Influences of matrix viscosity on alignment of multi-walled carbon nanotubes in one-dimensional confined space

Fabrication, Microstructures and Sensor Applications of Highly Ordered Electrospun Nanofibers: A Review

The review summarizes the fabrication, microstructures, and sensor applications of highly ordered electrospun nanofibers. In the traditional electrospinning process, electrospun nanofibers usually have disordered or random microstructures due to the chaotic oscillation of the electrospinning jet. Different electrospinning methods can be formed by introducing external forces, such as magnetic, electric, or mechanical forces, and ordered nanofibers can be collected. The microstructures of highly ordered nanofibers can be divided into three categories: uniaxially ordered nanofibers, biaxially ordered nanofibers and ordered scaffolds. The three microstructures are each characterized by being ordered in different dimensions. The regulation and control of the ordered microstructures can promote electrospun nanofibers' mechanical and dielectric strength, surface area and chemical properties. Highly ordered electrospun nanofibers have more comprehensive applications than disordered nanofibers do in effect transistors, gas sensors, reinforced composite materials and tissue engineering. This review also intensively summarizes the applications of highly ordered nanofibers in the sensor field, such as pressure sensors, humidity sensors, strain sensors, gas sensors, and biosensors.

Fabrication and Thermo-Electro and Mechanical Properties Evaluation of Helical Multiwall Carbon Nanotube-Carbon Fiber/Epoxy Composite Laminates

The development of advanced composite materials has taken center stage because of its advantages over traditional materials. Recently, carbon-based advanced additives have shown promising results in the development of advanced polymer composites. The inter- and intra-laminar fracture toughness in modes I and II, along with the thermal and electrical conductivities, were investigated. The HMWCNTs/epoxy composite was prepared using a multi-dispersion method, followed by uniform coating at the mid-layers of the CF/E prepregs interface using the spray coating technique. Analysis methods, such as double cantilever beam (DCB) and end notched flexure (ENF) tests, were carried out to study the mode I and II fracture toughness. The surface morphology of the composite was analyzed using field emission scanning electron microscopy (FESEM). The DCB test showed that the fracture toughness of the 0.2 wt.% and 0.4 wt.% HMWCNT composite laminates was improved by 39.15% and 115.05%, respectively, compared with the control sample. Furthermore, the ENF test showed that the mode II interlaminar fracture toughness for the composite laminate increased by 50.88% and 190%, respectively. The FESEM morphology results confirmed the HMWCNTs bridging at the fracture zones of the CF/E composite and the improved interlaminar fracture toughness. The thermogravimetric analysis (TGA) results demonstrated a strong intermolecular bonding between the epoxy and HMWCNTs, resulting in an improved thermal stability. Moreover, the differential scanning calorimetry (DSC) results confirmed that the addition of HMWCNT shifted the T_g to a higher temperature. An electrical conductivity study demonstrated that a higher CNT concentration in the composite laminate resulted in a higher conductivity improvement. This study confirmed that the demonstrated dispersion technique could create composite laminates with a strong interfacial bond interaction between the epoxy and HMWCNT, and thus improve their properties.

Laser irradiation method to prepare polyethylene porous fiber membrane with ultrahigh xylene gas filtration capacity

In recent years, volatile organic compound (VOC) gases have caused potential harm to people's health. This study reveals the preparation of polyethylene porous fiber membrane with excellent low-concentration VOCs filtration performance via laser irradiation technology. A neodymium-doped yttrium aluminum garnet (Nd:YAG) pulsed laser beam was used to scan the laser-sensitive low-density polyethylene/carbon black (LDPE/CB) fibers prepared by nanolayer coextrusion in the air. The controllable thermal energy generated by laser irradiation makes the surface of the fiber membrane to produce a porous carbon layer in situ. Laser power and scanning speed are important parameters for controlling laser-induced carbonization. The results indicate that the rich "fluffy" carbon structures on the surface of the porous fiber membrane can efficiently adsorb xylene gas. This study can provide a positive reference for the large-scale preparation of polyolefin porous fiber membrane with VOCs filtration by simple and efficient laser irradiation method.

Uniaxial Stretching-Induced Alignment of Carbon Nanotubes in Cross-Linked Elastomer Enabled by Dynamic Cross-Link Reshuffling

The fascinating properties of carbon nanotubes (CNTs) make them highly promising in fabricating polymer composites. Yet, the property enhancements of polymer/CNTs composites remain far behind the theoretical predictions. A critical issue to resolve this dilemma is to align CNTs in polymer matrices. Thus far, the state of art approaches to create CNT alignment either require complicated preparation processes and specific apparatuses, or is limited to thermoplastic polymers. Here, inspired by the network rearrangement ability of vitrimer in the solid state, we bring forth a facile methodology to align CNT in covalently cross-linked polymers by uniaxially stretching dynamic. Specifically, dynamic boronic ester bond-cross-linked epoxidized natural rubber/CNTs vitrimer composites with randomly dispersed CNTs are prepared, which are able to rearrange the network topologies and release stress at elevated temperatures through boronic ester transesterifications. The alignment of CNTs is performed by the uniaxial stretching of the composites and subsequent cross-link reshuffling at elevated temperatures, which results in anisotropic composites with remarkably enhanced mechanical properties and reduced electrical conductivity along the stretching direction. Furthermore, the mechanical properties of the composites can be readily adjusted by changing the applied strain, relaxation time and temperature due to the modulated CNT alignment degree. With this example, we envisage that this work offers a conceptual and facile approach to align anisotropic fillers in covalently cross-linked polymers.

Nanolayer coextrusion: An efficient and environmentally friendly micro/nanofiber fabrication technique

Researchers have developed many types of nanoscale materials with different properties. Among them, nanofibers have recently attracted increasing interest and attention due to their functional versatility and potential applications in diverse industries, including tapes, filtration, energy generation, and biomedical technologies. Nanolayer coextrusion, a novel polymer melt fiber processing technology, has gradually received attention due to its environmental friendliness, efficiency, simplicity and ability to be mass-produced. Compared with conventional techniques, nanolayer coextruded non-woven nanofibrous mats offer advantages such as a tunable fiber diameter, high porosity, high surface area to volume ratio, and the potential to manufacture composite nanofibers with different components to achieve desired structures and properties. Dozens of thermoplastic polymers have been coextruded for various applications, and the variety of polymers has gradually continued to increase. This review presents an overview of the nanolayer coextrusion technique and its promising advantages and potential applications. We discuss nanolayer coextrusion theory and the parameters (polymer and processing) that significantly affect the fiber morphology and properties. We focus on varied applications of nanolayer coextruded fibers in different fields and conclude by describing the future potential of this novel technology.

A review of the interfacial characteristics of polymer nanocomposites containing carbon nanotubes

This paper provides an overview of recent advances in research on the interfacial characteristics of carbon nanotube–polymer nanocomposites. The state of knowledge about the chemical functionalization of carbon nanotubes as well as the interaction at the interface between the carbon nanotube and the polymer matrix is presented. The primary focus of this paper is on identifying the fundamental relationship between nanocomposite properties and interfacial characteristics. The progress, remaining challenges, and future directions of research are discussed. The latest developments of both microscopy and scattering techniques are reviewed, and their respective strengths and limitations are briefly discussed. The main methods available for the chemical functionalization of carbon nanotubes are summarized, and particular interest is given to evaluation of their advantages and disadvantages. The critical issues related to the interaction at the interface are discussed, and the important techniques for improving the properties of carbon nanotube–polymer nanocomposites are introduced. Additionally, the mechanism responsible for the interfacial interaction at the molecular level is briefly described. Furthermore, the mechanical, electrical, and thermal properties of the nanocomposites are discussed separately, and their influencing factors are briefly introduced. Finally, the current challenges and opportunities for efficiently translating the remarkable properties of carbon nanotubes to polymer matrices are summarized in the hopes of facilitating the development of this emerging area. Potential topics of oncoming focus are highlighted, and several suggestions concerning future research needs are also presented.

The state of research on the characteristics at the interface in polymer nanocomposites is reviewed. Special emphasis is placed on the recent advances in the fundamental relationship between interfacial characteristics and nanocomposite properties.