Direct Ink Writing of Strained Carbon Nanotube-Based Sensors: Toward 4D Printable Soft Robotics

Four-dimensional (4D) printing has attracted significant attention, because it enables structures to be reconfigured based on an external stimulus, realizing complex architectures that are useful for different applications. Nevertheless, most previously reported 4D-printed components have focused on actuators, which are just one part of a full soft robotic system. In this study, toward achieving fully 4D-printed systems, the design and direct ink writing of sensors with a straining mechanism that mimics the 4D effect are explored. Solution-processable carbon nanotubes (CNTs) were used as the sensing medium, and the effect of a heat-shrinkable shape-memory polymer-based substrate (i.e., potential 4D effect) on the electronic and structural properties of CNTs was assessed, followed by their application in various sensing devices. Herein, we reveal that substrate shrinking affords a more porous yet more conductive film owing to the compressive strain experienced by CNTs, leading to an increase in the carrier concentration. Furthermore, it improves the sensitivity of the devices without the need for chemical functionalization. Interestingly, the results show that, by engineering the potential 4D effect, the selectivity of the sensor can be tuned. Finally, the sensors were integrated into a fully 4D-printed flower structure, exhibiting their potential for different soft robotic applications.

Development of the PANI/MWCNT Nanocomposite-Based Fluorescent Sensor for Selective Detection of Aqueous Ammonia

The present work reported the polyaniline (PANI) and multiwalled carbon nanotube (MWCNT)-based nanocomposite as a sensing material for the determination of aqueous ammonia by the enhanced fluorescence method. The excitation wavelength-dependent photoluminescence (PL) intensity has shown dual emission peaks at 340 and 380 nm that correspond to two different excitation energy states. The pH-based PL intensity and zeta potential variation were analyzed to optimize the suitable medium for aqueous ammonia sensing. Zeta potential was found to shift from 4 to -21 mV upon changing the pH of the the solution from acidic to alkaline medium. The fluorescence intensity of PANI/MWCNTs was found to increase upon increasing the pH from 3.0 to 6.0 (acidic region) and exhibits a plateau upon further increasing the pH from 7.0 to 12 (basic region). The PANI/MWCNT composite has shown a linear response to aqueous ammonia concentration varying from 25 to 200 μM with a correlation coefficient (R ²) of 0.99 and a limit of detection of 15.19 μM. The presence of relevant interference molecules and physiological ions had no influence on the detection of aqueous ammonia. Field-level study demonstrated that the level of aqueous ammonia can be determined selectively by using the PANI/MWCNT composite for various applications. The mechanism for the selective detection of aqueous ammonia is deliberated in detail.

Advances in the study of piezoelectric polymers

The literature review based on the works published over the last decade concerns the progress in research on innovative piezoelectric materials with current or potential practical applications. At the beginning, the nature of piezoelectric phenomenon is clarified. The main emphasis is put on presentation of polymers, biopolymers and polymer composites as well as hybrid materials with piezoelectric properties. Moreover, carbon nanomaterials are also included. These materials have recently become an intensively developing field, as evidenced by numerous scientific publications. Furthermore, the recently reported main methods of characterizations and selected examples of modern applications of piezoelectric materials in various fields (electronics, industry, medicine) have been discussed.

The bibliography includes 217 references.

Polyaniline Anchored MWCNTs on Fabric for High Performance Wearable Ammonia Sensor

Polyaniline (PANI) functionalized multiwall carbon nanotubes (MWCNTs) were prepared via in situ chemical polymerization process of aniline, in which MWCNTs were spray coated on the fabric for wearable ammonia sensor. Structural, morphological, thermal properties and wettability were analyzed by scanning electron microscope, X-ray diffraction, Raman analysis and contact angle measurement. No substantial change in base resistance of MWCNTs/PANI fabric sensor was observed for a wide range of bending (from 90° to 270°) shows excellent wearability. The sensors were exposed to 20-100 ppm ammonia vapor at room temperature. It was observed that the sensing response of PANI coated MWCNTs was enhanced than MWCNTs and PANI. The sensor has the capability to detect ammonia with high sensitivity (92% for100 ppm), excellent selectivity quick response (9 s), and recovery time (30 s). The lower detection limit (LOD) for the MWCNTs/PANI fabric sensor was found to be 200 ppb. The influence of humidity on sensing parameters was studied. Sensing response and resistance of sensor have shown excellent stability after one month. We observed that PANI have a dual role in enhancing flexibility as well as improve the sensor performance toward ammonia. The results reveal the potential application of fabric based sensor for monitoring NH₃ gas under ambient conditions.

A Room Temperature VOCs Gas Sensor Based on a Layer by Layer Multi-Walled Carbon Nanotubes/Poly-ethylene Glycol Composite

Sensitive detection of volatile organic compounds (VOCs) is significant for environmental monitoring and medical applications. In this work, multi-walled carbon nanotubes (MWCNTs) and polyethylene glycol (PEG) that have good adsorption for VOCs, were sprayed layer by layer on an interdigitated electrode (IDE) to build a sensitive VOCs gas sensor. The relative resistance change (△R/R) when the sensor was exposed to VOCs was measured. The sensor showed high sensitivity to acetone, ethanol, isopropanol and isoprene with fast response (110 ± 5 s) and recovery (152 ± 5 s) at room temperature, and the lower detection limit (LDL) of the sensor reached 9 ppm. With the micro-fabricated IDE structure, the sensor can be easily built into an electric nose for VOC recognition and measurement.

Tailoring in vitro biological and mechanical properties of polyvinyl alcohol reinforced with threshold carbon nanotube concentration for improved cellular response

The development of living bone tissue constructs with structural, mechanical and functional similarities to natural bone are the major challenges in bone tissue engineering.

Hydrogen production by methane decomposition over Ni–Cu–SiO2 catalysts: effect of temperature on catalyst deactivation

The activities of 65% Ni–10% Cu–SiO₂ catalysts under different reaction temperatures using route I and route II.