Reinforcement of SC-15 epoxy with CNT/CNF under high magnetic field: an investigation of mechanical and thermal response

We report here reinforcement of SC-15 epoxy matrix with 1.0 wt% loading of carbon nanotubes (CNTs)/carbon nanofibers (CNFs), and cured under a high (28 T) magnetic field. The improvement in mechanical properties such as compressive strength and stiffness was phenomenal with CNT inclusion, about 126% and 166% increase in strength and modulus, respectively. Enhancement in the glass transition (T _g) and thermal decomposition temperatures was also significant, by about 30 and 23 °C, respectively. Although the degree of anisotropy introduced by the magnetic field was not significant, it was observed that almost half of the improvement was due to magnetic flocculation. In the following is described the results of initial experiments conducted in the National High Magnetic Field Laboratory (NHMFL). Enhanced properties of the nanocomposites strongly suggest improved ordering of nanoparticles within the matrix.     

Effect of particle size and weight fraction on the flexural strength and failure mode of TiO2 particles reinforced epoxy

Effect of inclusions size and weight fraction on flexural strength and failure mode of composite containing SC-15 epoxy resin and TiO₂ particles has been studied in this investigation. The sizes of particles varied from macro (0.02 mm) to nano (5 nm) scale, and these particles were infused into the part-A of SC-15 through sonic cavitations and then mixed with part-B of SC-15 by using a high speed mechanical agitator. Three-point bending tests were performed on unfilled, 0.5 wt.%, 1.0 wt.% and 1.5 wt.% particles filled SC-15 epoxy to identify the loading effect on mechanical properties of the composites. Results show that 1.0 wt.% nanoparticles reinforced epoxy exhibit the highest mechanical performance. Higher than 1.0%, strength of composite decreased because of poor dispersion. Experimental results also shown that micro-sized particles have little effect on strength of epoxy at such low loading, and strength of composite increased as the size of particles decreased to nano scale. However, degradation in strength was found in 5 nm TiO₂/epoxy system due to agglomeration.     

Effect of magnetic nanoparticles on the properties of magnetic rubber

A new kind of magnetic rubber was prepared through conventional rubber mixing techniques on a two-roll mill, in which the magnetic filler was Fe₃O₄ nanoparticles and was surface modified. The effect of Fe₃O₄ nanoparticles’ content on the mechanical and magnetic properties of nature rubber was further investigated. The obtained results of six different compositions for nature rubber with 0, 5, 10, 15, 20 and 25 phr of Fe₃O₄ nanoparticles were compared. It was found that the magnetic rubber has higher magnetic properties and tensile strength, comparing with unfilled nature rubber. The result suggests that when the magnetic filler is nanoparticles and surface modified, the mechanical and magnetic properties of the rubber can be synchronously improved, which is difficult to be observed in previous work.     

Facile attachment of magnetic nanoparticles to carbon nanotubes via robust linkages and its fabrication of magnetic nanocomposites

Magnetic nanoparticles were facilely attached to multi-walled carbon nanotubes (MWCNTs) by high-temperature reaction of ferric triacetylacetonate in 1-methyl-2-pyrrolidone in the presence of carboxylated MWCNTs. X-ray diffraction, transmission electron morphology and thermogravimetric analysis were used to demonstrate the successful attachment of iron oxide nanoparticles to MWCNTs. It was found that the attached nanoparticles were mainly magnetite. Investigations using Fourier transform infrared spectroscopy proved that the tight attachment was due to the robust linkages: metal-carbonyl coordination. Modified carbon nanotubes were introduced into epoxy resins to fabricate magnetic nanocomposites. Magnetic properties were analyzed by vibrating sample magnetometer.     

Ultrasonic-assisted synthesis and magnetic studies of iron oxide/MCM-41 nanocomposite

Iron oxide nanoparticles were stabilized within the pores of mesoporous silica MCM-41 amino-functionalized by a sonochemical method. Formation of iron oxide nanoparticles inside the mesoporous channels of amino-functionalized MCM-41 was realized by wet impregnation using iron nitrate, followed by calcinations at 550 °C in air. The effect of functionalization level on structural and magnetic properties of obtained nanocomposites was studied. The resulting materials were characterized by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy and selected area electron diffraction (HRTEM and SAED), vibrating sample and superconducting quantum interface magnetometers (VSM and SQUID) and nitrogen adsorption–desorption isotherms measurements. The HRTEM images reveal that the most of the iron oxide nanoparticles were dispersed inside the mesopores of silica matrix and the pore diameter of the amino-functionalized MCM-41 matrix dictates the particle size of iron oxide nanoparticles. The obtained material possesses mesoporous structure and interesting magnetic properties. Saturation magnetization value of magnetic iron oxide nanopatricles stabilized in MCM-41 amino-functionalized by in situ sonochemical synthesis was 1.84 emu g⁻¹. An important finding is that obtained magnetic nanocomposite materials exhibit enhanced magnetic properties than those of iron oxide/MCM-41 nanocomposite obtained by conventional method. The described method is providing a rather short preparation time and a narrow size distribution of iron oxide nanoparticles.     

Effect vapor grown carbon nanofiber on thermal and mechanical properties of epoxy

In the present investigation, dynamic mechanical analysis (DMA), thermo gravimetric analysis (TGA), tensile tests, fatigue tests and the single edge notch tensile (SENT) tests were performed on unfilled, 1, 2 and 3 wt.% vapor grown carbon nanofiber (CNF) filled SC-15 epoxy to identify the loading effect on thermal and mechanical properties of the composites. DMA studies revealed that filling the 3% carbon nanofiber into epoxy can produce 65% enhancement in storage modulus at room temperature and 6 °C increase in T _g. However, TGA results show that thermal stability of composite is insensitive to the CNF content. Tensile tests were carried out at the strain rate range from 0.02 min⁻¹ to 2 min⁻¹. Results show that CNF/epoxy are strain rate sensitive materials, the modulus and tensile strength increased with increasing of strain rate. Experimental results also indicate that modulus of the nanophased epoxy increases continuously with increasing CNF content. But the 2% CNF infusion system exhibit maximum enhancement in tensile strength, fatigue performance and fracture toughness as compared with other system.     

An investigation of anisotropy of cobalt-surface-modified ironoxide magnetic particles

Surface treatment experiments on nonstoichiometric iron oxide are described, along with a theoretical analysis which suggests that the uniaxial anisotropy of cobalt-surface-modified iron oxide particles is not induced by the magnetic field of the inner core of iron oxides, but rather is due to the shape anisotropy being larger than the magnetocrystalline anisotropy of imperfectly crystallized CoFe₂ O₄. It is concluded that the crystalline imperfection of CoFe₂O₄ on the outer layer of iron oxides particles decreases the magnetocrystalline anisotropy and limits the enhancement rate of the coercivity of cobalt-surface-treated iron oxide particles     

混合型固化剂对环氧树脂室温和低温力学性能的影响

研究了一种刚性和柔性胺混合型固化剂（芳香胺DETD和聚醚胺D-400）固化环氧树脂浇铸体的力学性能、材料断裂表面的微观形貌和玻璃化转变温度等性能。结果表明:当D-400加入量占固化剂总量的40%时,其室温拉伸强度呈现最大值,为82.52 MPa,弹性模量为2.30 GPa,与未加D-400的体系相比分别提高了6.3%和14.4%,其低温冲击强度提高了14%。对冲击断面形貌进行扫描电子显微分析表明:D-400的加入致使断口形貌变得粗糙,抗开裂能力得到提高。热分析实验结果显示,体系的玻璃化转变温度随着D-400含量的增加而降低。此外,还探讨了环氧树脂体系低温增韧机制。      

Fe-Si磁性颗粒/环氧树脂复合材料的冲击和磁学性能

采用双酚A型WSR-615和缩水甘油胺型AG-80环氧树脂为基体,以Fe-Si磁性颗粒为填料,通过热压成型方法制备了高含量磁性Fe-Si颗粒/环氧树脂复合材料。研究了环氧树脂基体的玻璃化温度和冲击强度及Fe-Si磁性颗粒含量对Fe-Si/环氧树脂复合材料的冲击强度和磁化强度的影响及温度敏感性。研究结果表明：随着磁性颗粒含量的增加,Fe-Si/环氧树脂复合材料的冲击强度和磁性能增加。当磁性颗粒体积分数由54 vol%增加到66 vol% 时,Fe-Si/环氧树脂的冲击强度和饱和磁化强度分别由4.03 kJ/m²和162.07 emu/g增加到7.16 kJ/m²和175.04 emu/g。Fe-Si/环氧复合材料在-60 ℃~140 ℃ 范围内的温度敏感性低,符合实际应用对复合材料稳定性的要求。     

Fabrication and characterization of carbon fiber reinforced clay/epoxy composite

In this study, dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and flexural tests were performed on unfilled, 1, 2, 3, and 4 wt% clay filled SC-15 epoxy to identify the effect of clay weight fraction on thermal and mechanical properties of the epoxy matrix. The flexural results indicate that 2.0 wt% clay filled epoxy showed the highest improvement in flexural strength. DMA studies also revealed that 2.0 wt% system exhibit the highest storage modulus and T _g as compared to neat and other weight fraction. However, TGA results show that thermal stability of composite is insensitive to the clay content. Based on these results, the nanophased epoxy with 2 wt% clay was then utilized in a vacuum assisted resin transfer molding set up with carbon fabric to fabricate laminated composites. The effectiveness of clay addition on thermal and mechanical properties of composites has been evaluated by TGA, DMA, tensile, flexural, and fatigue test. 5 °C increase in glass transition temperature was found in nanocomposite, and the tensile and flexural strengths improved by 5.7 and 13.5 %, respectively as compared to the neat composite. The fatigue strength was also improved significantly. Based on the experimental result, a linear damage model combined with the Weibull distribution function has been established to describe static failure processing of neat and nanophased carbon/epoxy. The simulated stress–strain curves from the model are in good agreement with the test data. Simulated results show that damage processing of neat and nanophased carbon/epoxy described by bimodal Weibull distribution function.     

Cellular uptake of protein-bound magnetic nanoparticles in pulsed magnetic field

A method for fast delivery of proteins conjugated to superparamagnetic iron oxide nanoparticles (SPION) into mammalian cells by applying a strong magnetic field in pulses was proposed. Firstly, SPION were prepared from an alkaline solution of divalent and trivalent iron ions and covalently bound with protein through the activation of N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC). After fluorescently labelling, the protein-nanoparticle conjugate was mixed with mammalian cell line and exposed to a pulsed magnetic field for short durations of few milliseconds. Results suggested that superparamagnetic nanoparticles were able to carry proteins into living cells immediately. Cellular internalization of the fluorescently labelled protein-nanoparticle conjugate was proved by the observation of cell fluorescence in a fluorescent microscopy, as well as cell analysis by a flow cytometer. We found that the cellular uptake was accomplished dominantly by the process of bombardment of magnetic nanoparticles.     

石墨烯-多壁碳纳米管协同增强环氧树脂复合材料的低温力学性能

为了提高环氧树脂的低温力学性能,采用石墨烯与多壁碳纳米管(MWCNTs)协同改性环氧树脂,系统研究了石墨烯-MWCNTs/环氧树脂复合材料的室温(RT)和低温(77K)力学性能。结果表明:当石墨烯的质量分数为0.1wt%,MWCNTs的质量分数为0.5wt%时,纳米填料的加入可同时改善环氧树脂的低温拉伸强度、弹性模量和冲击强度;在此最佳含量下,石墨烯-MWCNTs/环氧树脂复合材料在RT和77K时的拉伸强度皆达到最大值,比纯环氧树脂的拉伸强度分别提高了11.04%和43.78%。石墨烯和MWCNTs能协同提高环氧树脂的低温力学性能。     

Core-shell iron-iron oxide nanoparticles synthesized by laser-induced pyrolysis

Passivated iron nanoparticles (10-30 nm) have been synthesized by laser pyrolysis of a mixture of iron pentacarbonyl and ethylene vapors followed by controlled oxidation. The nanoparticles show a well-constructed iron-iron oxide core-shell structure, in which the thickness and nature (structure similar to maghemite, gamma-Fe2O3) of the shell is found to be independent of the initial conditions. On the other hand, the composition of the core is found to change with the particle size from the alpha-Fe structure to a highly disordered Fe phase (probably containing C atoms in its structure). The dependence of the magnetic properties on the particle size, iron oxide fraction, and temperature was also investigated. In the case of smaller particles, the magnetic data indicate the existence at low temperature of a large exchange anisotropy field, the magnitude of which increases with decreasing temperature in correspondence with the freezing of magnetic moments in the oxide shell.     

LHRH-functionalized superparamagnetic iron oxide nanoparticles for breast cancer targeting and contrast enhancement in MRI

This paper shows that superparamagnetic iron oxide nanoparticles (SPIONs) conjugated to luteinizing hormone releasing hormone (LHRH) (LHRH–SPIONs), can be used to target breast cancer cells. They also act as contrast enhancement agents during the magnetic resonance imaging of breast cancer xenografts. A combination of transmission electron microscopy (TEM) and spectrophotometric analysis was used in our experiments, to investigate the specific accumulation of the functionalized superparamagnetic iron oxide nanoparticles (SPIONs) in cancer cells. The contrast enhancement of conventional T2 images obtained from the tumor tissue and of breast cancer xenograft bearing mice is shown to be much greater than that in saline controls, when the tissues were injected with LHRH–SPIONs. Magnetic anisotropy multi-CRAZED images of tissues extracted from mice injected with SPIONs were also found to have enhanced MRI contrast in breast cancer xenografts and metastases in the lungs.     

Characterization of the biocompatible magnetic colloid on the basis of Fe3O4 nanoparticles coated with dextran, used as contrast agent in magnetic resonance imaging

The magnetic resonance imaging contrast agent, the so-called Endorem colloidal suspension on the basis of superparamagnetic iron oxide nanoparticles (mean diameter of 5.5 nm) coated with dextran, were characterized on the basis of several measurement techniques to determine the parameters of their most important physical and chemical properties. It is assumed that each nanoparticle is consisted of Fe3O4 monodomain and it was observed that its oxidation to gamma-Fe2O3 occurs at 253.1 degrees C. The M?ssbauer spectroscopy have shown a superparamagnetic behavior of the magnetic nanoparticles. The Magnetic Resonance results show an increase of the relaxation times T1, T2, and T2* with decreasing concentration of iron oxide nanoparticles. The relaxation effects of SPIONs contrast agents are influenced by their local concentration as well as the applied field strength and the environment in which these agents interact with surrounding protons. The proton relaxation rates presented a linear behavior with concentration. The measured values of thermo-optic coefficient dn/dT, thermal conductivity kappa, optical birefringence delta n0, nonlinear refractive index n2, nonlinear absorption beta' and third-order nonlinear susceptibility |chi(3)| are also reported.     

Dominant dipolar interaction and glassy magnetic behaviour in polymer-coated magnetite nanoparticles

The static and dynamic properties of magnetization have been investigated for polymer-coated magnetite nanoparticles with sizes from 5 to 15?nm. The analysis of the temperature dependence of zero-field-cooled magnetization indicates that the effective anisotropy constant is found to increase with the decrease of particle size, which is ascribed to the increase of surface anisotropy. The relaxation of the remanent magnetization clearly shows the signature of dominant dipolar interparticle interaction. The dynamics of magnetization also indicates the signature of glassy magnetic behaviour. The memory effect in the temperature dependence of field-cooled magnetization is noticed, which is inconsistent with the glassy magnetic behaviour.     

Microstructural evolution and magnetic properties of pressureless-sintered nanosized iron prepared by a facile combustion-based route

High-activity iron nanopowders were prepared through a facile combustion-based route, combining solution combustion synthesis and hydrogen reduction. The as-synthesized iron nanopowders were densified by pressureless sintering. The densification behavior, microstructure, mechanical properties and magnetic properties of the iron bulk sintered at different temperatures were studied in detail. At a low sintering temperature of 700 °C, the relative density of the sintered iron reaches 97.3%, because the iron nanopowders exhibit a low sintering activation energy of 123 KJ/mol. The iron bulk sintered at 700 °C exhibits relatively regular equiaxed grains with an average grain size of 0.45 μm, and has a maximum tensile strength of 510.1 MPa, a high microhardness of 201.9 HV, and a saturation induction of 1.75 T. As the sintering temperature increases, the grain size and magnetic properties of the sintered iron enhance, while the mechanical strength decreases. For the sintered iron prepared at 1300 °C with the average grain size ~ 80.9 μm, the saturation induction value reaches 1.78 T and the tensile strength is 334.9 MPa.     

Size reduction of WO3 nanoparticles by ultrasound irradiation and its applications in structural nanocomposites

The porous WO₃ (pore size 2–5 nm) nanoparticles were synthesized using a high intensity ultrasound irradiation of commercially available WO₃ nanoparticles (80 nm) in ethanol. The high resolution transmission electron microscopic (HRTEM) and X-ray studies indicated that the 2–5 nm uniform pores have been created in commercially available WO₃ nanoparticles without much changing the initial WO₃ nanoparticles (80 nm) sizes. The nanocomposites of WO₃/SC-15 epoxy were prepared by infusion of 1 wt.%, 2 wt.% and 3 wt.% of porous WO₃ nanoparticles into SC-15 epoxy resin by using a non-contact (Thinky) mixing technique. Finally the neat epoxy and nanocomposites were cured at room temperature for about 24 h in a plastic rectangular mold. The cured epoxy samples were removed and precisely cut into required dimensions and tested for their thermal and mechanical properties. The HRTEM and SEM studies indicated that the sonochemically modified porous WO₃ nanoparticles dispersed more uniformly over the entire volume of the epoxy (without any settlement or agglomeration) as compared to the unmodified WO₃/epoxy nanocomposites.     

In situ synthesis and magnetic studies of iron oxide nanoparticles in calcium-alginate matrix for biomedical applications

In this work we applied a new route to synthesize magnetic iron oxide nanoparticles into alginate polymer for future application as drug delivery system activated by magnetic external stimuli. Calcium-alginate was used to encapsulate iron oxide nanoparticles, and as scaffold for particle nucleation and its influence on particles size and magnetic properties were studied. The iron oxide mean sizes were between 4.3 and 9.5 nm. Iron is dispersed throughout the polymer matrix mainly as iron oxide particles, and a small fraction as iron (III) occupying calcium sites in the polymer network. The temperature dependence of the Mössbauer spectra is typical of superparamagnetic particles in agreement with the magnetic susceptibility data.     

Influence of ultrasonic dual mixing on thermal and tensile properties of MWCNTs-epoxy composite

Multiwalled carbon nanotubes (MWCNTs) reinforced epoxy based composites were fabricated by using an innovative ultrasonic dual mixing (UDM) process consists of ultrasonic mixing with simultaneous magnetic stirring. The effect of addition of varying amount of MWCNTs on thermal stability and tensile properties of the epoxy based composite has been investigated. It is found that the thermal stability, tensile strength and toughness of the epoxy base improves with the increase of MWCNTs addition up to 1.5 wt.% and UDM processing at certain capacity of the system. Tensile tests and thermal gravimetric analysis (TGA) were performed on each group of composites containing different amount of MWCNTs to determine their mechanical and thermal properties respectively. The dispersion of 1.5 wt.% MWCNTs fillers in epoxy nanocomposites was studied by transmission electron microscopy (TEM) as well as by field emission scanning electron microscopy (FESEM) applied on their tensile fracture surface.