Laser-assisted exfoliation of Ti3C2Tx.

As an emerging two-dimensional material, MXene has shown a wide range of applications, which has triggered the demand for efficient exfoliation of nanoflakes with large size and specific surface area. Here, we took advantage of the efficient photo-thermal conversion of Ti3C2Tx and employed 532 nm continuous wave laser irradiation to assist the traditional ultrasonic exfoliation, with no need for complex equipment and an expensive femtosecond or picosecond laser. This approach greatly improves the exfoliation efficiency, increases the size, uniformity and specific surface area of the Ti3C2Tx nanoflakes, and reduces energy consumption as well. The electrical conductivity of Ti3C2Tx film is also significantly enhanced (from 3135 to 7433 S m-1). It is demonstrated that the laser promotes the formation of Ti-OH and enhances the solubility of Ti3C2Tx in water, facilitating the exfoliation and preventing oxidation as a result.

Revealing the linear relationship between electrical, thermal, mechanical and structural properties of carbon nanocoils.

The special helical morphologies and polycrystalline-amorphous internal structures differ carbon nanocoils (CNCs) from carbon nanotubes or carbon nanofibers, but bring difficulties in illuminating the correlations between physical and structural properties. In this paper, we measure the electrical conductivity (σ), thermal diffusivity (α) and Young's modulus (E) of single CNCs at the same time, using a transient electrothermal technique and an electromechanical vibration technique. Based on the statistical results of 8 single CNC samples, a linear correlation between the three parameters is uncovered, expressed as σ = 0.052(α - 2.5) × 104 S m-1, E = (-10.38σ + 14.04) GPa and E = (-0.59α + 16.08) GPa, where the unit of α is 10-7 m2 s-1. Concise proportional relations between the three parameters and average graphite grain size (ld) are deduced, expressed as σ = Ald(C1 - T)-1, α = Bld(C2 + T)-1 and E = -Dld + E0. The proportional relation between physical parameters and ld demonstrates the confinement originated from the nano-grain system.

Layered MXene/Aramid Composite Film for a Soft and Sensitive Pressure Sensor.

In recent years, the two-dimensional material MXene has shown great advantages in the field of wearable electronics and pressure sensors. Toward advanced applications, achieving a conformal pressure sensor with ultrathin thickness and great flexibility through a simple preparation principle, while maintaining its high sensitivity and wide detection range, is still a key challenge for the development of high-performance pressure sensors. Herein, we proposed an optimized mild LiF/HCl etching scheme and successfully achieved a high-concentration (>25 mg/mL) preparation of few-layer Ti3C2Tx MXene. Combining the prepared MXene with an aramid nanofiber (ANF), we designed an ultrathin layered pressure sensor based on an MXene/ANF composite through layer-by-layer suction filtration. The mechanical strength is greatly enhanced by composition with the ANF, while the pure MXene film is fragile. The sensor achieves a high sensitivity of 16.7 kPa-1, wide detection range (>100 kPa), only 10 µm thickness, great flexibility, and up to 10% stretchability, which are greatly beneficial to practical sensors. We demonstrated the wide application perspective of the sensor in human motion monitoring and human-machine interfaces from low pressure (human pulse) to high pressure (push-up).

Gulf War agents pyridostigmine bromide and permethrin cause hypersensitive nociception that is restored after vagus nerve stimulation.

Gulf war illness (GWI) is a chronic multi-symptom disease that afflicts 25-33% of troops that were deployed in the 1990-1991 Gulf War. GWI symptoms include cognitive, behavioral and emotional deficits, as well as migraines and pain. It is possible that exposure to Gulf War agents and prophylactics contributed to the reported symptomology. Pyridostigmine bromide (PB) and permethrin (PER) were given to protect from nerve gas attacks and insect vector born disease, respectively. Previous studies have demonstrated that 10 days of exposure to these chemicals can cause symptoms analogous to those observed in GWI, including impairment of long-term memory in mice. Other studies using this model have shown chronic neuroinflammation, and chronic neuroinflammation can lead to altered nociceptive sensitivity. At 10-weeks after the 10-day PB and PER exposure paradigm, we observed lowered nociceptive threshold on the Von Frey test that was no longer evident at 28 weeks and 38 weeks post-exposure. We further determined that vagus nerve stimulation, initiated at 38 weeks after exposure, restores the lowered nociceptive sensitivity. Therefore, stimulating the vagus nerve appears to influence nociception. Future studies are need to elucidate possible mechanisms of this effect.

High performance strain sensor based on buckypaper for full-range detection of human motions.

A high-performance strain sensor based on buckypaper has been fabricated and studied. The sensor with an ultrahigh gauge factor of 20 216 can detect a maximum and a minimum strain range of 75% and 0.1%, respectively. During stretching, the strain sensor achieves a high stability and reproducibility of 10 000 cycles, and a fast response time of less than 87 ms. On the other hand, the sensor shows an excellent sensing performance upon pressure. The pressure range, pressure sensitivity and loading-unloading cycles are 0-1.68 MPa, 89.7 kPa-1 and 3000 cycles, respectively. A concept of the optimal value is utilized to evaluate the strain and pressure performances of the sensor. The optimal values of the sensor upon tensile strain and pressure are calculated to be 3.07 × 108 and 1.35 × 107, respectively, which are much higher than those of most strain and pressure sensors reported in the literature. Precise detection of full-range human motions, acoustic vibrations and even pulse waves at a small scale has been successfully demonstrated by the buckypaper-based sensor. Owning to its advantages including ultrahigh sensitivity, wide detection range and good stability, the buckypaper-based sensor suggests a great potential for applications in wearable sensors, electronic skins, micro/nano electromechanical systems, vibration sensing devices and other strain sensing devices.

A flexible, ultra-sensitive strain sensor based on carbon nanocoil network fabricated by an electrophoretic method.

An ultra-sensitive strain sensor has been fabricated and studied, whose sensing medium is a network structure composed of plenty of carbon nanocoils (CNCs) and deposited between two gold electrodes via electrophoresis. The sensor owns a gauge factor close to 10 000 for tensile strain. A high stability and reproducibility of more than 5000 cycles and a fast response time of approximately 50 ms have been achieved. It has a high sensitivity for bending strain as well. Practically, it has shown an excellent performance in the detection of breathing, wrist pulse, and vibration. The sensor can be fabricated with a facile technology and low cost, suggesting great potential applications in micro-nano electromechanical systems, wearable devices and electronic skins.

A super stretchable and sensitive strain sensor based on a carbon nanocoil network fabricated by a simple peeling-off approach.

Despite the tremendous progress in wearable and smart strain sensors, it is still a challenge to develop a highly sensitive, stretchable, and low-cost sensor. Herein, a super stretchable and sensitive strain sensor fabricated by a simple peeling-off approach is reported. The strain sensor is prepared by peeling off a thin as-grown carbon nanocoil (CNC) film from a substrate using a stretchable polydimethylsiloxane (PDMS) film or a flexible adhesive tape. Herein, we took advantage of the spring-like morphology and the original network of the CNCs. The sensor is used to detect pressure, tension, and bend. The strain range and maximum real-time gauge factor reach 260% and 190, respectively, with a rapid response time (less than 12 ms). The contrary resistance responses under tension and bend make it possible to distinguish the direction and type of strain. The sensor is used to monitor a strain over a wide range, from human pulse to the impact of a 0.9 kg weight. The high sensitivity and stretchability, easy and cheap fabrication, and effective interaction with human motions suggest the great potential applications of this sensor in wearable strain sensors and smart systems.

Thermal Diffusivity of a Single Carbon Nanocoil: Uncovering the Correlation with Temperature and Domain Size.

The helical geometries and polycrystalline-amorphous structure of carbon nanocoils (CNCs), an exotic class of low-dimensional carbon nanostructures, distinguish them from carbon nanotubes and graphene. These distinct structures result in very different energy transport from that in carbon nanotubes and graphene, leading to important roles in applications as wave absorbers, near-infrared sensors, and nanoelectromechanical sensors. Here we report a systematic study of the thermal diffusivity (α) and conductivity (κ) of CNCs from 290 to 10 K and uncover their property-structure aspects. Our room-temperature α study reveals a correlation between α and the line diameter (d): α = (5.43 × 104 × e-d/37.7 + 9.5) × 10-7 m2/s. Combined with the Raman-based grain size (La) characterization, α and La are correlated as α = [81.2 × (La - 3.32)1.5 + 9.5] × 10-7 m2/s. With temperature decreasing from 290 K to 10 K, α has a 1-1.6-fold increase, and κ shows a peak around 75 K. To best understand the defect level and polycrystalline-amorphous structure of CNCs, the thermal reffusivity (Θ = α-1) of CNCs is studied and compared with that of graphite and graphene foam from 290 K down to 10 K. Very interestingly, CNC's Θ linearly decreases with decreased temperature, while Θ of graphite and graphene foam have an exponential decrease. The extrapolated 0 K-limit Θ is determined by low-momentum phonon scattering and gives a structure domain size of CNC samples (d = 455, 353, and 334 nm) of 1.28, 2.03 and 3.24 nm. These sizes are coherent with the X-ray diffraction results (3.5 nm) and the Raman spectroscopy study and confirm the correlation among d, La, and α.