Processing and properties of poly(ε-caprolactone)/carbon nanofibre composite mats and films obtained by electrospinning and solvent casting

Composite materials based on poly(ε-caprolactone) (PCL) and carbon nanofibres (CNFs) were processed by solvent casting and electrospinning. The main objective was to investigate the effects of the CNFs on the microstructural, thermal and mechanical properties of the PCL matrix composites processed by two different routes. The hybrid materials obtained with different CNF content (1, 3 and 7 wt%) were analysed by electron microscopy (FESEM), differential scanning calorimeter (DSC), thermogravimetry (TGA) and mechanical testing. The composite films showed a good dispersion in the PCL matrix while electrospun samples were consisted of homogeneous and uniform fibres up to 3 wt% CNFs with average fibre diameter ranged between 0.5 and 1 μm. Composite films and mats revealed an increased crystallization temperature with respect to the neat PCL matrix. Mechanical properties of solvent cast films and electrospun mats were assessed by uniaxial tensile tests. A stiffness increase was achieved in PCL films depending on the CNF content, while mechanical properties of mats were only slightly affected by CNF introduction.     

Transparent conductive polymer composites obtained via electrostatically assembled carbon nanotubes–poly (methyl methacrylate) composite particles

Interest in the controlled formation of advanced carbon-based composite materials with good transparency for lightweight and portable device applications has been increasing. This study reports on the feasible formation of carbon nanotubes (CNT)-incorporated poly (methyl methacrylate) (PMMA) composite pellets, which exhibited good electrical conductivities with high optical transparency. Despite using a low amount of CNT incorporation (0.0068～0.068 vol%), conductive channels were generated through the homogeneous decoration of CNT onto PMMA particles obtained via an electrostatic assembly method. The conductive channels formed at pressed interface of CNT–PMMA pellets were confirmed using a scanning probe microscope with contact current imaging. The findings of this study present a promising prospect for carbon-based composite materials fabrication via powder metallurgy inspired method that can be used for manufacturing of lightweight, transparent and conductive polymers.     

Sol–gel synthesis of tantalum oxide and phosphonic acid-modified carbon nanotubes composite coatings on titanium surfaces

Carbon nanotubes used as fillers in composite materials are more and more appreciated for the outstanding range of accessible properties and functionalities they generate in numerous domains of nanotechnologies. In the framework of biological and medical sciences, and particularly for orthopedic applications and devices (prostheses, implants, surgical instruments, …), titanium substrates covered by tantalum oxide/carbon nanotube composite coatings have proved to constitute interesting and successful platforms for the conception of solid and biocompatible biomaterials inducing the osseous regeneration processes (hydroxyapatite growth, osteoblasts attachment). This paper describes an original strategy for the conception of resistant and homogeneous tantalum oxide/carbon nanotubes layers on titanium through the introduction of carbon nanotubes functionalized by phosphonic acid moieties (P(O)(OH)₂). Strong covalent CP bonds are specifically inserted on their external sidewalls with a ratio of two phosphonic groups per anchoring point. Experimental results highlight the stronger “tantalum capture agent” effect of phosphonic-modified nanotubes during the sol–gel formation process of the deposits compared to nanotubes bearing oxidized functions (OH, CO, C(O)OH). Particular attention is also paid to the relative impact of the rate of functionalization and the dispersion degree of the carbon nanotubes in the coatings, as well as their wrapping level by the tantalum oxide matrix material. The resulting effect on the in vitro growth of hydroxyapatite is also evaluated to confirm the primary osseous bioactivity of those materials. Chemical, structural and morphological features of the different composite deposits described herein are assessed by X-ray photoelectron spectroscopy (XPS), scanning (SEM) and transmission (TEM) electronic microscopies, energy dispersive X-rays analysis (EDX) and peeling tests.     

Low temperature charge transport and microwave absorption of carbon coated iron nanoparticles–polymer composite films

In this paper, the low temperature electrical conductivity and microwave absorption properties of carbon coated iron nanoparticles–polyvinyl chloride composite films are investigated for different filler fractions. The filler particles are prepared by the pyrolysis of ferrocene at 980 °C and embedded in polyvinyl chloride matrix. The high resolution transmission electron micrographs of the filler material have shown a 5 nm thin layer graphitic carbon covering over iron particles. The room temperature electrical conductivity of the composite film changes by 10 orders of magnitude with the increase of filler concentration. A percolation threshold of 2.2 and an electromagnetic interference shielding efficiency (EMI SE) of ～18.6 dB in 26.5–40 GHz range are observed for 50 wt% loading. The charge transport follows three dimensional variable range hopping conduction.     

Non-isothermal crystallization of poly(ε-caprolactone)-grafted multi-walled carbon nanotubes

Non-isothermal crystallization behavior of poly(ε-caprolactone) (PCL)-grafted multi-walled carbon nanotubes (MWNTs) was studied in order to determine the effects of functionalized MWNTs (f-MWNTs) on its crystallization behavior. Differential scanning calorimeter measurements showed that an introduction of f-MWNTs into the PCL molecules induced heterogeneous nucleation and the crystal growth process was significantly affected. X-ray diffraction showed a decrease in the crystallinity of composites with the addition of f-MWNTs in PCL, likely due to the occurrence of more heterogeneous nucleation induced by f-MWNTs in the samples. The activation energy for crystallization of PCL drastically reduced with the presence of 2 wt.% f-MWNTs in the samples and increased slightly with increasing content of f-MWNTs. A spherulite structure of PCL-grafted MWNTs with MWNTs at the center was developed, clearly indicating the nucleating action of MWNTs in the crystallization process. The experimental data were also analyzed using various kinetic models e.g., Avrami, Tobin, Ozawa, etc.     

Architected poly(lactic acid)/poly(ε-caprolactone)/halloysite nanotube composite scaffolds enabled by 3D printing for biomedical applications

Journal of Materials Science - Herein, we report the physicochemical, thermal, mechanical and biological characteristics, including bioactivity, biodegradation and cytocompatibility of additive...     

Poly(DMAEMA-co-VP)/Fe_3O_4纳米复合水凝胶的制备及性能

以甲基丙烯酸-N,N-二甲氨基乙酯(DMAEMA)、4-乙烯基吡啶(VP)为单体,N,N-亚甲基双丙烯酰胺(BIS)为交联剂,在Fe_3O_4纳米粒子分散液中原位共聚制备了具有温度、pH、磁场三重响应性的纳米复合水凝胶。对纳米复合水凝胶的溶胀性能、温敏性、pH敏感性、磁场响应性等性能进行了研究,进而考察了纳米复合水凝胶对重金属离子(Cu~(2+))的吸附脱附行为。结果表明,纳米复合水凝胶具有良好的温敏性、pH敏感性和磁场响应性,并且对重金属离子(Cu~(2+))有可逆的吸附-脱附作用。     

Enhanced oxidation of diclofenac sodium at a nano-structured electrochemical sensing film constructed by multi-wall carbon nanotubes–surfactant composite

A multi-walled carbon nanotubes (MWNTs)–dihexadecyl hydrogen phosphate (DHP) film-coated glassy carbon electrode (GCE) was fabricated, and the voltammetric determination method of diclofenac sodium was investigated on this modified electrode by using different kinds of electrochemical techniques. The results showed that this nano-structured film electrode exhibits excellent enhancement effects on the electrochemical oxidation of diclofenac sodium. The oxidation peak current of diclofenac sodium at this film-modified electrode increased significantly compared with that at a bare glassy carbon electrode. Based on the experiment outcomes a possible mechanism was proposed and discussed. The proposed method was demonstrated by using diclofenac sodium tablets and the result was satisfying.     

Dielectric behaviors of PHBHHx–BaTiO3 multifunctional composite films

Multifunctional polymeric composites were investigated for potential use in high energy storage capacitors and tissue engineering. The polymeric composites were fabricated by employing biodegradable polyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), as the matrix. Ferroelectric BaTiO₃ ceramic powders were added to the composites as fillers. The dielectric spectroscopy of the composites was measured over a wide frequency range (10⁰–10⁷ Hz) from −100 to 60 °C. The composition dependent dielectric behavior was modeled by a self-consistent effective medium theory. A percolation threshold of 0.367 was observed in the composites. The glass transition relaxation of the composite was also discussed by comparing the popular Vögel–Fulcher–Tammann law with a new glass model. The composites show attractive ferroelectricity and piezoelectricity for biomedical applications.     

Effect of γ-ray irradiation on the microstructure and self-heating property of carbon fiber/polyethylene composite films

High-density polyethylene composite films filled with various contents of carbon fiber (CF) were manufactured by melt mixing. The electrical and self-heating properties of the composite films were investigated. The composite films containing 10 wt% CF were exposed to γ-ray irradiation. The structural, morphological, and self-heating properties of the irradiated composite films were examined. The results indicated that the surface temperature (T_s) of the composite films was strongly dependent on the applied voltage and filler content. The T_s of the irradiated composite films was higher than that of the non-irradiated films, which contributed to the lower thermal expansion and the higher degree of crystallization of the irradiated composite films. In addition, the mechanical properties of the irradiated composite films were significantly improved. Using a rechargeable battery as the applied voltage source to evaluate the self-heating property of the irradiated composite films, a heating temperature of 54.2 °C was achieved, which lasted for 6 h.     

Poly(VBMIMPF_6)/BMIMPF_6离子凝胶的制备与性能

以1-乙烯基-3-丁基咪唑六氟磷酸盐(VBMIMPF6)为单体,1-丁基-3-甲基咪唑六氟磷酸盐(BMIMPF6)为溶剂和电解质,并以聚乙二醇二丙烯酸酯(PEGDA)为交联剂,采用原位紫外交联的方法制备出了一种新型聚离子液体基离子凝胶电解质。通过扫描电子显微镜、流变性能、力学拉伸和电化学交流阻抗等手段,考察了离子凝胶电解质的微观结构、流变性能、力学性能和电学性能。流变性能测试结果表明,离子凝胶具有很高的储能模量(10~4~10~5 Pa),且温度200℃内储能模量基本保持不变。拉伸性能测试结果表明,体系具有很强的力学性能且拉伸强度达到10~5 Pa数量级。电学性能测试结果表明室温下离子凝胶具有很高的电导率(10~(-4)~10~(-3)S/cm),且电导率随BMIMPF6含量的增加而增大。     

高强度Poly(AM-co-IA)/Al_2O_3纳米复合水凝胶的制备及形状记忆行为

以氧化铝(Al_2O_3)纳米粒子作为无机交联剂,丙烯酰胺(AM)和衣康酸(IA)为单体,原位自由基聚合制备了高强度PAI/Al_2O_3纳米复合水凝胶,并提出了水凝胶的交联机理。对纳米复合水凝胶的力学性质、微观结构和溶胀性质进行了表征。结果表明,制备的水凝胶具有优异力学性能,拉伸和压缩强度分别可达477 k Pa和13.45 MPa。此外,PAI/Al_2O_3纳米复合水凝胶还表现出透明的外观,规整的网络结构,较低的溶胀率以及水驱动的形状记忆行为。因此,这种水凝胶在生物医学领域有广阔的应用前景。     

Chemical-physical and preliminary biological properties of poly (2-hydroxyethylmethacrilate)/poly-(ɛ-caprolactone)/hydroxyapa- tite composite

In the present study, the synthesis of a semi-Interpenetrating Polymer Network (semi-IPN) incorporating linear poly-(ɛ-caprolactone) (PCL) into cross-linked poly-(2-hydroxyethylmethacrilate) (PHEMA) reinforced with hydroxyapatite (HA) has been described. The aim of this study was to improve the mechanical and biological performance of the PHEMA/PCL in the hydrated state, for orthopaedic applications. The swelling behaviour, mechanical (compressive and tensile) and surface chemical-physical (morphology, stoichiometric composition) characterisation of the novel HA reinforced composite based on PHEMA/PCL polymer matrix, PHEMA/PCL 70/30 (w/w) + 50% (w/w) HA (PHEMA/PCL/HA), were evaluated. Furthermore, a preliminary in vitro biological evaluation was also performed on the composite using a fully characterised primary human osteoblast-like (HOB) cell model. The inclusion of HA in the composite improved the mechanical performance in the swollen state, with values of elastic modulus in a similar range to that of trabecular bone. The composite surfaces showed a porous, irregular topography with the presence of: oxygen (O), carbon (C); phosphorous (P); calcium (Ca) where the Ca/P ratio was 1.78. Biological evaluation indicated undetectable weight loss of the sample, no release of toxic leachables from the composite and pH values within an acceptable range for cell growth. The results indicate that the novel PHEMA/PCL/HA composite is a promising candidate as filler or substitute for spongy bone for orthopaedic applications.     

溶胶-凝胶法合成层状锂离子电池正极材料LiNi(1-x)/3Mn(1-x)/3Co(1-x)/3CrxO2及其电化学性能的研究

采用溶胶-凝胶法制备了层状锂离子电池正极材料LiNi(1-x)/3Co(1-x)/3Mn(1-x)/3CrxO2 (x=0,0.02,0.05,0.1).利用XRD、电化学测试等手段对材料的结构、电化学等性能进行表征.结果表明:LiNi(1-x)/3Co(1-x)/3Mn(1-x)/3CrxO2仍然为层状α-NaFeO2结构;当x=0.02,0.2C充放电首次放电比容量达到195mAh/g,首次放电效率高达到91.7％,并且有着良好的循环性能.     

Tensile properties of in situ synthesized (TiB + La2O3)/β-Ti composite

A novel (TiB + La₂O₃)/Ti-alloy composite was In situ synthesized through homogeneously melting in a non-consumable vacuum arc remelting furnace. Ti–35Nb–2Ta–3Zr β titanium alloy was chosen as the matrix Ti-alloy and different mass fractions of LaB₆ were chosen as additions. Microstructure observations were examined by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The phase analysis was identified by X-ray diffraction (XRD). Largest ultimate tensile strength around 580 MPa and highest elongation around 30% is obtained in 0.1% LaB₆-additioned specimen. The appearance of too many La₂O₃ particles and the reduction of oxygen in the matrix alloy also attribute much to the strength and plasticity of (TiB + La₂O₃)/Ti composites. Lower ultimate tensile strength around 526 MPa is obtained in 0.5% LaB₆-additioned specimen.     

WO3∕SiO2 composite optical films for the fabrication of electrochromic interference filters

New security devices based on innovative technologies and ideas are essential in order to limit counterfeiting's profound impact on our economy and society. Interference security image structures have been in circulation for more than 20 years, but commercially available iridescent products now represent a potential threat. Therefore, the introduction of active materials, such as electrochromic WO3, to present-day optical security devices offers interesting possibilities. We have previously proposed electrochromic interference filters based on porous and dense WO3, which possessed an angle-dependent and voltage-driven color shift. However, the low index contrast required filters with a high number of layers. In this article, we increase the index contrast (0.61) by mixing WO3 with SiO2 and study the physical and electrochromic properties of mixtures. We next combine high and low index films in tandem configurations to observe the bleaching/coloration dynamics. To account for the film performance, we propose a simple explanation based on the differences in electron diffusion coefficients. An 11 layer electrochromic interference filter (EIF) based on the alternation of pure WO3 and (WO3)0.17(SiO2)0.83 films with a blue to purple angular color shift is then presented. Finally, we discuss possible applications of these EIFs for security.     

Synthesis and crystallization of lead–zirconium–titanate (PZT) nanotubes at the low temperature using carbon nanotubes (CNTs) as sacrificial templates

Pb(Zr_0.52Ti_0.48)O₃ (PZT) nanotubes with diameters of 80–100 nm and a wall thickness of 15–20 nm were prepared by sol–gel template technique and using multi-walled carbon nanotubes (MWCNT) as sacrificial templates. The coating process of MWCNT with PZT precursor sol and removal of the carbon nanotubes by an interrupt heat treatment were discussed and studied by Raman spectroscopy. Simultaneous thermal analysis (STA) revealed that PZT nanotube crystallized at the low temperature of 410 °C by the significantly low activation energy of crystallization of 103.7 kJ/mol. Moreover, based on the X-ray diffraction (XRD) pattern and selected area electron diffraction pattern the crystal structure of the PZT nanotube was determined as perovskite. High resolution transmission electron microscope (HRTEM) and field-emission scanning electron microscope (FE-SEM) images proved that the final PZT had a tubular structure.     

Carbon fiber/epoxy composite property enhancement through incorporation of carbon nanotubes at the fiber–matrix interphase – Part I: The development of carbon nanotube coated carbon fibers and the evaluation of their adhesion

A new method to realize the uniform coating of carbon nanotubes (CNTs) to carbon fibers (CFs) has been developed, which enables the scalable fabrication of CNT containing CF/epoxy composites. In this method, CNTs are treated by cationic polymers, then, the CNTs are coated to CFs by immersion into a CNT/water suspension. Good dispersion is achieved by repulsive force between positively charged CNTs and uniform coating of the CNTs is achieved by attractive forces between positively charged CNTs and negatively charged CFs. It is found that the use of specific cationic polymers including polyethyleneimine (PEI) results in stable CNT/water suspensions, and uniform coating of the CNTs. Single fiber fragmentation tests of the CF/epoxy composites were conducted to evaluate the strength of interface and interphase under shear loading. The results show that the combination of epoxy resin sizing and PEI treated CNT coating to CFs results in high interfacial shear strength.