Weibing Zhong

Stretchable conductive polypyrrole/polyurethane (PPy/PU) strain sensor with netlike microcracks for human breath detection.

The development of wearable electronics that can monitor human physiological information demands specially structured materials with excellent stretchability and electrical conductivity. In this study, a new stretchable conductive polypyrrole/polyurethane (PPy/PU) elastomer was designed and prepared by surface diffusion and in situ polymerization of PPy inside and on porous PU substrates. The structures allowed the formation of netlike microcracks under stretching. The netlike microcrack structures make possible the reversible changes in the electrical resistance of PPy/PU elastomers under stretching and releasing cycles. The variations in morphology and chemical structures, stretchability, and conductivity as well as the sensitivity of resistance change under stretching cycles were investigated. The mechanism of reversible conductivity of the PPy/PU elastomer was proposed. This property was then used to construct a waistband-like human breath detector. The results demonstrated its potential as a strain sensor for human health care applications by showing reversible resistance changes in the repeated stretching and contracting motion when human breathes in and out.

A facile route to the production of polymeric nanofibrous aerogels for environmentally sustainable applications

Mesoporous polymeric aerogels with high compressibility and durability have attracted great attention due to their environmentally sustainable applications. However, it is still challenging to develop polymeric aerogels in a simple, low-cost and mass produced way. Herein, we report a strategy to prepare a high porosity polymeric nanofibrous aerogel (referred to as NFA) by direct freeze-drying of the poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofibrous suspension. It is noteworthy that this process is free of gelation and any solvent exchange. In addition, the PVA-co-PE nanofibers were mass-produced from our production line, based on a high throughput Melt-Extrusion-Phase-Separation technique. Additionally, the network of the NFA aerogels can be tuned by the host–guest assembly of the nanofibers and the foreign PVA nano-lamellae from disordered/ordered cellular to a leaf-like structure. Further modification of the NFA by gaseous methyltrichlorosilane (MTS) led to covalently bonded siloxane nanoparticles formed on the surface, thereby facilely realizing the nanofibrous aerogel from hydrophilic to hydrophobic as well as achieving excellent resilience. The corresponding hydrophobic aerogel (designated as HNFA) possessed a slightly larger density of 11.1 mg cm−3 with an almost unchanged porosity of 99% and meso–macroporous pores of 5–100 nm compared with the NFA (8.3 mg cm−3). They are demonstrated as good thermal insulators (0.033–0.044 W m−1 K−1), high-performance air filters (99.2% filtration efficiency with 64 Pa pressure drop), organic pollutants absorbers (2500–5329% weight gain) and continuous water/oil separators. Therefore, this study opens up a new approach for simple and large-scale preparation of polymeric aerogels for versatile applications.

Concurrent filtration and inactivation of bacteria using poly(vinyl alcohol-co-ethylene) nanofibrous membrane facilely modified using chitosan and graphene oxide

Integrating multiple nanoscale components with antibacterial properties into a single membrane filter is indispensable for efficient application in water treatment. Herein, we prepare a poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofibrous membrane (NFM) decorated using chitosan (CS) and graphene oxide (GO), via a melt-phase-separated nanofiber/CS-GO suspension coating technique. As indicated by morphology and structure analysis, CS and GO have tight physical attachment to the surface of the nanofibers throughout the PVA-co-PE layer, with diminished pore size and contact angle. Compared to commercial PVDF membrane, NFMs exhibit enhanced retention rate of pigmented nanoparticles and bacterial cells and higher and more stable water flux due to their relatively small thickness and high stacking density. The performance for inactivation of bacteria is also improved by employing NFM. Particularly after CS/GO modification, the inactivation rate of the membrane is increased to the range of 97.8–99.5% against E. coli and S. aureus with superior repetitive-use performance. These results can be attributed to the enhancement effect of the nanofiber network on the activity of the hydroxyl groups in PVA-co-PE, NH3+ in chitosan and the 2D structure of graphene oxide. The present membranes have much potential for use in long-term water treatment with high efficiency and stability.

Continuously Producible Ultrasensitive Wearable Strain Sensor Assembled with Three-Dimensional Interpenetrating Ag Nanowires/Polyolefin Elastomer Nanofibrous Composite Yarn

Fiber-shaped strain sensors with great flexibility and knittability have been tremendously concerned due to the wide applications in health manager devices, especially in human motion detection and physiological signal monitoring. Herein, a novel fiber-shaped strain sensor has been designed and prepared by interpenetrating Ag nanowires (NWs) into polyolefin elastomer nanofibrous yarn. The easy-to-obtain structure and simple roll-to-roll process make the continuous large-scale production of nanofibrous composite yarn possible. The continuous and alternating stretching and releasing reversibly change the contact probability between AgNWs in this interpenetrating network, leading to the variations of electrical resistance of the sensor. The gauge factors of strain sensors are calculated to be as high as 13920 and the minimum detection limit is only 0.065%. In addition, the strain sensor shows excellent durability during 4500 cycles with the strain of 10%. The response times of stretching and releasing strains are 10 and 15 ms, respectively. Furthermore, the strain sensor has been successfully applied in human motion detections both in single yarn and knitted fabrics. The result shows the practicability in applications of monitoring limbs movements, eye motion changes, artificial vocal cords, human pulse, and complex motions, which shows great potential in wearable sensors and electronic skin.

Photosensitizer–AgNP composite with an ability to selectively recognize pathogen and enhanced photodynamic efficiency

BODIPY-functionalized glycopolymer-modified AgNPs were prepared as a PDT agent. The agent was “smart”, i.e., it could distinguish pathogens from normal cells, and showed a photodynamic efficiency three times greater than that of free photosensitizer under the same light intensity. The work is a good attempt to make a new generation of PDT agents for antibacterial applications.

A novel PU/PVA-co-PE composite nanofiber membrane for water filtration

Filter membranes with high efficiency and low energy consumption are gaining more attention owing to the increase in water pollution. To enhance the filtration performance, a novel spindle polyurethane (PU) / poly(vinyl alcoholco-ethylene) (PVA-co-PE) composite nanofiber membrane was prepared. It is the first time that the spindle composite nanofibers and nanofiber membranes are prepared based on the PU/PVA-co-PE/CAB (cellulose acetate butyrate) immiscible polymer blends. The effects of PU concentration on the morphology, size distribution, and hydrophilicity of PU/PVA-co-PE nanofiber membranes were analyzed. The pure PVA-co-PE nanofiber membrane and PU/PVA-co-PE composite nanofiber membranes were used to filtrate the nanoparticle suspension with scarlet pigments (50–300 nm). Due to the smaller pore size, looser structure, and larger porosity, the rejection rate and flux of spindle PU/PVA-co-PE composite nanofiber membranes are both higher than that of pure PVA-co-PE nanofiber membrane. When the basic weight of nanofiber layer is 6 g/m2, the rejection rate of all the PU/PVA-co-PE membranes are above 99%. This study provided a novel, facile, and high-throughput method to prepare spindle nanofiber membranes and indicated the advantage of spindle PU/PVA-co-PE composite nanofiber membranes in the application of water filtration.