Search Results (16)

A polydimethylsilosane/multiwalled carbon nanotube (PDMS/MWCNT) nanocomposite, as a tensile-strain-sensing material, was manufactured using a simple solution casting method. The percolation threshold, the relationship between the temperature and resistance, the tensile sensitivity, and the mechanism of the tensile sensitivity of the PDMS/MWCNT nanocomposite were studied, along with its application in concrete crack monitoring. The results show that the PDMS/MWCNT nanocomposite demonstrated a significant percolation phenomenon. The resistance change ratio of the PDMS/MWCNT nanocomposite changed linearly with the environmental temperature, gradually decreasing with an increasing environmental temperature. The PDMS/MWCNT nanocomposite had a higher tensile sensitivity, and the sensing factor was 6.65 when the volume fraction of carbon nanotubes was 1.26 v/v% near the percolation threshold, and the sensing factor of the PDMS/MWCNT nanocomposite decreased with an increase in the volume fraction of carbon nanotubes. The relationship between the relative electrical conductivity of the PDMS/MWCNT nanocomposite and the tensile strain can be expressed as ln(σ/σ₀) = Aε. In addition, the quantitative relationship between the electrical conductivity of the PDMS/MWCNT nanocomposite and the volume fraction of carbon nanotubes was obtained based on the tunneling effect theory and the effective medium model. PDMS/MWCNT nanocomposites can be used as a sensing material to monitor the propagation of concrete cracks under the impact of a free-falling ball. Full article

In this work, the synergistic effect of graphene nanosheets (GNs), as well as multiwalled carbon nanotubes (MWCNTs), as reinforcing agents of polydimethylsiloxane (PDMS) was investigated, in order to explore the possibilities of designing composite materials, tailored for use in the field of coatings, which might be, in fact, a very interesting application. It was shown that the addition of GNs and MWCNTs in PDMS matrices significantly improves the thermal stability of the obtained nanocomposites, especially those reinforced exclusively with GNs. The tensile tests indicated that strength increased for all the examined composites. It was also observed that the Young’s moduli had an increasing trend, with the exception of the composites containing only GNs, while those reinforced solely with MWCNTs exhibited the best performance. The O₂ permeability measurements revealed that the highest reduction in the permeability was observed in GN-MWCNT/PDMS composite membranes, in comparison to those reinforced only with graphene or carbon nanotubes. Dielectric relaxation spectroscopy showed that all the examined composites, and especially those of MWCNTs, possess electrical conductivity, apart from the samples reinforced exclusively with graphene. The electromagnetic shielding effectiveness was also improved at higher filler loadings, which is more evident in composites reinforced with MWCNTs. It was concluded that the improved properties of the above studied hybrid composites make them suitable for protective coating applications. Full article

Soft robotics is an expanding area with multiple applications; however, building low-cost, soft, and flexible robots requires the development of sensors that can be directly integrated into the soft robotics fabrication process. Thus, the motivation for this work was the design of a low-cost fabrication process of flexible sensors that can detect touch and deformation. The fabrication process proposed uses a flexible polymer nanocomposite with permanent magnets strategically placed where the conductive electrodes should be. The nanocomposite is based on poly(dimethylsiloxane) (PDMS) and multi-walled carbon nanotubes (MWCNTs). The MWCNT contains ferromagnetic impurities remaining from the synthesis process, which can be used for magnetic manipulation. Several electrode geometries were successfully simulated and tested. The magnetic patterning was simulated, allowing the fabrication of conductive patterns within the composite. This fabrication process allowed the reduction of the electrical resistivity of the nanocomposites as compared to the composites with homogeneous MWCNT dispersion. It also allowed the fabrication of piezoresistive and triboelectric sensors at MWCNT concentration as low as 0.5 wt.%. The fabrication process proposed is flexible, allows the development of sensors for soft robotics, as well as monitoring large and unconventional areas, and may be adapted to different mould shapes and polymers at low cost. Full article

Any surface immersed in sea water will suffer from marine fouling, including underwater sound absorption coatings. Traditional underwater sound absorption coatings rely heavily on the use of toxic, biocide-containing paints to combat biofouling. In this paper, an environmentally-friendly nanocomposite with integrated antifouling and underwater sound absorption properties was fabricated by adopting MWCNTs-COOH and SiO₂ into PDMS at different ratios. SEM, FTIR and XPS results demonstrated MWCNTs were mixed into PDMS, and the changes in elements were also analyzed. SiO₂ nanoparticles in PDMS decreased the tensile properties of the coating, while erosion resistance was enhanced. Antibacterial properties of the coatings containing MWCNTs-COOH and SiO₂ at a ratio of 1:1, 1:3, and 1:5 reached 62.02%, 72.36%, and 74.69%, respectively. In the frequency range of 1500–5000 Hz, the average sound absorption coefficient of PDMS increased from 0.5 to greater than 0.8 after adding MWCNTs-COOH and SiO₂, which illustrated that the addition of nanoparticles enhanced the underwater sound absorption performance of the coating. Incorporating MWCNTs-COOH and SiO₂ nanoparticles into the PDMS matrix to improve its sound absorption and surface antifouling properties provides a promising idea for marine applications. Full article

One of the main challenges during the integration of a carbon/polymer-based nanocomposite sensor on textile substrates is the fabrication of a homogeneous surface of the nanocomposite-based thin films, which play a major role in the reproducibility of the sensor. Characterizations are therefore required in every fabrication step to control the quality of the material preparation, deposition, and curing. As a result, microcharacterization methods are more suitable for laboratory investigations, and electrical methods can be easily implemented for in situ characterization within the manufacturing process. In this paper, several textile-based pressure sensors are fabricated at an optimized concentration of 0.3 wt.% of multiwalledcarbon nanotubes (MWCNTs) composite material in PDMS. We propose to use impedance spectroscopy for the characterization of both of the resistive behavior and capacitive behavior of the sensor at several frequencies and under different loads from 50 g to 500 g. The impedance spectra are fitted to a model composed of a resistance in series with a parallel combination of resistance and a constant phase element (CPE). The results show that the printing parameters strongly influence the impedance behavior under different loads. The deviation of the model parameter $\alpha$ of the CPE from the value 1 is strongly dependent on the nonhomogeneity of the sensor. Based on an impedance spectrum measurement followed by parameter extraction, the parameter $\alpha$ can be determined to realize a novel method for homogeneity characterization and in-line quality control of textile-integrated wearable sensors during the manufacturing process. Full article

The paper presents the use of surfactant-induced MWCNTs/PDMS-based nanocomposites for tactile sensing applications. The significance of nanocomposites-based sensors has constantly been growing due to their enhanced electromechanical characteristics. As a result of the simplified customization for their target applications, research is ongoing to determine the quality and quantity of the precursor materials that are involved in the fabrication of nanocomposites. Although a significant amount of work has been done to develop a wide range of nanocomposite-based prototypes, they still require optimization when mixed with polydimethylsiloxane (PDMS) matrices. Multi-Walled Carbon Nanotubes (MWCNTs) are one of the pioneering materials used in multifunctional sensing applications due to their high yield, excellent electrical conductivity and mechanical properties, and high structural integrity. Among the other carbon allotropes used to form nanocomposites, MWCNTs have been widely studied due to their enhanced bonding with the polymer matrix, highly densified sampling, and even surfacing throughout the composites. This paper highlights the development, characterization and implementation of surfactant-added MWCNTs/PDMS-based nanocomposites. The prototypes consisted of an optimized amount of sodium dodecyl sulfonate (SDS) and MWCNTs mixed as nanofillers in the PDMS matrix. The results have been promising in terms of their mechanical behaviour as they responded well to a maximum strain of 40%. Stable and repeatable output was obtained with a response time of 1 millisecond. The Young’s Modulus of the sensors was 2.06 MPa. The utilization of the prototypes for low-pressure tactile sensing applications is also shown here. Full article

Wearable sensors are gaining attention in human health monitoring applications, even if their usability is limited due to battery need. Flexible nanogenerators (NGs) converting biomechanical energy into electrical energy offer an interesting solution, as they can supply the sensors or extend the battery lifetime. Herein, flexible generators based on lead-free barium titanate (BaTiO₃) and a polydimethylsiloxane (PDMS) polymer have been developed. A comparative study was performed to investigate the impact of multiwalled carbon nanotubes (MWCNTs) via structural, morphological, electrical, and electromechanical measurements. This study demonstrated that MWCNTs boosts the performance of the NG at the percolation threshold. This enhancement is attributed to the enhanced conductivity that promotes charge transfer and enhanced mechanical property and piezoceramics particles distribution. The nanogenerator delivers a maximum open-circuit voltage (V_OC) up to 1.5 V and output power of 40 nW, which is two times higher than NG without MWCNTs. Additionally, the performance can be tuned by controlling the composite thickness and the applied frequency. Thicker NG shows a better performance, which enlarges their potential use for harvesting biomechanical energy efficiently up to 11.22 V under palm striking. The voltage output dependency on temperature was also investigated. The results show that the output voltage changes enormously with the temperature. Full article

Foot pressure measurement plays an essential role in healthcare applications, clinical rehabilitation, sports training and pedestrian navigation. Among various foot pressure measurement techniques, in-shoe sensors are flexible and can measure the pressure distribution accurately. In this paper, we describe the design and characterization of flexible and low-cost multi-walled carbon nanotubes (MWCNT)/Polydimethylsiloxane (PDMS) based pressure sensors for foot pressure monitoring. The sensors have excellent electrical and mechanical properties an show a stable response at constant pressure loadings for over 5000 cycles. They have a high sensitivity of 4.4 k$\mathsf{\Omega }$/kPa and the hysteresis effect corresponds to an energy loss of less than 1.7%. The measurement deviation is of maximally 0.13% relative to the maximal relative resistance. The sensors have a measurement range of up to 330 kPa. The experimental investigations show that the sensors have repeatable responses at different pressure loading rates (5 N/s to 50 N/s). In this paper, we focus on the demonstration of the functionality of an in-sole based on MWCNT/PDMS nanocomposite pressure sensors, weighing approx. 9.46 g, by investigating the foot pressure distribution while walking and standing. The foot pressure distribution was investigated by measuring the resistance changes of the pressure sensors for a person while walking and standing. The results show that pressure distribution is higher in the forefoot and the heel while standing in a normal position. The foot pressure distribution is transferred from the heel to the entire foot and further transferred to the forefoot during the first instance of the gait cycle. Full article

The presented study deals with the fabrication of highly stable and active nanobiocatalysts based on Candida antarctica lipase B (CALB) immobilization onto pristine and poly(dimethylsiloxane) modified MWCNTs. The MWCNTs/PDMS nanocomposites, containing 40 wt.% of the polymer with two molecular weights, were successfully synthesized via adsorption modification. The effect of PDMS chains length on the textural/structural properties of produced materials was studied by means of the nitrogen adsorption–desorption technique, Raman spectroscopy, and attenuated total reflectance Fourier transform infrared spectroscopy. P-MWCNTs and MWCNTs/PDMS nanocomposites were tested as supports for lipase immobilization. Successful deposition of the enzyme onto the surface of P-MWCNTs and MWCNTs/PDMS nanocomposite materials was confirmed mainly using ATR-FTIR spectroscopy. The immobilization efficiency, stability, and catalytic activity of the immobilized enzyme were studied, and the reusability of the produced biocatalytic systems was examined. The presented results demonstrate that the produced novel biocatalysts might be considered as promising materials for biocatalytic applications. Full article

Piezoresistive tactile sensors made using nanocomposite polymeric materials have been shown to possess good flexibility, electrical performance, and sensitivity. However, the sensing performance, especially in the low-pressure range, can be significantly improved by enabling uniform dispersion of the filler material and utilization of effective structural designs that improve the tactile sensing performance. In this study, a novel flexible piezoresistive tactile sensor with a grid-type microstructure was fabricated using polymer composites comprising multi-walled carbon nanotubes (MWCNTs) as the conductive filler and polydimethylsiloxane (PDMS) as the polymeric matrix. The research focused on improving the tactile sensor performance by enabling uniform dispersion of filler material and optimizing sensor design and structure. The doping weight ratio of MWCNTs in PDMS varied from 1 wt.% to 10 wt.% using the same grid structure-sensing layer (line width, line spacing, and thickness of 1 mm). The sensor with a 7 wt.% doping ratio had the most stable performance, with an observed sensitivity of 6.821 kPa⁻¹ in the lower pressure range of 10–20 kPa and 0.029 kPa⁻¹ in the saturation range of 30–200 kPa. Furthermore, the dimensions of the grid structure were optimized and the relationship between grid structure, sensitivity, and sensing range was correlated. The equation between pressure and resistance output was derived to validate the principle of piezoresistance. For the grid structure, dimensions with line width, line spacing, and thickness of 1, 1, and 0.5 mm were shown to have the most stable and improved response. The observed sensitivity was 0.2704 kPa⁻¹ in the lower pressure range of 50–130 kPa and 0.0968 kPa⁻¹ in the saturation range of 140–200 kPa. The piezoresistive response, which was mainly related to the quantum tunneling effect, can be optimized based on the dopant concentration and the grid microstructure. Furthermore, the tactile sensor showed a repeatable response, and the accuracy was not affected by temperature changes in the range of 10 to 40 °C and humidity variations from 50 to 80%. The maximum error fluctuation was about 5.6% with a response delay time of about 1.6 ms when cyclic loading tests were performed under a normal force of 1 N for 10,200 cycles. Consequently, the proposed tactile sensor shows practical feasibility for a wide range of wearable technologies and robotic applications such as touch detection and grasping. Full article

The intersection between nanoscience and additive manufacturing technology has resulted in a new field of printable and flexible electronics. This interesting area of research tackles the challenges in the development of novel materials and fabrication techniques towards a wider range and improved design of flexible electronic devices. This work presents the fabrication of a cost-effective and facile flexible piezoresistive pressure sensor using a 3D-printable carbon nanotube-based nanocomposite. The carbon nanotubes used for the development of the material are multi-walled carbon nanotubes (MWCNT) dispersed in polydimethylsiloxane (PDMS) prepolymer. The sensor was fabricated using the direct ink writing (DIW) technique (also referred to as robocasting). The MWCNT-PDMS composite was directly printed onto the polydimethylsiloxane substrate. The sensor response was then examined based on the resistance change to the applied load. The sensor exhibited high sensitivity (6.3 Ω/kPa) over a wide range of applied pressure (up to 1132 kPa); the highest observed measurement range for MWCNT-PDMS composite in previous work was 40 kPa. The formulated MWCNT-PDMS composite was also printed into high-resolution 3-dimensional shapes which maintained their form even after heat treatment process. The possibility to use 3D printing in the fabrication of flexible sensors allows design freedom and flexibility, and structural complexity with wide applications in wearable or implantable electronics for sport, automotive and biomedical fields. Full article

Soft compliant strain gauges are key devices for wearable applications such as body health sensor systems, exoskeletons, or robotics. Other than traditional piezoresistive materials, such as metals and doped semiconductors placed on strain-sensitive microsystems, a class of soft porous materials with exotic mechanical properties, called auxetics, can be employed in strain gauges in order to boost their performance and add functionalities. For strain electronic read-outs, their polymeric structure needs to be made conductive. Herein, we present the fabrication process of an auxetic electrode based on a polymeric nanocomposite. A multiwalled carbon nanotube/polydimethylsiloxane (MWCNT/PDMS) is fabricated on an open-cell polyurethane (PU) auxetic foam and its effective usability as an electrode for strain-gauge sensors is assessed. Full article

In this paper, polydimethylsiloxane (PDMS) and multi-walled carbon nanotube (MWCNT) nanocomposites with piezoresistive sensing function were fabricated using microwave irradiation. The effects of precuring time on the mechanical and electrical properties of nanocomposites were investigated. The increased viscosity and possible nanofiller re-agglomeration during the precuring process caused decreased microwave absorption, resulting in extended curing times, and decreased porosity and electrical conductivity in the cured nanocomposites. The porosity generated during the microwave-curing process was investigated with a scanning electron microscope (SEM) and density measurements. Increased loadings of MWCNTs resulted in shortened curing times and an increased number of small well-dispersed closed-cell pores. The mechanical properties of the synthesized nanocomposites including stress–strain behaviors and Young’s Modulus were examined. Experimental results demonstrated that the synthesized nanocomposites with 2.5 wt. % MWCNTs achieved the highest piezoresistive sensitivity with an average gauge factor of 7.9 at 10% applied strain. The piezoresistive responses of these nanocomposites were characterized under compressive loads at various maximum strains, loading rates, and under viscoelastic stress relaxation conditions. The 2.5 wt. % nanocomposite was successfully used in an application as a skin-attachable compression sensor for human motion detection including squeezing a golf ball. Full article

Harmonious developments of electrical and mechanical performances are crucial for stretchable sensors in structural health monitoring (SHM) of flexible aircraft such as aerostats and morphing aircrafts. In this study, we prepared a highly durable ternary conductive nanocomposite made of polydimethylsiloxane (PDMS), carbon black (CB) and multi-walled carbon nanotubes (MWCNTs) to fabricate stretchable strain sensors. The nanocomposite has excellent electrical and mechanical properties by intensively optimizing the weight percentage of conducting fillers as well as the ratio of PDMS pre-polymer and curing agent. It was found that the nanocomposite with homogeneous hybrid filler of 1.75 wt % CB and 3 wt % MWCNTs exhibits a highly strain sensitive characteristics of good linearity, high gauge factor (GF ~ 12.25) and excellent durability over 10⁵ stretching-releasing cycles under a tensile strain up to 25% when the PDMS was prepared at the ratio of 12.5:1. A strain measurement of crack detection for the aerostats surface was also employed, demonstrating a great potential of such ternary nanocomposite used as stretchable strain sensor in SHM. Full article

Nanocomposites based on Multi-Walled Carbon Nanotubes (MWCNT)—Polydimethylsiloxane (PDMS) polymer achieve pressure sensors sensitive even at very low pressure less than 5 N. For film homogeneity and sensitivity, fabrication procedure and especially the dispersion quality are decisive. Because of high viscosity of PDMS, a solvent is necessary. Solvents exhibit themselves different dispersion quality and in turn different piezoresistive response of the films under pressure. In this paper, the influence of solvents in fabricating the nanocomposite is investigated considering dispersion quality and stability. The best dispersion stability was achieved with isopropanol and the nanocomposite show better results considering sensitivity and hysteresis behavior under pressure. Full article