Syndiotactic polystyrene/multi-walled carbon nanotube nanocomposites: Polymorphism,thermal properties,electrical conductivity,and rheological properties

Syndiotactic polystyrene (sPS)/multi-walled carbon nanotube (MWNT) nanocomposites were prepared using a melt mixing technique. SEM images demonstrated the fine dispersion of MWNTs through the sPS matrix. DSC results illustrated that the MWNTs facilitated the nucleation of sPS (up to ca. 12.2 °C increase), but retarded the subsequent crystals growth. Based on the Avrami analysis, the dimension of sPS crystals growth in the composites decreased because of the effects of extensive nucleation and the formation of a nanoconfined/constrained environment from the MWNTs. XRD data confirmed that the presence of MWNTs facilitated the formation of β-form sPS crystals. The thermal stability of sPS improved to approximately 31 °C at 3 phr of MWNT loading. A rheological percolation threshold between an MWNT loading of 0.5 and 1 phr was determined by measuring the rheological properties of the samples. The incorporation of MWNTs reduced the electrical resistivity of sPS by 10 orders of magnitude.     

Analysis of the electrical and rheological behavior of different processed CNF/PMMA nanocomposites

Carbon nanofiber (CNF)/poly(methyl methacrylate) (PMMA) nanocomposites were prepared via melt-compounding, solvent casting and in situ polymerization. Mechanical properties, rheological behavior and electrical resistivity were investigated in specimens with varying CNF loadings. The three processing techniques were compared. Improved properties were obtained in the solvent processed and in situ polymerized composites. The rheological and electrical percolation of these nanocomposites appeared in the same concentration set (between 1 and 5 wt%). No changes were found in melt-compounding, even by the addition of 10 wt% of CNFs. Electrical resistivity of the samples prepared by solvent casting was measured before and after pressing in the hot plate press. It is remarkable that in the non-pressed samples the CNFs formed an efficient 3-D conductive network, yielding composites with percolation thresholds even six orders of magnitude lower than after pressing, where this 3-D network was destroyed.     

原位聚合PA11/GO纳米复合材料的流变性能研究

采用原位聚合法制备了PA11(尼龙11)/GO(GO)纳米复合材料,并采用XLY-Ⅱ型毛细管流变仪研究了共混物的流变特性。结果表明:PA11及其复合材料均为假塑性流体,呈现切力变稀的现象;非牛顿指数n均小于1。随着GO含量的增加,PA11/GO纳米复合材料的表观黏度升高,粘流活化能下降,表明共混材料的表观黏度对温度的敏感性降低,易于加工成型。     

Investigation of the fracture mechanism and mechanical properties of polystyrene/silica nanocomposite in various silica contents

There is limited research on the effect of silica on the mechanical properties of polystyrene. For this lack of information, this study has focused on the fracture mechanism and mechanical properties of Polystyrene/silica nanocomposite. Transmission electron microscopy showed proper dispersion of nanoparticles in PS matrix in both low and high filler loadings. Scanning electron microscopy, TOM micrography, and non-contact surface profiler were used to study the fracture surface and fracture mechanism characteristics of the nanocomposite. It seems that the debonding mechanism is an important mechanism in toughening of Polystyrene/silica nanocomposites. In addition, mechanical behavior of the samples was investigated. Tensile, flexural, and compressive strength and also impact and plain-strain fracture toughness of nanocomposite samples showed different behaviors in low and high nanoparticle loadings and interestingly, we found an optimum value less than 2% for nanoparticle loading in which we observed the highest improvement in mechanical properties of the nanocomposite.     

Synthesis of multi-walled carbon nanotube/silica nanoparticle/polystyrene microsphere/polyaniline based hybrids for EMI shielding application

Novel polystyrene microsphere (PSMS)-based PSMS/Si and polystyrene/silica nanoparticle/multi-walled carbon nanotube (PS/Si/MWCNT) nanocomposite has been prepared using in situ sol-gel and chemical amalgamation methods. Aniline monomer was introduced by in situ route to form PSMS/PANI, PSMS/PANI/Si and PSMS/PANI/Si/MWCNT nanocomposite. FESEM of nanocomposite indicated core-shell spherical and tubular morphology. Glass transition temperature (T_g) and maximum decomposition temperature (T_max) of PSMS/PANI/Si/MWCNT nanocomposite were found as 295°C and 524°C, respectively, which were higher than the PSMS/PANI (T_g = 245°C; T_max = 387°C) and PSMS/PANI/Si (T_g = 257°C; T_max = 388°C) nanocomposite. For nanocomposite dispersion, tetrahydrofuran was studied as fine solvent. XRD depicted amorphous nature of PSMS/Si and PSMS/PANI/Si; however MWCNT reduced amorphous character of PSMS/PANI/Si/MWCNT. Electromagnetic interference (EMI) shielding effectiveness improved from 0.1 dB (PSMS) to 12.3 dB (PSMS/PANI/Si) to 24.5 dB (PSMS/PANI/Si/MWCNT). The increase in EMI shielding effectiveness was also observed with variation in log of conductivity from ?14 mho m^?1 (PSMA) to 1.17 mho m^?1 (PSMS/PANI/Si/MWCNT).     

LDPE/EVA/蒙脱土熔融插层纳米复合体系稳态剪切流变行为

用平行板和毛细管流变仪测定并研究了具有剥离结构的低密度聚乙烯(LDPE)／乙烯-醋酸乙烯共聚物(EVA)／蒙脱土纳米复合材料熔体的稳态剪切流变行为。研究结果表明,蒙脱土含量较低的复合物熔体,在低剪切速率下,即出现剪切变稀现象；而在较高剪切速率下,填充物浓度对体系熔体的剪切粘度影响较小；与基体树脂相比较,蒙脱土的加入,使其熔体的非牛顿指数降低,粘流活化能略有增加。     

Enhanced electrical conductivity in polystyrene nanocomposites at ultra-low graphene content

We compared the electrical conductivity of multiwalled-carbon-nanotube/polystyrene and graphene/polystyrene composites. The conductivity of polystyrene increases from ～6.7 × 10(-14) to ～3.49 S/m, with an increase in graphene content from ～0.11 to ～1.1 vol %. This is ～2-4 orders of magnitude higher than for multiwalled-carbon-nanotube/polystyrene composites. Furthermore, we show that the conductivity of the graphene/polystyrene system can be significantly enhanced by incorporation of polylactic acid. The volume-exclusion principle forces graphene into the polystyrene-rich regions (selective localization) and generates ～4.5-fold decrease in its percolation threshold from ～0.33 to ～0.075 vol %.     

Synthesis of polymaleimide/silica nanocomposites

Polymaleimide/Silica nanocomposites were synthesized from N--Triethoxysilylpropyl- maleamic acid (TESPMA) through sol-gel process, imidation reaction of the maleamic acid functional groups and thermal polymerization of the formed maleimide at elevated temperature. These nanocomposite materials were characterized by Fourier transform infrared analysis (FT-IR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and field emission scanning electron microscopy (FE-SEM). It was found that the inorganic networks chemically bound to polymaleimides enhanced the thermal stability of these nanocomposites greatly. Nevertheless, incorporation of colloidal silica did not make positive contributions to the thermal stability, although the weight fraction of the inorganic part in the composite was increased significantly.     

Thermophysical and rheological properties of certain biological fluids

The dependence of the thermophysical properties of blood on its physicochemical composition and rheological properties is determined. Measurements are carried out by the probe technique.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 3, pp. 467–472, September, 1977.     

Effective holographic recordings in the photopolymer nanocomposites with functionalized silica nanoparticle and polyurethane matrix

Effective holographic nanocomposites were developed by the surface-functionalized silica nanoparticles and two acrylate monomers/polyurethane (PU) matrix polymer. The functionalization was done with silane compounds carrying long alkyl chain or vinyl group. We evaluated the holographic nanocomposite films by the diffraction efficiency, volume shrinkage, optical loss, and the film morphology. It was found that acrylate monomers/PU system gave higher diffraction efficiency than those of two monomers due to the high refractive index mismatch between the acrylate-rich and PU-rich regions. With the modification of silica particle, up to 35% of particle loading was possible to give a maximum diffraction efficiency of 93.6% for a film of 20 μm in thickness, along with improved refractive index modulation and the sensitivity.     

聚酰亚胺/二氧化硅复合薄膜的热物性及其影响因素

应用自行研制的亚微米/微米薄膜激光脉冲法热扩散率测定仪和差示扫描量热仪(DSC)分别测定了聚酰亚胺(PI)薄膜和PI/SiO_2复合薄膜在不同温度下的热扩散率、热导率和比热,解决了激光脉冲法测定热导试样的透光问题.研究了PI/SiO_2复合薄膜的热物性随SiO_2添加量和温度的变化关系.结果表明:随着温度的升高,PI薄膜及PI/SiO_2复合薄膜的热扩散率下降,比热和热导率线性增加.在PI薄膜中添加SiO_2颗粒可降低PI薄膜的比热,明显增强导热性能,但是不会改变PI薄膜热导率随温度升高而增大的变化规律.     

蒙脱土含量对聚乙烯/蒙脱土纳米复合材料动态流变行为的影响

用有机蒙脱土(OMMT)/MgCl2负载TiCl4的Ziegler-Natta插层型催化剂,通过原位聚合法制备了具有不同MMT含量的PE/MMT纳米复合材料。利用DHR-Ⅱ型动态流变仪和熔融指数(MFI)仪分析了MMT含量对其动态流变行为和熔融指数的影响。结果表明,随MMT含量的增加,复合材料的储能模量(G')、损耗模量(G″)、复合粘度(η*)和粘流活化能(ΔEη*)先升高后降低且低于HDPE;熔融指数(MFI)和损耗因子(tanδ)先降低后升高且低于HDPE。相比于HDPE,MMT含量为4.58%的复合材料,在高频区域tanδ高于HDPE;MFI提高489%;ΔEη*降低22.4%,该性质有利于PE/MMT纳米复合材料的成型加工。     

Catalytic properties of silica/silver nanocomposites

The catalytic properties of silver nanoparticles supported on silica and the relation between catalytic activity of silver particles and the support (silica) size are investigated in the present article. The silver nanoparticles with 4 nm diameters were synthesized and were attached to silica spheres with sizes of 40, 78, 105 nm, respectively. The reduction of Rhodamine 6G (R6G) by NaBH4 was designed by using the SiO2/Ag core-shell nanocomposites as catalysts. The experimental results demonstrated that the catalytic activity of silica/silver nanoparticles depends on not only the concentration of catalysts (silver) but also the support silica size. Silver particles supported on small SiO2 spheres (approximately 40 nm) show high catalytic activity. Moreover, by making a comparison between the UV-vis spectra of the catalyst before and after the catalytic reaction, we found that the position of surface plasma resonance (SPR) peak of Ag nanoparticles changes little. The above results suggested that the size and morphology of silver particles were probably kept unchanged after the reduction of R6G and also implied that the catalytic activity of silver particles was hardly lost during the catalytic reaction.     

丁苯胶/甲基丙烯酸锌/气相法白炭黑纳米复合材料

制备了三相纳米复合材料SBR／ZDMA／气相法白炭黑。采用了两种气相法白炭黑,U—fumed silica是一种未改性的气相法白炭黑,M—fumed silica是一种采用硅烷偶联剂Si69表面改性的气相法白炭黑。主要研究了气相法白炭黑和ZDMA之间的协同补强效应。研究结果显示,单独添加同样份数的改性气相法白炭黑和未改性气相法白炭黑对硫化胶物理机械性能的影响不同,改性气相法白炭黑的效果明显优于未改性气相法白炭黑。单独添加气相法白炭黑,体系的物理机械性能仍然维持在较低值。当同时添加气相法白炭黑和ZDMA时,会观察到明显的协同补强效应。交联密度和丙酮抽出试验表明对气相法白炭黑进行表面改性和在体系中添加ZDMA均会减弱气相法白炭黑表面羟基的影响。扫描电镜显示改性后气相法白炭黑在SBR中的分散性得到提高。在体系中添加ZDMA会提高气相法白炭黑的分散性。     

Ultrasonically prepared polystyrene/multi-walled carbon nanotube nanocomposites

Polystyrene (PS) and multi-walled carbon nanotube (MWNT) nanocomposites were synthesized via an in situ bulk polymerization by employing an ultrasonicator without adding an initiator, in which the ultrasonication was found to do a favor in producing well-dispersed MWNT in the PS matrix. Morphology of the as-synthesized PS/MWNT nanocomposite was investigated by both scanning electron microscopy and transmission electron microscopy. Electrical conductivity of the PS/MWNT nanocomposite film fabricated by a solvent casting method was also examined to be enhanced with MWNT content, while average molecular weights of the synthesized PS in the PS/MWNT nanocomposites analyzed by a gel permeation chromatography increased and then saturated at 2 wt% MWNT. Rheological properties of MWNT containing PS were enhanced because of improved dispersion of the MWNT through an interaction between MWNT and PS.     

剥离型聚苯乙烯-丙烯酰胺共聚物/蒙脱土纳米复合材料

采用乳液聚合法制备了苯乙烯-丙烯酰胺共聚物/蒙脱土纳米复合材料,研究了苯乙烯用量和体系pH值对复合材料剥离效果的影响;通过XRD、FT-IR和TEM对复合材料的层间结构、界面状态和共聚结构等进行了表征。结果表明:当丙烯酰胺与苯乙烯单体质量比为1∶1～1.4∶1、反应体系pH为1～9时,膨润土层间域发生了剥离,苯乙烯-丙烯酰胺发生了共聚反应,且剥离膨润土以片层结构均匀分散在聚苯乙烯-丙烯酰胺基体中。     

Self-assembled natural rubber/silica nanocomposites: Its preparation and characterization

A novel natural rubber/silica (NR/SiO₂) nanocomposite is developed by combining self-assembly and latex-compounding techniques. The results show that the SiO₂ nanoparticles are homogenously distributed throughout NR matrix as nano-clusters with an average size ranged from 60 to 150 nm when the SiO₂ loading is less than 6.5 wt%. At low SiO₂ contents (4.0 wt%), the NR latex (NRL) and SiO₂ particles are assembled as a core-shell structure by employing poly (diallyldimethylammonium chloride) (PDDA) as an inter-medium, and only primary aggregations of SiO₂ are observed. When more SiO₂ is loaded, secondary aggregations of SiO₂ nanoparticles are gradually generated, and the size of SiO₂ cluster dramatically increases. The thermal/thermooxidative resistance and mechanical properties of NR/SiO₂ nanocomposites are compared to the NR host. The nanocomposites, particularly when the SiO₂ nanoparticles are uniformly dispersed, possess significantly enhanced thermal resistance and mechanical properties, which are strongly depended on the morphology of nanocomposites. The NR/SiO₂ has great potential to manufacture medical protective products with high performances.     

High-performance silica nanoparticle reinforced poly (vinyl alcohol) as templates for bioactive nanocomposites

Silica nanoparticle reinforced poly (vinyl alcohol) cast sheets 40 μm thick were tested for mechanical and biological properties. The films were characterized using X-ray diffraction, scanning electron microscopy, and infrared spectroscopy. The crystallinity decreased with increased silica content. Changes in the morphology and structure upon the addition of silica suggest the formation of cross-linking. The modulus increased from 300 MPa for PVA to 7.2 GPa for 120 wt.% silica nanoparticle in the blend and the tensile strength increased from 3.5 MPa to 35 MPa. The modulus estimated using dynamic tests, tensile tests, and nanoindentation was comparable and was predicted well using the Halpin-Tsai's equation. The nanocomposites were an order of magnitude tougher than the pure polymer. Silica based nanocomposite was also found to be an excellent template for the deposition of calcium hydroxyapatite when immersed in simulated body fluid. The modulus and tensile strength of apatite coated silica nanoparticle (120 wt.%)–PVA composite increased to 11 GPa and 65 MPa respectively, close to that of cortical bone. The results represent one of the largest increases in mechanical properties of nanocomposite mimicking the properties of human bone. The addition of silica can also aid in osseointegration.     

Thermal stability and degradation kinetics of polystyrene/organically-modified montmorillonite nanocomposites

Organically-modified montmorillonite (MMT) clays have been prepared using ammonium salts containing quinoline, pyridine, benzene, and styrenic groups. The nanocomposites were prepared by melt blending and the formation of nanocomposites was characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermal stability and flammability were evaluated by thermogravimetric analysis (TGA) and cone calorimetry measurements, respectively. The presence of modified MMT at 5% loading resulted in significant improvement in thermal stability compared to the virgin polymer. Effective activation energies for mass loss were determined via a model-free isoconversional approach from TGA data obtained under N2 and under air. The additives served to raise the activation energy, with a more significant impact observed under pyrolysis conditions. The onset temperature of degradation and temperature of maximum decomposition rate are increased, while the peak heat release rate and mass loss rates are significantly reduced in the presence of three of the modified clays. No reduction in the total heat released is observed.     

Microwave-absorbing properties of silver nanoparticle/carbon nanotube hybrid nanocomposites

Silver (Ag) nanoparticles fabricated by chemical reduction process were grafted onto the surface of carbon nanotubes (CNTs) to prepare hybrid nanocomposites. The Ag/CNT hybrid nanomaterials were characterized using transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The Ag/CNT hybrid nanomaterials were then loaded in paraffin wax, and pressed into toroidal shape with thickness of 1 mm to evaluate their complex permittivity and complex permeability by scattering parameters measurement method in reflection mode using vector network analyzer. The reflection loss of the samples was calculated according to the transmission line theory using their measured complex permittivity and permeability. The minimum reflection loss of the Ag/CNT hybrid nanocomposite sample with a thickness of 1 mm reached 21.9 dB (over 99 % absorption) at 12.9 GHz, and also exhibited a wide response bandwidth where the frequency bandwidth of the reflection loss of less than ?10 dB (over 90 % absorption) was from 11.7 to 14.0 GHz. The Ag/CNT hybrid nanocomposite with thickness of 6 mm showed a minimum reflection loss of ~?32.1 dB (over 99.9 % absorption) at 3.0 GHz and was the best absorber when compared with the other samples of different thickness. The reflection loss shifted to lower frequency as the thickness of the samples increased. The capability to modulate the absorption band of these samples to suit various applications in different frequency bands simply by manipulating their thickness indicates that these hybrid nanocomposites could be a promising microwave absorber.