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.     

Effect of silica coating thickness on the thermal conductivity of polyurethane/SiO2 coated multiwalled carbon nanotube composites

Silica coated multiwalled carbon nanotubes (SiO₂@MWCNTs) with different coating thicknesses of ∼4 nm, 30–50 nm, and 70–90 nm were synthesized by a sol–gel method and compounded with polyurethane (PU). The effects of SiO₂@MWCNTs on the electrical properties and thermal conductivity of the resulting PU/SiO₂@MWCNT composites were investigated. The SiO₂ coating maintained the high electrical resistivity of pure PU. Meanwhile, incorporating 0.5, 0.75 and 1.0 wt% SiO₂@MWCNT (70–90 nm) into PU, produced thermal conductivity values of 0.287, 0.289 and 0.310 W/mK, respectively, representing increases of 62.1%, 63.3% and 75.1%. The thermal conductivity of PU/SiO₂@MWCNT composites was also increased by increasing the thickness of the SiO₂ coating.     

The thermal and mechanical properties of graphite foam/epoxy resin composites

A series of epoxy resin (EP) filled graphite foam (GF) composites were prepared to explore a new material with good heat transfer property. The effects of the mass fraction of EP and the network structure of GFs on the thermal diffusivity and the compression strength of the composites were investigated. The thermal diffusivity of the GF/EP composite with EP mass fraction of 91.45% was raised to 6.541 mm²/s, which was 45.7 times higher than the pure EP. The thermal conductivity reached to 14.67 W/(m K), which was 43.1 times higher than the pure EP. The compression strength of the GF/EP increased 55% above the value of pure EP. In addition, the thermal diffusivity of GF/EP increased with the decrease of the mass fraction of EP. A model was formulated to calculate the pressure needed for a mass fraction of EP.     

Preparation of Nylon-6/flake graphite derivatives composites with antistatic property and thermal stability

Nylon-6/flake graphite (FG) composite, Nylon-6/graphene intercalation compounds (GIC) composite and Nylon-6/exfoliated graphite (EG) composite were prepared by FG, GIC, EG and caprolactam via in situ polymerization, and the volume resistivities of Nylon-6/flake graphite derivatives composites were also investigated. Meanwhile, the structure of Nylon-6/EG composite was characterized and the thermal stability of Nylon-6/EG composite was investigated as well. When the mass percents of FG, GIC and EG were 1%, 2–4% and 1%, the volume resistivities of flake graphite derivatives composites would reach 7.5 × 10⁶ Ω cm, 3.6 × 10⁸–1.4 × 10⁶ Ω cm and 2.3 × 10⁶ Ω cm. When the mass percent of EG increases from 0% to 9%, the thermal stability temperature of Nylon-6/EG composite would enhance from 70 to 196 °C. This shows that Nylon-6/flake graphite derivatives composites can have the antistatic property and thermal stability synchronously.     

Synergistic effect of hybrid graphene nanoplatelet and multi-walled carbon nanotube fillers on the thermal conductivity of polymer composites and theoretical modeling of the synergistic effect

We found that the thermal conductivity of polymer composites was synergistically improved by the simultaneous incorporation of graphene nanoplatelet (GNP) and multi-walled carbon nanotube (MWCNT) fillers into the polycarbonate matrix. The bulk thermal conductivity of composites with 20 wt% GNP filler was found to reach a maximum value of 1.13 W/m K and this thermal conductivity was synergistically enhanced to reach a maximum value of 1.39 W/m K as the relative proportion of MWCNT content was increased but the relative proportion of GNP content was decreased. The synergistic effect was theoretically estimated based on a modified micromechanics model where the different shapes of the nanofillers in the composite system could be taken into account. The waviness of the incorporated GNP and MWCNT fillers was found to be one of the most important physical factors determining the thermal conductivity of the composites and must be taken into consideration in theoretical calculations.     

Damping behavior and acoustic performance of polyurethane/lead zirconate titanate ceramic composites

0–3 Type PU-based lead zirconate titanate ceramic (PZT) composites are prepared by in situ polymerization method, this PU/PZT composite material has excellent sound absorption property at low frequencies because of damping property and piezoelectric property. The dispersion of PZT particles in PU matrix, dielectric loss tangent (tan δ), dynamic storage modulus (E′), dynamic loss modulus (E″), and the acoustic absorption coefficient (α) of PU/PZT composites are studied by scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) and two-microphone impedance tube, respectively. The results indicate that the modified PZT particles dispersed well in PU matrix with the content of 30 wt%; the tan δ, E′ and E″ are 0.62, 3.75 GPa and 6.05 GPa, respectively, when the composite with 30 wt% of polarizing PZT; the acoustic absorption coefficient is found to increase with an increase of PZT content, and the average acoustic absorption coefficient is 0.32 at low frequencies from 125 to 500 Hz.     

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.     

Enhanced thermal-conductive and anti-dripping properties of polyamide composites by 3D graphene structures at low filler content

In this work, 3D graphene structures constructed by graphene foam (GF) were introduced into polyamide-6 (PA6) matrix for the purpose of enhancing the thermal-conductive and anti-dripping properties of PA6 composites. The GF were prepared by one-step hydrothermal method. The PA6 composites were synthesized by in-situ thermal polycondensation method to realize PA6 chains covalently grafted onto the graphene sheets. The 3D interconnected graphene structure favored the formation of the consecutive thermal conductive paths or networks even at relatively low graphene loadings. As a result, the thermal conductivity was improved by 300% to 0.847 W·m⁻¹·K⁻¹ of PA6 composites at 2.0 wt% graphene loading from 0.210 W·m⁻¹·K⁻¹ of pure PA6 matrix. The presence of self-supported 3D structure alone with the covalently-grafted PA6 chains endowed the PA6 composites good anti-dripping properties.     

Magnetically-sensitive shape memory polyurethane composites crosslinked with multi-walled carbon nanotubes

Magnetically-sensitive polyurethane composites, which were crosslinked with multi-walled carbon nanotubes (MWCNTs) and were filled with Fe₃O₄ nanoparticles, were synthesized via in situ polymerization method. MWCNTs pretreated with nitric acid were used as crosslinking agents. Because of the crosslinking of MWCNTs with polyurethane prepolymer, the properties of the composites with a high content of Fe₃O₄ nanoparticles, especially the mechanical properties, were significantly improved. The composites showed excellent shape memory properties in both 45 °C hot water and an alternating magnetic field (f = 45 kHz, H = 29.7 kA m⁻¹). The shape recovery time was less than one minute and the shape recovery rate was over 95% in the alternating magnetic field.     

Magnetically-functionalized self-aligning graphene fillers for high-efficiency thermal management applications

We report on heat conduction properties of thermal interface materials with self-aligning “magnetic graphene” fillers. Graphene enhanced nano-composites were synthesized by an inexpensive and scalable technique based on liquid-phase exfoliation. Functionalization of graphene and few-layer-graphene flakes with Fe₃O₄ nanoparticles allowed us to align the fillers in an external magnetic field during dispersion of the thermal paste to the connecting surfaces. The filler alignment results in a strong increase of the apparent thermal conductivity and thermal diffusivity through the layer of nano-composite inserted between two metallic surfaces. The self-aligning “magnetic graphene” fillers improve heat conduction in composites with both curing and non-curing matrix materials. The thermal conductivity enhancement with the oriented fillers is a factor of two larger than that with the random fillers even at the low ~ 1 wt.% of graphene loading. The real-life testing with computer chips demonstrated the temperature rise decrease by as much as 10 °C with use of the non-curing thermal interface material with ~ 1 wt.% of the oriented fillers. Our proof-of-concept experiments suggest that the thermal interface materials with functionalized graphene and few-layer-graphene fillers, which can be oriented during the composite application to the surfaces, can lead to a new method of thermal management of advanced electronics.     

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.     

Functionalizing graphene decorated with phosphorus-nitrogen containing dendrimer for high-performance polymer nanocomposites

In this paper, we demonstrate a novel strategy for fabricating advanced polymer composites based on functionalized graphene oxide decorated with phosphorus-nitrogen-containing dendrimers (PND-GO). Both X-ray diffraction and transmission electron microscopy results show that reduced PND-GO uniformly disperses within polymer matrix and is exfoliated in polyurethane (PU) via in situ polymerization. Cone calorimetry results show that incorporating 2 wt% reduced PND-GO into PU decreases the peak heat release rate by 53% and prolongs the time to ignition by 28 s as compared with the PU bulk. Besides, the tensile strength and Young’s modulus are remarkably enhanced by about 2 times and 5 times, respectively.     

Thermally reduced graphene oxide acting as a trap for multiwall carbon nanotubes in bi-filler epoxy composites

The effect of thermally reduced graphene oxide (TRGO) on the electrical percolation threshold of multi wall carbon nanotube (MWCNT)/epoxy cured composites is studied along with their combined rheological/electrical behavior in their suspension state. In contrast to MWCNT and carbon black (CB) based epoxy composites, there is no prominent percolation threshold for the bi-filler (TRGO–MWCNT/epoxy) composite. Furthermore, the electrical conductivity of the bi-filler composite is two orders of magnitude lower (∼1 × 10⁻⁵ S/m) than the pristine MWCNT/epoxy composites (∼1 × 10⁻³ S/m). This result is primarily due to the strong interaction between TRGO and MWCNTs. Optical micrographs of the suspension and scanning electron micrographs of the cured composites indicate trapping of MWCNTs onto TRGO sheets. A morphological model describing this interaction is presented.     

Effect of copper content on the thermal conductivity and thermal expansion of Al–Cu/diamond composites

Al–Cu matrix composites reinforced with diamond particles (Al–Cu/diamond composites) have been produced by a squeeze casting method. Cu content added to Al matrix was varied from 0 to 3.0 wt.% to detect the effect on thermal conductivity and thermal expansion behavior of the resultant Al–Cu/diamond composites. The measured thermal conductivity for the Al–Cu/diamond composites increased from 210 to 330 W/m/K with increasing Cu content from 0 to 3.0 wt.%. Accordingly, the coefficient of thermal expansion (CTE) was tailored from 13 × 10⁻⁶ to 6 × 10⁻⁶/K, which is compatible with the CTE of semiconductors in electronic packaging applications. The enhanced thermal conductivity and reduced coefficient of thermal expansion were ascribed to strong interface bonding in the Al–Cu/diamond composites. Cu addition has lowered the melting point and resulted in the formation of Al₂Cu phase in Al matrix. This is the underlying mechanism responsible for the strengthening of Al–Cu/diamond interface. The results show that Cu alloying is an effective approach to promoting interface bonding between Al and diamond.     

Enhancement of fracture toughness,mechanical and thermal properties of rubber/epoxy composites by incorporation of graphene nanoplatelets

Carboxyl terminated butadiene acrylonitrile (CTBN) was added to epoxy resins to improve the fracture toughness, and then two different lateral dimensions of graphene nanoplatelets (GnPs), nominally <1 μm (GnP-C750) and 5 μm (GnP-5) in diameter, were individually incorporated into the CTBN/epoxy to fabricate multi-phase composites. The study showed that GnP-5 is more favorable for enhancing the properties of CTBN/epoxy. GnPs/CTBN/epoxy ternary composites with significant toughness and thermal conductivity enhancements combined with comparable stiffness to that of the neat resin were successfully achieved by incorporating 3 wt.% GnP-5 into 10 wt.% CTBN modified epoxy resins. According to the SEM investigations, GnP-5 debonding from the matrix is suppressed due to the presence of CTBN. Nevertheless, apart from rubber cavitation and matrix shear banding, additional active toughening mechanisms induced by GnP-5, such as crack deflection, layer breakage and separation/delamination of GnP-5 layers contributed to the enhanced fracture toughness of the hybrid composites.     

In situ fabrication and characterization of cobalt ferrite nanorods/graphene composites

Cobalt ferrite nanorods/graphene composites were prepared by a one-step hydrothermal process using NaHSO₃ as the reducing agent and 1-propyl-3-hexadecylimidazolium bromide as the structure growth-directing template. The reduction of graphene oxide and the in situ formation of cobalt ferrite nanorods were accomplished in a one-step reaction. The structure and morphology of as-obtained composites were characterized by field emission scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, atomic force microscope, X-ray diffractometer, Fourier transform infrared spectra, X-ray photoelectron spectroscopy and Raman spectroscopy. Uniform rod-like cobalt ferrites with diameters of about 100 nm and length of about 800 nm were homogeneously distributed on the graphene sheets. The hybrid materials showed a saturation magnetization of 42.5 emu/g and coercivity of 495.1 Oe at room temperature. The electromagnetic parameters were measured using a vector network analyzer. A minimum reflection loss (RL) of − 25.8 dB was observed at 16.1 GHz for the cobalt ferrite nanorods/graphene composites with a thickness of 2 mm, and the effective absorption frequency (RL < − 10 dB) ranged from 13.5 to 18.0 GHz. The composites exhibited better absorbing properties than the cobalt ferrite nanorods and the mixture of cobalt ferrite nanorods and graphene.     

High performance cellulose acetate propionate composites reinforced with exfoliated graphene

This paper deals with the preparation, structural characterization, and physical performances of composites composed of biomass-based cellulose acetate propionate (CAP) and exfoliated graphene (EG). As a reinforcing nanofiller, EG is thus prepared by an oxidation/thermal expansion process of natural graphite flakes and it is characterized to consist of disordered graphene platelets. Structural features, thermal stability, mechanical modulus, and electrical resistivity of CAP/EG composites are investigated as a function of EG content. SEM and X-ray diffraction data demonstrate that graphene platelets of EG are well dispersed and exfoliated in the CAP matrix for the composites with up to ～1 wt.% EG, although they are partially aggregated in the composites with higher EG contents above ～3 wt.%. Thermo-oxidative stability of CAP/EG composites under active oxygen gas condition is improved substantially due to the gas barrier effect of graphene platelets of EG dispersed in the CAP matrix. Dynamic mechanical modulus of the composites is also enhanced significantly with increasing the EG content. This mechanical enhancement of CAP/EG composites is analyzed by adopting the Halpin–Tsai model. The electrical volume resistivity of CAP/EG composites prepared by melt-compounding is decreased dramatically from ～10¹⁵ to ～10⁶ Ω cm by forming the electrical conduction path at a certain EG content between 5 and 7 wt.%.     

High performance cellulose acetate propionate composites reinforced with exfoliated graphene

This paper deals with the preparation, structural characterization, and physical performances of composites composed of biomass-based cellulose acetate propionate (CAP) and exfoliated graphene (EG). As a reinforcing nanofiller, EG is thus prepared by an oxidation/thermal expansion process of natural graphite flakes and it is characterized to consist of disordered graphene platelets. Structural features, thermal stability, mechanical modulus, and electrical resistivity of CAP/EG composites are investigated as a function of EG content. SEM and X-ray diffraction data demonstrate that graphene platelets of EG are well dispersed and exfoliated in the CAP matrix for the composites with up to ∼1 wt.% EG, although they are partially aggregated in the composites with higher EG contents above ∼3 wt.%. Thermo-oxidative stability of CAP/EG composites under active oxygen gas condition is improved substantially due to the gas barrier effect of graphene platelets of EG dispersed in the CAP matrix. Dynamic mechanical modulus of the composites is also enhanced significantly with increasing the EG content. This mechanical enhancement of CAP/EG composites is analyzed by adopting the Halpin–Tsai model. The electrical volume resistivity of CAP/EG composites prepared by melt-compounding is decreased dramatically from ∼10¹⁵ to ∼10⁶ Ω cm by forming the electrical conduction path at a certain EG content between 5 and 7 wt.%.     

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.     

Thermal conductivity of graphene nanoplatelets filled composites fabricated by solvent-free processing for the excellent filler dispersion and a theoretical approach for the composites containing the geometrized fillers

The thermal conductivity of polymer composites containing nanofillers such as GNP (graphene nanoplatelet) and carbon black (CB) was investigated using experimental and theoretical approaches. We developed a fabrication method that allows different shapes and sizes of nanofillers to be highly dispersed in polymer resin. When the bulk and in-plane thermal conductivities of the fabricated composites were measured, they were found to increase rapidly as the GNP filler content increased. The in-plane thermal conductivity of composites with 20 wt.% GNP filler was found to reach a maximum value of 1.98 W/m K. The measured thermal conductivities were compared with the calculated values based on a micromechanics model where the waviness of nanofillers could be taken into account. The waviness of the incorporated GNP filler is an important physical factor that determines the thermal conductivity of composites and must be taken into consideration in theoretical calculations.