Response Characteristics of Strain Sensors Based on Closely Spaced Nanocluster Films with Controlled Coverage

Flexible strain sensor devices were fabricated by depositing Pd nanoclusters on PET membranes patterned with interdigital electrodes. The sensors responded to the deformation of the PET membranes with the conductance changes of the nanocluster films and were characterized by both high gauge factor and wide detection range. The response characteristics of the strain sensors were found to depend strongly on the nanocluster coverage, which was attributed to the percolative nature of the electron transport in the closely spaced nanocluster arrays. By controlling the nanocluster deposition process, a strain sensor composed of nanocluster arrays with a coverage close to the effective percolation threshold was fabricated. The sensor device showed a linear response with a stable gauge factor of 55 for the applied strains from the lower detection limit up to 0.3%. At higher applied strains, a gauge factor as high as 200 was shown. The nanocluster films also demonstrated the ability to response to large deformations up to 8% applied strain, with an extremely high gauge factor of 3500.     

The influence of bending on the performance of flexible carbon black/polymer composite gas sensors

The performance of electronics on flexible substrates suffers under substrate bending leading to reduced device performance. In this article, we highlighted the influence of bending strain on a conductive polymer composite gas sensor and developed a model to investigate the influence of strain. We evaluated the strain influence on the resistance of a gas sensor with respect to sensitivity, filler content, cyclic loading, and electrode orientation. The sensitivity of gas sensors increased with decreasing tensile bending radii. The influence of strain was dominant for gas sensors with less carbon black concentration. Cyclic bending tests showed a decrease of sensor resistance versus time and a plastic deformation. A sensor geometry orientations effect to reduce the sensitivity to bending strain was achieved by aligning the electrode fingers parallel to the strain. A model was successfully implemented to simulate strain influences inside the polymer incorporating the Poisson ratio. We suggest a concept to achieve a strain insensitive gas sensor by creating an orientation between single particles inside the composite. Implementing this results into existing gas sensors will improve the measurement quality and reliability of sensors on flexible substrates. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Carbon-based conductive rubber composite for 3D printed flexible strain sensors

Polymeric-based flexible electronic devices are in high demand due to its wide range of applications. Natural rubber (NR) shows a great potential as matrix phase for flexible conductive polymer composites with its high elasticity and fatigue resistance. In this study, a new 3D printable conductive NR (CNR) composite was developed for strain sensor applications. Different contents of conductive carbon black (CCB) were mixed with NR latex to investigate the effect of the filler content on electrical and mechanical properties of the composites. The best-known CNR composite with the CCB content of 12 phr was selected in order to produce the feedstock for the stereolithography process (SLA). The morphological, electrical, and mechanical properties of cast and 3D-printed samples were investigated and compared. Although the 3D-printed CNR sample had slightly lower conductivity than the cast one, it possessed comparable tensile strength and elongation at break, with values of 12.4 MPa and 703%, respectively. In addition, electrical responses of the CNR samples were investigated to demonstrate the electromechanical property of the material as a strain sensor. The 3D-printed CNR sample exhibited the highest electromechanical sensitivity with a gauge factor (GF) of 361.4 (ε = 210%–300%) and showed good repeatability for 500 cycles. In conclusion, the development of this 3D printable functional material with great sensing capability will pave the way for innovative designs of personalized sensing textiles and other smart wearable devices.     

A new modified conducting carbon composite electrode as sensor for ascorbate and biosensor for glucose

A new carbon-based conducting composite has been developed as electrochemical sensor and biosensor for the amperometric detection of ascorbate and glucose. Electrocatalytic oxidation of ascorbate has been done successfully at unmodified cellulose acetate-graphite composite electrodes, the sensor being highly sensitive, selective and with a low detection limit at 0.0 V vs. SCE and was successfully applied for ascorbate determination in commercial fruit juice samples. An interference free glucose biosensor has also been developed, based on the immobilisation of glucose oxidase by cross-linking with glutaraldehyde on poly (neutral red) modified composite electrodes. The biosensor exhibits a higher sensitivity of 31.5 ± 1.7 µA cm^− 2 mM^− 1 than other carbon-composite-based glucose biosensors, a detection limit of 20.3 µM and a very short response time.     

Non‐oxidized graphene/elastomer composite films for wearable strain and pressure sensors with ultra‐high flexibility and sensitivity

It remains challenging to prepare wearable strain and pressure sensors with excellent mechanical properties, ultra‐high flexibility and sensitivity. Electrically conductive graphene platelets (GnPs) with high structural integrity are used in making a composite film fabricated using robust fabrication techniques. The gauge factor for the strain is up to 100 at 0%‐5% strain and 50 at 5%‐30% strain, and the sensitivity to pressure is 2.7×10^‐2 kPa^‐1 between 0 and 10 kPa and 1.5×10^‐4 kPa^‐1 between 300 and 1000 kPa. In addition, the flexible sensor demonstrates good repeatability and durability after 1000 cycles of tensile and compression tests. The flexible sensor has fast response ability and a wide operating temperature range, suggesting the excellent response to temperature. The flexible sensor is applied in monitoring several human motions as a wearable device with high accuracy. The ability to detect strain, pressure and temperature of the flexible sensor extends its applications to multifunctional wearable devices.     

Multiparametric optimization of a new high-sensitive and disposable mercury (II) electrochemical sensor

An electrochemical sensor for mercury (II) determination was developed by modifying the surface of a commercial screen-printed carbon electrode (SPCE) with a polystyrene sulfonate-NiO-carbon nanopowder composite material. Mercury measurements were performed by differential pulse anodic stripping voltammetry (DPASV). Sensor composition and measurement conditions were optimized using a multivariate experiment design. A screening experiment by using a Plackett-Burman design was first performed in order to determine the main contributing factors to the electrochemical response. The most important factors were employed to establish the interactions between different experimental variables and get the best conditions for mercury determination. For this purpose, a five level central composite design and a response surface methodology were used. The optimized method using the developed NiO-PSS-SPCE sensor presents a very low limit of detection of 0.021 μg L⁻¹ and a linear response over two concentration ranges with two different slopes, from 0.05 to 2.0 μg L⁻¹ and between 2.0 and 75 μg L⁻¹. The sensor was successfully applied to mercury determination in water samples.     

Fabrication of highly sensitive and selective nanocomposite film based on CuNPs/fullerene-C60/MWCNTs: An electrochemical nanosensor for trace recognition of paracetamol

Designing an electrochemical sensor for versatile clinical applications is a sophisticated task and how dedicatedly functionalized composite materials can perform on this stage is a challenge for today and tomorrow's Nanoscience and Nanotechnology. In the present work, we demonstrate a new strategy for the development of novel electrochemical sensor based on catalytic nanocomposite film. Fullerene-C₆₀ and multi-walled carbon nanotubes (MWCNTs) were dropped on the pre-treated carbon paste electrode (CPE) and copper nanoparticles (CuNPs) electrochemically deposited on the modified CPE to form nanocomposite film of CuNPs/C₆₀/MWCNTs/CPE. In this work, an electrochemical method based on square wave voltammetry (SWV) employing CuNPs/C₆₀/MWCNTs/CPE has been presented for the recognition and determination of paracetamol (PT). Developed electrochemical sensor was characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronocoulometry. The composite film made the fabricated sensor to display high sensitivity and good selectivity for PT detection. The influence of the optimization parameters such as pH, accumulation time, deposition potential, scan rate and effect of loading of composite mixture of C₆₀-MWCNTs and CuNPs on the electrochemical performance of the sensor were evaluated. A linear range from 4.0 × 10⁻⁹ to 4.0 × 10⁻⁷ M for PT detection was obtained with a detection limit of 7.3 × 10⁻¹¹ M. The fabricated sensor was successfully applied to the detection of PT in biological samples with good recovery ranging from 99.21 to 103%.     

Polymer microcantilever biochemical sensors with integrated polymer composites for electrical detection

Micro fabricated sensors based on nanomechanical motion with piezoresistive electrical readout have become a promising biochemical sensing tool. The conventional microcantilever materials are mostly silicon-based. The sensitivity of the sensor depends on Young's modulus of the structural material, thickness of the cantilever as well as on the gauge factor of the piezoresistor. UV patternable polymers such as SU-8 have a very low Young's modulus compared to the silicon-based materials. Polymer cantilevers with a piezoresistive material having a large gauge factor and a lower Young's modulus are therefore highly suited for sensing applications. In this work, a spin coatable and photopatternable mixture of carbon black (CB) and SU-8, with proper dispersion characteristics, has been demonstrated as a piezoresistive thin film for polymer microcantilevers. Results on percolation experiments of SU-8/CB composite and fabrication of piezoresistive SU-8 microcantilevers using this composite are presented. With our controlled dispersion experiments, we could get a uniform piezoresistive thin film of thickness less than 1.2 μm and resistivity of 2.7 Ω cm using 10 wt% of CB in SU-8. The overall thickness of the SU-8/composite/SU-8 is approximately 3 μm. We further present results on the electromechanical characterization and biofunctionalization of the cantilever structures for biochemical sensing applications. These cantilevers show a deflection sensitivity of 0.55 ppm/nm. Since the surface stress sensitivity is 4.1 × 10⁻³ [N/m]⁻¹, these cantilevers can well be used for detection of protein markers for pathological applications.     

Thin and high conductive multi-walled carbon nanotubes/polydimethylsiloxane composite film prepared via solvent method as strain sensors

Flexible strain sensors based on conductive fillers and flexible polymers possessed significant advantages in human motion detection. Preparing a strain sensing layer with high electrical conductivity and excellent mechanical property under high content of conductive filler contributed to the stability of flexible strain sensors. In this study, MWCNTs/PDMS composite film was prepared by the organic solvent method. The microstructure, electrical conductivity, mechanical property, and piezoresistive characteristics of the composite film at different MWCNTs contents were characterized and discussed. When the mass fraction of MWCNTs in the composite film was 5%, the composite film exhibited a high electrical conductivity of 9.56 S/m while maintaining ideal mechanical properties, and the film thickness was just about 180 μm. The relationship between electrical signals and film strain was performed. The piezoresistive characteristic results demonstrated that the prepared composite film could be used as flexible strain sensor for human motion detection. The prepared thin MWCNTs/PDMS composite film in this paper illustrated high conductive and desired flexibility, and was an alternative material for human motion detection.     

Real-time in situ monitoring of manufacturing process and CFRP quality by relative resistance change measurement

In situ monitoring of resin flow, impregnation of carbon fiber fabrics, and curing during composite manufacturing are very important for determining the quality of composite parts. In conventional methods, sensors, such as optical fibers and strain gages, are bonded to or embedded in the composites for measuring the changes in mechanical and chemical properties. Although they can detect resin curing behavior and impregnation of carbon fibers, they may adversely affect the manufacturing process or structural integrity of the composites. In this study, carbon fiber itself was used as a sensor that minimizes the degradation of mechanical properties and increases the efficiency of monitoring the manufacturing process. The change in the electrical resistance of carbon fiber fabrics was monitored during the various manufacturing processes when the resin flowed through the carbon fiber fabric and curing progressed. The effectiveness of this monitoring method was confirmed, and it is expected to be applicable in monitoring the quality of the finished composite parts.     

Construction of three-dimensional/one-dimensional heterostructure of flower-like Sr nanoflowers on Se microrods decorated on reduced graphene oxide: an efficient electrocatalyst for oxidation of promethazine hydrochloride

Three-dimensional (3D) strontium flowers were grown on well-defined one-dimensional (1D) selenium microrods using a simple hydrothermal technique at 180 °C. This resulted in the formation of a unique 3D/1D material which was ultrasonically treated with reduced graphene oxide to form a hybrid composite. The structural and functional analysis were performed using X-ray diffraction spectroscopy which rendered the material as pure and crystalline and Fourier transform infrared spectroscopy, respectively. X-ray photoelectron spectroscopy was performed to unravel the elemental composition and successful formation of the composite. Field emission scanning electron microscopy and transmission electron microscopy were performed to study the unique morphological features of the material. It was further used to fabricate a sensor for the detection of promethazine hydrochloride (PMZH) drug. The sensor showed a very low detection limit of 7.7 nM at a linear working range of 0.99 μM–900 μM and a sensitivity of 5.282 μA μM^?1 cm^?2. The sensor showed an excellent analyte recovery rate for real-time analysis in biological and environmental samples. The results suggested that the sensor is effective for the detection of PMZH with feasibility for future commercialization.     

A multiwalled carbon nanotube/dihydropyran composite film electrode for insulin detection in a microphysiometer chamber

We have developed a multiwalled carbon nanotube/dihydropyran (MWCNT/DHP) composite sensor for the electrochemical detection of insulin in a microfluidic device. This sensor has been employed for physiological measurements of secreted insulin from pancreatic islets in a Cytosensor^® previously modified to be a multianalyte microphysiometer (MAMP). When compared with other established electrochemical insulin sensors, the MWCNT/DHP composite film sensor presented improved resistance to fluidic shear forces, while achieving enhanced electrode kinetics. In addition, the preparation of the composite film is straightforward and facile with a self-polymerizing monomer, DHP, used to add mechanical stability to the film. The sensor film was able to detect insulin concentrations as low as 1 μM in the MAMP during calibration experiments. The MWCNT/DHP composite sensor has been successfully used for the direct detection of insulin secreted by islets in the microphysiometer.     

Synthesis and Characterization of Nanostructured a-C:H (Hydrogenated Amorphous Carbon) Thin Films by Gaseous Thermionic Vacuum Arc (G-TVA) Deposition Technique

The aim of this contribution is to present the properties of the nanostructured hydrogenated carbon thin films and to study their growth carried out in a special deposition technique based on Thermionic Vacuum Arc method. The Gaseous Thermionic Vacuum Arc (G-TVA) technology is an original deposition method performed in a special configuration, consisting of a heated thermionic cathode which provides an electron beam on the anode. The surface free energy was evaluated by contact angle and their optical properties were studied by Filmetrics F20 spectrometry system. Structure of the film has been investigated by Raman spectroscopy as well as the mechanical properties like hardness, wear resistance, film-substrate adhesion. The films showed two distinct Raman characteristic peaks located at 1,350 cm⁻¹ (D-line) and 1,550 cm⁻¹ (G-line), broad for Si and very sharp for glass substrates. The G-TVA enables to prepare soft (hardness ~6 GPa) or hard (~24 GPa) films.     

Hydrophobic association and ionic coordination dual crossed-linked conductive hydrogels with self-adhesive and self-healing virtues for conformal strain sensors

As a promising functional material, conductive hydrogel has attracted extensive attention, especially in flexible sensor field. Despite the recent developments, current hydrogels still experience several issues, such as limited stretchability, lack of self-recovery and self-healing capability, and insufficient self-adhesion. Herein, dual cross-linked (DC) poly (AA-co-LMA)_SDS/Fe³⁺ hydrogels are fabricated subtly on the basis of ionic coordination interactions and the poly (AA-co-LMA)_SDS hydrophobic association networks, which may provide one plausible routine to compensate the mentioned drawback of hydrogels. The hydrophobic association and ionic coordination networks work synergistically to endow the hydrogels remarkable stretchability (>1200%), high-fracture strength (≈ 820 kPa), and excellent self-healing capability. In addition, the DC hydrogel-based strain sensors displayed a broad sensing range (0 ∼ 900%), conspicuous sensitivity (strain 0% ∼ 200%, gauge factor = 0.53; strain 200% ∼ 500%, gauge factor = 1.23; strain 500% ∼ 900%, gauge factor = 2.09), and pronounced durability. What's more, the self-adhesive feature ensures the strain sensor always forming a good conformal contact with the skin during human movements and displaying remarkable bidirectional detection capability.     

Impact behaviour of Dyneema® fabric-reinforced composites with different resin matrices

This paper presents an experimental study on the impact behaviour of composite laminates made of a Dyneema^® woven fabric and four different resin matrices. Three thicknesses of each kind of resin laminate were subjected to impact by a spherical steel projectile in a velocity regime ranging from 100 to 200 m/s. The results revealed that the laminates having flexible matrices performed much better in perforation resistance and energy absorption, but had a greater extent of deformation and damage than the counterparts with rigid matrices. It was found that the matrix rigidity played a crucial role in controlling the propagation of transverse deformation, and thereby the local strain and perforation resistance of laminates. The more rigid matrix restrained the laminate's transverse deformation to a smaller area at a given time, which led to higher local strain and lower perforation resistance. Fibre failure in tension was identified as the dominant failure mechanism for the tested laminates.     

Nickel containing diamond like carbon thin films

Diamond like carbon (DLC) coatings are well established for multiple applications. The electrical conductivity of DLC or amorphous carbon can be influenced by several orders of magnitude via doping with different metals. Depending on the deposition process hydrogen may be incorporated as well, thereby decreasing the conductivity. Recent investigations of DLC disclose nice piezoresistive properties.Our work was focused on Ni:a-C:H thin films on different substrates by reactive sputtering from a nickel target. Several carbon precursors were added to the sputtering gas to create an amorphous carbon hydrogen network with embedded crystal clusters. In order to optimize the piezoresistive properties we varied various process parameters. The piezoresistive response was monitored by measuring the resistance change during bending. Our Ni:a-C:H films develop gauge factors of approx. 12 in a wide range of process parameters.For sensor applications the temperature coefficient of resistance (TCR) is important as well. It depends on the metal concentration in the thin film and can be adjusted by the concentration of the incorporated nickel. It can be set to approximately zero in a wide temperature range of 80–400 K. The combination of a high gauge factor and a very small TCR is achieved and described in this paper.XRD measurements reveal nickel or nickel carbide clusters with diameters of approx. 8–30 nm depending on the metal concentration. The clusters crystallize in the hexagonal hcp structure which could be transformed into the cubic fcc structure of nickel by thermal annealing in a vacuum.     

复合材料柔软性对倒金字塔微结构阵列传感器性能的影响

采用模压成型方法制备了2种柔软性不同的热塑性聚氨酯/短切碳纤维/碳纳米管(TPU/SCF-CNT)复合材料复制物, 其表面上具有倒金字塔微结构阵列, 内部有SCF与CNT共同构成的导电通路. 将复合材料复制物和相应的复合材料平整片封装成柔性传感器. 结果表明, 压力作用下传感器内复制物和平整片之间的接触电阻因倒金字塔底棱的形变而显著降低. 对使用柔软性较高的复合材料封装的传感器, 虽然其相对迟滞稍大, 但压力作用下倒金字塔底棱形变量较大, 且复制物和平整片内导电通路增加量较大, 因此其在0~2.5 kPa的线性区内具有较高的灵敏度(0.32 kPa^?1). 制备的2种传感器均具有快速响应特性, 且能在500 s(约1580次)的循环压缩/释放测试(峰值压力约3 kPa)中保持较稳定的电阻响应. 研究表明, 利用模压成型的表面倒金字塔结构复合材料复制物封装成的柔性压力传感器具有良好的传感性能.     

Sensor integration in rubber gaskets for structural health monitoring made by compression molding

This research work shows the integration process and characterization of a miniaturized strain gauge sensor in rubber O-rings for structural health monitoring (SHM). Strain gauges have been successfully embedded during compression molding, which is a commonly used fabrication method of rubber components. The sensor signal is correlated with the contact pressure of the gasket that abates over time due to aging processes. This can be exploited for lifetime prediction. Embedding sensors into rubber applying compression molding is a novel method that allows the integration into non-liquid elastomers. The strain gauge resistance correlates linearly to the contact pressure. An artificial aging test exhibits an exponential decrease in the resistance caused by the relaxation processes during the accelerated aging of the elastomer at 70 °C for 72 h. Uniaxial tensile testing with dumbbell specimens reveals the influence of the integrated sensors. It is demonstrated that the influence heavily depends on the sensor size.     

Construction of zinc selenide microspheres decorated with octadecylamine-functionalized reduced graphene oxide as an effective catalyst for the dual-mode detection of chloroquine phosphate

Zinc selenide microspheres were constructed using a simple hydrothermal technique at 180°C. It was ultrasonically treated with reduced graphene oxide modified with octadecylamine alkyl amine to form a hybrid nanocomposite. The optical, structural, and functional analysis by ultraviolet (UV) absorbance, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy revealed the crystal nature of the microspheres and the successful formation of the nanocomposite. Field emission scanning electron microscopy and transmission electron microscopy were done to study the morphological properties of the material. It was further used to fabricate a dual-modality sensor using both electrochemical and absorbance techniques for the detection of antimalarial drug chloroquine phosphate (CQP), which was used for the treatment of COVID-19 (SARS-CoV-2) virus. For electrochemical detection, the sensor showed a very low detection limit of 1.43 nM at a linear working range of 0.199–250.06 μM and a high sensitivity of 43.912 μA/μM/cm². For UV-based detection, the sensor showed a very low detection limit of 6.88 nM at a linear working range of 0.045–7.324 μM. The sensor showed excellent analyte recovery rate for real-time analysis in biological as well as environmental samples. The results suggested that the sensor is effective for the detection of CQP with feasibility for future commercialization.     

A metal–organic gel‐based fluorescent chemosensor for selective Al3+ detection

As an important metal element, aluminium has a significant impact on the environment and human health, and thus the detection of Al³⁺ has become the subject of much research. We synthesized a Ni(II)‐based metal–organic gel (Ni‐MOG), which can serve as an Al³⁺ fluorescence sensor with high selectivity and sensitivity, the limit of detection being calculated to be 0.5 μM. In addition, a composite film was further fabricated by hybridization of this Ni‐MOG with poly(vinyl alcohol). The composite film produced a rapid fluorescence response to Al³⁺ solutions at concentrations above 5 × 10^?5 M in 5 min. The Ni‐MOG composite film can also be successfully applied for the sensitive detection of Al³⁺ in real samples of tap water and seawater. The effective detection of Al³⁺ described in this contribution provides a new insight into water quality monitoring and has promising application value.