Investigations on printed elastic resistors containing carbon nanotubes

This paper presents the results of authors investigations on elaboration of a new thick film composition filled with carbon nanotubes (CNTs). The polymer composition consists of polymer vehicle, which is the solution of organic resin in certain combination of solvents, and functional phase—carbon nanotubes well dispersed in the vehicle. The pastes were applied with screen-printing on several substrates and temperature cured. The properties of obtained layers were characterized. Series of samples were prepared with different amount of CNTs to evaluate electrical properties. Changes in resistance were investigated during periodic mechanical and temperature stresses, realized through cyclical bending and rapid temperature change. Tensometric effect was also investigated. Investigations have proved that polymer composites based on carbon nanotubes exhibit high resilience to stress factors. Resistance change in function of temperature was also investigated to evaluate temperature coefficient of resistance (TCR). All this aspects are important for elastic resistors fabrication in printed electronics microcircuits. Resistance and noise measurements in cryostats have also been involved. 1/f type noise has been observed. Noise intensity, calculated in decade frequency bands, rises significantly with increasing temperature. Activation energies of thermally activated noise sources (TANS) have been revealed using low-frequency noise spectroscopy. Relatively large value of negative TCR has been obtained from resistance versus temperature curve. Calculated dimensionless sensitivity is similar to that observed in cryogenic temperature sensors. However, bulk noise intensity of resistive layer is larger than obtained for lead containing RuO₂ based resistive layers.     

Review on the effects of injection moulding parameters on the electrical resistivity of carbon nanotube filled polymer parts

The electrical resistivity of injection moulded carbon nanotube filled polymer parts is a result of the process history and the raw material. Key factors of the process are temperature and shear history of the melt. Various process parameters affect the aforementioned factors. Articles reviewed in here discuss effects of injection moulding and related processes, such as melt compounding. Furthermore, articles have been reviewed which describe the effect of shear, composition and temperature on the structure of the conductive CNT network. These effects are then related to the solidification of the part, resulting in the variation of the percolated network of CNTs. The variation of the network structure results in a variation of the electrical resistivity within the part.     

Influence of filler waviness and aspect ratio on the percolation threshold of carbon nanomaterials reinforced polymer nanocomposites

Adding a small amount of conductive high aspect one-dimensional nanomaterials such as carbon nanotubes and carbon nanofibers to the initially non-conductive polymeric matrix can induce an insulator to conductor transition which has both scientific merit and application importance. The critical fiber concentration necessary for this transition is called the percolation threshold, which is determined by the filler shape and size. This study investigates the filler waviness effect on the critical behavior of composite conductivity, since the high aspect ratio fillers in actual composites are often bent and entangled instead of being straight. Individual filler was modeled by a linked three straight-segment components with three-dimensional (3D) bending characteristics. In addition, 3D Monte Carlo method has been used to simulate the random distribution of the fillers. Statistical analyses of the fiber networks reveal waviness influence on the percolation threshold in terms of the average contacts per fiber with other fibers. The critical number of average contacts per fiber (B _c) for percolation strongly depends on the waviness and deviates substantially from identity for straight fillers. The study demonstrates that the semi-analytic excluded volume theory cannot be used to predict the percolation threshold until the correct B _c value is determined.     

Trimming studies on polymer thick-film resistors

PVC-graphite polymer thick-film resistors were trimmed by a conventional air abrasive technique and the post-trim drift in resistance with time was found to be negative. The net decrease in resistance of trimmed resistors in a given time was found to be a function of resistor composition, cutting speed and temperature. Detailed studies showed this decrease to be due to a decrease in cut width with time. Two new methods, namely bombardment trimming and radiation trimming, were also tried for adjusting the resistance of these resistors and the results were compared with those obtained from abrasive trimming studies.     

Photo-responsive shape memory polymer composites enabled by doping with biomass-derived carbon nanomaterials

As photothermal conversion agents,carbon nanomaterials are widely applied in polymers for light-triggered shape memory behaviors on account of their excellent light absorption.However,they are usually derived from non-renewable fossil resources,which go against the demand for sustainable development.Biomass-derived carbon nanomaterials are expected as alternatives if they are designed with good dispersibility as well as splendid photothermal properties.Up to date,very few researches focused on this area.Herein,we report a novel light-triggered shape memory composite by incorporating renewable biomass-derived carbon nanomaterials into acrylate polymers without deep purification and processing.These functionalized carbon nanomaterials not only have stable dispersion in polymers as fillers,but also can endow the polymers with excellent and stable thermal and photothermal responsive properties in biological friendly environment.With the introduction of biomass-derived carbon nanomaterials,the mechanical properties of the composites are also further enhanced with the formation of hydrogen bonding between the carbon nanomaterials and the polymers.Notably,the doping of 1%carbon nanomaterials endows the polymer with sufficient hydrogen bonds that not only exhibit excellent thermal and photothermal responsive properties,but also with enough space for the motion of chains.These properties make such composite a promising and safe candidate for shape memory applications,which provide a new avenue in smart fabrics or intelligent soft robotics.     

电热作用对碳纤维/树脂复合材料界面应力的影响电热作用对碳纤维/树脂复合材料界面应力的影响

碳纤维/树脂复合材料广泛应用于民用航空器结构中,在服役期间会受到复杂环境（湿热、腐蚀、复杂应力和电热作用等）的作用,低强度电流对碳纤维/树脂复合材料的影响受到的关注较少。以碳纤维/树脂复合材料为研究对象,根据碳纤维的温敏效应和通电时的电阻变化规律,计算出碳纤维单丝/环氧树脂复合试样的界面温度范围,之后采用拉曼光谱测试和单丝断裂实验研究了低强度电流对单丝复合体系界面应力和界面剪切强度的影响。结果表明:随着电流强度的提高,单丝复合体系的界面温度随之升高,电流为8 mA时,界面温度高达约200℃。随着电流强度的增大,单丝复合体系的界面压缩应力表现为先增大后减小的趋势,电流高于7 mA后,界面处树脂出现烧蚀降解破坏;单丝断裂实验结果表明随着电流强度增大,单丝复合体系的界面剪切强度呈现先升后降的趋势,在6 mA时界面剪切强度达到最大值62.39 MPa,而8 mA时界面剪切强度仅为34.95 MPa。      

Influence of carbon nanomaterials on the properties of paint coatings

The conditions for obtaining carbon nanomaterials with the use of a low-temperature plasma are described. The product obtained was analyzed using the electron microscopy and a laser diffraction particle-size analyzer. The influence of the carbon nanomaterials on the physicochemical properties of paint coatings, their adhesion, impact and bending strengths, hardness, and protection characteristics was investigated.     

Influence of surface chemistry on inkjet printed carbon nanotube films

Carbon nanotube ink chemistry and the proper formulation are crucial for direct-write printing of nanotubes. Moreover, the correct surface chemistry of the self-assembled monolayers that assist the direct deposition of carbon nanotubes onto the substrate is equally important to preserve orientation of the printed carbon nanotubes. We report that the successful formulation of two single walled carbon nanotube (SWNT) inks yields a consistent, homogenous printing pattern possessing the requisite viscosities needed for flow through the microcapillary nozzles of the inkjet printer with fairly modest drying times. The addition of an aqueous sodium silicate allows for a reliable method for forming a uniform carbon nanotube network deposited directly onto unfunctionalized surfaces such as glass or quartz via inkjet deposition. Furthermore, this sodium silicate ingredient helps preserve applied orientation to the printed SWNT solution. Sheet resistivity of this carbon nanotube ink formula printed on quartz decreases as a function of passes and is independent of the substrate. SWNTs were successfully patterned on Au. This amine-based surface chemistry dramatically helps improve the isolation stabilization of the printed SWNTs as seen in the atomic force microscopy (AFM) image. Lastly, using our optimized SWNT ink formula and waveform parameters in the Fuji materials printer, we are able to directly write/print SWNTs into 2D patterns. Dried ink pattern expose and help orient roped carbon nanotubes that are suspended in ordered arrays across the cracks.     

The electrical properties of polymer nanocomposites with carbon nanotube fillers

The electrical properties of polymer nanocomposites containing a small amount of carbon nanotube (CNT) are remarkably superior to those of conventional electronic composites. Based on three-dimensional (3D) statistical percolation and 3D resistor network modeling, the electrical properties of CNT nanocomposites, at and after percolation, were successfully predicted in this work. The numerical analysis was also extended to investigate the effects of the aspect ratio, the electrical conductivity, the aggregation and the shape of CNTs on the electrical properties of the nanocomposites. A simple empirical model was also established based on present numerical simulations to predict the electrical conductivity in several electronic composites with various fillers. This investigation further highlighted the importance of theoretical and numerical analyses in the exploration of basic physical phenomena, such as percolation and conductivity in novel nanocomposites.     

Influence of carbon nanomaterials on the properties of cement and concrete

Results of investigations of the influence of an addition of carbon nanomaterials to a cement paste on its properties, the morphological characteristics of the cement-hydration products, and the structure and strength of the concrete obtained on the basis of this paste are presented.     

The electrical properties of epoxy resin composites filled with Cnts and carbon black

This work introduces an experimental activity related to the realization of an epossidic nanostructured material that develops the function of covering for electronic circuits in aeronautical field. This covering meets the demand of protection of these circuits from possible troubles of electromagnetic nature. In order to realize this covering we used an epoxy resin as matrix (Epon 828) loaded with conductive nanofillers or carbon nanotubes (Cnts). To check the efficiency of the coating we have considered the carbon black, filler widely used as a conductive covering for screenings. We have considered different percentages of the different fillers, precisely 0.1%, 0.25% and 0.5% wt (% valued in comparison to the weight of the resin). From every mixture 12 samples have been obtained (the size of every sample is 10 mm x 10 mm x 10 mm). Every sample has been subjected to electrical measurements, that have concerned the measurement of current intensity and resistance (so as to allow the evaluation of the enhancement of the conductivity), through the application of different values of voltage. The results have demonstrated that the epoxy matrix loaded with Cnts yields higher values of electrical conductivity than the same matrix loaded with carbon black.     

炭黑-碳纤维填充双组分聚合物体系的导电网络及其阻温特性

以2种不同形态尺寸的导电填料炭黑(CB)、 碳纤维(CF)填充双组分聚合物体系高密度聚乙烯(HDPE)聚丙烯(PP), 制备了四元导电复合材料。研究了导电网络的结构形态及其对材料阻温特性的影响。光学显微镜及SEM 观察表明: 炭黑选择性地分布于HDPE中, 体系中HDPE与PP呈双连续相分布, 形成双渗流导电网络结构。而具有较高长径比的碳纤维在两相基体中均匀分布并贯通多个相区, HDPE导电相区的碳纤维相互桥接形成导电网络。电性能测试结果表明: 体系的体积电阻率与CB/HDPEPP及CBCF/HDPE三元复合体系相比下降了1~5个数量级。同时, 双渗流导电网络的存在也有效抑制了负温度系数(NTC)效应, 提高了循环稳定性。与CBCF/HDPE体系相比, CBCF/HDPEPP体系的NTC效应从2个数量级下降到0.6个数量级, 电阻特征弛豫时间从951s增加到了2370s。      

Chemically integrated nickel-based resistors on printed circuits and its resistance precisely controlled

Journal of Materials Science: Materials in Electronics - Embedded resistors in printed circuit boards (PCBs) are fabricated to provide high integration, improved electrical performance, and reduced...     

燃料和基板对火焰法制备一维碳纳米材料的影响

以乙醇、甲醇及液化石油气为碳源，低碳钢及含Ni合金钢等为基板，采用火焰法成功地制备出了一维碳纳米材料，包括碳纳米管（CNTs）和一种新的“实心”碳纳米纤维（CNFs）。利用场发射枪高分辨扫描电镜（SEM）、透射电镜（TEM）和激光Raman光谱对碳纳米材料的结构进行了表征。发现基板材料决定燃烧生成物的性质，含Fe元素及其化合物的基板材料倾向于合成“实心”碳纳米纤维，而含Nj元素及其化合物的基板材料倾向于合成“空心”的碳纳米管，认为这是由于碳与Fe的亲和力比Ni大而造成的。不同碳源对一维碳纳米材料的形态也有影响，这与它们的含碳量和燃烧热等不同有关。     

Development and electrical characterization of carbon soot filled polyester graded composites

In this paper a novel method to develop carbon soot filled polyester graded composites has been reported. Dielectric measurements were conducted on these graded composites in the temperature range from 30 to 150 °C and in the frequency range 1–10 kHz to study and analyse the effect of temperature and frequency variation on dielectric constant (ε′) and dielectric dissipation factor (tan δ). It was observed that an increase of carbon soot content increased the dielectric constant gradually, which established the formation of a graded structure. Dielectric data were analysed using existing theoretical models. It was observed that Maxwell–Garnett model fits best for the dielectric data obtained experimentally for these graded composites. Compensation law confirmed the semi conducting behaviour of the composites. Cole–Cole plot for graded composites showed dielectric relaxation probably due to dipolar groups of polyester and interfacial polarization that occurred in the composites.     

Differential detection of enantiomeric gaseous analytes using carbon black-chiral polymer composite, chemically sensitive resistors

Carbon black-chiral polymer composites were used to provide diagnostic differential resistance responses in the presence of enantiomers of chiral gaseous analytes. Vapors of (+)-2-butanol and (-)-2-butanol, (+)-α-pinene and (-)-α-pinene, (+)-epichlorohydrin and (-)-epichlorohydrin, and methyl (+)-2-chloropropionate and methyl (-)-2-chloropropionate were generated and passed over a chemically sensitive carbon black-poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate) (77% butyrate) composite resistor. Each enantiomer of a pair produced a distinct relative differential resistance change on the chiral detector, whereas both enantiomers of a set produced identical signals on achiral carbon black-poly(ethylene-co-vinyl acetate) (82% ethylene) detectors.     

Fracture toughness and electrical conductivity of epoxy composites filled with carbon nanotubes and spherical particles

The attainment of both high toughness and superior electrical conductivity of epoxy composites is a crucial requirement in some engineering applications. Herein, we developed a strategy to improve these performances of epoxy by combining the multi-wall carbon nanotubes (MWCNTs) and spherical particles. Two different types of spherical particles i.e. soft submicron-rubber and rigid nano-silica particles were chosen to modify the epoxy/MWCNT composites. Compared with the binary composites with single-phase particles, the ternary composites with MWCNTs and spherical particles offer a good balance in glass transition temperature, electrical conductivity, stiffness and strength, as well as fracture toughness, exhibiting capacities in tailoring the electrical and mechanical properties of epoxy composites. Based on the fracture surface analysis, the complicated interactions between multiscale particles and the relative toughening mechanisms were evaluated to explain the enhancement in fracture toughness of the ternary composites.     

Micro orientation and anisotropy of conductivity in liquid crystalline polymer films filled with carbon nanotubes

In this communication we report the preferential orientation of single wall carbon nanotubes (SWNT) in a nematic liquid crystalline (LC) polymer matrix. The alignment of the nanotubes was characterized through anisotropy of electrical conductivity of the composite measured in directions parallel and perpendicular to the nematic director. The anisotropy of the nanocomposite films strongly depends on the nanotube concentration in the range from 1 to 10% and vanished at higher loads. The electrical conductivity of nanocomposites is related to their structural features revealed by atomic force microscopy and Raman spectroscopy experiments and is explained by a strong coupling between the nanotubes and the polymer matrix.