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Wu K.,Sichuan University | Lei C.,Sichuan University | Huang R.,Sichuan University | Yang W.,Sichuan University | And 4 more authors.
ACS Applied Materials and Interfaces | Year: 2017

It is still a challenge to fabricate polymer-based composites with excellent thermal conductive property because of the well-known difficulties such as insufficient conductive pathways and inefficient filler-filler contact. To address this issue, a synergistic segregated double network by using two fillers with different dimensions has been designed and prepared by taking graphene nanoplates (GNPs) and multiwalled carbon nanotubes (MWCNT) in polystyrene for example. In this structure, GNPs form the segregated network to largely increase the filler-filler contact areas while MWCNT are embedded within the network to improve the network-density. The segregated network and the randomly dispersed hybrid network by using GNPs and MWCNT together were also prepared for comparison. It was found that the thermal conductivity of segregated double network can achieve almost 1.8-fold as high as that of the randomly dispersed hybrid network, and 2.2-fold as that of the segregated network. Meanwhile, much higher synergistic efficiency (f) of 2 can be obtained, even greater than that of other synergistic systems reported previously. The excellent thermal conductive property and higher f are ascribed to the unique effect of segregated double network: (1) extensive GNPs-GNPs contact areas via overlapped interconnections within segregated GNPs network; (2) efficient synergistic effect between MWCNT network and GNPs network based on bridge effect as well as increasing the network-density. © 2017 American Chemical Society.


Wu K.,Sichuan University | Wu L.,Sichuan University | Yang W.,Sichuan University | Chai S.,Guangdong Shengyi Technology Ltd Corporation | And 2 more authors.
RSC Advances | Year: 2016

It has been demonstrated that introducing another non-conductive particle into conductive filler filled composites could result in a better conductivity due to a volume exclusion effect. It was also reported that combining electrically conductive fillers with different geometric shapes and aspect ratio together could enhance the electrical conductivity due to the synergistic effect. To further explore these two effects on the electrical property enhancement, we firstly encapsulated neat silica (SiO2) with graphene oxide (GO) through electrostatic self-assembly to render SiO2 with surface conductivity. Then neat SiO2 or SiO2@GO together with multi-walled carbon nanotubes (MWCNT) were mixed with polystyrene (PS) to prepare conductive composites. In this way, the volume exclusion effect in the PS/MWCNT/SiO2 system and combined effect of volume exclusion and synergy in the PS/MWCNT/SiO2@rGO system could be investigated and compared. An obvious increased conductivity was observed only in the transition composition region for the PS/MWCNT/SiO2 system compared with the PS/MWCNT system. However, a largely enhanced conductivity was achieved through the composition region for the PS/MWCNT/SiO2@rGO system compared with the PS/MWCNT/SiO2 system and PS/MWCNT, accompanied by great enhancement of the electromagnetic interference (EMI) shielding effectiveness. Given the SEM characterization and rheological properties, we attributed this obvious enhanced electrical property to both a volume exclusion effect and a synergistic effect. © 2016 The Royal Society of Chemistry.


Chen L.,Sichuan University | He Y.,Sichuan University | Chai S.,Guangdong Shengyi Technology Ltd Corporation | Qiang H.,Sichuan University | And 2 more authors.
Nanoscale | Year: 2013

Two-dimensional graphene and graphene-based materials have attracted tremendous interest, hence much attention has been drawn to exploring and applying their exceptional characteristics and properties. Integration of graphene sheets into macroscopic fibers is a very important way for their application and has received increasing interest. In this study, neat and macroscopic graphene fibers were continuously spun from graphene oxide (GO) suspensions followed by chemical reduction. By varying wet-spinning conditions, a series of graphene fibers were prepared, then, the structural features, mechanical and electrical performances of the fibers were investigated. We found the orientation of graphene sheets, the interaction between inter-fiber graphene sheets and the defects in the fibers have a pronounced effect on the properties of the fibers. Graphene fibers with excellent mechanical and electrical properties will yield great advances in high-tech applications. These findings provide guidance for the future production of high performance graphene fibers. © 2013 The Royal Society of Chemistry.


Jiang H.,Sichuan University | Chen L.,Sichuan University | Chai S.,Guangdong Shengyi Technology Ltd Corporation | Yao X.,Sichuan University | And 2 more authors.
Composites Science and Technology | Year: 2014

Dispersion of graphene nanosheets (GNs) in a polymer matrix as mono layers was an important step towards fabricating high performance polymer/GNs nanocomposites. However, the insoluble and infusible properties of poly (tetrafluoroethylene) (PTFE) made the incorporation of nanofillers in PTFE matrix difficult. In this paper, a novel method based on poly (tetrafluoroethylene) (PTFE) latex that assured the fine dispersion of GNs in PTFE matrix was developed. PTFE latex was first modified by polyethylenimine (PEI) to create the positive charges on the surface of the PTFE particles, and then assembled with negatively charged graphene oxide sheets directly in water through electrostatic interaction, followed with chemical reduction, cold briquetting and hot sintering. Nanocomposites with controllable content and uniformly distributed GNs in PTFE matrix were prepared. The electrostatic coupling interactions improved the dispersion of GNs and facilitated the formation of filler networks in the PTFE matrix. Both the mechanical and wear performance of PTFE/GNs nanocomposites were greatly improved. PTFE/GNs nanocomposites also exhibited excellent electrical properties with a percolation threshold as low as 0.5. wt% and an electrical conductivity of 1.4. S/m at only 2. wt% graphene loadings. The new method agrees well with the latex technical process in PTFE bulk industrial manufacture and paves the way for an environmentally benign process for the bulk production of high quality polymer-graphene nanocomposites. © 2014 Elsevier Ltd.


Wu K.,Sichuan University | Lei C.,Sichuan University | Yang W.,Sichuan University | Chai S.,Guangdong Shengyi Technology Ltd Corporation | And 2 more authors.
Composites Science and Technology | Year: 2016

Adding conductive filler is an effective way to enhance the dielectric constant while usually also increases the dielectric loss of polymer. In this study, we demonstrated that polymer composites with much improved dielectric constant while maintaining ultra-low dielectric loss could be achieved via using hybrid filler and controlling the dispersion of conductive filler in polymer matrix. To do this, the graphene oxide was designed to be immobilized on the surface of large-sized insulating hexagonal boron nitride (h-BN) via electrostatic self-assembly, and afterwards introducing this hybrid filler into epoxy accompanied with chemical reduction. In this case, since the reduced graphene oxide (rGO) sheets were fixed on the surface of h-BN, rGO sheets were well separated from each other even at high loading. Hence not only significantly enhanced dielectric constant was observed, but also a very low dielectric loss comparable to that of neat epoxy was achieved. This low dielectric loss was believed to be ascribed to both embedded insulating network of h-BN to inhibit the mobility of charge carrier and well-separated rGO sheets via immobilization. In addition to obviously improved dielectric properties, the nanocomposites also exhibited good thermal conductivity. We believe that this special structure will provide a new thought for fabricating dielectric materials with much enhanced dielectric constant as well as well-suppressed dielectric loss. © 2016 Elsevier Ltd


Wu K.,Sichuan University | Xue Y.,Sichuan University | Yang W.,Sichuan University | Chai S.,Guangdong Shengyi Technology Ltd Corporation | And 2 more authors.
Composites Science and Technology | Year: 2016

In this study, we report a sharp increase of both thermal and electrical conductivity in polypropylene (PP) via formation of double percolated filler network with dense small-sized multi-wall carbon nanotubes (MWCNT) network located within loosened large-sized expanded graphite (EG) network. The electrical conductivity of PP/EG composites which levels off after the percolation threshold can be further enhanced by adding MWCNT and is increased two orders of magnitude as the content of MWCNT reaches to its threshold. Besides, the thermal conductivity of PP/EG-MWCNT increases by 38.5% compared to PP/EG and is much higher than PP/MWCNT. Furthermore, an excellent electromagnetic interference shielding effectiveness of ∼60 dB is obtained at the sample thickness of only 1.3 mm. Then, effective medium theory model is applied to analyze the mechanism for the largely enhanced thermal and electrical conductivity. It is suggested that formation of double percolated filler network, in which three types of connections exist between EG and EG, EG and MWCNT as well as MWCNT and MWCNT, could effectively reduce the interface thermal resistance. Our work is important and provides some new idea for the preparation of polymer composites with excellent thermal and electrical conductivity via constructing double percolated filler network. © 2016 Elsevier Ltd


Deng S.,Sichuan University | Wang J.,Sichuan University | Zong G.,Sichuan University | Chen F.,Sichuan University | And 2 more authors.
RSC Advances | Year: 2016

The thermal conductivity of expanded graphite (EG)/polymer composites is investigated in terms of polymer chain structures. The EG/polyphenylene sulfide (PPS) composite with a backbone of benzene rings shows the continuous highest thermal conductivity and the fastest rate of enhanced ratio at the same content. Then it is followed by EG/syndiotactic polystyrene (sPS) composites with side groups of regularly arranged benzene rings. The last are the EG/amorphous polystyrene (aPS) composites with side groups of randomly arranged benzene rings. Our results show that the chain structures of polymer matrices have a great influence on the interaction and crystallization of EG/polymer composites, which leads to the different thermal behavior. More precisely, the strong π-π interaction between EG and polymer, the nucleation of crystal at the interface of EG/polymer and the relatively rich EG content in the amorphous phase are benefits to the enhancement of thermal conductivity. These factors are proved to be extremely important for the design of high thermally conductive composites in the fields of science and engineering. © The Royal Society of Chemistry 2016.


Chen L.,Sichuan University | Chai S.,Guangdong Shengyi Technology Ltd Corporation | Liu K.,Sichuan University | Ning N.,Sichuan University | And 4 more authors.
ACS Applied Materials and Interfaces | Year: 2012

Controlling the interface interaction of polymer/filler is essential for the fabrication of high-performance polymer composites. In this work, a core-shell structured hybrid (SiO 2-GO) was prepared and introduced into an epoxy polymer matrix as a new filler. The incorporation of the hybrid optimized the modulus, strength and fracture toughness of the composites simultaneously. The ultrathin GO shells coated on silica surfaces were regarded as the main reason for the enhancement. Located at the silica-epoxy interface, GO served as an unconventional coupling agent of the silica filler, which effectively enhanced the interfacial interaction of the epoxy/SiO 2-GO composites, and thus greatly improved the mechanical properties of the epoxy resin. We believe this new and effective approach that using GO as a novel fillers surface modifier may open a novel interface design strategy for developing high performance composites. © 2012 American Chemical Society.


Wang J.,Sichuan University | Wu M.,Sichuan University | Li Y.,Sichuan University | Luo F.,Sichuan University | And 3 more authors.
Journal of Materials Science | Year: 2013

A simple and effective method to add large amounts of expanded graphite (EG) to poly (phenylene sulfide) (PPS) was developed. Before conventional melt processing, solid-state PPS and EG powders were mixed using high-speed rotation. In this way, the loose and porous vermicular structure of EG could be effectively destroyed and partly exfoliated, which made EG easy to be adsorbed on the surface of the PPS powders. This was extraordinarily helpful to achieve good dispersions of EG during the subsequent melt mixing even at high loading, which was difficult to achieve by conventional direct melt mixing. As a result of the good dispersions and strong interactions, the EG/PPS composites prepared showed a dramatically improved thermal conductivity (15.8 Wm-1K -1) and electrical conductivity (125.3 Sm-1) as the addition of EG reached 60 wt%. © 2012 Springer Science+Business Media New York.


Zhang Y.,University of Sichuan | Chen L.,University of Sichuan | Chen L.,Guangdong Shengyi Technology Ltd Corporation | Zhao J.-J.,University of Sichuan | And 6 more authors.
Polymer Chemistry | Year: 2014

In this study, a novel phosphorus-containing ionic monomer, named sodium salt of 10H-phenoxaphosphine-2,8-dicarboxylic acid,10-hydroxy-,2,8- dihydroxyethyl ester,10-oxide (DHPPO-Na), was synthesized, characterized, and then copolymerized to prepare poly(ethylene terephthalate)-based ionomers. The chemical structure of the resulting ionomers was confirmed by 1H, 13C, and 31P NMR spectroscopy. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to investigate the thermal properties of the ionomers. Compared with that of neat PET, the initial decomposition temperature of PETIs decreased in a nitrogen atmosphere while it increased in air. The crystallinity of PETIs was enhanced firstly and then destroyed with the ionic group increase. The limiting oxygen index (LOI) test and cone calorimeter were used to characterize the flame-retardant properties of the ionomers. The results showed that the introduction of DHPPO-Na could endow an expected flame-retardant performance, meanwhile it considerably restricted the melt-dripping behavior and suppressed the smoke release. The rheology test confirmed that the ionic groups increased the melt viscosity via ionic aggregation during heating, which was a benefit for the flame-retardant property of the copolyester. This journal is © The Royal Society of Chemistry.

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