Ding-Xiang Yan

Temperature dependence of graphene oxide reduced by hydrazine hydrate

Graphene oxide (GO) was successfully prepared by a modified Hummers method. The reduction effect and mechanism of the as-prepared GO reduced with hydrazine hydrate at different temperatures and time were characterized by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), x-ray diffractions (XRD), Raman spectroscopy and thermo-gravimetric analysis (TGA). The results showed that the reduction effect of GO mainly depended on treatment temperature instead of treatment time. Desirable reduction of GO can only be obtained at high treatment temperature. Reduced at 95 °C for 3 h, the C/O atomic ratio of GO increased from 3.1 to 15.1, which was impossible to obtain at low temperatures, such as 80, 60 or 15 °C, even for longer reduction time. XPS, 13C NMR and FTIR results show that most of the epoxide groups bonded to graphite during the oxidation were removed from GO and form the sp(2) structure after being reduced by hydrazine hydrate at high temperature (>60 °C), leading to the electric conductivity of GO increasing from 1.5 × 10(-6) to 5 S cm(-1), while the hydroxyls on the surface of GO were not removed by hydrazine hydrate even at high temperature. Additionally, the FTIR, XRD and Raman spectrum indicate that the GO reduced by hydrazine hydrate can not be entirely restored to the pristine graphite structures. XPS and FTIR data also suggest that carbonyl and carboxyl groups can be reduced by hydrazine hydrate and possibly form hydrazone, but not a C = C structure.

Efficient electromagnetic interference shielding of lightweight graphene/polystyrene composite

A combination of high-pressure compression molding plus salt-leaching was first proposed to prepare porous graphene/polystyrene composites. The specific shielding effectiveness of the lightweight composite was as high as 64.4 dB cm3 g−1, the highest value ever reported for polymer based EMI shielding materials at such a low thickness (2.5 mm).

Cellulose composite aerogel for highly efficient electromagnetic interference shielding

An ultra-light and highly conductive cellulose composite aerogel was fabricated by a simple, efficient and environmentally benign strategy. The scaffold structure was well designed from nanofibrillar networks to nanosheet networks by controlling the concentration of cellulose in the sodium hydroxide/urea solution. The obtained conductive aerogel was first reported as an electromagnetic interference shielding material; it exhibits an electromagnetic interference (EMI) shielding effectiveness of ∼20.8 dB and a corresponding specific EMI shielding effectiveness as high as ∼219 dB cm3 g−1 with microwave absorption as the dominant EMI shielding mechanism in the microwave frequency range of 8.2–12.4 GHz at a density of as low as 0.095 g cm−3. This result demonstrates that this type of green conductive aerogel has the potential to be used as lightweight shielding material against electromagnetic radiation, especially for aircraft and spacecraft applications.

Electrically conductive and electromagnetic interference shielding of polyethylene composites with devisable carbon nanotube networks

This paper reports a comparative study of the electrical and electromagnetic interference (EMI) shielding performance of three carbon nanotube/polyethylene (CNT/PE) composites with different conductive networks, i.e., segregated structure (s-CNT/PE), partially segregated structure (p-CNT/PE) and randomly distributed structure (r-CNT/PE). The s-CNT/PE composite exhibits superior electrical conductivity up to 2 orders of magnitude over that of p-CNT/PE and r-CNT/PE composites, at the same CNT loading. Only 5 wt% CNT addition in the s-CNT/PE composite realizes an excellent EMI shielding effectiveness (SE) as high as 46.4 dB, which is 20% and 46% higher than that for p-CNT/PE and r-CNT/PE composites, respectively. The selectively distributed CNTs at the interfaces between PE polyhedrons would certainly increase the effective CNT concentrations that form conducting pathways and thus increase the electrical conductivity and EMI SE in the s-CNT/PE composites. Such special structure also provides numerous interfaces that absorb the electromagnetic waves, resulting in an absorption-dominated shielding mechanism. Our work suggests that designing conductive networks in polymer composites is a promising approach to develop high-performance EMI shielding materials.

Super-tough conducting carbon nanotube/ultrahigh-molecular-weight polyethylene composites with segregated and double-percolated structure

Super-tough conducting carbon nanotube (CNT)/ultrahigh-molecular-weight polyethylene (UHMWPE) composites were prepared by a facile method; a very small amount of high-density polyethylene (HDPE) was used as the percolated polymer phase to load the CNTs. A structural examination revealed the formation of unique conductive networks by combination of the typical segregated and double-percolated structure, in which the fully percolated CNT/carrier polymer layers were localized at the interfaces between UHMWPE granules. Owing to the synergistic effect of the segregated and double-percolated structures, only 0.3 wt% of CNTs can make the composite very conductive. More interestingly, after the addition of only 2.7 wt% of HDPE, the ultimate strain, tear strength, and impact strength reached 478%, 35.3 N and 58.1 kJ m−2, respectively; these corresponded to remarkable increases of 265%, 61.9%, and 167% in these properties compared with the conventional segregated materials. These results were ascribed to the intensified interfacial adhesion between UHMWPE granules, which resulted from the strong inter-diffusion and heat-sealing between the HDPE and UHMWPE molecules. A model was proposed to explain the outstanding ductility and toughness properties of the segregated and double-percolated CPC material.

Double-segregated carbon nanotube–polymer conductive composites as candidates for liquid sensing materials

Double-segregated conductive polymer composites were fabricated as candidates for liquid sensing materials; these composites exhibited ultralow percolation (∼0.09 vol%), good reproducibility, and a large liquid sensing capacity (∼8 × 104%) with a balanced electrical conductivity (∼1 S m−1).

Super-Robust Polylactide Barrier Films by Building Densely Oriented Lamellae Incorporated with Ductile in Situ Nanofibrils of Poly(butylene adipate-co-terephthalate)

Remarkable combination of excellent gas barrier performance, high strength, and toughness was realized in polylactide (PLA) composite films by constructing the supernetworks of oriented and pyknotic crystals with the assistance of ductile in situ nanofibrils of poly(butylene adipate-co-terephthalate) (PBAT). On the basis that the permeation of gas molecules through polymer materials with anisotropic structure would be more frustrated, we believe that oriented crystalline textures cooperating with inerratic amorphism can be favorable for the enhancement of gas barrier property. By taking full advantage of intensively elongational flow field, the dispersed phase of PBAT in situ forms into nanofibrils, and simultaneously sufficient row-nuclei for PLA are induced. After appropriate thermal treatment with the acceleration effect of PBAT on PLA crystallization, oriented lamellae of PLA tend to be more perfect in a preferential direction and constitute into a kind of network interconnecting with each other. At the same time, the molecular chains between lamellae tend to be more extended. This unique structure manifests superior ability in ameliorating the performance of PLA film. The oxygen permeability coefficient can be achieved as low as 2 × 10(-15) cm(3) cm cm(-2) s(-1) Pa(-1), combining with the high strength, modulus, and ductility (104.5 MPa, 3484 MPa, and 110.6%, respectively). The methodology proposed in this work presents an industrially scalable processing method to fabricate super-robust PLA barrier films. It would indeed push the usability of biopolymers forward, and certainly prompt wider application of biodegradable polymers in the fields of environmental protection such as food packaging, medical packaging, and biodegradable mulch.

Facile, green and affordable strategy for structuring natural graphite/polymer composite with efficient electromagnetic interference shielding

An electromagnetic interference (EMI) shielding composite based on natural, economical graphite and ultrahigh molecular weight polyethylene (UHMWPE) with a typical segregated structure was first fabricated by a facile and green method, i.e., mechanical mixing plus hot compaction, without the use of intensive dispersion and any organic solvents. Superior shielding effectiveness of 51.6 dB was achieved at a low graphite loading of only 7.05 vol%, which was comparable to or even superior to the expensive carbon nanofillers (e.g., carbon nanotube and graphene) based polymer composites owning to the successful creation of the segregated structure in which the graphite particles were selectively located at the interfaces of UHMWPE polyhedrons. Our work suggests a new way of effectively utilizing economical graphite in conductive polymer composites, especially for EMI shielding applications.

A strong and tough polymer–carbon nanotube film for flexible and efficient electromagnetic interference shielding

Carbon nanotube (CNT) films exhibit potential use in broad areas including energy-storage, thermal management, and electromagnetic interference (EMI) shielding; however, their inefficient, expensive, and energy-consuming fabrication processes reported so far and mechanical brittleness are a major deficiency. Herein, a strong and tough carbon nanotube (CNT) film with the inclusion of natural rubber (NR) was fabricated for flexible and efficient EMI shielding by a facile, efficient, and energy-saving method. Compared to the pure CNT film, the incorporation of 50 wt% NR leads to a tremendous mechanical improvement of the CNT-NR films, e.g., a 3.1 and 486 times increase in tensile strength and toughness. The origin of the reinforcing and toughening effect of the CNT films by the addition of a rubber material mainly arises from enhanced stress transfer and the uniformly dispersed stress. The CNT-NR film displays excellent EMI shielding performance albeit at tiny thickness owing to the extremely high aspect ratio and electrical conductivity of CNTs. The critical thickness required to satisfy commercial EMI shielding applications (shielding effectiveness (SE) of 20 dB) is only 50 μm, and a very high EMI SE of 44.7 dB is achieved as the film thickness reaches 250 μm. Meanwhile, the CNT-NR film exhibits highly reliable EMI SE even after bending 5000 times at a radius of 2.0 mm. These intriguing properties of CNT-NR films, together with their advantages of environmentally friendly and facile large-scale fabrication, open up the possibility of designing highly thin and flexible films for promising electromagnetic protection, especially in aerospace, aviation, and next-generation flexible electronics.

Tunable electromagnetic interference shielding effectiveness via multilayer assembly of regenerated cellulose as a supporting substrate and carbon nanotubes/polymer as a functional layer

Hybrid systems integrating carbon nanotubes (CNTs) with cellulose showcase several key properties that can address emerging multifunctional needs, such as good electrical conductivity and electromagnetic interference (EMI) shielding. Herein, a subtle approach is accordingly developed to prepare CNTs/cellulose composite films that feature a layered structure consisting of a poly(ethylene oxide) (PEO)/CNTs layer as the EMI shielding layer and a regenerated cellulose layer as the supporting substrate. PEO acts as a robust enhancer of interfacial adhesion between the CNTs and the cellulose layers due to its favorable compatibility with cellulose chains, which is effective to prevent deterioration of the mechanical properties of the material; moreover, the high content of CNTs with trace amounts of PEO shows an extremely high electrical conductivity of 20 S cm−1. The layer-structured film shows an extremely high electrical conductivity of 20 S cm−1 and an excellent EMI shielding effectiveness (SE) of above 35 dB in the X-band, together with high tensile strength and a Youngs modulus of 26.9 and 2615.4 MPa, respectively. Moreover, the composite shows extremely high specific SE (up to 1372.4 dB cm2 g−1) – an unprecedented result for CNT/cellulose materials. Comparatively, a plain-structured composite counterpart prepared via the normal direct-mixing process exhibits a much lower electrical conductivity of 2 S cm−1 and an inferior EMI shielding performance of 20 dB. Furthermore, the plain-structured composite suffers profound deterioration in mechanical strength and Youngs modulus (12.4 and 1274.3 MPa, respectively). The film thickness and number of conducting layers significantly influence the EMI shielding performance, which indicates tunable EMI SE for this composite. Specifically, an increase in the total thickness leads to ultrahigh SE exceeding 65 dB. Although they have the same total thickness as monolayer films, a distinct enhancement in EMI SE for the multilayer films is clearly demonstrated, driven by the coherent multiple reflections at the internal interfaces of the conductive and cellulose layers. This study may provide a broader context for exploiting cellulose-based composite films with tunable electromagnetic interference shielding effectiveness; these films may find applications in portable electronic devices and radiation sources.