-bituminous coal deduced from solvation studies. 1. Anthracene-oil solvents

In order to study coal structure indirectly and the role of hydrogen donors, an investigation of the major parameters involved in the solvation of a Wyoming sub-bituminous coal has been made. This study utilized the catalytic and non-catalytic hydrogenation of anthracene oil and coal-solvent slurries. Indirect evidence concerning major structural units in the coal was obtained and the net contribution of coal to liquefaction products was estimated. The significance of each parameter to the degradation of coal molecules was also estimated. Data support the concept that coal liquefaction follows a solid → asphaltene → resin → oil route. This stepwise dissociation of the solid is directly related to the breaking of CO, CN, and to a lesser degree CC bonds, resulting in the formation of free radicals of relatively low molecular weight. These free radicals are stabilized by hydrogen transfer from hydroaromatic solvent molecules. A lack of significant quantities of high-molecular-weight hydrocarbons derived from coal solvation implies the prevalence of small molecular units in the coal structure.     

Reaction Mechanisms of Silicon Carbide Fiber Synthesis by Heat Treatment of Polycarbosilane Fibers Cured by Radiation: II, Free Radical Reaction

Silicon carbide (SiC) fibers were synthesized by the pyrolysis of radiation-cured polycarbosilane (PCS) fibers. The pyrolytic reaction was analyzed through free radicals by electron spin resonance (ESR). Free radicals on Si and C atoms were produced in the pyrolysis, and their yield as a function of reaction temperature depended on the oxygen content in the cured PCS fibers. There were two temperature ranges for the reactions related to Si and C atoms in PCS fibers. The radical concentration reflects the rate differences between the radical formation by the cleavage of Si-H and C-H bonds and the decay by recombination of radicals. The reaction of Si-H was strongly influenced by the oxygen content in the cured PCS fibers, and the decay rate of radicals decreased with an increase of the oxygen content in PCS fibers introduced in the curing process.     

THERMAL INDUCED HOMOLYTIC SCISSIONS OF LIGNIN INTERUNITARY BONDS IN THE HARDWOOD LIGNIN SOLUTION. AN ESR STUDY COMBINED WITH A SPIN TRAPPING METHOD

An electron spin resonance (ESR) method combined with a spin trapping reagent was successfully applied to trap and characterize unstable free radicals which were generated by heat-treatment of the dimethylsulfoxide (DMSO) solution of a hardwood, Japanese beech (Fagus crenata) lignin. It was found, consequently, that two unstable secondary carbon radicals, ～ CH? in the solution were created and the resulting radicals were trapped as the stable nitroxide spin adducts when the DMSO solution was heat-treated in the presence of a spin trapping reagent: 2,4,6-tri-tert-butylnitrosobenzene (BNB) at ca. 91°C. This means that so-called alkyl phenyl ether bonds, ～ CH-O- phenyl, known as important lignin interunitary bonds were homolytically scissoned by the heat-treatment of the lignin solution. Further the detailed analysis of the observed ESR spectrum revealed that two positions of alkyl phenyl ether bonds, i.e., β-O-4 and/or α-O-4 bonds as the interunitary linkages in the lignin are homolytically scissioned, although the phenoxy radical, Ph-O ? as the counter radical of the secondary carbon radicals was not trapped by the BNB spin trap. This suggests that fairly large steric hindrances operate between the syringyl with two methoxy moieties at the ortho positions and/or guaiacyl moieties with a methoxy moiety at the ortho position, and the BNB molecule bearing two bulky ortho tert-butyl groups in the phenyl ring.     

O-substituted phenolic antioxidant traps both alkyl and peroxy radicals

Phenolic antioxidants are well known for trapping peroxy radicals to prevent oxidative degradation in organic materials such as plastics. To eliminate such degradation it is also important to trap alkyl radicals, because autoxidation includes both peroxy and alkyl radicals as chain carriers. In general, alkyl radicals cannot be trapped because they react too quickly.This is a short news story only. Visit www.addcomp.com for the latest additives and compounding industry news.     

Bulk polymerization of methyl methacrylate initiated by high intensity ultrasonic irradiation and ESR study

High‐intensity ultrasound was used to initiate the bulk polymerization of methyl methacrylate. The polymerization rate varied with the sonication time, the intensity of the ultrasound, and the initiator concentration of poly (methyl methacrylate) in the monomer. Electron spin resonance (ESR) spectra, obtained by the spin trapping technique, testified that free radicals were produced during the sonication process, and the concentration of radicals also changed with the sonication condition. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1731–1735, 2002     

Free volume-based modelling of free radical crosslinking polymerisation of unsaturated polyesters

A new mechanistic kinetic model is presented for the cure behaviour of unsaturated polyester (UP) resins. The model is based on free radical polymerisation mechanism and the free volume concept. The quasi steady-state assumption for the free radical concentration is not used, and the decrease in initiator efficiency with conversion and radical trapping are modelled separately. The glass transition temperature of partially cured samples was measured employing differential scanning calorimetry (DSC) in conjunction with dynamic mechanical analysis (DMA), and the values obtained were incorporated into the model. DSC obtained conversion-time data for a standard commercially available UP resin under isothermal conditions. The kinetic parameters of the model were estimated using parameter optimisation procedures resulting in good agreement between model predictions and experimental data. Modelling in combination with experimental cure data showed that at higher isothermal cure temperatures a greater extent of physical trapping of radicals occurs rendering them inactive.     

Charge trapping characteristics of alumina based ceramics

The space charge dynamics is very important for electrical breakdown of alumina based ceramics. In this paper, the charge trapping/detrapping characteristics of alumina based ceramics were studied by means of isothermal surface potential decay (ISPD) method. For alumina and zirconia toughened alumina (ZTA) ceramic samples, the ISPD curves charged by corona discharge as well as microstructure characterization were carried out. For the first time, crossover phenomenon and hollow shaped potential profile were observed and reported in alumina based ceramics, indicating a surface potential decay process dominated by charge injection and volume conduction affected by the trap states in materials. In addition, the comparative trapping characteristics were evaluated based on a charge detrapping controlled decay model. The correlation between trap distribution and microstructure of alumina based ceramics was investigated. It was proposed that different charge trapping characteristics of alumina based ceramic samples was caused by varied shallow trap density of grain boundary.     

A novel economical grain boundary engineered ultra-high performance ZnO varistor with lesser dopants

A varistor having ultra-high performance was developed from doped ZnO nanopowders using a novel composition consisting of only three (Bi, Ca and Co oxides) dopants. Improved varistor properties were obtained (breakdown field (E_b) 27.5?±?5?kVcm^?1, coefficient of nonlinearity (α) 72?±?3 and leakage current density (L_c) 1.5?±?0.06?μAcm^?2) which are attributed to the small grain size and grain boundary engineering by phases such as Ca₄Bi₆O₁₃ and Ca_0.89Bi_3.11O_5.56 along with Co⁺² doping in the ZnO lattice. Complex impedance data indicated three relaxations at 25?°C and two relaxations at high temperature (>100?°C). The complex impedance data were fitted into two parallel RC model to extract electrical properties. Two stages of activation energy for DC conductivity were observed in these varistor samples where region I (<150?°C) is found to be due to shallow traps and region II (<225?°C) is due to deep traps. The novel composition is useful for commercial exploitation in wide range of surge protection applications.