Growing polystyrene chains from the surface of graphene layers via RAFT polymerization and the influence on their thermal properties

The polystyrene (PS) macromolecular chains were grafted on the surface of graphene layers by reversible addition-fragmentation chain transfer (RAFT) polymerization. In this procedure, a RAFT agent, 4-Cyano-4-[(dodecylsulfanylthiocarbonyl) sulfanyl] pentanoic acid, was used to functionalize the thermal reduced graphene oxide (TRGO) to obtain the precursor (TRGO-RAFT). It can be calculated that the grafting density of PS/graphene (PRG) composites was about 0.18 chains per 100 carbons. Successful in-plain attachment of RAFT agent to TRGO and PS chain to TRGO-RAFT was shown an influence on the thermal property of the PRG composites. The thermal conductivity (λ) improved from 0.150 W m⁻¹ K⁻¹ of neat PS to 0.250 W m⁻¹ K⁻¹ of PRG composites with 10 wt% graphene sheets loading. The thermal property of PRG composites increased due to the homogeneous dispersion and ordered arrangement of graphene sheets in PS matrix and the formation of PRG composites.     

Mechanical reinforcement while remaining electrical insulation of glass fibre/polymer composites using core–shell CNT@SiO2 hybrids as fillers

Carbon nanotubes (CNTs) have been widely used as mechanical reinforcement agents of composites. However, their aggregations, weak interfacial interaction with polymer, as well as high electrical conductivity limit their use in some especial applications. In this paper, the silicon oxide (SiO₂)-coated (CNT@SiO₂) core–shell hybrids with different SiO₂ thickness were prepared and employed to reinforce glass fibre-reinforced bismaleimide–triazine (BT) resin (GFRBT) composites. The results indicated the mechanical properties, including tensile strength and Young’s modulus increased with the increase of SiO₂ thickness and CNT@SiO₂ loading. Such enhanced mechanical properties were mainly attributed to the intrinsically nature of CNTs, homogeneous dispersion of the hybrids, as well as improved interfacial interaction. Meanwhile, the composites remained high electrical insulation (9.63 × 10¹² Ω cm) due to the existence of SiO₂ layer on CNT surface. This study will guide the design of functionalized CNTs and the construction of high-performance composites.     

Study on thermal properties of graphene foam/graphene sheets filled polymer composites

The polymer composites composed of graphene foam (GF), graphene sheets (GSs) and pliable polydimethylsiloxane (PDMS) were fabricated and their thermal properties were investigated. Due to the unique interconnected structure of GF, the thermal conductivity of GF/PDMS composite reaches 0.56 W m⁻¹ K⁻¹, which is about 300% that of pure PDMS, and 20% higher than that of GS/PDMS composite with the same graphene loading of 0.7 wt%. Its coefficient of thermal expansion is (80–137) × 10⁻⁶/K within 25–150 °C, much lower than those of GS/PDMS composite and pure PDMS. In addition, it also shows superior thermal and dimensional stability. All above results demonstrate that the GF/PDMS composite is a good candidate for thermal interface materials, which could be applied in the thermal management of electronic devices, etc.     

Effects of poly(oxyethylene)-block structure in polyetheramines on the modified carbon nanotube/poly(lactic acid) composites

The hybrids of multi-walled carbon nanotube and poly(lactic acid) (MWCNT/PLA) were prepared by a melt-blending method. In order to enhance the compatibility between the PLA and MWCNTs, the surface of the MWCNTs was covalently modified by Jeffamine® polyetheramines by functionalizing MWCNTs with carboxylic groups. Different molecular weights and hydrophilicity of the polyethermaines were grafted onto MWCNTs with the assistance of a dehydrating agent. The results showed that low-molecular-weight Jeffamine® polyetheramine modified MWCNTs can effectively improve the thermal properties of PLA composites. On the other hand, high-molecular-weight and poly(oxyethylene)-segmented polyetheramine could render the modified MWCNTs of well dispersion in PLA, and consequently affecting the improvements of mechanical properties and conductivity of composite materials. With the addition of 3.0 wt% MWCNTs, the increment of E′ of the composite at 40 °C was 79%. For conductivity, the surface resistivity decreased from 1.27 × 10¹² Ω/sq for neat PLA to 8.30 × 10⁻³ Ω/sq for the composites.     

Enhanced thermal conductivity and dielectric properties of Al/β-SiCw/PVDF composites

Polymeric composites with high thermal conductivity, high dielectric permittivity but low dissipation factor have wide important applications in electronic and electrical industry. In this study, three phases composites consisting of poly(vinylidene fluoride) (PVDF), Al nanoparticles and β-silicon carbide whiskers (β-SiC_w) were prepared. The thermal conductivity, morphological and dielectric properties of the composites were investigated. The results indicate that the addition of 12 vol% β-SiC_w not only improves the thermal conductivity of Al/PVDF from 1.57 to 2.1 W/m K, but also remarkably increases the dielectric constant from 46 to 330 at 100 Hz, whereas the dielectric loss of the composites still remain at relatively low levels similar to that of Al/PVDF at a wider frequency range from 10⁻¹ Hz to 10⁷ Hz. With further increasing the β-SiC_w loading to 20 vol%, the thermal conductivity and dielectric constant of the composites continue to increase, whereas both the dielectric loss and conductivity also rise rapidly.     

Enhanced conductivity behavior of polydimethylsiloxane (PDMS) hybrid composites containing exfoliated graphite nanoplatelets and carbon nanotubes

Polydimethylsiloxane (PDMS) hybrid composites consisting of exfoliated graphite nanoplatelets (xGnPs) and multiwalled carbon nanotubes functionalized with hydroxyl groups (MWCNTs-OH) were fabricated, and the effects of the xGnP/MWCNT-OH ratio on the thermal, electrical, and mechanical properties of polydimethylsiloxane (PDMS) hybrid composites were investigated. With the total filler content fixed at 4 wt%, a hybrid composite consisting of 75% × GnP/25% MWCNT-OH showed the highest thermal conductivity (0.392 W/m K) and electrical conductivity (1.24 × 10⁻³ S/m), which significantly exceeded the values shown by either of the respective single filler composites. The increased thermal and electrical conductivity found when both fillers are used in combination is attributed to the synergistic effect between the fillers that forms an interconnected hybrid network. In contrast, the various different combinations of the fillers only showed a modest effect on the mechanical behavior, thermal stability, and thermal expansion of the PDMS composite.     

A facile assembly of polyimide/graphene core–shell structured nanocomposites with both high electrical and thermal conductivities

Polyimide/reduced graphene oxide (PI/r-GO) core–shell structured microspheres were fabricated by in-situ reduction of graphene oxide (GO), which was coated on the surface of PI microspheres via hydrogen bonding and π–π stacking interaction. The highly ordered 3D core–shell structure of PI/r-GO microspheres with graphene shell thickness of 3 nm was well characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM) and Raman spectra. The glass transition temperature (T_g) of PI/r-GO microspheres was slightly increased because of the interaction of r-GO and PI matrix while the temperature at 5% weight loss (T_5%) of PI/r-GO microspheres was decreased due to the side effect of reductant hydrazine hydrate. The PI/r-GO nanocomposites exhibited highly electrical conductivity with percolation threshold of 0.15 vol% and ultimate conductivity of 1.4 × 10⁻² S/m. Besides, the thermal conductivity of PI/r-GO nanocomposites with 2% weight content of r-GO could reach up to 0.26 W/m K.     

Thermal conductivity of Cu/diamond composites prepared by a new pretreatment of diamond powder

Cu/diamond composites were fabricated by spark plasma sintering (SPS) after the surface pretreatment of the diamond powders, in which the diamond particles were mixed with copper powder and tungsten powder (carbide forming element W). The effects of the pretreatment temperature and the diamond particle size on the thermal conductivity of diamond/copper composites were investigated. It was found that when 300 μm diamond particles and Cu–5 wt.% W were mixed and preheated at 1313 K, the composites has a relatively higher density and its thermal conductivity approaches 672 W (m K)⁻¹.     

High thermal conductivity of flexible polymer composites due to synergistic effect of multilayer graphene flakes and graphene foam

Research on flexible thermal interface materials (TIMs) has shown that the interconnected network of graphene foam (GF) offers effective paths of heat transportation. In this work, a variant amount of multilayer graphene flakes (MGFs) was added into 0.2 vol% GF/polydimethylsiloxane (PDMS) composite. A remarkable synergistic effect between MGF and GF in improving thermal conductivity of polymer composites is achieved. With 2.7 vol% MGFs, the thermal conductivity of MGF/GF/PDMS composite reaches 1.08 W m⁻¹ K⁻¹, which is 80%, 184% and 440% higher than that of 2.7 vol% MGF/PDMS, GF/PDMS composites and pure PDMS, respectively. The MGF/GF/PDMS composite also shows superior thermal stability. The addition of MGFs and GF decreases slightly the elongation at break, but observably increases the Young’s modulus and tensile strength of composites compared with pure PDMS. The good performance of MGF/GF/PDMS composite makes it a good TIM for possible application in thermal management of electronics.     

Chinese ink-facilitated fabrication of carbon nanotube/polyvinyl alcohol composite sheets with a high nanotube loading

Fabricating carbon nanotube-based composites requires high degree of dispersion of carbon nanotubes into a polymer matrix. The widely used approaches reported in open literature for such a purpose are usually complicated and high-cost. Herein, we found that Chinese ink could be used to prepare composites composed of multi-walled carbon nanotubes (MWCNTs) and polyvinyl alcohol (PVA). The Chinese ink acted as a solvent and a dispersant. The MWCNT-ink-PVA ternary composite possessed both high flexibility and high electrical conductivity, with an optimized electrical conductivity of 8.17 S cm⁻¹. This simple method is believed to be applicable to other nanosacle carbon materials.     

Thermal conductivity of Cu–Zr/diamond composites produced by high temperature–high pressure method

Copper matrix composites reinforced with about 90 vol.% of diamond particles, with the addition of zirconium to copper matrix, were prepared by a high temperature–high pressure method. The Zr content was varied from 0 to 2.0 wt.% to investigate the effect on interfacial microstructure and thermal conductivity of the Cu–Zr/diamond composites. The highest thermal conductivity of 677 W m⁻¹ K⁻¹ was achieved for the composite with 1.0 wt.% Zr addition, which is 64% higher than that of the composite without Zr addition. This improvement is attributed to the formation of ZrC at the interface between copper and diamond. The variation of thermal conductivity of the composites was correlated to the evolution of interfacial microstructure with increasing Zr content.     

Preparation and characterization of poly(3-octylthiophene)/carbon fiber thermoelectric composite materials

Poly(3-alkylthiophene) (P3AT) with a high Seebeck coefficient has recently been reported. However, P3AT/inorganic conductive composites exhibit relatively poor thermoelectric performance because of their low electrical conductivity. In this work, carbon fiber sheets with a high electrical conductivity were chosen as the inorganic phase, and poly(3-octylthiophene)(P3OT)/carbon fiber composites were prepared by casting P3OT solution onto the carbon fiber sheets. The carbon fiber sheets incorporated into the composites can provide good electrical conductivity, and P3OT can provide a high Seebeck coefficient. The highest power factor of 7.05 μW m⁻¹ K⁻² was obtained for the composite with 50 wt% P3OT. This work suggests a promising method for preparing large-scale thermoelectric composites with excellent properties.     

Aramid fibers reinforced silica aerogel composites with low thermal conductivity and improved mechanical performance

Aramid fibers reinforced silica aerogel composites (AF/aerogels) for thermal insulation were prepared successfully under ambient pressure drying. The microstructure showed that the aramid fibers were inlaid in the aerogel matrix, acting as the supporting skeletons, to strengthen the aerogel matrix. FTIR revealed AF/aerogels was physical combination between aramid fibers and aerogel matrix without chemical bonds. The as prepared AF/aerogels possessed extremely low thermal conductivity of 0.0227 ± 0.0007 W m⁻¹ K⁻¹ with the fiber content ranging from 1.5% to 6.6%. Due to the softness, low density and remarkable mechanical strength of aramid fibers and the layered structure of the fiber distribution, the AF/aerogels presented nice elasticity and flexibility. TG–DSC indicated the thermal stability reaching approximately 290 °C, can meet the general usage conditions, which was mainly depended on the pure silica aerogels. From mentioned above, AF/aerogels present huge application prospects in heat preservation field, especially in piping insulation.     

Electrical conductivities of carbon powder nanofillers and their latex-based polymer composites

The electrical conductivity of graphene, multi-wall carbon nanotubes, carbon black nanopowders and graphite powder is characterized using paper-like films and by means of powder compression. The large difference in surface area of these materials results in different packing density and number of contact spots, influencing the macroscopic conductivity of the compacts during powder compression. The results are compared with the percolation threshold and final conductivity of polypropylene (PP) composites, using latex technology for the incorporation of the carbon fillers in the polymer. Even though the PP composites produced in this work exhibit percolation thresholds as low as 0.3 wt.%, the final conductivity for all the composites is below 1.5 S/m. Reasons why the high value of ∼10³ S/m, which is obtained for graphene- and nanotube-based paper films or graphite compacts, is not reached for the composites are investigated.     

High conductive ethylene vinyl acetate composites filled with reduced graphene oxide and polyaniline

A conductive network composed of reduced graphene oxide (RGO) planes and polyaniline (PANI) chains was designed and fabricated by in situ polymerization of aniline monomer on the RGO planes. It was further used for fabrication of conductive composites with a polymer matrix–ethylene vinyl acetate (EVA). The composites achieve improved conductivity at a low filler loading although the host polymer–EVA–is of insulator. For instance, compared to the pure EVA polymer, the conductivity of the composite filled with 4.0 wt.% RGO and 8.0 wt.% PANI increases from 1.2 × 10^?14 S cm^?1 to 1.07 × 10^?1 S cm^?1. In addition, thermal stability of the composites is also enhanced by the filler loading.     

Single-walled carbon nanotube–epoxy composites for structural and conductive aerospace adhesives

Single-walled carbon nanotubes (SWCNTs) were incorporated at low loading (up to ∼1 wt%) into an unfilled aerospace-grade epoxy system, to impart electrical conductivity while maintaining structural bonding capability, as a route for development of a structural and conductive adhesive. At these low SWCNT loadings the tensile properties were maintained or improved, while strength decreased in a higher loading case. The structural bonding performance of composite-to-composite joints, evaluated in lap-shear and peel tests, was reasonably maintained for adhesives containing 0.5 wt% or 1 wt% SWCNTs. In the case of the 0.5 wt% SWCNT–adhesive, peel and lap-shear strength were unchanged while the addition of 1 wt% resulted in 30% increase of peel strength but the lap-shear strength was reduced by 10–15%. For 1 wt% SWCNT–adhesives, conductivities as high as 10⁻¹ S m⁻¹ and typically ∼10⁻³ S m⁻¹ were achieved. Joint electrical resistance measured between aluminum adherends was larger than predicted by the bulk conductivity, but was reduced by a post-treatment step resulting in apparent joint conductivities within one order of magnitude of the bulk samples.     

Polysaccharidic binders for the conception of an insulating agro-composite

The objective of this study is the formulation of a natural polysaccharidic binder for the conception of an insulating bio-based composite made with sunflower stalk particles. The formulation was performed using chitosan cross-linked with Genipin and mixed with alginate, guar gum and starch. A fractional factorial experimental design within 32 essays was established to find the formulation leading to composites with the best combination between good mechanical properties and limited amount of chitosan in the binder. Composites with a thermal conductivity (κ) of 0.07 W m⁻¹ K⁻¹ and a maximum tensile stress (σ_max) of 0.2 MPa were obtained with a total binder ratio of 5.5% (w/w). The results of this study show that the insulating bio-based composites evaluated have competitive mechanical and thermal performances compared with other eco-friendly insulating materials available on the market.     

Effect of polymer modifier chain length on thermal conductive property of polyamide 6/graphene nanocomposites

The influence of polymer modifier chain length on the thermal conductivity of polyamide 6/graphene (GA) nanocomposites, including through-plane (λ_z) and in-plane (λ_x) directions were investigated. Here, three chain lengths of double amino-terminated polyethylene glycol (NH₂–PEG–NH₂) were used to covalently functionalize graphene with graphene content of 5.0 wt%. Results showed that λ_z was enhanced with the chain length of NH₂–PEG–NH₂ increased, but λ_x reached a maximum value at a certain chain length of NH₂–PEG–NH₂. The maximum λ_z and λ_x of GA are 0.406 W m⁻¹ K⁻¹ and 9.710 W m⁻¹ K⁻¹, respectively. This study serves as a foundation for further research on the thermal conductive property of graphene nanocomposites using different chain lengths of polymer modifier to improve the λ_z and λ_x of the thermal conductive materials.     

Synthesis and electrochemical performance of a simple and low-cost sulfur/porous carbon composite cathode for rechargeable lithium sulfur battery

The sugar and phenolic resin were used as source materials to prepare porous carbons labeled as PC1 and PC2 respectively, which were activated by chemical methods with CaCO₃ as active agent. Sulfur/porous carbon composites were synthesized by thermally treating a mixture of sublimed sulfur and porous carbon. The morphology, structure, and electrochemical performance of the composite were investigated by scanning electron microscopy, Brunauer–Emmett–Teller, and a variety of electrochemical techniques. The electrochemical measurements show that the SPC2 electrode presents a more favorable electrochemical kinetics than the SPC1 electrode. In comparison with SPC1, it is shown that the rate of Li⁺ diffusion with SPC2 is significantly higher and the charge transfer resistance is much lower. The PC2 with high surface area (735.2 m² g⁻¹) and large pore volume (1.56 cm³ g⁻¹) not only increases the electronic conductivity of composites, but also facilitates transfer of the Li ion in the composite electrode.     

The AMWCNTs supported porous nanocarbon composites for high-performance supercapacitor

The porous nanocarbons supported by acid-treated multiwall carbon nanotubes (PC@ACNTs) were prepared by the combination of the hydrothermal polymerization of glucose on ACNTs, carbonization under N₂ protection and final activation with ZnCl₂. The materials were characterized by transmission electron microscopy, X-ray powder diffraction and Raman spectra. The results indicated that the ACNTs distributed uniformly into the framework of the porous carbon. The composites showed the high BET specific surface area up to 1712 m² g⁻¹ and good conductivity. The electrochemical measurements indicated that the composites processed good performances for electrochemical energy storage (210 F g⁻¹ at 0.5 A g⁻¹), and high stability (>99.9%), much higher than the corresponding ACNTs, porous carbons and the samples prepared by using raw MWCNTs as source. The good performance of PC@ACNTs composites was relative with the synergy of good conductivity of ACNTs and large specific surface areas of PC.