Carbon Nanotube Polydimethylsiloxane Research Articles

Sandwich-Structured Carbon Nanotube Composite Films for Multifunctional Sensing and Electrothermal Application.

Electro-conductive films with excellent flexibility and thermal behavior have great potential in the fields of wearable electronics, artificial muscle, and soft robotics. Herein, we report a super-elastic and electro-conductive composite film with a sandwich structure. The composite film was constructed by spraying Polyvinyl alcohol (PVA) polymers onto a buckled conductive carbon nanotube-polydimethylsiloxane (CNTs-PDMS) composite film. In this system, the PVA and PDMS provide water sensing and stretchability, while the coiled CNT film offers sufficient conductivity. Notably, the composite film possesses high stretchability (205%), exceptional compression sensing ability, humility sensing ability, and remarkable electrical stability under various deformations. The produced CNT composite film exhibited deformation (bending/twisting) and high electro-heating performance (108 °C) at a low driving voltage of 2 V. The developed CNT composite film, together with its exceptional sensing and electrothermal performance, provides the material with promising prospects for practical applications in wearable electronics.

Hadamard acoustic correlated imaging based on photoacoustic modulation with a single transducer

Conventional ultrasound technology based on spot scanning or phased array encounters significant challenge in real-time imaging with a single detector. In this paper, we present a Hadamard acoustic correlated imaging based on photoacoustic modulation with one transducer. The process of accurately generating the Hadamard acoustic field is to apply the carbon-nanotubes–polydimethylsiloxane composite to absorb the optimized Hadamard basis pattern. Taking advantage of correlated imaging, our system without scanning can reduce imaging artifacts and its resolution could be about four times higher than that of traditional ultrasound imaging. The use of a single transducer rather than an array of transducers can reduce the cost of the imaging system. Therefore, the proposed scheme can find applications in biomedical imaging and nondestructive evaluation.

A Theoretical Investigation of the Electrical and Dielectric Properties of PDMS‐CNT

AbstractIn the present study, the dielectric and electrical properties of the carbon nanotube/polydimethylsiloxane (CNT/PDMS) composite are theoretically analyzed for various doping concentrations. For both single‐walled and multiwalled CNTs (SCNTs and MCNTs), the work is done between 75 and 750 THz. The behavior of the dielectric constant, loss factor, and conductivity are analyzed as functions of frequency. It is observed that there is no appreciable change in the real part of the dielectric constant at high frequencies in single‐walled CNT. The loss tangent is high at lower frequencies, and the loss peak is observed at a particular frequency. The Cole–Cole plot is used to interpret the static‐ and high‐frequency dielectric constants and relaxation time of the composite. With increasing concentrations of SCNT and MCNT, the conductivity at the obtained peak maximum shifts to a lower frequency.

Optical and ultrasonic dual-sensitive sensor and its application in photoacoustic microscopy

Multi-modality imaging is significant for biomedical applications. We propose a dual-sensitive sensor to simultaneously detect optical and ultrasonic signals. Based upon the classical piezoelectric structure, we attach a photosensitive layer made of carbon nanotubes-polydimethylsiloxane (CNTs-PDMS) composite to the surface. The photosensitive layer absorbs light and converts it into ultrasound, while allowing acoustic energy to transmit through concurrently. After optimizing the ratio of PDMS to CNTs, we increase the sensor’s light detection sensitivity and maintain the ultrasound detection sensitivity. Finally, the successful implementation in mouse ear optical attenuation–photoacoustic imaging demonstrates the dual-sensitive sensor’s potential application in multi-modality imaging.

Development of highly sensitive/durable porous carbon nanotube–polydimethylsiloxane sponge electrode for wearable human motion monitoring sensor

Herein, we present a novel approach for fabricating porous carbon nanotube–polydimethylsiloxane (CNT–PDMS) sponge electrodes for piezoelectric/piezoresistive sensing.

Design of Superhydrophobic Shape Memory Composites with Kirigami Structures and Uniform Wetting Property.

With the continuous increase in human demand to improve aircraft performance, intelligent aircraft technologies have become a popular research field in recent years. Among them, the deformable skin structure has become one of the key technologies to achieve excellent and reliable performance. However, during the service, deformable skin structures may encounter problems such as surface impact and adhesion of droplets in rainy weather or surface icing in low-temperature environments, which can seriously affect the flight safety of the aircraft. One way to overcome these issues is to use superhydrophobic shape memory materials in the structure. In this regard, first, shape memory composites were prepared with shape memory epoxy resin as the matrix and carbon fiber orthogonal woven fabric as the reinforcement material. Superhydrophobic shape memory composites (SSMCs) were then obtained by casting the kirigami composite with superhydrophobic carbon nanotube-polydimethylsiloxane (CNT@PDMS) mixture, and the surface was processed by laser micromachining. Shape memory performance and surface wetting performance were determined by material testing methods. The results showed that the shape memory recovery rate can reach 85.11%, the surface is superhydrophobic, the average water contact angle is 156.9 ± 4.4°, and the average rolling angle is 3 ± 0.5°. The three-point bending test of the specimens with different kirigami cell configurations showed that the shape memory composite based on the rectangular structure has the best deformability with an aspect ratio of 0.4. From the droplet impact test, it was found that the impact speed of water droplets and the curvature of the surface can greatly affect the dynamic performance of water. This work is expected to be of significant research value and importance for developing functional deformable skin materials.

Predicting and Controlling Ribbing Instabilities of Carbon Nanotube–PDMS Thin‐Film Systems for Multifunctional Applications

The manufacturing of thin films with structured surfaces by large‐scale rolling has distinct advantages over other techniques, such as lithography, due to scalability. However, it is not well understood or quantified how processing conditions can affect the microstructure at different physical scales. Hence, the objective of this investigation is to develop a validated computational model of the symmetric forward‐roll coating process to understand, predict, and control the morphology of carbon nanotube (CNT)–polydimethylsiloxane (PDMS) pastes. The effects of the thin‐film rheological properties and the roller gap on the ribbing behavior are investigated and a ribbing instability prediction model is formulated from experimental measurements and computational predictions. The CNT–PDMS thin‐film system is modeled by a nonlinear implicit dynamic finite‐element method that accounts for ribbing instabilities, large displacements, rolling contact, and material viscoelasticity. Dynamic mechanical analysis is used to obtain the viscoelastic properties of the CNT–PDMS paste for various CNT weight distributions. Furthermore, a Morris sensitivity analysis is conducted to obtain insights on the dominant predicted characteristics pertaining to the ribbing microstructure. Based on the sensitivity analysis, a critical ribbing aspect ratio is identified for the CNT–PDMS system corresponding to a critical roller gap.

Adhesive Wearable Sensors for Electroencephalography from Hairy Scalp.

Electroencephalography has garnered interest for applications in mobile healthcare, human-machine interfaces, and Internet of Things. Conventional electroencephalography relies on wet and dry electrodes. Despite favorable interface impedance of wet electrodes and skin, the application of a large amount of gel at their interface with skin limits the electroencephalography spatial resolution, increases the risk of shorting between electrodes, and makes them unsuited for long-term mobile recording. In contrast, dry electrodes are better suited for long-term recordings but susceptible to motion artifacts. In addition, both wet and dry electrodes are non-adhesive to the hairy scalp and mechanical support, or chemical adhesives are used to hold them in place. Herein, a conical microstructure array (CMSA) based sensor made of carbon nanotube-polydimethylsiloxane composite is reported. The CMSA sensor is fabricated using the innovative, cost-effective, and scalable method of viscosity-controlled dip-pull process. The sensor adheres to the hairy scalp by generating negative pressure in its conical microstructures when it is pressed against scalp. Aided by the application of a trace amount of gel, CMSA sensor establishes good electrical contact with the skin, enabling its applications in mobile electroencephalography over extended periods. Notably, the signal quality of CMSA sensors is comparable to that of medical-grade wet gel electrodes.

3D Printing of Stretchable Strain Sensor Based on Continuous Fiber Reinforced Auxetic Structure

Stretchable strain sensors play a key role in motion detection and human-machine interface functionality, and deformation control. However, their sensitivity is often limited by the Poisson effect of elastic substrates. In this study, a stretchable strain sensor based on a continuous-fiber-reinforced auxetic structure was proposed and fabricated using a direct ink writing (DIW) 3D printing process. The application of multi-material DIW greatly simplifies the fabrication process of a sensor with an auxetic structure (auxetic sensor). The auxiliary auxetic structure was innovatively printed using a continuous-fiber-reinforced polydimethylsiloxane composite (Fiber-PDMS) to balance the rigidity and flexibility of the composite. The increase in stiffness enhances the negative Poisson's ratio effect of the auxetic structure, which can support the carbon nanotube-polydimethylsiloxane composite (CNT-PDMS) stretchable sensor to produce a significant lateral expansion when stretched. It is shown that the structural Poisson's ratio of the sensor decreased from 0.42 to −0.33 at 20% tensile strain, and the bidirectional tensile strain increases the sensor sensitivity by 2.52 times (gage factor to 18.23). The Fiber-PDMS composite maintains the excellent flexibility of the matrix material. The auxetic sensor exhibited no structural damage after 150 cycles of tension and the signal output exhibited high stability. In addition, this study demonstrates the significant potential of auxetic sensors in the field of deformation control.

Salt-blocking three-dimensional Janus evaporator with superwettability gradient for efficient and stable solar desalination

Solar interfacial steam power generation is a prospective method for seawater desalination. In this work, a salt-blocking three-dimensional (3D) Janus evaporator with a superhydrophobic to superhydrophilic gradient was fabricated by spraying a composite dispersion of multi-walled carbon nanotubes/polydimethylsiloxane (CNTs/PDMS) onto the top side of a polyurethane (PU) foam and polyvinyl alcohol (PVA) solution onto the bottom side. The CNTs/PDMS composite dispersion with nanostructured CNTs and low surface energy PDMS combined with the porous structure of the PU foam rendered the top side superhydrophobic. Therefore, a layer suitable for photothermal conversion was obtained. The hydrophilic PVA combined with the porous structure of the foam rendered the bottom side superhydrophilic, facilitating water absorption and transportation. The asymmetric wettability gradient of the CNTs/PDMS-PU-PVA as a 3D evaporator caused the evaporation rate and transportation speed of water to reach a balance, and the salt was quickly dissolved at the superhydrophilic interface. This 3D salt-resistant Janus evaporator achieved an evaporation rate of 2.26 kg m-2 h−1 under 1 kW m−2 illumination.

Multichannel Flexible Pulse Perception Array for Intelligent Disease Diagnosis System.

Pressure sensors with high sensitivity, a wide linear range, and a quick response time are critical for building an intelligent disease diagnosis system that directly detects and recognizes pulse signals for medical and health applications. However, conventional pressure sensors have limited sensitivity and nonideal response ranges. We proposed a multichannel flexible pulse perception array based on polyimide/multiwalled carbon nanotube-polydimethylsiloxane nanocomposite/polyimide (PI/MPN/PI) sandwich-structure pressure sensor that can be applied for remote disease diagnosis. Furthermore, we established a mechanical model at the molecular level and guided the preparation of MPN. At the structural level, we achieved high sensitivity (35.02 kPa-1) and a broad response range (0-18 kPa) based on a pyramid-like bilayer microstructure with different upper and lower surfaces. A 27-channel (3 × 9) high-density sensor array was integrated at the device level, which can extract the spatial and temporal distribution information on a pulse. Furthermore, two intelligent algorithms were developed for extracting six-dimensional pulse information and automatic pulse recognition (the recognition rate reaches 97.8%). The results indicate that intelligent disease diagnosis systems have great potential applications in wearable healthcare devices.

Flexible conductivity-temperature-depth-strain (CTDS) sensor based on a CNT/PDMS bottom electrode for underwater sensing

Marine hydrological information has a significant impact on human development and the utilization of the oceans, which can be monitored with underwater sensors. In the past, ocean research has relied on the use of bulky underwater recorders and sensory telemetry networks. In this study, an integrated flexible sensor is developed for underwater conductivity, temperature, depth, and strain detection. Platinum resistance sensors were used for temperature and strain measurements, conductivity sensors with interdigitated electrodes were used for salinity measurements, and capacitive pressure sensors for depth measurements. Two kinds of flexible capacitive pressure sensors were fabricated with a carbon nanotube/polydimethylsiloxane (CNT/PDMS) bottom electrode and copper/polyimide (Cu/PI) bottom electrode. The sensor with the CNT/PDMS bottom electrode outperformed the sensor with the Cu/PI bottom electrode over a wide pressure range (<5 MPa) and showed stable capacitance up to 1000 cycles. COMSOL simulations also support our experimental results with high sensitivity of the sensor with a CNT/PDMS bottom electrode. The integrated flexible sensor is durable and lightweight, making it ideal for use as a stationary monitoring sensor or for attachment to a variety of marine animals.

Study of flexible piezoresistive sensors based on the hierarchical porous structure CNT /PDMS composite materials

Flexible piezoresistive sensors (FPS) are important components of wearable electronics for human-machine interaction, human physiological signal monitoring and electronic skin. In this work, carbon nanotube (CNT)-polydimethylsiloxane (PDMS) (abbreviated as CP) composite materials with hierarchical porous structures were prepared by a facile solvothermal method. The electrical conductivity and mechanical elasticity of the porous structure CP composite materials can be separately tuned by varying the CNT mass fraction and PDMS composition ratio, respectively. A flexible piezoresistive sensor using porous structure CP composite materials as the sensing material was designed and fabricated. The optimized sensor exhibits a sensitivity of 0.59 kPa −1 in the pressure ranges of 0–260 kPa, a low detection limit of 12 Pa, a fast response time of 25 ms and outstanding cycling stability over 1,700 cycles. Such sensor design can be integrated into flexible wearable electronic devices for physiological signal monitoring in real-time. • The hierarchical porous structure CNT/PDMS composite materials were prepared by solvothermal method. • Mechanical and electrical properties of CNT/PDMS composite materials can be adjusted by changing the process parameters. • Sensing mechanism and sensor performance of FPS based on CNT/PDMS composite materials were studied. •Application of FPS for recording human respiratory volume and rate and human activity were examined.

Bioinspired Spinosum Capacitive Pressure Sensor Based on CNT/PDMS Nanocomposites for Broad Range and High Sensitivity.

Flexible pressure sensors have garnered much attention recently owing to their prospective applications in fields such as structural health monitoring. Capacitive pressure sensors have been extensively researched due to their exceptional features, such as a simple structure, strong repeatability, minimal loss and temperature independence. Inspired by the skin epidermis, we report a high-sensitivity flexible capacitive pressure sensor with a broad detection range comprising a bioinspired spinosum dielectric layer. Using an abrasive paper template, the bioinspired spinosum was fabricated using carbon nanotube/polydimethylsiloxane (CNT/PDMS) composites. It was observed that nanocomposites comprising 1 wt% CNTs had excellent sensing properties. These capacitive pressure sensors allowed them to function at a wider pressure range (~500 kPa) while maintaining sensitivity (0.25 kPa−1) in the range of 0–50 kPa, a quick response time of approximately 20 ms and a high stability even after 10,000 loading–unloading cycles. Finally, a capacitive pressure sensor array was created to detect the deformation of tires, which provides a fresh approach to achieving intelligent tires.

Crack Sensing of Cardiomyocyte Contractility with High Sensitivity and Stability.

Measuring myocardial contractility is of great value in exploring cardiac pathogenesis and quantifying drug efficacy. Among the biosensing platforms developed for detecting the weak contractility of a single layer of cardiomyocytes (CMs), thin brittle metal membrane sensors with microcracks are highly sensitive. However, their poor stability limits the application in long-term measurement. Here, we report a high stability crack sensor fabricated by deposition of a 105 nm thick Ag/Cr with microcracks onto a carbon nanotubes-polydimethylsiloxane (CNT-PDMS) layer. This brittle-tough bilayer crack sensor achieved high sensitivity (gauge factor: 108 241.7), a wide working range (0.01-44%), and high stability (stable period >2 000 000 cycles under the strain caused by a monolayer of CMs). During 14-day continuously monitoring CMs culturing and drug treatment testings, the device demonstrated high sensitivity and stability to record the dynamic change caused by contractility of the CMs.

Preparation of superhydrophobic conductive CNT/PDMS film on paper by foam spraying method

Paper-based materials are widely used in agriculture, industry and daily life because of their biodegradability, sustainability, biocompatibility and low cost. However, due to the hydrophilic nature of plant fibers in paper-based materials, the mechanical properties of paper will be reduced after absorbing water, thus limiting its application field. In this paper, carbon nanotubes/polydimethylsiloxane (CNT/PDMS) films with hydrophobicity and conductivity were prepared on filter paper by foam spraying method. Firstly, CNT and PDMS were added into water and stirred vigorously, and CNT/PDMS foam homogenate was prepared by foaming agent and stabilizer. Then, the homogenate was sprayed on the filter paper with a spray gun, and the multilevel rough structure was prepared on the paper. The results showed that the contact angle of the sample surface is greater than 150° when the spraying amount is 0.4-CNT, 0.6-CNT and 0.8-CNT, and the contact angle of 0.6-CNT is 156.33°, which is the largest. The drops on the surface of the sprayed sample have good bounce and self-cleaning performances. In addition, benefiting from the excellent conductivity of CNT, the particles composed of CNT and PDMS contact each other on the surface of the sample, forming a conductive network. The aforementioned properties will broaden the application scenarios of paper-based superhydrophobic materials.

Paper-based electrochemical immunosensor for label-free detection of multiple avian influenza virus antigens using flexible screen-printed carbon nanotube-polydimethylsiloxane electrodes

Many studies have been conducted on measuring avian influenza viruses and their hemagglutinin (HA) antigens via electrochemical principles; most of these studies have used gold electrodes on ceramic, glass, or silicon substrates, and/or labeling for signal enhancement. Herein, we present a paper-based immunosensor for label-free measurement of multiple avian influenza virus (H5N1, H7N9, and H9N2) antigens using flexible screen-printed carbon nanotube-polydimethylsiloxane electrodes. These flexible electrodes on a paper substrate can complement the physical weakness of the paper-based sensors when wetted, without affecting flexibility. The relative standard deviation of the peak currents was 1.88% when the electrodes were repeatedly bent and unfolded twenty times with deionized water provided each cycle, showing the stability of the electrodes. For the detection of HA antigens, approximately 10-μl samples (concentration: 100 pg/ml–100 ng/ml) were needed to form the antigen–antibody complexes during 20–30 min incubation, and the immune responses were measured via differential pulse voltammetry. The limits of detections were 55.7 pg/ml (0.95 pM) for H5N1 HA, 99.6 pg/ml (1.69 pM) for H7N9 HA, and 54.0 pg/ml (0.72 pM) for H9N2 HA antigens in phosphate buffered saline, and the sensors showed good selectivity and reproducibility. Such paper-based sensors are economical, flexible, robust, and easy-to-manufacture, with the ability to detect several avian influenza viruses.

Carbon Black/PDMS Based Flexible Capacitive Tactile Sensor for Multi-Directional Force Sensing.

Flexible sensing tends to be widely exploited in the process of human–computer interactions of intelligent robots for its contact compliance and environmental adaptability. A novel flexible capacitive tactile sensor was proposed for multi-directional force sensing, which is based on carbon black/polydimethylsiloxane (PDMS) composite dielectric layer and upper and lower electrodes of carbon nanotubes/polydimethylsiloxane (CNTs/PDMS) composite layer. By changing the ratio of carbon black, the resolution of carbon black/PDMS composite layer increases at 4 wt%, and then decreases, which was explained according to the percolation theory of the conductive particles in the polymer matrix. Mathematical model of force and capacitance variance was established, which can be used to predict the value of the applied force. Then, the prototype with carbon black/PDMS composite dielectric layer was fabricated and characterized. SEM observation was conducted and a ratio was introduced in the composites material design. It was concluded that the resolution of carbon sensor can reach 0.1 N within 50 N in normal direction and 0.2 N in 0–10 N in tangential direction with good stability. Finally, the multi-directional force results were obtained. Compared with the individual directional force results, the output capacitance value of multi-directional force was lower, which indicated the amplitude decrease in capacity change in the normal and tangential direction. This might be caused by the deformation distribution in the normal and tangential direction under multi-directional force.

Broadband All-Optical Plane-Wave Ultrasound Imaging System Based on a Fabry-Perot Scanner.

A broadband all-optical plane-wave ultrasound imaging system for high-resolution 3-D imaging of biological tissues is presented. The system is based on a planar Fabry-Perot (FP) scanner for ultrasound detection and the photoacoustic generation of ultrasound in a carbon-nanotube-polydimethylsiloxane (CNT-PDMS) composite film. The FP sensor head was coated with the CNT-PDMS film which acts as an ultrasound transmitting layer for pulse-echo imaging. Exciting the CNT-PDMS coating with nanosecond laser pulses generated monopolar plane-wave ultrasound pulses with MPa-range peak pressures and a -6-dB bandwidth of 22 MHz, which were transmitted into the target. The resulting scattered acoustic field was detected across a 15 mm ×15 mm scan area with a step size of 100 [Formula: see text] and an optically defined element size of [Formula: see text]. The -3-dB bandwidth of the sensor was 30 MHz. A 3-D image of the scatterer distribution was then recovered using a k -space reconstruction algorithm. To obtain a measure of spatial resolution, the instrument line-spread function (LSF) was measured as a function of position. At the center of the scan area, the depth-dependent lateral LSF ranged from 46 to 65 [Formula: see text] for depths between 1 and 12 mm. The vertical LSF was independent of position and measured to be [Formula: see text] over the entire field of view. To demonstrate the ability of the system to provide high-resolution 3-D images, phantoms with well-defined scattering structures of arbitrary geometry were imaged. To demonstrate its suitability for imaging biological tissues, phantoms with similar impedance mismatches, sound speed and scattering properties to those present in the tissue, and ex vivo tissue samples were imaged. Compared with conventional piezoelectric-based ultrasound scanners, this approach offers the potential for improved image quality and higher resolution for superficial tissue imaging. Since the FP scanner is capable of high-resolution 3-D photoacoustic imaging of in vivo biological tissues, the system could ultimately be developed into an instrument for dual-mode all-optical ultrasound and photoacoustic imaging.

Large-Area, Crosstalk-Free, Flexible Tactile Sensor Matrix Pixelated by Mesh Layers.

Tactile sensor arrays have attracted considerable attention for their use in diverse applications, such as advanced robotics and interactive human-machine interfaces. However, conventional tactile sensor arrays suffer from electrical crosstalk caused by current leakages between the tactile cells. The approaches that have been proposed thus far to overcome this issue require complex rectifier circuits or a serial fabrication process. This article reports a flexible tactile sensor array fabricated through a batch process using a mesh. A carbon nanotube-polydimethylsiloxane composite is used to form an array of sensing cells in the mesh through a simple "dip-coating" process and is cured into a concave shape. The contact area between the electrode and the composite changes significantly under pressure, resulting in an excellent sensitivity (5.61 kPa-1) over a wide range of pressure up to 600 kPa. The mesh separates the composite into the arranged sensing cells to prevent the electrical connection between adjacent cells and simultaneously connects each cell mechanically. Additionally, the sensor shows superior durability compared with previously reported tactile sensors because the mesh acts as a support beam. Furthermore, the tactile sensor array is successfully utilized as a Braille reader via information processing based on machine learning.