Three-Dimensional Graphene Foam-Filled Elastomer Composites with

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3D Graphene Foam Filled Elastomer Composites with High Thermal and Mechanical Properties Haoming Fang, Yunhong Zhao, Yafei Zhang, Yanjuan Ren, and Shulin Bai ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b07650 • Publication Date (Web): 21 Jul 2017 Downloaded from http://pubs.acs.org on July 23, 2017

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ACS Applied Materials & Interfaces

3D Graphene Foam Filled Elastomer Composites with High Thermal and Mechanical Properties Haoming Fang, Yunhong Zhao, Yafei Zhang, Yanjuan Ren, Shu-Lin Bai*

Department of Materials Science and Engineering, HEDPS/CAPT, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, College of Engineering, Peking University, Beijing 100871, China *

Corresponding author. Tel.: +86-10-6275 9379. E-mail address: [email protected]

ABSTRACT：： In order to meet the increasing demands for effective heat management of electronic devices, graphene based polymeric composite is considered to be one of the candidate materials due to the ultrahigh thermal conductivity of graphene. However, poor graphene dispersion, low quality of exfoliated graphene and strong phonon scattering at graphene/matrix interface restrict the heat dissipation ability of graphene filled composites. Here, a facile and versatile approach to bond graphene foam (GF) with polydimethylsiloxane (PDMS) is proposed and the corresponding composite with considerable improvement of thermal conductivity and insulativity is fabricated. Firstly, three dimensional GF was coated with polydopamine (PDA) via π-π stack and functional groups from PDA reacted with 3-aminopropyltriethoxysilane (APTS). Then, the modified GF was compressed (c-GF) to enhance density and infiltrated with PDMS to get c-GF/PDA/APTS/PDMS composite. As a result, these processes endow the composite with high thermal conductivity of inplane 28.77Wm−1K−1 and out-of-plane 1.62 Wm−1K−1 at 11.62wt% GF loading. Besides, the composite manifests obvious improvement in mechanical properties, thermal stability and insulativity compared to neat PDMS and GF/PDMS composite. An attempt to apply the composite to cooling of ceramic heater is found to be successful. Above results open a way for such composite to be applied for heat management of electronic devices. KEYWORDS: three dimensional graphene; elastomer; noncovalent modification; thermal and mechanical properties; thermal interface material 1. INTRODUCTION With the rapid development in miniaturization and integration of electronic devices, there is no need to emphasize repeatedly the importance of heat management 1-4. The most efficient method to solve this challenge is to develop novel thermal interface materials (TIMs) with high thermal conductivity, insulativity and softness. In current electronic packaging technology, flexible polymeric composites based thermal pad is one of the best choices 5-6. To enhance the thermal conductivity of elastomers from ultralow value (commonly less than 0.5WK-1m-1)4, the common strategy is to incorporate various nano-fillers with high thermal conductivity into them, including metals (Ag nanowires 7-9, Cu nanowires 10-11 etc.), carbon-based materials (carbon black, carbon 1 ACS Paragon Plus Environment


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nanotube, graphene)4, ceramics (aluminum nitride nanoparticle 12 , boron nitride nanosheet 13) and their hybrid mixtures 14-15. Graphene, a superstar material, has attracted tremendous attention in both academia and industry, and been regarded as the most promising filler to improve the performance of polymeric composites for its high thermal conductivity (～5300Wm-1 K-1) and excellent mechanical properties 16-17. To gain ideal thermal properties of the composites, an efficient strategy is to build three-dimensional (3D) interconnected framework inside the polymer matrix. From our previous studies 18, graphene foam (GF) based polymer composites achieved a high enhancement of thermal conductivity by 300% at a filler loading of 0.7 wt%. Alam et al. 19 fabricated cellular graphene framework/polyethylene composite with a thermal conductivity of 1.84 Wm-1 K-1 at 10w% loading. However, as TIMs, there are two vital problems to be solved, i.e. interface between graphene and matrix and balance between graphene loading and softness of TIMs. Unlike the traditional fillers such as silicon oxide, calcium carbonate as well as glass fibers with lots of hydroxyl functional groups on the surface, the surface of graphene is rather smooth and lack of functional groups. Thus, the reported graphene based composites showed a mediocre thermal performance. The poor interface between graphene and matrix, largely based on weak van der Waals interaction, leads to additional phonon scattering within the contact interface. Recently, some researchers tried to improve the interface via covalence 20-21 or non-covalence 22-23 functionalized modification. Though the bonding of graphene and polymer via covalence modification is tough, the general first step is to oxidize graphene with strong oxidant such as concentrated sulfuric acid 24-25 or nitric acid 26. This step would introduce inevitable voids and defects on the graphene surface, resulting in serious phonon scattering and limited enhancement of thermal conductivity. Either, the improvement by directly modifying graphene with the silane coupling agent is unsatisfactory 27-28, which is accounted for few reactive sites and lack of coupling molecule chains onto the surface of graphene. For the sake of using pristine graphene and avoiding defects of carbon honeycomb scaffold, some molecules with organic-aromatic components like pyrene 23, pyrenebutyric acid 29 were used as the non-covalence bridge between graphene and matrix. However, due to the weak π- π stacking interaction, low volume of reactive sites and high poisonousness, there are few of applications of these molecules in thermal conductive composites being reported. If the loading of fillers is low, it’s hard to obtain high thermal conductive composites according to the law of mixture 30. High loading of fillers will sacrifice the softness of composites. On the base of applying 3D GF, second fillers were introduced into the matrix, such as multilayer graphene flakes 31, carbon fibers 32 and carbon blacks 33, the effectiveness of these strategies was not remarkable and thermal conductivity of composites was not enhanced greatly. Polydopamine (PDA), a mussel-inspired surface chemistry for multifunctional coatings 34, has been widely used in surface-functionalization of graphene oxide for the substrates of organic dyes 35 and heavy metal ions36. Due to the abundant functional groups and similar aramid π-π structure, PDA coating owns a promising application in functionalization of 3D GF directly without introducing defects and improves the interfacial interaction between graphene and matrix. Further, other important reason for coating GF with ultrathin molecule layer PDA is to decrease the electrical conductivity of graphene while maintaining the excellent thermal properties for the wider applications in the thermal management of electronics and systems. The traditional method is constructing the insulated oxide layers such as silica 37, alumina 38 onto graphene surface. These methods can decrease the electrical conductivity of graphene remarkably, but would increase 2 ACS Paragon Plus Environment

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interface thermal resistance at the same time. PDA could be used as an insulated layer to decrease the electrical conductivity of carbon nanotubes (CNT) 39. Therefore, it is regarded as a feasible strategy to increase breakdown strength and electric resistance of graphene based composites. Herein, we propose a facile, versatile and green approach to overcome the two fore mentioned challenges. First, by introducing bio-inspired PDA coating and silane coupling agent, a tough bonding was achieved between 3D GF and matrix. Second, by compressing 3D GF to a certain level, the graphene loading was increased and the interconnected network of graphene along the thickness of composite samples was still maintained. Therefore, the thermal, mechanical and insulated performances of composites were all improved. Finally, these composites were employed as the TIMs in the practical application and the temperature of hot device dropped down obviously. 2. MATERIALS AND EXPERIMENT 2.1 Materials Nickel foams of 1.8mm in thickness and 3.9 x 10-2 g cm-2 in density were supplied by Shanghai Zhongwei Co., Ltd. Dopamine hydrochloride, tris(hydroxymethyl) aminomethane (Tris) and 3aminopropyltriethoxysilane (APTS) were purchased from Aladdin. Polydimethylsiloxane (PDMS, Sylgard184) was purchased from Dow Corning. The fabrication process of GF was reported in our previous work18. 2.2 Non-covalent modification of GF A piece of GF was immersed into the mixed solution of 80mg of dopamine hydrochloride, 300ml of Tris-buffer solution (10 mM, pH 8.5) and 100ml of ethanol, then stirring the mixed solution for 12h at room temperature. After that, the GF was washed by deionized water and ethanol for several times. The polydopamine (PDA) modified GF (GF/PDA) was attained via lyophilizing for 12h. 2.3 Silane coupling agent modification of GF and GF/PDA The GF/PDA and GF were separately immersed into 100 mL deionized water, then 5mL APTS was added into the solution with the magnetic stirring at room temperature for 24h. The modified GF/PDA/APTS and GF/APTS were gained after washing with deionized water several times and lyophilizing. 2.4 Fabrication of composites The GF, GF/APTS, GF/PDA and GF/PDA/APTS samples were infiltrated with liquid PDMS (base agent/curing agent = 10/1 in weight) at ambient temperature. Then, the mixture was vacuumized and cured at 80°C for 4h to get the GF/PDMS, GF/APTS/PDMS, GF/PDA/PDMS and GF/PDA/APTS/PDMS composites. 2.5 Characterization 3 ACS Paragon Plus Environment


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The microstructures and morphology of all materials studied were measured by scanning electron microscopy (SEM, S-4800, HITACHI), transmission electron microscope (TEM, JEM-2100F, JEOL), and atomic force microscope (AFM, MFP-3D-BIO, Asylum Research). The Raman spectra was obtained on a Fourier HORIBA Jobin Yvon LabRAM HR Evolution Raman spectrometer with He–Ne laser excited at 632.8nm and under the power of 150 mW cm-2. X-ray photoelectron spectroscopy (XPS) measurements were carried out by Axis Ultra imaging photoelectron spectrometer (Kratos Analytical Ltd., Japan) with a monochromatic Al Ka X-ray source at 225 W. Contact angle measurements were conducted by contact angle instrument (SL200B, Kino) equipped with a charge coupled device (CCD) camera. A liquid droplet of 2µL was formed at the end of the syringe and carefully deposited onto the sample surface. The contact angle was calculated by vendor-supplied software. All the contact angle tests were repeated for five times. The mechanical properties were measured by a miniature tensile testing machine (2000, MiniMat) at a loading rate of 1.5 mm/min. The thickness and length of dumbbell shape samples are 2mm and 35mm, respectively. Valid parallel part of sample is 2mm in width and 12mm in length according to GB/T 528-92. Five samples of each kind of composites were tested. Thermal conductivity was calculated from the equation: λ = α × C × ρ, where , , , and represent thermal conductivity, thermal diffusivity, heat capacity, and material density, respectively. The thermal diffusivity coefficient of samples with the diameter of 12.7mm was measured by laser-flash diffusivity instrument (DXF-500, TA Instruments, America) from 25°C to 150°C. The specific heat (c) was obtained by differential scanning calorimetry (DSC) Q100 (TA Instruments, America) at a heating rate of 10°C/min from 20°C to 200°C. The density of samples was measured using an automatic density analyzer (PEAB, XS105DU, METTLER TOLEDO, Switzerland). The thermal stability was studied by dynamic thermogravimetric analysis (Q600 SDT, TA) at the nitrogen atmosphere from room temperature to 800°C at a heating rate of 10°C/min. The IR images were recorded by the thermal imager (SC7300M, Flir Systems USA). The electrical conductivity was measured by the insulation resistance tester (TH2683, TongDe Ltd.) The breakdown voltage was tested by voltage withstand test instrument (RK2674A, Rek) according to GB/T 1408-1-2006. 3. RESULTS AND DISCUSSION The schematic procedure for fabrication and modification of graphene foam is illustrated in Figure 1. In addition, the chemical equation of these procedures and molecular model are shown in Figure 2. When coated with PDA, GF seems to be put on a tight overcoat with plentiful functional groups like hydroxyl and amidogen. Due to the π-π stacking interaction between graphene and PDA, there are few of defects being introduced on the surface of GF. Then, it is easy to graft the APTS on the surface and improve the performance of the interface between GF and polymers.

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Figure 1. Schematic of fabrication procedure of GF, c-GF, GF/PDA, GF/APTS, GF/PDA/APTS and c- GF/PDA/APTS. (c-GF means compressed graphene foam)

Figure 2. (a) Chemical reactions during the procedures, (b) molecular model of GF/PDA/APTS/PDMS 3.1. Surface properties of GF and its derivatives The effectiveness of PDA modification is obviously, as shown in Figure 3 (b, e, h, k). At the beginning, the surface of GF is smooth and rigid, and there are few changes when treated with 5 ACS Paragon Plus Environment


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APTS directly. When self-polymerization of dopamine occurred onto the graphene, its surface morphology becomes rough and wrinkled, which is consistent with reported results 40-41. From Figure 3 (g, h, j, k), GF was coated with PDA molecule layers tightly in a large range, but there are few cracks at the corner of GF arm. TEM images of GF and its derivative are shown in Figure 3 (c, f, i, l), there are ten layers of graphene at the edge of one piece. The SAED pattern in Figure 3(c) presents the hexagonal symmetry nature of graphene. PDA layers on GF surface are obviously visible after PDA coating as shown in Figure 3(i, l). Moreover, the surface becomes more obscure when treated with APTS due to the amorphous form of organic layers. Further surface characteristic was measured by AFM and contact angle test. From the AFM image in Figure 4, the surface is rougher and rougher after step-by-step modification. The average deviation (Ra) of height increases from 0.81, 1.446, and 5.491 to 13.65nm. To confirm the wettability of surfaces of GF and its derivatives, contact angle test via water and ethylene glycol drops was carried out. There is no obvious change of contact angle for graphene directly treated with APTS. However, the angle decreases obviously when coated with PDA. And the GF/PDA/APTS shows a smallest value of contact angle with both water and ethylene glycol at 16° and 30.8°, respectively. The surface energy and work adhesion are figured out according to Fowkes model42-43 and Dupre-Young’s equation44 and present the same trends as shown in Figure S1. The surface energy of GF/PDA/APTS is 94.88 mJ/m2, which is more than 4 times that of GF. Due to higher surface energy and rough surface, GF/PDA/APTS shows much better wettability than GF, which endows a better interface interaction between graphene and polymer.


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Figure 3. Microstructure of GF and its derivatives. (a, d, g, j) SEM images of GF, GF/APTS, GF/PDA and GF/PDA/APTS, respectively, (b, e, h, k) magnified images of the white rectangle areas, (c, f, i, l) TEM images of GF, GF/APTS, GF/PDA and GF/PDA/APTS, respectively, the inset in (c) is SAED patterns of graphene.

Figure 4. Surface roughness by AFM of (a) GF, (b) GF/APTS, (c) GF/PDA and (d) GF/PDA/APTS. Plots for (e) average deviation of height and (f) contact angle of GF and its derivatives. Identification of PDA coating and APTS modification of GF was made by XPS analysis as shown in Figure 5. GF and its derivatives show an edge peak of C 1s. The peak of O 1s becomes intense and the peaks of N 1s can be observed obviously for GF/PDA and GF/PDA/APTS samples. When GF and GF/PDA are treated by silane coupling agent in the same process, only the peaks of Si 2s and Si 2p can be found for GF/PDA/APTS sample and the content of silicon is 2.78%. The content of oxygen varies as 1.02, 1.75, 8.26 and 8.94% for GF, GF/APTS, GF/PDA and GF/PDA/APTS, respectively, which reveals that PDA layers can provide graphene with oxygenrich reaction sites for silicon coupling. C 1 s XPS spectrum of GF and GF/APTS were deconvoluted into five peaks with binding energies at 284.5, 285, 286.1(286.3), 287.8 and 289.0 7 ACS Paragon Plus Environment


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eV corresponding to C=C, C–C, C–O, C=O, and O–C=O components, respectively 45. After coated with PDA, the peaks of C–N component at binding energy of 285.7 eV appear 46. And the content of –OH group, corresponding to the peak at 533.7eV, increases from 12.03% to 46.08%, which means there are about 4 times of hydroxyl groups after silane coupling treatment of GF/PDA. From Figure 4(e), the disappearance of pyrrolic-N at 398.5eV also indicates the happening of silane coupling reaction after coating. The secondary amine corresponding to the peak at 399.8 (400) eV means the formation of indole structure of PDA via self-oxidative polymerization. Peaks of –NH2 (401.5, 401.7 eV) reveal the self-assembly in graphene surface. Last, the peak from Si2p at 102.8eV indicates the chemical bonding of GF/PDA and APTS.

Figure 5. XPS spectra of GF, GF/APTS, GF/PDA and GF/PDA/APTS. (a) survey scans, (b) element content percentage, (c) C1s (red line), (d) O1s (blue line), (e) N1s (green line) and Si2p (orange line).


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In contrast with covalent functionalization, the non-covalent bonding of PDA would not introduce defects and voids onto surface of graphene. As shown in Figure 6 (a), the absence of D peak at 1348 cm-1 and D’ peak at 1620 cm-1 corresponding to the defect of graphene suggests the high quality of CVD grown GF 47, and there is no damage on the surface during modification of PDA and silane coupling reaction. And the IG/IG’ ratio is about 2.2 for all samples48-50, suggesting the signal of multilayer graphene which endows 3D GF with good mechanical properties. TGA analysis of GF and its derivatives is shown in Figure 6 (b). The instant weight drop of GF happened at around 600°C suggesting the oxidation and decomposition of graphene. As for modified graphene samples, the decomposition process is relatively slow, indicating the gradual decomposition of organic molecules and PDA layers. In addition, the PDA coating can increase the decomposition temperature and enhance the thermal stability of GF.

Figure 6. (a) Raman spectra and (b) TGA thermograms (in air) of GF, GF/APTS, GF/PDA and GF/PDA/APTS. 3.2 Morphology of composites The SEM images of cryo-fractured surfaces of GF/PDMS and GF/APTS/PDA/PDMS composites are shown in Figure 7 (a, b). 3D GF frameworks can be identified clearly and there are no obvious gaps and cracks inside the composites. The PDA-APTS modification on GF surface is apparent. After tensile tests, GF inside the GF/PDMS composite was obviously pulled out under tension due to the weak interface as shown in Figure 7 (c) While, the modified GF inside the GF/APTS/PDA/PDMS composite was broken off rather than pulled out from the matrix as shown in Figure 7 (d). This phenomenon suggests that a tough interface has been built up after the treatment of GF surface. After compressing the GF from 1.8mm to 0.18mm in thickness, GF becomes denser in both vertical and horizontal directions. The densification treatment of GF provides denser heat transfer networks and higher GF loading for composites while maintaining 3D interconnection structures. PDA layers can be identified easily onto the surface of compressed GF (c-GF) as shown in Figure 7(f). Moreover, it is rough and wrinkled compared with the rigid and smooth surface of c-GF as 9 ACS Paragon Plus Environment


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shown in Figure S2 (b). The densities of c-GF/PDMS and c-GF/PDA/APTS/PDMS composites are 1.20±0.006 and 1.31±0.035 g/cm3, respectively. The higher density of c-GF/PDA/APTS/PDMS composite indicates that there are fewer voids inside the composite. As given in Table. S2, the void fraction of GF/PDMS composite calculated by formula (S6, S7) is 9.7%, namely six and half times than that of c-GF/PDA/APTS/PDMS composite. In addition, it is also found that the hollow GF arm was not completely filled with PDMS as shown in Figure 7(g).


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Figure 7. SEM images of (a, b) Cryo-fractured surfaces and (c, d) tensile fractured surfaces of GF/PDMS and GF/APTS/PDA/PDMS composites, (e, g) surface microstructure of cGF/PDA/APTS, c-CF/PDMS composites, (f, h) magnified images of the white rectangle area of images (e, g). 3.3 Mechanical properties of composites For further examination of the usefulness of PDA-APTS modification, the mechanical properties of composites were measured via tensile tests. The typical stress-strain curves are shown in Figure 8(a). Compared to neat PDMS, the tensile strength and Young’s modulus of composites are all increased, because the interconnected framework of GF can efficiently resist the deformation and bear the force. However, when directly treating GF via single PDA or APTS, the mechanical properties have no obviously change as shown in Figure 8(b, c, d). The reason is that the silane coupling reaction is hard to occur on the smooth graphene surface without functional groups, which has been demonstrated in previous results such as XPS measurement. Secondly, although PDA coating would endow many hydroxyl groups on GF surface, short molecule chains of PDA are difficult to interact with PDMS molecule chains, leading to few chemical bonds to connect GF and matrix. Therefore, only building a chemical bonding bridge via PDA-ATPS functionalization can enhance the mechanical properties of composites. The tensile strength, elongation at break and Young’s modulus of GF/APTS/PDA/PDMS composite increase from 2.15±0.22 to 3.07±0.29MPa, 74.39±4.32 to 89.4±3.88% and 2.28±0.011 to 2.97±0.309 MPa respectively, compared with GF/PDMS composite. The schematic of toughening and reinforcing mechanisms for composites is shown in Figure 9(a). The mechanism of interface reinforcement can be explained by three factors, i.e. chemical bonding, excellent wettability and mechanical interlocking. Under strain or shear stress, the organic molecule of APTS serves as a spring-like bond to resist the deformation. Secondly, thanks to the good wettability after modification, the total contact areas between graphene and polymer would enlarge and so provide more interlocking sites that are useful to resist shear force. Thus, the mechanical properties of composites can be improved largely. While, as shown in Figure 9(b), the direct contact between PDMS and GF via a smooth and non-chemical bonding interface, leading to interfacial debonding easily and the poor mechanical properties.



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Figure 8. (a) Typical stress–strain curves, (b) tensile strength, (c) elongation at break and (d) Young’s modulus of neat PDMS and composites.


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Figure 9. (a) Schematic of toughening and reinforcing mechanisms for GF/PDA/APTS filled PDMS composite and (b) corresponding schematic for GF filled PDMS composite. 3.4 Thermal performances Thermal conductivity (TC) and thermal diffusivity of these composites are shown in Figure 10 and Figure S4, respectively. From the results, TC increases from 0.18Wm−1K−1 of neat PDMS to 0.62Wm−1K−1 of GF/PDA/APTS/PDMS composite with 247% enhancement. For a better performance of thermal conductivity, the GF/PDA/APTS foam was compressed into one-tenth in height. Ainsi obtained c-GF/PDA/APTS/PDMS composite shows a remarkable enhancement in TC, the values of out-of-plane and in-plane TC are 1.62 and 28.77Wm−1K−1 at 11.62wt% GF loading, respectively. As the compression forces the interconnected arm of GF to lie down along the sample plane, the phonon transport is easier in the in-plane than in the out-of-plane. Therefore, the in-plane TC is much higher. This means also the anisotropy of as-prepared composites. In addition, the interface state between graphene and matrix makes a notable impact on thermal conduction. The GF/PDMS and GF/PDA/PDMS composites present similar TC of 0.52 Wm−1K−1 and 0.54 Wm−1K−1, respectively. But after PDA-APTS functionalization, TC of GF/PDA/APTS/PDMS composite increases to 0.62Wm−1K−1 with 15% enhancement compared with GF/PDMS composite. This phenomenon can be explained that coating of PDA layer on graphene via weak π−π interaction introduces an additional weak interface, and then phonon scattering would happen when it comes across the interface. Besides, the weak van der Waals' force rather than tough chemical bonding between PDMS and PDA creates thermal resistance at interface, which results in the reduction of TC. Fortunately, through bonding PDA and PDMS by using APTS molecule chains, phonon can transfer smoothly from PDA to PDMS via APTS vibration, thus heat transfer performance is enhanced. When compressed, the surface properties of GF play a more significant role. From our results, 13 ACS Paragon Plus Environment


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bad wettability of GF surface would hinder complete infiltration of PDMS precursor, further introduce voids inside composite. The existence of voids will certainly reduce the TC of composite due to the much lower TC of air. Therefore, c-GF/PDA/APTS/PDMS composite having 1.5% voids presents 47% and 29.2% increases in out-of-plane and in-plane TC respectively, compared to GF/PDMS composite having 9.7% voids. To compare with other kinds of thermal conductive composites, TC enhancement efficiency (η) is considered to be an important index, and defined as TC enhancement per 1 wt% loading, as follows.

η = × 100

(1)

Where is TC enhancement efficiency, TC and TC0 are TC of composite and pure polymer, W is the weight loading of fillers. The values of reported composites are summarized in Figure 10 (c) and Table.1. Clearly, the c-GF/PDA/APTS/PDMS composite shows the highest TC at same loading not only in in-plane but also in out-of-plane direction.


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Figure 10. (a) Out-of-plane and (b) In-plane TC of composites. (c) Comparison of TC enhancement efficiency of reported composites. Table.1 Summary on TC of polymer composites filled with different fillers. Sample

TC of matrix

TC of

−1

composites

−1

(Wm K )

−1

Loading

TC

Reference and

(wt%)

enhancement

years

−1

(Wm K )

GNPs/BN/PS fGNPs/epoxy GNPs/BN/PA GNPs/bisphenol-A epoxy resin BN/GF/PA Al2O3/GNP/epoxy Cellular graphene framework/PP 3D carbon nanotube/PDMS Graphene aerogel/PDMS GF/PDA/APTS/PDMS c-GF/PDA/APTS/PDMS (out-of-plane) c-GF/PDA/APTS/PDMS (in-plane)

efficiency (η)

0.16 0.23 0.28 0.20 0.20 0.22 0.22 0.18 0.46 0.18 0.18

0.67 1.49 1.69 1.70 0.89 1.49 1.53 0.82 0.67 0.62 1.62

21.50 30.00 21.50 30.00 8.40 12.00 10.00 5.00 1.00 0.40 11.62

15.33 17.85 23.14 24.83 42.21 48.11 59.55 71.11 46.15 617.76 69.00

201551 201752 201551 201653 201614 201638 201719 201654 201555 This work This work

0.18

28.77

11.62

1367.30

This work

Thermogravimetric tests were carried out to investigate the thermal stability of composites as shown in Figure 11 and the corresponding characteristic data are presented in Table. S2. The heat resistance index (THRI) is used to compare the thermal stability of composites56-58 and the definition is presented by formula (S8). From the results, c-GF/PDA/APTS/PDMS composite shows the highest THRI value of 251.06°C, related to the tough chemical bonding between graphene and PDMS, which hinders the movement and decomposition of PDMS molecular chains. On the contrary, without chemical bonding and rigid interface, c-GF/PDMS composite presents the worst performance. It can be explained that the PDMS in c-GF/PDMS composite would be easier to decompose at relatively low temperature because of the relative freedom state of molecule chains at the interface, leading to degraded thermal stability.



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Figure 11. TGA curves of PDMS and composites 3.5 Heat dissipation performance as TIMs To exhibit the potential of the c-GF/PDA/APTS/PDMS composite as TIMs in electronic devices, a testing system was designed as presented in Figure 12(a). Firstly, the films (about 0.2mm thick) of PDMS, c-GF/PDMS and c-GF/PDA/APTS/PDMS composites were separately attached as thermal pad onto the backside of a ceramic heater (10×10×1.2mm, 20Ω). Then, one ceramic heater was stuck with the commercial heat sink with fan (provided by PC Partner Ltd.) via the thermal pad to simulate the practical application. For the accurate measurements by infrared photography, the top surface of ceramic heater was sprayed with thin carbon layer. The temperature-time curve of ceramic heater at voltage of 4V is shown in Figure 12(b) and the inserted pictures captured by the IR camera show the evolution of temperature at intervals of 0, 5, 10, 20 and 30s. In addition, the maximum temperature of ceramic heater in the steady state was used as the equilibrium temperature to compare the heat transfer ability of composites. Obviously, the equilibrium temperature (42°C) by applying c-GF/PDA/APTS/PDMS composite is much lower than that of pure PDMS (60°C) and c-GF/PDMS composite (52°C). Further, equilibrium temperatures of ceramic heater at different voltages are exhibited in Figure 12(c). Although turning on the fan would cool down the heater, the temperature drops are limited only for 3 to 5°C. However, with the increasing voltage, the difference of equilibrium temperature among three kinds of thermal pads increases. This means that higher is the power, greater is the temperature drop by applying c-GF/PDA/APTS/PDMS composite. Mechanical degradation of polymer matrix composites is one of the key problems during thermal cycling 59. The occurrence of cracks and voids would be detrimental to thermal and mechanical performance of composites. Therefore, thermal cycling test is strongly necessary for evaluating the potential damage from thermal stress. The temperature variation of ceramic heater mounted 16 ACS Paragon Plus Environment

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with c-GF/PDA/APTS/PDMS composite as thermal pad during heating and cooling cycles is shown in Figure 12(d). In the whole process of 200 cycles, there is no significant rise and fall of temperature, indicating the excellent thermal stability of c-GF/PDA/APTS/PDMS composite in the mimic situation of real application.

Figure 12. Practical application of studied materials. (a) Photograph of in-situ test system (inserted photographs are the TIM of c-GF/PDA/APTS/PDMS composite and ceramic heater attached with TIM at the backside). (b) Profiles of the surface temperature-time of ceramic heater at 4V with fan cooling (inserts are IR images of c-GF/PDA/APTS/PDMS composite). (c) Surface temperature-voltage relation and IR images of the surface temperature of ceramic heater at 6V with and without fans. (d) Temperature variation of ceramic heater during thermal cycling using c-GF/PDA/APTS/PDMS composite as TIM. 3.6 Breakdown strength and electrical resistivity In practical application of TIMs, insulativity is another important parameter. In general, the 17 ACS Paragon Plus Environment


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standard breakdown strength and electrical resistivity of TIMs are required to be higher than 1KV/mm and 13×1013 Ωcm, respectively 60. Due to insulated performance of PDA layer, the cGF/PDA/APTS/PDMS composite shows an enough insulated property. Compared to c-GF/PDMS composite, its breakdown strength and electrical resistivity increase from 0.96±0.29 to 2.38±0.45KV/mm and 4.05±0.82×1012 Ωcm to 9.02±1.07×1013 Ωcm, respectively, as shown in Figure13.

Figure 13. (a) Breakdown strength and (b) electrical resistivity of studied materials, respectively. 4. CONCLUSIONS In this work, an efficient and facile approach to fabricate three dimensional (3D) graphene foam (GF) filled elastomer composites was invented and satisfactory improvement on thermal, mechanical and electrical properties was achieved. The 3D GF was modified via polydopamine (PDA) and 3-aminopropyltriethoxysilane (APTS) functionalization and so a tough chemical bonding was formed between graphene and polydimethylsiloxane (PDMS) matrix. Further, the GF was intentionally compressed before infiltrating PDMS in order to get compacted structure. Above procedures are proved to be very effective to enhance the performance of as-prepared composites. The thermal conductivity of c-GF/PDA/APTS/PDMS composite is highly anisotropic, with values of in-plane 28.77Wm−1K−1 and out-of-plane 1.62 Wm−1 K−1 at 11.62wt% GF loading. Besides, the composite shows good mechanical properties, excellent thermal stability and enough insulativity. A mimic application of using the composite as thermal pad demonstrates well its good ability to dissipate the heat. The outstanding performance of cGF/PDA/APTS/PDMS composite will see a promising application in the heat management of electronic devices. ASSOCIATED CONTENT Supporting Information Work of adhesion and surface energy of GF and its derivatives; SEM images of c-GF and its composites; theoretical and measured density, and calculated void fraction of composites; characteristic thermal stability data.


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ACKNOWLEDGMENTS The work is supported by NSFC and NSFC-RGC Joint Research Scheme (Nos., 11361161001, CUHK450/13, and 11672002). REFERENCES 1. Burger, N.; Laachachi, A.; Ferriol, M.; Lutz, M.; Toniazzo, V.; Ruch, D., Review of Thermal Conductivity in Composites: Mechanisms, Parameters and Theory. Prog. Polym. Sci. 2016, 61, 1-28. 2. Chen, H.; Ginzburg, V. V.; Yang, J.; Yang, Y.; Liu, W.; Huang, Y.; Du, L.; Chen, B., Thermal Conductivity of Polymer-Based Composites: Fundamentals and Applications. Prog. Polym. Sci. 2016, 59, 41-85. 3. Han, Z.; Fina, A., Thermal Conductivity of Carbon Nanotubes and Their Polymer Nanocomposites: A Review. Prog. Polym. Sci. 2011, 36 (7), 914-944. 4. Sadasivuni, K. K.; Ponnamma, D.; Thomas, S.; Grohens, Y., Evolution from Graphite to Graphene Elastomer Composites. Prog. Polym. Sci. 2014, 39 (4), 749-780. 5. Wong, C.; Moon, K.-S.; Li, Y., Nano-Bio-Electronic, Photonic and Mems Packaging. 1 ed.; Springer: 2010; p 277-314. 6. Hansson, J.; Zandén, C.; Ye, L.; Liu, J. In Review of Current Progress of Thermal Interface Materials for Electronics Thermal Management Applications, 2016 IEEE 16th International Conference on Nanotechnology (IEEE-NANO), 22-25 Aug. 2016; 2016; pp 371-374. 7. Lan, W.; Chen, Y.; Yang, Z.; Han, W.; Zhou, J.; Zhang, Y.; Wang, J.; Tang, G.; Wei, Y.; Dou, W.; Su, Q.; Xie, E., Ultraflexible Transparent Film Heater Made of Ag Nanowire/Pva Composite for Rapid-Response Thermotherapy Pads. ACS Appl. Mater. Interfaces 2017, 9 (7), 6644-6651. 8. Doganay, D.; Coskun, S.; Kaynak, C.; Unalan, H. E., Electrical, Mechanical and Thermal Properties of Aligned Silver Nanowire/Polylactide Nanocomposite Films. Composites, Part B 2016, 99, 288-296. 9. Rivière, L.; Lonjon, A.; Dantras, E.; Lacabanne, C.; Olivier, P.; Gleizes, N. R., Silver Fillers Aspect Ratio Influence on Electrical and Thermal Conductivity in Peek/Ag Nanocomposites. Eur. Polym. J. 2016, 85, 115125. 10. Barako, M. T.; Roy-Panzer, S.; English, T. S.; Kodama, T.; Asheghi, M.; Kenny, T. W.; Goodson, K. E., Thermal Conduction in Vertically Aligned Copper Nanowire Arrays and Composites. ACS Appl. Mater. Interfaces 2015, 7 (34), 19251-19259. 11. Chen, W.; Wang, Z.; Zhi, C.; Zhang, W., High Thermal Conductivity and Temperature Probing of Copper Nanowire/Upconversion Nanoparticles/Epoxy Composite. Compos. Sci. Technol. 2016, 130, 63-69. 12. Zhou, Y.; Hu, J.; Chen, X.; Yu, F.; He, J., Thermoplastic Polypropylene/Aluminum Nitride Nanocomposites with Enhanced Thermal Conductivity and Low Dielectric Loss. IEEE Trans. Dielectr. Electr. Insul. 2016, 23 (5), 2768-2776. 13. Fang, H.; Bai, S. L.; Wong, C. P., “White Graphene” – Hexagonal Boron Nitride Based Polymeric Composites and Their Application in Thermal Management. Composites Communications 2016, 2, 19-24. 14. Shao, L.; Shi, L.; Li, X.; Song, N.; Ding, P., Synergistic Effect of Bn and Graphene Nanosheets in 3d Framework on the Enhancement of Thermal Conductive Properties of Polymeric Composites. Compos. Sci. Technol. 2016, 135, 83-91. 15. Yao, Y.; Zeng, X.; Sun, R.; Xu, J. B.; Wong, C. P., Highly Thermally Conductive Composite Papers Prepared Based on the Thought of Bioinspired Engineering. ACS Appl. Mater. Interfaces 2016, 8 (24), 15645-15653. 16. Shehzad, K.; Xu, Y.; Gao, C.; Duan, X., Three-Dimensional Macro-Structures of Two-Dimensional Nanomaterials. Chem. Soc. Rev. 2016, 45 (20), 5541-5588. 17. Stankovich, S.; Dikin, D. A.; Dommett, G. H.; Kohlhaas, K. M.; Zimney, E. J.; Stach, E. A.; Piner, R. D.; Nguyen, S. T.; Ruoff, R. S., Graphene-Based Composite Materials. Nature 2006, 442 (7100), 282-286.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

18. Zhao, Y.-H.; Wu, Z.-K.; Bai, S.-L., Study on Thermal Properties of Graphene Foam/Graphene Sheets Filled Polymer Composites. Composites, Part A 2015, 72, 200-206. 19. Alam, F. E.; Dai, W.; Yang, M.; Du, S.; Li, X.; Yu, J.; Jiang, N.; Lin, C.-T., In Situ Formation of a Cellular Graphene Framework in Thermoplastic Composites Leading to Superior Thermal Conductivity. J. Mater. Chem. A 2017, 5 (13), 6164-6169. 20. Rohini, R.; Katti, P.; Bose, S., Tailoring the Interface in Graphene/Thermoset Polymer Composites: A Critical Review. Polymer 2015, 70, A17-A34. 21. Gu, H.; Ma, C.; Gu, J.; Guo, J.; Yan, X.; Huang, J.; Zhang, Q.; Guo, Z., An Overview of Multifunctional Epoxy Nanocomposites. J. Mater. Chem. C 2016, 4 (25), 5890-5906. 22. Georgakilas, V.; Tiwari, J. N.; Kemp, K. C.; Perman, J. A.; Bourlinos, A. B.; Kim, K. S.; Zboril, R., Noncovalent Functionalization of Graphene and Graphene Oxide for Energy Materials, Biosensing, Catalytic, and Biomedical Applications. Chem. Rev. 2016, 116 (9), 5464-5519. 23. Teng, C.-C.; Ma, C.-C. M.; Lu, C.-H.; Yang, S.-Y.; Lee, S.-H.; Hsiao, M.-C.; Yen, M.-Y.; Chiou, K.-C.; Lee, T.M., Thermal Conductivity and Structure of Non-Covalent Functionalized Graphene/Epoxy Composites. Carbon 2011, 49 (15), 5107-5116. 24. Wang, R.; Zhuo, D.; Weng, Z.; Wu, L.; Cheng, X.; Zhou, Y.; Wang, J.; Xuan, B., A Novel Nanosilica/Graphene Oxide Hybrid and Its Flame Retarding Epoxy Resin with Simultaneously Improved Mechanical, Thermal Conductivity, and Dielectric Properties. J. Mater. Chem. A 2015, 3 (18), 9826-9836. 25. Bao, C.; Guo, Y.; Song, L.; Kan, Y.; Qian, X.; Hu, Y., In Situ Preparation of Functionalized Graphene Oxide/Epoxy Nanocomposites with Effective Reinforcements. J. Mater. Chem. 2011, 21 (35), 13290-13298. 26. Zhu, J.; Wei, S.; Ryu, J.; Budhathoki, M.; Liang, G.; Guo, Z., In Situ Stabilized Carbon Nanofiber (Cnf) Reinforced Epoxy Nanocomposites. J. Mater. Chem. 2010, 20 (23), 4937-4948. 27. Qian, X.; Yu, B.; Bao, C.; Song, L.; Wang, B.; Xing, W.; Hu, Y.; Yuen, R. K. K., Silicon Nanoparticle Decorated Graphene Composites: Preparation and Their Reinforcement on the Fire Safety and Mechanical Properties of Polyurea. J. Mater. Chem. A 2013, 1 (34), 9827-9836. 28. Xu, Y.; Gao, Q.; Liang, H.; Zheng, K., Effects of Functional Graphene Oxide on the Properties of Phenyl Silicone Rubber Composites. Polym. Test. 2016, 54, 168-175. 29. Song, S. H.; Park, K. H.; Kim, B. H.; Choi, Y. W.; Jun, G. H.; Lee, D. J.; Kong, B. S.; Paik, K. W.; Jeon, S., Enhanced Thermal Conductivity of Epoxy-Graphene Composites by Using Non-Oxidized Graphene Flakes with Non-Covalent Functionalization. Adv. Mater. 2013, 25 (5), 732-737. 30. Okamoto, S.; Ishida, H., A New Theoretical Equation for Thermal Conductivity of Two‐Phase Systems. J. Appl. Polym. Sci. 1999, 72 (13), 1689-1697. 31. Zhao, Y.-H.; Zhang, Y.-F.; Bai, S.-L., High Thermal Conductivity of Flexible Polymer Composites Due to Synergistic Effect of Multilayer Graphene Flakes and Graphene Foam. Composites, Part A 2016, 85, 148155. 32. Zhao, Y.-H.; Zhang, Y.-F.; Bai, S.-L.; Yuan, X.-W., Carbon Fibre/Graphene Foam/Polymer Composites with Enhanced Mechanical and Thermal Properties. Composites, Part B 2016, 94, 102-108. 33. Zhao, Y.-H.; Zhang, Y.-F.; Wu, Z.-K.; Bai, S.-L., Synergic Enhancement of Thermal Properties of Polymer Composites by Graphene Foam and Carbon Black. Composites, Part B 2016, 84, 52-58. 34. Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B., Mussel-Inspired Surface Chemistry for Multifunctional Coatings. Science 2007, 318 (5849), 426-430. 35. Dong, Z.; Wang, D.; Liu, X.; Pei, X.; Chen, L.; Jin, J., Bio-Inspired Surface-Functionalization of Graphene Oxide for the Adsorption of Organic Dyes and Heavy Metal Ions with a Superhigh Capacity. J. Mater. Chem. A 2014, 2 (14), 5034-5040. 36. Guo, L.; Liu, Q.; Li, G.; Shi, J.; Liu, J.; Wang, T.; Jiang, G., A Mussel-Inspired Polydopamine Coating as a Versatile Platform for the in Situ Synthesis of Graphene-Based Nanocomposites. Nanoscale 2012, 4 (19), 5864-5867. 37. Hsiao, M. C.; Ma, C. C.; Chiang, J. C.; Ho, K. K.; Chou, T. Y.; Xie, X.; Tsai, C. H.; Chang, L. H.; Hsieh, C. K., Thermally Conductive and Electrically Insulating Epoxy Nanocomposites with Thermally Reduced Graphene Oxide-Silica Hybrid Nanosheets. Nanoscale 2013, 5 (13), 5863-5871. 38. Sun, R.; Yao, H.; Zhang, H.-B.; Li, Y.; Mai, Y.-W.; Yu, Z.-Z., Decoration of Defect-Free Graphene Nanoplatelets with Alumina for Thermally Conductive and Electrically Insulating Epoxy Composites. Compos. Sci. Technol. 2016, 137, 16-23.


Page 20 of 22

Page 21 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


39. Ryu, S.; Chou, J. B.; Lee, K.; Lee, D.; Hong, S. H.; Zhao, R.; Lee, H.; Kim, S. G., Direct Insulation-toConduction Transformation of Adhesive Catecholamine for Simultaneous Increases of Electrical Conductivity and Mechanical Strength of Cnt Fibers. Adv. Mater. 2015, 27 (21), 3250-3255. 40. Liebscher, J.; Mrowczynski, R.; Scheidt, H. A.; Filip, C.; Hadade, N. D.; Turcu, R.; Bende, A.; Beck, S., Structure of Polydopamine: A Never-Ending Story? Langmuir 2013, 29 (33), 10539-48. 41. Lynge, M. E.; van der Westen, R.; Postma, A.; Städler, B., Polydopamine—a Nature-Inspired Polymer Coating for Biomedical Science. Nanoscale 2011, 3 (12), 4916-4928. 42. Kozbial, A.; Li, Z.; Conaway, C.; McGinley, R.; Dhingra, S.; Vahdat, V.; Zhou, F.; D'Urso, B.; Liu, H.; Li, L., Study on the Surface Energy of Graphene by Contact Angle Measurements. Langmuir 2014, 30 (28), 85988606. 43. Wang, S.; Zhang, Y.; Abidi, N.; Cabrales, L., Wettability and Surface Free Energy of Graphene Films. Langmuir 2009, 25 (18), 11078-11081. 44. Kendall, K., Adhesion: Molecules and Mechanics. Science 1994, 263 (5154), 1720-1726. 45. Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.; Kleinhammes, A.; Jia, Y.; Wu, Y.; Nguyen, S. T.; Ruoff, R. S., Synthesis of Graphene-Based Nanosheets Via Chemical Reduction of Exfoliated Graphite Oxide. Carbon 2007, 45 (7), 1558-1565. 46. Lee, W.; Lee, J. U.; Jung, B. M.; Byun, J.-H.; Yi, J.-W.; Lee, S.-B.; Kim, B.-S., Simultaneous Enhancement of Mechanical, Electrical and Thermal Properties of Graphene Oxide Paper by Embedding Dopamine. Carbon 2013, 65, 296-304. 47. Ferrari, A. C.; Robertson, J., Interpretation of Raman Spectra of Disordered and Amorphous Carbon. Phys. Rev. B 2000, 61 (20), 14095. 48. Li, Y.; Peng, Z.; Larios, E.; Wang, G.; Lin, J.; Yan, Z.; Ruiz-Zepeda, F.; José-Yacamán, M.; Tour, J. M., Rebar Graphene from Functionalized Boron Nitride Nanotubes. ACS nano 2014, 9 (1), 532-538. 49. Yan, Z.; Peng, Z.; Casillas, G.; Lin, J.; Xiang, C.; Zhou, H.; Yang, Y.; Ruan, G.; Raji, A.-R. O.; Samuel, E. L., Rebar Graphene. ACS nano 2014, 8 (5), 5061-5068. 50. Casiraghi, C.; Hartschuh, A.; Lidorikis, E.; Qian, H.; Harutyunyan, H.; Gokus, T.; Novoselov, K.; Ferrari, A., Rayleigh Imaging of Graphene and Graphene Layers. Nano Lett. 2007, 7 (9), 2711-2717. 51. Cui, X.; Ding, P.; Zhuang, N.; Shi, L.; Song, N.; Tang, S., Thermal Conductive and Mechanical Properties of Polymeric Composites Based on Solution-Exfoliated Boron Nitride and Graphene Nanosheets: A Morphology-Promoted Synergistic Effect. ACS Appl. Mater. Interfaces 2015, 7 (34), 19068-19075. 52. Gu, J.; Liang, C.; Zhao, X.; Gan, B.; Qiu, H.; Guo, Y.; Yang, X.; Zhang, Q.; Wang, D.-Y., Highly Thermally Conductive Flame-Retardant Epoxy Nanocomposites with Reduced Ignitability and Excellent Electrical Conductivities. Compos. Sci. Technol. 2017, 139, 83-89. 53. Gu, J.; Yang, X.; Lv, Z.; Li, N.; Liang, C.; Zhang, Q., Functionalized Graphite Nanoplatelets/Epoxy Resin Nanocomposites with High Thermal Conductivity. Int. J. Heat Mass Transfer 2016, 92, 15-22. 54. Cho, E.-C.; Chang-Jian, C.-W.; Hsiao, Y.-S.; Lee, K.-C.; Huang, J.-H., Three-Dimensional Carbon Nanotube Based Polymer Composites for Thermal Management. Composites, Part A 2016, 90, 678-686. 55. Zhang, Q.; Xu, X.; Li, H.; Xiong, G.; Hu, H.; Fisher, T. S., Mechanically Robust Honeycomb Graphene Aerogel Multifunctional Polymer Composites. Carbon 2015, 93, 659-670. 56. Gu, J.; Guo, Y.; Yang, X.; Liang, C.; Geng, W.; Tang, L.; Li, N.; Zhang, Q., Synergistic Improvement of Thermal Conductivities of Polyphenylene Sulfide Composites Filled with Boron Nitride Hybrid Fillers. Composites, Part A 2017, 95, 267-273. 57. Gu, J.; Lv, Z.; Wu, Y.; Guo, Y.; Tian, L.; Qiu, H.; Li, W.; Zhang, Q., Dielectric Thermally Conductive Boron Nitride/Polyimide Composites with Outstanding Thermal Stabilities Via in-Situ PolymerizationElectrospinning-Hot Press Method. Composites, Part A 2017, 94, 209-216. 58. Gu, J.; Meng, X.; Tang, Y.; Li, Y.; Zhuang, Q.; Kong, J., Hexagonal Boron Nitride/Polymethyl-Vinyl Siloxane Rubber Dielectric Thermally Conductive Composites with Ideal Thermal Stabilities. Composites, Part A 2017, 92, 27-32. 59. Wu, Y.; Chen, M.; Chen, M.; Ran, Z.; Zhu, C.; Liao, H., The Reinforcing Effect of Polydopamine Functionalized Graphene Nanoplatelets on the Mechanical Properties of Epoxy Resins at Cryogenic Temperature. Polym. Test. 2017, 58, 262-269. 60. Li, S.; Yu, S.; Feng, Y., Progress in and Prospects for Electrical Insulating Materials. High Voltage 2016, 1 (3), 122-129.



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