Novel way to control PDMS cross-linking by gamma-irradiation

Using a ⁶⁰Co gamma source polydimethylsiloxane-based materials have been prepared by gamma-irradiation of a mixture of polydimethylsiloxane, PDMS, silanol-terminated and the tetraethylortosilicate, TEOS, with no other chemicals. Samples were prepared with varying TEOS concentrations. The obtained materials are monolithic, flexible and transparent. X-ray measurements have shown them to be amorphous. The thermal behaviour has also been investigated by using differential scanning calorimetry and thermal gravimetric analysis. The results suggest that TEOS have a tailoring effect on the conformation of the polymer chains, affecting the network formation, as shown by the swelling behaviour of the material.     

SANS investigation of PDMS hybrid materials prepared by gamma-irradiation

Gamma-irradiation from a ⁶⁰Co source was used to prepare hybrid materials from a mixture of polydimethylsiloxane with tetraethylortosilicate and zirconium propoxide.The obtained materials are monolithic and transparent after drying in air. They had been previously characterized by thermal analysis, X-ray diffraction, Rutherford backscattering and elemental analysis. The present work reports a small angle neutron scattering study on a few samples of these materials to investigate their microstructure at the nanoscale. This study showed the presence of inorganic oxide regions with mass fractal structure, their size and fractal density increasing with the tetraethylortosilicate content. Although the presence of zirconium propoxide is required to obtain a stable hybrid material yet the increase in its content leads to less dense mass fractal oxide units. It was found that the structure of the oxide regions developed through a reaction-limited aggregation mechanism. The further addition of isopropanol in the sample preparation stage causes the inorganic fractal structure to extend over the whole sample.     

Hybrid PDMS-Silica-Zirconia materials prepared by γ-irradiation

Hybrids are a class of materials that enable the integration of organic and inorganic characteristics at the molecular level in a single material. In this way materials with unusual optical, mechanical or even bioactive properties are obtained, which are especially suitable for applications as sensors, non-linear optical (NLO) materials, lasers, selective membranes, catalysts and protective coatings. Sol-gel processing is often used for the preparation of hybrids, usually through the alkoxides method that leads to high purity products at relatively low temperatures. The authors have developed a new method for the preparation of these materials based on gamma irradiation of the precursors mixture. The precursors used are polydimethylsiloxane (PDMS), tetraethylortosilicate (TEOS) and zirconium propoxide (PrZr). The irradiations were performed using the ⁶⁰Co source at the Portuguese Gamma Irradiation Facility (UTR) located in the ITN campus at Sacavém. The materials at room temperature are macroscopically transparent, relatively flexible and amorphous. The details of the preparation of these hybrid materials by gamma irradiation are presented.     

Use of poly(methyl methacrylate) in radioactive waste management: II. Monte Carlo simulations

Radioactive waste is generated from the nuclear applications and it should properly be managed in a radioactive waste management system. Different methods are available for treatment and conditioning of radioactive waste. Polymers can be used in the radioactive waste management as an embedding matrix. Poly(methyl methacrylate (PMMA) is a possible candidate material that can be used in the low level radioactive waste management. In this study, based on total resistible dose for PMMA, maximum waste activity that can be embedded into a waste drum was found via Monte Carlo simulations. In addition, Monte Carlo simulations for radioactive waste embedded into above mentioned polymer was performed and the dose rate distribution in the polymer matrix was determined for the initial and different periods of 15.1, 30.2 and 302 years after embedding of waste. Changes of mechanical properties in the polymer embedded waste drum was simulated for PMMA embedded waste matrices based on experimental data.     

Matrix-assisted pulsed laser evaporation of polymeric materials: a molecular dynamics study

Matrix-assisted pulsed laser evaporation (MAPLE) has been recently developed to deposit high-quality thin films for a wide range of polymeric materials. To analyze the evaporation of polymer molecules in MAPLE, we present a molecular dynamics (MD) simulation of laser ablation where the target material is modeled as a solution of polymer molecules in a molecular matrix. The breathing sphere model is used for MD simulations of laser ablation of the molecular matrix. Polymer molecules are described using a bead-spring model, where each bead represents one or several polymer groups. The initial stage of polymer ejection is investigated at different laser fluences and pulse durations. The influence of polymer molecules on the stability of clusters formed in the plume and the processes that can lead to polymer decomposition are discussed.     

Photoluminescence and radiation effect of Er and Pr implanted silicon-rich silicon oxide thin films

Er and Pr ions were implanted into silicon-rich silicon oxide (SRSO) thin films with Si crystals embedded in SiO₂ matrix. The 525 and 546 nm luminescence peaks were clearly observed in Er-only doped film, but disappeared in the photoluminescence (PL) spectra of Er-Pr codoped films. Instead, a broad PL spectrum extending from 450 to 700 nm was obtained for Er-Pr codoped films with Er/Pr concentration ratio of 1. Concentration profiles of Si, Er and Pr ions in films were simulated by SRIM2006 and related radiation effect on PL response was also discussed. Our results indicate that this material is a potential candidate for the development of white light-emitting diode (LED) and field emission displays for its visible luminescence.     

Effect of SHI on dielectric and magnetic properties of metal oxide/PMMA nanocomposites

Magnetic nanoparticles embedded in polymer matrices have excellent potential for electromagnetic device applications like electromagnetic interference suppression, etc. The NiO nanoparticles were synthesized by simple method. These nanoparticles were dispersed in PMMA matrix and films were prepared by casting method with varying concentrations of nickel oxide nanoparticles. These films were irradiated with 50 MeV Li⁺³ ions at a fluence of 5 × 10¹² ions/cm². AC electrical properties of pristine and irradiated samples were studied in wide frequency range. Dependence of dielectric properties on frequency, ion beam fluence and filler concentration was studied. The results reveal the enhancement in dielectric properties after doping nanoparticles and also upon irradiation, which is also corroborated with field-cooled-zero-field-cooled (FC-ZFC) susceptibility measurement in which magnetization is increased upon irradiation. The Fourier transform infrared (FTIR) spectroscopy analysis revealed the change in the intensity of functional groups after irradiation. Average surface roughness observed to change with filler concentration and also with the irradiation fluence as obtained from AFM analysis.     

以环氧化合物为凝胶促进剂制备块状氧化铁气凝胶

以无机铁盐FeCl₃为前驱体，环氧丙烷及其衍生物作为凝胶促进剂，采用溶胶-凝胶工艺制备氧化铁凝胶。以氯化铁的醇溶液为前驱体、环氧化合物为凝胶促进剂，制备氧化铁的醇凝胶，通过CO₂超临界干燥工艺得到氧化铁气凝胶。用透射电镜（TEM）对气凝胶微观结构的表征结果表明，气凝胶样品主要由超细微粒堆积而成。BET和BJH测试结果表明，气凝胶样品平均孔径为9.4～18.3nm，比表面积为430～500m²/g。     

Development of a non-destructive micro-analytical method for stable carbon isotope analysis of transmission electron microscope (TEM) samples

The biogenicity of ancient morphological microfossil-like objects can be established by linking morphological (e.g. cell remnants and extracellular polymeric matrix) and chemical (e.g. isotopes, biomarkers and biominerals) evidence indicative of microorganisms or microbial activity. We have developed a non-destructive micro-analytical ion beam system capable of measuring with high spatial resolution the stable carbon isotope ratios of thin samples used for transmission electron microscopy. The technique is based on elastic scattering of alpha particles with an energy of 2.751 MeV. At this energy the ¹³C cross section is enhanced relative to the pure Rutherford cross section for ¹³C, whereas the ¹²C cross section is reduced relative to its pure Rutherford cross section. Here we report the initial results of this experimental approach used to characterize ultramicrotomed sections of sulfur-embedded graphite and microbial cells.     

Hydrophilicity and morphological investigation of polycarbonate irradiated by ArF excimer laser

Lasers are used to modify polymeric materials. In this work, a number of polycarbonate (PC) pieces were exposed by ArF excimer laser, 193 nm, at various UV doses from 10 to 100 J/cm² with 50-500 mJ/pulse at 10 Hz pulse repetition rate. Morphology of PC has been investigated by scanning electron microscope (SEM) at three regimes pre-ablation, slow and fast ablation. SEM identifies that the conical defects are created on the polymer surface to grow opposite to the direction of laser irradiation. It increases the superficial absorptivity of the material dependent on the ArF laser induced conical microstructure geometry. The contact angle measurement was performed here, in order to determine the hydrophilicity of the irradiated polymer at various coherent doses. It is shown that the contact angle of PC samples which are exposed to the ArF laser significantly alters with UV dose below 7 J/cm².     

Ti-PS nanocomposites by plasma immersion ion implantation and deposition

We synthesize Ti-PS nanocomposites by plasma immersion ion implantation and deposition (PIII&D) technique. Ti nanoparticles at size of 5-15 nm are found in PS matrix. We propose the formation of Ti nanoparticles as a result of the combined effect of ion implantation and ion condensation in PIII&D process. X-ray photoelectron spectroscopy measurements reveal that Ti atoms have three different chemical states, metal, oxide and carbide. While surface Ti atoms are oxidized, embedded Ti atoms keep their metallic states by surrounding PS matrix. We characterize optical absorbance of Ti-PS nanocomposites by UV-VIS measurements. An adsorption peak due to the excitation of localized surface plasmon is found at wavelength 337.5 nm and the fractal nature of Ti-PS nanocomposites broaden absorption wavelength from UV to infrared. In addition, we use a protein assay to measure protein immobilization. It is found that the amount of protein immobilized on Ti-PS nanocomposites is almost twice than that on pristine PS. The enhancement mechanisms are attributed to the increased surface roughness as well as covalent linkages between protein molecules and functional groups on the surface of Ti-PS nanocomposites.     

Drug release assays from new chitosan/pHEMA membranes obtained by gamma irradiation

With the purpose of obtaining a biocompatible and microbiologically safe matrix that simultaneously could be used as wound dressing material and as a controlled drug release system, membranes with different thickness and different contents in chitosan and hydroxyethyl methacrylate (HEMA) have been prepared by γ irradiation from a ⁶⁰Co source. Antibiotic release experiments were performed before or after irradiation over amoxicillin loaded chitosan/pHEMA membranes in physiological saline solution, and monitored by UV-Vis spectrometry.Results point out a fast amoxicillin release with similar release profile in all studied membranes. The amount of released drug was shown to be dependent on membranes network crosslinking due composition, radiation and membrane thickness.     

Low-temperature synthesis of silicon carbide inert matrix fuel through a polymer precursor route

A low temperature process of mixing different sizes of silicon carbide (SiC) particles with a polymer precursor was utilized to synthesize SiC pellets for potential use as inert matrix fuels (IMF) for light water reactors. The lower temperature process is required to prevent the reactions between SiC and the dispersed PuO₂ fuel material. The effect of the polymer content and the cold pressing pressure on the packing of SiC particles was investigated. The effect of mixing coarse and fine SiC particles on the density and the pore size distribution was also investigated. It was found that the density and pore size distribution can be tailored by controlling the SiC size compositions, polymer content and pressing pressure at room temperature. A possible mechanism has been proposed to explain the forming of the pores with respect to the geometric arrangement between SiC particles and the polymer precursor. SEM images showed that ceria (cerium oxide) which is a PuO₂ surrogate in this study, was well distributed in the pellet.     

先进聚合物可燃毒物燃耗特性分析

针对当前新提出的先进聚合物材料(PACS),分析聚合物可燃毒物的材料特性与慢化特性,基于秦山核电厂与Crystal River Three两类堆型燃料组件,对比分析采用不同类型可燃毒物材料时组件的燃耗特性。结果表明:聚合物材料的慢化特性随含氢量呈线性变化关系,调节聚合物分子组成可以改变毒物的燃耗特性。相对传统的可燃毒物材料,先进聚合物可燃毒物体现了良好的毒物特性,全寿期具有更低的局部功率峰,在燃耗初期PACS聚合物可燃毒物有较低的初始k_(inf)值,而在燃耗后期释放高于1%的k_(inf)值,可燃吸收体核素B-10消耗更加充分,且具有较大的热通量,可提高热中子利用率,并促进裂变核素Pu的消耗。     

Surface reliefs on diacrylate monomer films by spatially controlled UV photopolymerization

The non-uniform ultraviolet (UV) photopolymerization of acrylic films allows the formation of surface reliefs through a self-developing process. The parameters that influence the growth of the reliefs for polymer films made of bis-phenol-A-diglycidil-ether diacrylate (BGEDA), an aliphatic polyurethane diacrylate and an aromatic polyurethane diacrylate, mixed with tri-propylen-glycol diacrylate as promoter, have been investigated. The results show that the time of photopolymerization, the after-curing self-developing time, the mixture composition and the polymer film thickness influence the relief development in a complex way. The behaviours of the different monomers were explained on the basis of two main factors: the properties of the polymeric network and the diffusion phenomena which take place in the polymer bulk.     

Study of low work function materials for hot cavity resonance ionization laser ion sources

The selectivity of a hot cavity resonance ionization laser ion source (RILIS) is most often limited by contributions from competing surface ionization of the hot walls of the ionization cavity. In this article we present investigations on the properties of designated high temperature, low work function materials regarding their performance and suitability as cavity material for RILIS. Tungsten test cavities, impregnated with a mixture of barium oxide and strontium oxide (BaOSrO on W), or alternatively gadolinium hexaboride (GdB₆) were studied in comparison to a standard tungsten RILIS cavity as being routinely used for hot cavity laser ionization at ISOLDE. Measurement campaigns took place at the off-line mass separators at ISOLDE/CERN, Geneva and RISIKO/University of Mainz.     

Separation of strontium from low level radioactive waste solutions using hydrous manganese dioxide composite materials

⁹⁰Sr is one of the major isotopes present in the low level radioactive liquid waste (LLW) generated during operation of nuclear reactors and spent fuel reprocessing plants. A composite ion exchange material consisting of hydrous manganese oxide and poly methyl methacrylate (PMMA) was developed for removal of strontium from aqueous radioactive waste. The prepared composite material showed very good strontium adsorption properties in aqueous solutions. Sorption of strontium on the composite material as a function of pH, equilibration time and strontium ion concentrations were studied. The process of sorption of strontium from solution was analysed using different isotherm models like Langmuir, D-R and Freundlich. Four different error functions were employed to find out the most suitable isotherm model to represent the experimental data and it was found that Freundlich model best fits the sorption of strontium on the composite material. Analysis of the data obtained from the sorption kinetics studies showed that the data fitted better to the pseudo-second order kinetic model. Lab scale column performance study of the composite material revealed that the material could be effectively used in column operations to remove strontium from LLW solutions.     

Interaction of energetic clusters (Au3, Au400 and C60) with organic material and adsorbed gold nanoparticles

Using molecular dynamics simulations (MD), this contribution compares the interaction of three energetic clusters (Au₃, Au₄₀₀ and C₆₀) with a hybrid surface of crystalline polyethylene (PE) covered by a layer of gold nanoparticles. This model system mimics the situation encountered in metal-assisted secondary ion mass spectrometry. The chosen impact points are representative of the PE surface, the metal particles and the frontier between the metal and the polymer. The simulations show the differences between the impact over the Au nanoparticle and the polymer surface, in terms of projectile penetration, crater formation and sputtering yield of PE and gold species. For C₆₀ and Au₃ projectiles, a simple correlation is found between the quantity of energy deposited in the top polymeric layers and the quantity of sputtered polymer material, including all the impact points. The results obtained with Au₄₀₀ do not fit on this line, indicating that other physical parameters are prevalent. The mechanistic view of the interaction provided by the MD helps explain the differences. In short, while C₆₀ and Au₃ quickly break apart, creating energetic recoils and severing many bonds in the surface, Au₄₀₀, with the largest total momentum by far (∼10 times larger than the others) and the lowest energy per atom (25 eV), tends to act and implant in the solid as a single entity, pushing the polymeric material downwards and breaking few bonds in the surface.     

几种去污工艺对压水堆一回路模拟氧化物的溶解及腐蚀研究

为了获得较高的去污系数以及对被去污件较低的腐蚀程度,需要选择相对适宜的去污工艺。本研究工作选取不锈钢1Cr18Ni9Ti和Inconel 690合金,通过高压釜制备模拟氧化物试片,采用不同去污工艺,进行试片表面模拟氧化物的溶解及腐蚀试验。结果表明:酸性高锰酸钾溶液对于压水堆模拟氧化物的预氧化处理效果好于碱性高锰酸钾溶液;两种模拟氧化物试片经过四种不同去污工艺处理后,通过对去污后试片的宏观及微观观察,几种去污工艺均未对试片结构造成破坏;NP-CITROX是一种比较理想的去污工艺。     

用于脉冲n/γ混合场中n、γ甄别的新型探测器的研究

以塑料闪烁体和聚合物基复合材料为探测介质,开展用于脉冲n/γ混合场中n、γ甄别的新型探测器的研究。采用闪烁体探测器+契仑科夫探测器联合探测的方法,通过对n、γ产生的荧光和契仑科夫辐射的相关性测量,以实现n、γ的甄别,并给出脉冲中子的通量。利用蒙特卡罗方法计算了塑料闪烁体最佳厚度、n和γ在塑料闪烁体产生的次级电子能谱。同时利用模拟结果确定契仑科夫探测器探测介质的折射率,使得只有光子生成的次级电子可以在其中产生信号。