Effective thermal conductivity of CdS/ZnS nanoparticles embedded polystyrene nanocomposites

CdS/PS and ZnS/PS nanocomposites have been prepared by solution casting method with different wt% of cadmium sulphide (CdS) and zinc sulphide (ZnS) nanoparticles and characterized through X-ray diffraction and transmission electron microscope measurements. The effective thermal conductivity of polymer nanocomposites has been measured by transient plane source method over the temperature range from room to 150 °C. The experimental results showed that the thermal conductivity has been found to increase up to 4 wt% of CdS/ZnS nanoparticles and then decrease for 6 and 8 wt% of nanoparticles.     

In-situ constructing visible light CdS/Cd-MOF photocatalyst with enhanced photodegradation of methylene blue

Based on high specific surface area, high porosity of metal-organic frameworks (MOFs) and excellent visible light response of CdS, the CdS/Cd-MOF nanocomposites were constructed by in-situ sulfurization to form CdS using Cd-MOF as precursor and the CdS loading was controlled by the dose of thioacetamide. Under the irradiation of simulated sunlight, the degradation rate of methylene blue (MB) by 10 mg MOF/CdS-6 (mass ratio of MOF to thioacetamide is 6:1) was 91.9% in 100 min, which was higher than that of pure Cd-MOF (62.3%) and pure CdS (67.5%). This is attributed to the larger specific surface area of the composite catalysts, which provides more active sites. Meanwhile, the loading of CdS obviously broadens the light response range of Cd-MOF and improves the utilization of visible light. The Mott-Schottky model experiment shows that the formed type-II heterojunction between Cd-MOF and CdS can effectively inhibit the recombination of photogenerated electrons and holes. Meanwhile, the photocurrent intensity of MOF/CdS-6 is 8 times and 2.5 times of that of pure Cd-MOF and CdS. In addition, MOF/CdS-6 showed good photocatalytic performance after five cycles, showing excellent stability and reusability.     

Stress–softening effect of SBR/nanocomposites by a phenomenological Gent–Zener viscoelastic model

An experimental study of a tensile loading–unloading procedure, as well as multi-cyclic response in a strain-controlled program of a Styrene-Butadiene (SBR) elastomer reinforced with four different weight fractions of carbon nanotubes (CNTs) has been performed. The Mullins effect features, namely hysteresis, damage and residual strain, exhibited by the SBR/nanocomposites were analyzed by a modified Gent–Zener rheological model, and a damage function. Especially for the multi-cyclic stress–strain curves, phenomenological equation of the model parameters evolution with strain were also introduced. The same loading procedure was applied in pre-stressed materials, revealing a different stress–strain response due to strain prehistory. The model has been proven to accurately capture the loading–unloading behavior, the residual strain, hysteresis loops as well as the multi-cyclic behavior of the SBR/CNT nanocomposites.     

Linear viscoelasticity of styrenic block copolymers–clay nanocomposites

In this work, the rheological behavior of block copolymers with different morphologies (lamellar, cylindrical, spherical, and disordered) and their clay-containing nanocomposites was studied using small amplitude oscillatory shear. The copolymers studied were one asymmetric starblock styrene–butadiene–styrene copolymer and four styrene–ethylene/butylenes–styrene copolymers with different molecular architectures, one of them being modified with maleic anhydride. The nanocomposites of those copolymers were prepared by adding organophilic clay using three different preparation techniques: melt mixing, solution casting, and a hybrid melt mixing–solution technique. The nanocomposites were characterized by X-ray diffraction and transmission electron microscopy, and their viscoelastic properties were evaluated and compared to the ones of the pure copolymers. The influence of copolymer morphology and presence of clay on the storage modulus (G′) curves was studied by the evaluation of the changes in the low frequency slope of log G′× logω (ω: frequency) curves upon variation of temperature and clay addition. This slope may be related to the degree of liquid- or solid-like behavior of a material. It was observed that at temperatures corresponding to the ordered state, the rheological behavior of the nanocomposites depended mainly on the viscoelasticity of each type of ordered phase and the variation of the slope due to the addition of clay was small. For temperatures corresponding to the disordered state, however, the rheological behavior of the copolymer nanocomposites was dictated mostly by the degree of clay dispersion: When the clay was well dispersed, a strong solid-like behavior corresponding to large G′ slope variations was observed.     

Morphological and rheological properties of PET/clay nanocomposites

This work investigates the effects of clay chemistry and concentration on the morphology and rheology of polyethylene terephthalate (PET)/clay nanocomposites. The complex viscosity of the PET nanocomposites exhibited a more solid-like behavior, in contrast to the matrix that had a frequency-independent viscosity. In addition, at high frequencies where the behavior of the matrix should be dominant, a lower complex viscosity of the nanocomposites was observed due to PET degradation in the presence of the organoclays. The high-frequency data were used to estimate the matrix degradation using the Maron–Pierce equation. The apparent molecular weight of the PET matrix was found to decrease from 65 kg/mol for the neat PET to 30 kg/mol for a PET nanocomposite containing 8 wt% Cloisite®; 30B. The apparent yield stress in the nanocomposites was determined using the Herschel–Bulkley model. Yield stress increased with the level of exfoliation and clay concentration, from ～0 to 166 Pa when the clay concentration increased from 2 to 8 wt%.     

Investigation of nanomechanical properties of multilayered hybrid nanocomposites

Nanocomposites manufactured by combining two nano-structured phases are quite rare. While industry is seeking materials to meet difficult challenges with unique properties, there is no “rule of mixtures” to identify how to mix multiple nanomaterials in a composite structure and make available all required properties. Filler–matrix adhesion and its relation to materials’ properties have been the subject of continuing study due to composites advanced applications. Further on, studies at the interphase created in the area between the constituent materials can provide important information concerning materials interaction and composites behavior; this issue becomes even more interesting when discussing about nano-interphases. In the present investigation, a study of multi-layered nanocomposites is conducted. More precisely, the following four different types of multilayered hybrid nanocomposites were manufactured and tested: Pure titanium–carbon nanotubes–epoxy; pure titanium–epoxy–carbon nanotubes; titanium dioxide nanotubes–carbon nanotubes–epoxy and titanium dioxide nanotubes–epoxy–carbon nanotubes. The nano-mechanical properties of the above-mentioned nanocomposites were investigated using nanoindentation technique. The main conclusion of the present work is that in the case of multilayered nanocomposites, even if nanoindentation is executed on the surface of the same material, results greatly depend on the underlying substrates’ nature and their stacking sequence. Also, nano-interphases created at the contact surfaces between different layers affect the experimentally measured values of the nanomechanical properties (Young’s modulus and hardness) of multilayered nanocomposites.     

The effects of the interphase and strain gradients on the elasticity of layer by layer (LBL) polymer/clay nanocomposites

A synergistic stiffening effect observed in the elastic mechanical properties of LBL assembled polymer/clay nanocomposites is studied via two continuum mechanics approaches. The nanostructure of the representative volume element (RVE) includes an effective interphase layer that is assumed to be perfectly bonded to the particle and matrix phases. An inverse method to determine the effective thickness and stiffness of the interphase layer using finite element (FE) simulations and experimental data previously published in Kaushik et al. (2009), is first illustrated. Next, a size-dependent strain gradient Mori–Tanaka (M–T) model (SGMT) is developed by applying strain gradient elasticity to the classical M–T method. Both approaches are applied to LBL-assembled polyurethane–montmorillonite (PU–MTM) clay nanocomposites. Both two-dimensional (2D) and three-dimensional (3D) FE models used in the first approach are shown to be able to accurately predict the stiffness of the PU–MTM specimens with various volume fractions. The SGMT model also accurately predicts the experimentally observed increase in stiffness of the PU–MTM nanocomposite with increasing volume fraction of clay. An analogy between the strain gradient effect and the role of an interphase in accounting for the synergistic elastic stiffening in nanocomposites is provided.     

Photoelectrochemical glucose biosensor incorporating CdS nanoparticles

A novel photoelectrochemical biosensor incorporating nanosized CdS semiconductor crystals with enzyme to enhance photochemical reaction has been investigated. CdS nanoparticles were synthesized by using dendrimer PAMAM as inner templates. The CdS nanoparticles and glucose oxidase （GOD） were immobilized on Pt electrode via layer-by-layer （LbL） technique to fabricate a biological-inorganic hybrid system. Under ultraviolet light, the photo-effect of the CdS nanoparticles showed enhancement of the biosensor to detect glucose. Pt nanoparticles were mixed into the Nation film to immobilize the CdS/enzyme composites and to improve the charge transfer of the hybrid. Experimental results demonstrate the desirable characteristics of this biosensing system, e,g. a sensitivity of 1.83 μA/（mM cm^2）, lower detection limit （1 μM）, and acceptable reproducibility and stability,     

室温离子液体介质中CdS纳米微粒的制备及其摩擦磨损行为研究

合成了1-甲基-3-己基咪唑四氟硼酸盐离子液体,并以此为反应介质通过有机金属化合物热分解法制备出CdS纳米微粒,采用X射线粉末衍射仪和透射电子显微镜对CdS纳米微粒的结构和形貌进行表征,在四球摩擦磨损试验机上考察了含CdS纳米微粒离子液体的摩擦磨损行为．结果表明：所制备的CdS纳米微粒具有六方相结构,粒径均一,约为15nm;含CdS纳米微粒离子液体的减摩抗磨性能明显优于纯离子液体;CdS纳米微粒以滚动／滑动方式起到了减摩抗磨作用,同时可以加速离子液体中阴离子的分解,促进FeF2和FeF3的形成,使复合体系的减摩抗磨性能有所提高．     

MoO3-ZnO/镍基复合涂层制备及其摩擦学性能研究

利用等离子喷涂工艺制备了含氧化物(MoO₃-ZnO)的镍基复合涂层,通过UMT-3球盘式高温摩擦试验机评价了复合涂层在室温、400和800 ℃下的摩擦学性能,并采用扫描电镜(SEM)、能谱分析仪(EDS)、X射线衍射仪(XRD)以及拉曼光谱仪(Raman)等分析手段研究了涂层微观组织、物相组成以及磨损机理. 结果表明:在室温和400 ℃,复合涂层的摩擦系数和磨损率均高于Ni-5%Al金属基底,且随着氧化物含量的增加,润滑和耐磨性能均被削弱,主要表现为磨粒磨损和黏着磨损. 在800 ℃,MoO₃和ZnO的添加可以有效改善复合涂层的摩擦性能,随着其含量的增加,摩擦系数变化不明显,而磨损率逐渐增加. 特别是添加5%MoO₃和5%ZnO的复合涂层在800 ℃摩擦系数低至0.28,磨损率低至4.22×10?5 mm3/(N·m),其良好的高温润滑耐磨性能得益于摩擦表面二元氧化物(NiO、MoO₃和ZnO)和三元氧化物(ZnMoO₄和NiMoO₄)的协同作用.      

Compressive properties of epoxidized soybean oil/clay nanocomposites

High- and low strain-rate compression experiments were conducted on epoxidized soybean oil (ESO)/clay nanocomposites with nanoclay weights of 0%, 5%, and 8%. A pulse-shaped split Hopkinson pressure bar (SHPB) was employed to conduct high strain-rate experiments. The pulse shaping technique ensures nearly constant-strain-rate deformation under dynamically equilibrated stresses in specimens such that accurate stress–strain curves at various high rates were obtained. A MTS 810 hydraulically driven materials testing system was used to obtain low strain-rate stress–strain curves. Strain-rate and nanoclay weight effects on the compressive properties of the nanocomposites were experimentally determined. A phenomenological strain-rate-dependent material model was presented to describe the stress–strain response. The model agrees well with the experimental data at both large and small strains as well as high and low strain rates.     

Solvent-less synthesis of zinc oxide nanostructures from Zn(salen) as precursor and their optical properties

ZnO nanoparticles, 10–20 nm in size, were synthesized by heat treatment in air at 500 °C for 5 h., using [N,N′-bis(salicylaldehydo) ethylene diamine]zinc(II), i.e., Zn(salen), as precursor, which was obtained by a solvent-free solid–solid reaction. Heat-treated products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Room temperature photoluminescence spectra of ZnO nanostructures are dominated by green emission attributed to oxygen vacancy related donor–acceptor transition.     

Processing and characterization of biodegradable polymer nanocomposites: detection of dispersion state

Nanobiocomposites of poly(lactic acid) (PLA) with 3–5 wt% organically modified montmorillonite (OMMT) were prepared by melt compounding in two different mixers, miniature twin-screw extruder and internal batch mixer, leading to different degrees of dispersion. The progress of dispersion was characterized by melt rheology coupled with light attenuation. Processed PLA/OMMT samples showed percolating networks in the melt, detected by a step increase in low-frequency elastic moduli. The melt elasticity of nanocomposites increased, while the light attenuation coefficient and the loss tangent decreased progressively with mixing energy and reached saturation that can be attributed to the maximum level of clay dispersion achieved in the present experimental conditions. Results showed that a combination of low-frequency loss tangent and light attenuation coefficient provides a potentially sensitive method for the characterization of the degree of clay dispersion. The direct correlation between light attenuation coefficient and loss tangent follows linear dependence and may open an approach for the rapid inline analysis of the degree of dispersion in melt-processed nanocomposites.     

聚合物／无机纳米复合材料润滑油添加剂的摩擦学功能设计

选择3种具有不同抗磨性能的纳米组分,制备了具有不同界面特性的聚合物／无机纳米复合材料;考察了纳米复合材料的减摩抗磨性能和机理,探讨了关于纳米复合材料润滑油添加剂的摩擦学功能设计准则。结果表明：对聚合物与无机纳米组分界面进行设计优化后能明显提高纳米复合材料的摩擦学性能。实现聚合物与无机纳米组分界面的优化设计后,聚合物与无机纳米组分之间具有更好的相容性,无机纳米组分在聚合物基体中分布更均匀;当聚合物基体在摩擦热和剪切作用下熔融分解后,裸露出来的具有高活性的无机纳米组分可在摩擦副接触表面形成具有良好摩擦学性能的表面膜。     

Spectra of ZnO nanoparticles under low photon energy excitation

Time-integrated photoluminescence （PL） spectra between 1.2 and 2.25 eV of ZnO nanoparticles were observed at ambient temperatures when they were excited by a picosecond （ps） laser pulse at a low photon energy of 2.33 eV/532 rim, to show clear red shift when the excitation intensiW increased. Gaussian analysis shows that the red shift is due to increase of the relative magnitudes of the Gaussian combination in the low energy region. Temporal evolution of the dominant emissions exhibited a similar double-exponential decay process, in which the respective two distinct decay durations of 189 ps at the corresponding amplitude of 82% and 2081 ps at 18% were identified. Speculation based on the surfacestate emission due to the large surface-to-volume ratio of nanoscale materials is used to explain the phenomena.     

Enzyme–metal nanocomposites for antibacterial applications

Metal nanoparticles have been used as antibacterial agents widely, and the combined use of enzymes and metal nanoparticles promotes antibacterial activity, achieving a synergistic effect. Additionally, enzymes decrease the amounts of metals and increase biocompatibility, thereby reducing toxicity of metals. However, the efficiency of enzymes is hindered when coupled with metals, which causes deactivation in the function of enzymes. How can a balance be struck between metals and enzymes? Although the antibacterial mechanism of metal nanoparticles is relatively clear, how enzyme–metal nanocomposites work against bacteria is not conclusive. Here, we describe several examples on the synthesis of enzyme–metal nanocomposites via co-immobilization or in situ reduction and summarize how enzyme–metal nanocomposites combat microorganisms.     

Bonds between metals and nanocomposites created by explosion welding

This paper describes the study of the influence of a microstructure characterized by directed or chaotic distribution of nanoinclusions and strain rate on the deformability of nanocomposites. It is revealed that, under identical loading conditions, cracks are formed in nanocomposites whose structural elements are mostly directed in the same way at lower strain rates than in nanocomposites with chaotic distribution of the reinforcer. It is shown that, as the strain rate increases, the influence of the structural order on the limiting deformation reduces due to transition from shear strain to rotational strain. No cracks are formed in the creation of bonds between metals and nanocomposites by explosion welding. The experimental results obtained in the study of transverse bending of two-layer welded beams and the structure in the vicinity of the weld reveal that the obtained metal–nanocomposite bond has a uniform structure retained in deformation, with fracture occurring in the nanocomposite.     

Fractal Model of the Nanofiller Structure Affecting The Degree of Reinforcement of Polyurethane–Carbon Nanotube Nanocomposites

A percolation model of nanocomposite reinforcement is under study. It is shown that the degree of reinforcement of polyurethane–carbon nanotube nanocomposites depends on the structure of nanofillers, which are annular formations. This structure is most accurately characterized by its fractal dimension. It is established that the creation of a structure with negative percolation indices allows for a significant increase in the degree of reinforcement of considered nanocomposites at low nanofiller concentrations.     

Intensified photocatalytic degradation of nitrobenzene by Picketing emulsion of ZnO nanoparticles

In this paper, zinc oxide nanoparticles were first prepared and surface-modified. A Pickering emulsion was then prepared, consisting of nitrobenzene （oil phase）, water （water phase） and the modified zinc oxide nanoparticles located on the water-oil interface. The effects of different emulsions on the removal rate of nitrobenzene by photocatalytic degradation were studied. The results proved that use of a Pickering emulsion stabilized by surface-modified ZnO nanoparticles provides an effective and novel way to intensify the photocatalytic degradation of the organic contaminant.     

多壁碳纳米管/环氧树脂纳米复合材料的摩擦磨损性能研究

采用浇铸法,利用超声分散制备了多壁碳纳米管(MWNTs)/环氧树脂(EP)纳米复合材料,研究了MWNTs的添加量及分散程度对复合材料表面形貌和摩擦磨损性能的影响,并探讨了影响MWNTs/EP复合材料摩擦磨损性能的因素.结果表明:随着MWNTs加入量的提高(1%～4%),复合材料的摩擦系数和磨损率均呈现降低趋势,摩擦系数由0.60降到0.22,磨损率由1.11×10-4mg/(N·m)降为2.22×10-5mg/(N·m);在MWNTs添加量(1%)相同的情况下,MWNTs分散程度高的复合材料的摩擦性能更好.纯环氧树脂与45#钢对摩时发生粘着磨损和疲劳剥落,而由于MWNTs的增强和自润滑作用,MWNTs/EP复合材料的粘着磨损和疲劳剥落显著减轻.