Effect of carbon-black treatment by radiation emulsion polymerization on temperature dependence of resistivity of carbon-black-filled polymer blends

High dispersibility and stability of carbon black particles in low-density-polyethylene (LDPE) matrix were obtained by radiation emulsion polymerization on carbon particles surface, and electrical resistivities of its simple were examined. First carbon particles treatment on radiation emulsion polymerization on surface were synthesized by the reaction with a polymer-emulsion systems containing reactive group in the molecular unit, carbon particles and emulsifier. Then, the carbon particles treatment on radiation emulsion polymerization on surface was dispersed into LDPE, and its composites were prepared for electrical measurements. The effect of radiation crosslinking of the composite on the Positive temperature coefficient (PTC) and negative temperature coefficient (NTC) phenomenon was investigated. The experimental results showed that PTC and NTC effects of the composites were obviously influenced by the irradiation dose. Various microstructure-exploring means were used to study the conductive composite, such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM).     

基体分子运动对聚偏氟乙烯/碳纤维复合材料的聚合物基正温度系数性能的影响

聚合物基正温度系数(PTC)材料中,基体分子在熔体状态下的运动能力可显著影响填料分布、PTC强度及稳定重复性等,明确其机理有利于高灵敏性且稳定可重复的PTC复合材料的设计与制备.通过探究基体熔体黏度不同的聚偏氟乙烯(PVDF)/碳纤维(CF)的电阻-温度响应行为,可以发现复合材料PTC转变温度区间仅取决于基体化学结构与结晶性,而PTC循环稳定性却受到基体分子运动能力的显著影响.当基体分子运动能力较强时,分子链极易黏附填料在CF表面形成包覆层,导致局部填料间距增大到隧穿距离以上,不利于复合材料导电网络的重建,导致随热循环次数增加,复合材料的室温电阻率有所升高,PTC可重复性略微降低.而对基体分子链缠结明显的PVDF/CF复合材料中,运动能力较弱的分子链不会包覆CF粒子,在多次升温-降温循环后导电通路能恢复到初始状态,复合材料呈现良好的PTC可重复性,将其应用于电路过热保护装置时,复合材料表现出灵敏的温度响应特性及可多次循环的开关特性.     

Carbon Dots in a Matrix: Energy‐Transfer‐Enhanced Room‐Temperature Red Phosphorescence

High‐efficiency red room‐temperature phosphorescence (RTP) emissions have been achieved by embedding carbon dots (CDs) in crystalline Mn‐containing open‐framework matrices. The rationale of this strategy relies on two factors: 1) the carbon source, which affects the triplet energy levels of the resulting CDs and thus the spectral overlap and 2) the coordination geometry of the Mn atoms in the crystalline frameworks, which determines the crystal‐field splitting and thus the emission spectra. Embedding the carbon dots into a matrix with 6‐coordinate Mn centers resulted in a strong red RTP with a phosphorescence efficiency of up to 9.6 %, which is higher than that of most reported red RTP materials. The composite material has an ultrahigh optical stability in the presence of strong oxidants, various organic solvents, and strong ultraviolet radiation. A green‐yellow RTP composite was also prepared by using a matrix with 4‐coordinate Mn centers and different carbon precursors.     

Property tailoring of particulate polymer composites by reactive processing

This study explores reactive processing aimed at improving the mechanical properties of polyolefin/inorganic particulate filler based composites. Three different polymer matrix materials have been studied in combination with the nine inorganic particulate fillers with different particle size and of varying pH. The reactive modifier 1,3‐phenylene dimaleimide (BMI) has been shown in all cases to be very effective in terms of improving composite properties beyond those of the respective unmodified composites and in some cases beyond those of the unfilled matrix materials. The detrimental effect of BMI on melt viscosity can be overcome via judicious use of a suitable lubricant, and together with response surface methods, followed by optimization procedures, composite properties can be tailored for specific end use applications.     

Magnetic properties of polymer matrix nanocomposites on a basis of metal carboxylates

Metallopolymer nanocomposites on the bases of cobalt and iron acrylates as well as their cocrystallites have been obtained and characterized. Microstructure of the materials consists of both agglomerated and individual nanocrystallites which are homogeneously distributed in the polymer matrix. Mean crystallite size is 7-14 nm. All the composite materials exhibit soft magnetic properties at room temperature. The magnetic parameters are controlled by the intrinsic magnetic properties of the constituents and agglomeration of the particles.     

Preparation and characterization of sulfonated poly(phenylene oxide) proton exchange composite membrane doped with phosphosilicate gels

A new class of proton exchange composite membranes made by incorporating phosphosilicate gels into SPPO matrix was prepared and characterized. The thermal stability was evaluated by TGA and DSC, and the amorphous structure information was provided from XRD. The experimental results showed that the composite membranes have good stability to oxidation by Fenton's reagent test, and the membrane dimension is hardly changed, even at high temperature. The hydration number values of the persulfonic acid group of composite membranes were lower than that of Nafion 112 at room temperature, but the water uptake of composite membranes at 80°C was higher than that of Nafion 112. With increasing relative humidity and doping amount, the conductivity of the composite membranes increased. Moreover, the conductivities of water-equilibrated composite membranes were higher than that of Nafion 112 (0.0871 S/cm) at room temperature, and the highest conductivity for the composite membrane was 0.216 S/cm. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of ionizing radiation on the dynamic mechanical properties of an epoxy and a graphite fiber/epoxy composite

TGDDM/DDS epoxy and T300/NARMCO 5208 composite specimens were exposed to 0.5 MeV electrons to dose levels up to 10,000 Mrad, and the effects of radiation on the mechanical properties were characterized using dynamic mechanical analysis (DMA). In nominally cured specimens there remain unreacted epoxide groups because the epoxy system vitrifies during the cure, preventing additional reaction. DMA shows that ionizing radiation continues the reactions of epoxide groups. Also, the ultimate glass transition is shown to decrease monotonically with radiation dose. The room temperature elastic modulus of the epoxy increases slightly with radiation, but at temperatures exceeding 100°C there is a slight decrease with radiation. There is a dynamic loss phenomena associated with the composites, not seen in the epoxy, that is thought to be due to the interphase region between the fiber and the matrix.     

Intelligent gels and cryogels with entrapped emulsions

Smart thermoresponsive gels and cryogels with incorporated emulsions have been synthesized and studied. The gels were obtained by three-dimensional copolymerization of N-isopropylacrylamide and N,N'-methylene-bis-acrylamide or N,N'-bis(acryloyl)cystamine in the presence of dispersion of tetradecane stabilized with sodium dodecylsulfate. Polymerization was performed at room temperature and below the water crystallization temperature. Both composite gels and cryogels were capable of heat-induced collapse. The extent of the collapse of the composite gel prepared at room temperature was much smaller and without squeezing of the lipophilic phase out of the shrunk composite gel. In contrast, shrinking of the composite cryogel was accompanied by release of tetradecane emulsion.     

Glass-fibre reinforced composite materials based on unsaturated polyester resins

The effect of glass-fibre content on the thermal and mechanical properties of cross-linked composites based on unsaturated polyester resins have been investigated by thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical thermal analysis and by measuring the heat distortion temperature (HDT). Two different matrix resins and two different glass mats were used, and the glass-fibre contents varied. Altogether 12 composite systems were tested. The glass- transition temperature of each composite was characteristic to the matrix resin and did not depend on the glass-fibre content, as it was expected. The effect of glass-fibre content on the storage modulus and on HDT has been elucidated. It has been found that up to 12 mass% (6?vol%) glass-fibre content the HDT did not change, above this value it increased with increasing glass-fibre content for each composite, but not at the same extent. This means that matrix-fibre interaction has an important role in the performance of the composites at elevated temperatures. Storage moduli increased with increasing glass-fibre content. The temperatures detected by dynamic mechanical thermal analysis corresponding to the storage modulus of 750?MPa??calculated by Takemori??are above the glass-transition and also increased with higher glass-fibre content in accordance with the real heat-distortion temperature measurements. It may be concluded that the effect of reinforcement on the performance of the composite could be detected more reliably by HDT measurements, since it gives information on the deformation of the composites. Matrix-fibre interaction has an essential role on the performance and on the HDT of the composite materials.     

含共引发剂的环氧树脂电子束固化特性

对引发剂组成、含量不同的环氧树脂体系进行了低吸收剂量及高吸收剂量的电子束辐射固化,通过对不同样品辐射过程中的温度特性和辐射后的凝胶含量、内耗tanδ及动态模量变化趋势的研究,得到共引发剂对环氧树脂辐射固化的影响规律.在相同的树脂含量及吸收剂量下,共引发剂的加入可以提高环氧树脂体系的凝胶含量,但其提高幅度并不随着共引发剂含量的增多而增大,而是存在一个最佳值.随着碘盐引发剂含量的增加,共引发剂对体系凝胶含量的提高幅度减小.在辐射过程中,环氧树脂体系的温度会出现一个峰值,共引发剂对峰值温度和辐射后体系的玻璃化转变温度的影响与对凝胶含量的影响类似.碘盐引发剂含量较低时,加入共引发剂的体系的常温及高温模量与未加体系相比没有明显变化;碘盐引发剂含量较高时,加入共引发剂的体系的常温模量比未加体系有所上升,而高温模量则变化不大.     

Methylammonium bromocuprate (MeNH3)2CuBr3 as a new self-absorption-free solution-processable X-ray scintillator

We report the radioluminescent properties of the recently discovered hybrid bromocuprate (MeNH₃)₂CuBr₃ in a poly(methyl methacrylate) matrix in the form of solution- produced composite thick films. The obtained films demonstrate bright turquoise photoluminescence in UV light and intense radioluminescence due to CuKα and AgKα radiation at room temperature, exceeding the radioluminescence intensity of Cs₄PbBr₆@CsPbBr₃ films by more than an order of magnitude.     

A biocompatible nanocomposite based on allyl chitosan and vinyltriethoxysilane for tissue engineering

The synthesis, structure, and electrophysical properties of a polymer-inorganic biocompatible composite based on unsaturated chitosan ether, namely, allyl chitosan, and vinyltriethoxysilane are studied. During composite synthesis, allyl chitosan forms an individual nanophase with vinyltriethoxysilane and its condensation products in the polymer matrix of allyl chitosan. The size of nanoparticles embedded in a polymer matrix increases from 50 to 1000 nm as the fraction of the added vinyltriethoxysilane grows. Under exposure to UV radiation, both homopolycondensation and heteropolycondensation occur in the composite films via crosslinking according to the radical mechanism and the composite becomes insoluble in water. It has been shown that the resulting composites feature ionic conductivity under application of both direct current and high-frequency electric fields to the sample. Conductivity is provided by a proton–electron ensemble that concentrates at the nanoparticle/polymer matrix interface.     

Excited state proton transfer reaction of two new intramolecularly hydrogen bonded Schiff bases at room temperature and 77K.

Two new orthohydroxy Schiff bases, 7-phenylsalicylidene benzylamine (PSBA) and 7-ethylsalicylideneaniline (ESA) have been synthesized. The excited state intramolecular proton transfer (ESIPT) and the structure of PSBA and ESA in its crystalline form and in the solvents n-hexane, n-heptane and 1,4-dioxane have been investigated by means of absorption, emission and nanosecond spectroscopy at room temperature and 77K. One ground state species has been detected both in neutral and basic solutions of both PSBA and ESA: the cis-enol form with an intramolecular hydrogen bond. The ESIPT and formation of keto tautomer are evidenced by a large Stokes shifted emission (approximately 12000 cm(-1)) at room temperature only in the case of ESA. On the other hand the keto tautomer is the predominant species at 77K in a solid matrix and as a solid sample at room temperature both in the case of ESA and PSBA. In the case of both ESA and PSBA the more intense, higher energy emission is due to the species which has not undergone ESIPT and attributed mainly due to cis-enol form. The trans-enol form is also observed by changing the excitation wavelength. Both the compounds are found to undergo a structural change to a zwitterionic and intermolecular hydrogen bonded form in the presence of a strong base like triethylamine. From the nanosecond measurements and quantum yield of fluorescence we have estimated the decay rates of proton transfer reaction in the case of PSBA. Our theoretical calculation at the AM1 level of approximation shows that the ground singlet state has a rather large activation barrier both in the case of PSBA and ESA. The barrier height is much lower on the corresponding excited singlet surface only in the case of ESA. The process is predicted to be endothermic in the ground state and exotherrmic in the excited singlet state.     

Role of temperature during ageing under gamma irradiation of filled EPDM: consequences on mechanical properties

Filled EPDM materials have been processed and aged by gamma radiation at ambient temperature and at 80 °C to study the influence of the fillers presence in the material degradation. The acceleration of the polymer degradation by the ATH fillers, evidenced when irradiation is performed at 25 °C, is also effective at 80 °C. In addition, in the case of silica‐filled EPDM, the creation of strong filler‐matrix bonds, already reported for irradiation at 25 °C, is also thermally activated; this enables to this material to keep its integrity at high irradiation dose, whereas the irradiated ATH‐filled EPDM is so degraded that it flows. Thus, the introduction of fillers in the polymer has an impact on its resistance to irradiation, whatever the temperature at which the irradiation is performed. Moreover, the consequences of the degradation on the evolution of the mechanical properties of the composite are very dependent on the filler nature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1319–1328, 2010     

Radiation synthesis of a water-soluble temperature sensitive polymer, activated copolymer and applications in immobilization of proteins

In this work the radiation polymerization of N-isopropylacrylamide (NIPAAM) in aqueous solutions has been carried out and a water-soluble, temperature sensitive polymer and copolymer were obtained by using γ-rays from Co-60 source at room temperature. We have gained the optimum dose and dose—rate of radiation synthesis of linear polyNIPAAM through determining conversion yield and viscosity. In order to immobilize protein (BSA) and enzyme (HRP) into this water-soluble polymer, we prepared an activated copolymer, poly ( N-isopropylacrylamide-co-N-acryloxysuccinimide). The BSA and HRP has been immobilized onto the activated copolymer. The BSA (HRP) / copolymer conjugates still kept the original thermally sensitive properties of the linear polyNIPAAM. The conjugation yield of BSA to the activated copolymer decreased with increasing of dose. The thermal stability of the immobilized HRP was stable at 0 °C for a long time and has, at least, 4 days stability at room temperature. Immobilized HRP activity was lowered when the temperature was raised above its LCST. This phenomenon was reversible and the immobilized HRP regained activity below its LCST. The optimum pH of the immobilized HRP shifted from ca.5 upward to ca.7.     

Self-hardening of highly oriented polyethylene

Ultra-oriented polyethylene fibers obtained by drawing to approximately 30 times their original length have a Young's modulus of approximately 800 kbar. Such fibers, if unconstrained, contract on heating to a length near the original. We have studied the forces causing this contractile behavior by monitoring the stress in the fiber while maintaining it at constant length. In the course of this we observed a complex sequence of both reversible and irreversible behavior. In the reversible case we observed first energy and then entropy elastic behavior. The most significant feature observed is that at sufficiently high temperature the fiber stress relaxes to an unmeasurably low value. A fiber allowed to relax in this way possesses a much lower room temperature tensile modulus (ca. 80 kbar) immediately after relaxation but, remarkably, this modulus increases to approach the initial high value over a period of a few hours when the fiber is stored either clamped or unclamped at room temperature. High x-ray orientation is preserved throughout the storage period but the density which dropped during the stress decay rose again in the course of the spontaneous stiffening. None of the stress relaxed fibers displays large-scale contractile behavior on subsequent heating. A phenomenological composite model is proposed which involves stiff microfibrils of short length—surrounded by a matrix present as a minority component. The softening of this matrix on heating and its subsequent stiffening on storage, involving a certain amount of melting and recrystallization, respectively, could then be responsible for the observed variations in the macroscopic tensile properties using simple fiber composite theories. The fibers are likely to be of extended-chain type produced by the initial drawing while the matrix may consist of a combination of oriented amorphous material (tie chains), randomly oriented chains, and transverse lamellar overgrowth present in varying proportions in the different stages of sample treatment. The wider implications, fundamental and practical, of this remarkable self-hardening process are indicated.     

Behaviors of the positive temperature coefficient of resistance of poly(styrene‐co‐n‐butylacrylate) filled with Ni‐plated core‐shell polymeric particles

Conductive composite films of poly(styrene‐co‐n‐butylacrylate) copolymers filled with low‐density, Ni‐plated core‐shell polymeric particles were prepared and their behaviors of positive temperature coefficient of resistance (PTCR) were investigated. When the conductive fillers in the composite film were loaded beyond the critical volume, 10 up to 25 vol %, composite films exhibited a unique electrical resistant transition behavior, which the electrical resistance rapidly increased by several orders of magnitude at the critical temperature. The PTCR transition temperature, in general, occurred before the glass transition temperature of polymer matrix. Further increased the conductive filler loading to 30 vol %, the overpacked conduction paths were formed in the entire composite and the PTCR effects became blurred. While the composite film treated with thermal cycle several times from room temperature up to 120 °C, the electrical resistivity increased accompanied with the shift of the PTCR transition to lower temperature. The reason might have been caused by the formed interfacial cracks within the composite film. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 322–329, 2007     

The photodissociation of s-tetrazine and dimethyl-s-tetrazine

The photodissociation of s-tetrazine (ST) and its dimethyl derivative (DMST) has been investigated in hexane solutions at room temperature and in argon matrices and organic molecular crystals at cryogenic temperatures. Contrary to what has generally been assumed, only ST photodissociates upon excitation into its lowest excited singlet state at room temperature and in the rare gas matrix. Both ST and DMST in molecular crystal hosts exhibit a quadratic dependence of photodissociation on exciting light intensity. This we consider to be evidence of a sequential two photon photodissociation process.     

Metal,semiconductor and magnetic nanoparticle inclusions in gels

A room temperature chemical process has been developed to prepare composite materials formed of different nanometer particles trapped in a glass matrix. This involves a controlled precipitation of the crystallites using usual techniques of colloid chemistry, a grafting of a functionalized alkoxide on the particles and a sol-gel synthesis of transparent oxide matrices.     

Localized damage response of carbon fiber reinforced polymer composite sandwich panel after thermal exposure

An experimental study was conducted to investigate the effect of thermal exposure on indentation behavior of carbon fiber reinforced polymer composite sandwich panel (CFRPCSP) with pyramidal truss cores. Composite sandwich panels were fabricated by the hot press molding method. Subsequently, composite sandwich panels were exposed to different temperatures for 6 h. After thermal exposure, quasi-static indentation tests were carried out at room temperature. Then, the effect of thermal exposure on the failure mechanism, indentation load and energy absorption were analyzed and discussed. The results showed that the indentation load and energy absorption decreased as exposure temperature increased, which was caused by the degradation of the matrix properties and fiber-matrix interface properties at high temperature. In addition to the decrease of the indentation load and energy absorption, the failure modes also changed with exposure temperature. It is expected that this study can provide useful information for the design and application of composite sandwich panel with pyramidal truss cores at high temperature.