Dynamic Rebound Behavior of Silica/Natural Rubber Composites: Fly Ash Particles and Precipitated Silica

This article investigated the elastic response of natural rubber (NR) compounds filled with silica from fly ash particles (FASi) and commercial precipitated silica (PSi), through a dynamic rebound test. The effects of silica content and initial drop‐height on the height and number of rebounds, dynamic stiffness, and the energy loss were of interest. The results suggested that the unfilled NR vulcanizates exhibited a greater elastic response than the FASi and PSi‐filled vulcanized composites. For given silica contents, the NR compounds with FASi had better elastic response than those with PSi, where the elastic response decreased with an increase in silica content. The greater the silica contents, the higher the dynamic stiffness of the composites. The initial drop‐height had no effects on the elastic response change for the unfilled NR compound, but resulted in an increase in the energy loss for the silica‐filled NR composites. The differences in the elastic responses for the NR compounds filled with silica from FASi and PSi were associated with the differences in crosslink density and the filler–filler interaction influenced by content of bis(3‐triethoxysilylpropyl) tetrasulfane (designated as Si69) used.     

Properties of Natural Rubber Vulcanizates/Nanosilica Composites Prepared Based on the Method of In-situ Generation and Coagulation

Using the characteristics of silica sol dispersing well in water and easy formation of silica gel when the silica sol is heated, by mixing a system of concentrated natural rubber latex and silica sol, the silica sol can in-situ generate SiO₂ particles when heated. After coagulation of the mixed system, natural rubber/nanosilica composites C(NR/nSiO₂) were obtained. The composites C(NR/nSiO₂) and their vulcanizates were studied using a rubber processing analyzer (RPA), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The influence of silica contents on the C(NR/nSiO₂) vulcanizates mechanical properties, cross-linking degree, Payne effect, dissipation factor (tanδ), and the particle size and dispersion of SiO₂ in NR were investigated. The results obtained were compared with the NR/SiO₂ composites based on traditional dry mixing of bale natural rubber and precipitated silica (white carbon black). The results showed that when using a sulfur curing system with a silica coupling agent (Si69) in C(NR/nSiO₂), the vulcanizate had better mechanical properties, higher wet resistance, and lower rolling resistance than those without Si69. In the composites C(NR/nSiO₂) and their vulcanizates, the SiO₂ particles’ average grain diameter was 60 nm, and the good-dispersion of the in-situ generated SiO₂ in the rubber matrix were a significant contribution to the satisfactory properties of C(NR/nSiO₂) composites and their vulcanizates.     

有序介孔SiO2的制备及其在色谱填料方面的应用

利用水热合成方法,在低浓度盐酸下用三嵌段共聚物EO106PO70EO106（F127）作为模板剂,在100℃,130℃和150℃的条件下,制备了3种笼型介孔二氧化硅.通过粉末N2气吸附-脱附实验表征其孔径（PD）及比表面积（BET）、扫描电镜（SEM）观察其表面形貌、透射电子显微镜（TEM）分析其微观结构;通过表征结果分析,该材料具有笼型介孔结构.同时,将该介孔材料应用在色谱分离方面,对氯苯,苯乙烯,1,2-二苯乙烯,联苯4种物质混合物进行分离,与其他多种二氧化硅材料比较,150℃的条件下合成的KIT-5-150分离效果最好.     

金纳米棒核／二氧化硅壳纳米复合结构的可控制备及细胞成像

采用模板合成以及溶胶凝胶方法制备了金纳米棒核／二氧化硅壳（GNR@SiO2）纳米复合粒子,探讨了这种新型纳米复合结构的可控制备、光谱性质、细胞毒性和细胞成像。通过紫外可见分光光度计、透射电镜、共聚焦显微镜对样品进行表征,结果表明：通过对反应时间的调控,获得的纳米复合粒子的二氧化硅壳层厚度可以控制在20～30nm。由于二氧化硅壳层的存在,大大提高了金纳米棒的稳定性,同时降低了金纳米棒的细胞毒性;此外,由于二氧化硅壳层具有良好的化学修饰作用,因此可以将荧光探针分子标记在二氧化硅壳层表面,修饰后的纳米复合粒子可以通过细胞内吞作用进入细胞,从而实现细胞内的光学成像。因此,该纳米粒子复合材料在生物传感、细胞成像以及光热治疗等方面有着良好的应用前景。     

Structural change of mesoporous silica with sonochemically prepared gold nanoparticles in its pores

Ultrasonic irradiation of mesoporous silica soaked in a mixture of chloroauric acid and isopropanol for 120 min in Ar atmosphere at room temperature yielded Au/SiO₂ mesoporous composite, which was characterized by high resolution transmission electron microscopy and optical absorption measurement. The structure of mesoporous silica after sonochemical preparation of gold (Au) nanoparticles within its pores was studied by nitrogen adsorption technique. It has been shown that the structural parameters, such as specific surface area (SSA), porosity (P), the mean pore diameter (l_p) were increased significantly after ultrasonic irradiation. It is suggested that the collision of Au nanoparticles with pore walls and localized erosion induced by the asymmetric implosive collapse of cavities on the extensive liquid–solid interface that are responsible for the structural change in the mesoporous solid.     

Optical Properties of Ag and Au Nanoparticles Dispersed within the Pores of Monolithic Mesoporous Silica

The optical absorption of silver and gold nanoparticles dispersed within the pores of monolithic mesoporous silica upon annealing at elevated temperatures has been investigated. With decreasing particle size, the surface plasmon resonance position of the particles blue-shifts first and then red-shifts for silver/silica samples, but only red-shifts for gold/silica samples. This size evolution of the resonance position is completely different from that previously reported for fully embedded particles. We assume a local porosity at the particle/matrix interface, such that free surface of particles within the pores may be in contact with ambient air, and present a two-layer core/shell model to calculate the optical properties. These calculations also consider deviations from the optical constants of bulk matter to account for corresponding effects below about 10 nm particle size. From the good agreement between experimental results and model calculations, we conclude a peculiar particle/ambience interaction dominating the size evolution of the resonance. Because of the difference of core electron structure, the relative importance of the effects of local porosity and free surface, respectively, are different for silver and gold. For silver, the effect of the local porosity is stronger, but for gold the opposite is found.     

Enhanced blue emission from ZnS–ZnO composites confined in SBA-15

A new optical material, the ZnO nanoparticles that are modified with ZnS and confined in SBA-15, has been prepared through the controllable sulfuration at relatively low temperature (40 °C) from the ZnO/SBA-15 composites. The precursor composites can be prepared through a novel path in which the zinc is well dispersed by directly grinding zinc nitrate into the as-synthesized SBA-15 occluded with template followed by calcination, and it is possible to control the conversion of ZnO to ZnS by adjusting the reaction time. The resulting samples are characterized by XRD, nitrogen adsorption–desorption and photoluminescence (PL) spectroscopy. ZnO–ZnS composites, mainly confined in the mesopore of SBA-15, exhibit dramatically enhanced blue emission at the expense of the UV emission.     

Mesoporous titania films investigated by positron annihilation based on a slow positron beam

Tunable mesoporous titania (TiO₂) thin films were synthesized via a sol-gel method using an amphiphilic triblock copolymer F38 as the structural template. The dependence of crystalization, pore morphology and interconnectivity of TiO₂ films on the weight ratio of F38 was studied by wide-angle X-ray diffraction, field emission scanning electron microscopy and Doppler broadening of positron annihilation radiation spectroscopy based on a slow positron beam. By loading more F38, the crystallization of TiO₂ films is enhanced, accompanied by a decrement in oxygen vacancies/grain boundaries. Smaller and isolated mesopores are formed in the films prepared with F38 less than 15?wt%. The pore percolation occurs when the weight ratio of F38 is up to 20?wt% and larger and interconnected worm-like pores are formed.     

Emulsion Combustion and Flame Spray Synthesis of Zinc Oxide/Silica Particles

Two flame spray methods, emulsion combustion method (ECM) and flame spray pyrolysis (FSP), were compared for synthesis of pure and mixed SiO₂ and ZnO nanoparticles. The effect of silicon precursor was investigated using liquid hexamethyldisiloxane (HMDSO) or SiO₂ sol, while for ZnO zinc acetate (ZA) was used. Gas phase reaction took place when using HMDSO as Si precursor, forming nanoparticles, whereas the SiO₂ sol used as Si source was not evaporated in the flame, creating large aggregates of the sol particles (e.g. 1 m). The FSP of ZA produced ZnO homogeneous nanoparticles. Lower flame temperatures in ECM than in FSP resulted in mixed gas and liquid phase reaction, forming ZnO particles with inhomogeneous sizes. The FSP of HMDSO and ZA led to intimate gas-phase mixing of Zn and Si, suppressing each other's particle growth, forming nanoparticles of 19 nm in BET-equivalent average primary particle diameter. Nucleation of ZnO and SiO₂ occurred independently by ECM of HMDSO and ZA as well as by FSP of the SiO₂ sol and ZA, creating a ZnO and SiO₂ mixture. The reaction of ZnO with SiO₂ was likely to be enhanced by ECM of the SiO₂ sol and ZA where both Zn and Si species were not evaporated completely, resulting in ZnO, -willemite and Zn_1.7SiO₄ mixed phase.     

溶胶-凝胶法制备纳米多孔SiO2薄膜

以正硅酸乙酯(TEOS)为原料，采用旋转涂敷的方法，结合溶胶-凝胶技术在硅衬底上制备超低介电常数多孔SiO₂薄膜.采用两种不同的改性方法对薄膜表面进行改性，傅里 叶变换红外光谱分析发现改性后薄膜中含有大量的—CH₃键，从而减少了孔洞塌陷.用扫 描电子显微镜观察薄膜的表面形貌，发现薄膜内孔洞尺寸在70—80 nm之间.调节溶胶pH值，发现pH值越小凝胶时间越长.对改性样品热处理的结果表明，在300 ℃时介电常数最低达2.05. 关键词： 2')" href="#">多孔SiO₂ 低介电常数 溶胶-凝胶