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Hydrothermal synthesis of graphene nanosheets and its application in electrically conductive adhesives
Materials Letters 178 (2016) 181–184
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Hydrothermal synthesis of graphene nanosheets and its application in electrically conductive adhesives Hongru Ma a, Mingze Ma a, Jinfeng Zeng a, Xuhong Guo a,b, Yanqing Ma a,n a School of Chemistry and Chemical Engineering, Shihezi University/Key Laboratory for Green Processing of Chemical Engineering of XinJiang Bingtuan/ Engineering Research Center of Materials – Oriented Chemical Engineering of Xinjiang Bingtuan, Shihezi 832003, PR China b State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 29 March 2016 Received in revised form 28 April 2016 Accepted 1 May 2016 Available online 2 May 2016
A highly electrical conductive adhesive based on graphene nanosheets (GNs) was developed. In this study, we prepared highly electrical conductive GNs via a green and efficient method and investigated the influence of graphene materials on the properties of electrically conductive adhesives. Primarily aimed at improving the electrical conductivity properties of electrically conductive adhesives (ECAs), graphene nanosheets was dispersed into an epoxy matrix to play a role as a network for providing a carrier transfer pathway. The results demonstrate that filling graphene nanosheets and microsilver flakes obviously decrease the resistivity of electrically conductive adhesives. Further, with increasing the graphene nanosheets content, resistivity sharply decreases. With a filling ratio up to 0.5% and the filling of 69.5% with microsilver flakes, the lowest resistivity has been reached 5.0 10 5 Ω cm. & 2016 Elsevier B.V. All rights reserved.
Keywords: Hydrothermal Graphene nanosheets Electrically conductivity adhesives
1. Introduction Electrical conductive adhesives (ECAs) is always consist of conductive fillers and polymeric resin, which can achieve low cure temperature, high line resolutions, environment friendly and meet the development on the miniaturization of electronic products and high integration of chip interconnection techniques on printed circuit boards or substrate [1–5]. In addition to this, the process of prepared ECAs is simple and also can improve the processability distinctly. Despite many advantages of ECAs compared with Sn/Pb solders, they have some limitations, such as low electrical conductivity properties [6]. The electrical conductivity properties of ECAs are mainly determined by electrical conductive fillers. Many kinds of electrical conductive materials were used as electrical conductive fillers, such as silver [7–10], silicone [11], gold, copper [12,13], carbon black and carbon nanotubes [14]. Silver is used most widely during these materials due to low cost and high electrical conductivity properties. In recent years, carbon black and carbon nanotubes as conductive fillers applied in ECAs become popular, because these materials is low cost and stable performance. However, these carbon materials have lower electrical conductivity properties than that of metals fillers. Therefore, in n
Corresponding author. E-mail address: [email protected] (Y. Ma).
http://dx.doi.org/10.1016/j.matlet.2016.05.008 0167-577X/& 2016 Elsevier B.V. All rights reserved.
order to improve the electrical conductivity properties of ECAs, graphene as a charming material are introduced into ECAs. Graphene nanosheet (GNs) is a two-dimensional planar form of carbon with a thickness of a single atom or few atoms and graphene nanosheets (GNs) has a theoretical specific surface area is 2630 m2/g [15,16]. This is much larger than that reported to date for carbon black (smaller than 900 m2/g) or for carbon nanotubes (about 100–1000 m2/g) and unique thermal, optical and mechanical properties [17] that are different from those of carbon black and carbon nanotubes. The large theoretical specific surface area of GNs combined with its high electrical conductivity make it applied in many areas such as conductive membrane [18–20], catalytic [21], solar cells [22] and super capacitor [23]. But there were seldom researches using graphene as conductive filler in the ECA. In this paper, a simple hydrothermal route to convert GO to highly electrical conductive GNs is explored. The hydrothermal conversion method has several advantages over the common chemical reduction processes. First is the process requires very simple setup, just need an autoclave. Second is the whole process is intrinsically pure and environment friendly because it utilizes only water and glucose. Last but not least, is the closed system of relative high temperature and internal pressure promotes the recovery of π-conjugation after dehydration, which is favorable for minimum defects. So we added reduced GO via hydrothermal method into electrical conductive adhesive to display distinct
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electronic properties.
2. Experiment Graphene oxide (GO) was prepared from natural graphite flakes through a modified Hummers method. The typical procedure of prepared GNs as follows, the glucose was added to graphene oxide water solution under stirring. Then the mixture solution was transferred into a stainless steel autoclave with a Teflon liner of 100 ml capacity, and heated in an oven at 180 °C for 18 h. The detail is described in the support information.
3. Results and discussion The purpose of this study is to prepare highly electrical conductive GNs via a green and efficient method. In this work, GO is synthesized by oxidation by modified Hummers method. A large number of oxygen-containing functional groups at the edge of GO sheet and on the basal planes of GO sheet, which makes GO strongly hydrophilic. These oxygen-containing functional groups were able to reduce the interplanar forces and promote complete exfoliation of GO in water. During the reduction process, the color of the suspension shifts from brown to black, which indicates the change from GO to GNs. The proposed reduction mechanism of GO by glucose as follows, first mechanism probably involves hydride transfers from the 6-membered ring of the GO, yielding water molecules [24]. The second mechanism probably is the closed system of relation high temperature and internal pressure can promote the reduction ability of glucose and the recovery of πconjugation after dehydration [25]. Fig. 1 shows the SEM (Fig. 1(A)) image and TEM (Fig. 1(B)) image of GNs treated with hydrothermally method, the images demonstrate that the 2D molecular sheets were well preserved for hydrothermal reactions. The GNs were thin enough to be flexible and restack to some degree after drying. The surface of GNs were smooth. Also, a large number of GNs may be generated much restack and decrease conductivity, so the conductivity is established at lower GNs concentrations due to the formation of conductive channels which act as paths for charge propagation. Fig. 2 shows the XRD pattern of GNs (a) and GO (b). GO has a sharp peak at 11.05° which proved inter-planer spacing (0.83 nm) of typical feature of GO (d002). The XRD pattern of GNs (a) indicated the presence of two peaks at 25.0° and 43.5° which corresponded to the inter-layer spacing (0.34 nm) of GNs (d002) and the d(101) reflecting of the carbon atoms, respectively. After hydrothermal reduction, all of the intensities of the related oxygen peaks were clearly decreased in the GNs (a) compared to GO (a), indicating that the delocalized p conjugation is restored in GNs.
Fig. 2. XRD patterns of GNs (a) and GO (b).
The result demonstrates that the formation of GNs from GO. Besides, the broad nature of the reflection indicates poor ordering of the sheets along the stacking direction, implying that the sample is composed mostly of few layers of GNs [26]. Raman spectroscopy was used to characterize the GNs (a) and GO (b). The typical features in the Raman spectra are the D band at 1341.4 cm 1 and the G band at 1589.2 cm 1 (Fig. 1(S)). The D band is a breathing mode of κ-point phonons of A1g symmetry, while the G band is usually assigned to the E2g phonon of C sp2 atoms [27]. A prominent D band is an indication of disorder in the Raman of the GO, originating from defects associated with vacancies, grain boundaries, and amorphous carbon species. The intensity ratio (ID/IG) of D band to G band of the GO is about 1.27. Hydrothermal treatment at 180 °C for 18 h decreased the ID/IG to 0.96. This suggests that the hydrothermal reaction, besides reducing the GO, is also able to recover the aromatic structures by repairing defects [28]. It is instructive to note that for prior paper about chemical-reduced graphene oxide, the ID/IG ratio increased to 1.356 after treatment [29], and this is due to the presence of unrepaired defects that remained after the removal of oxygen moieties. Therefore, we can conclude that the hydrothermal reduction route is more effective than the chemical-reduced process in repairing sp2 network. To further investigate the chemical composition on the surface of GNs. XPS spectra are presence in Fig. 2(S). XPS wide scan of the surface of the hydrothermally method treated GO (a) and GO (b) showed that it was very pure and had no impurities, and the only two elements present were oxygen and carbon. The spectrum of GO exhibits the C 1s peak at 289 eV and the O 1s peak at 535 eV.
Fig. 1. FESEM image of the GNs (A) and HRTEM images of the GNs.
H. Ma et al. / Materials Letters 178 (2016) 181–184
Fig. 3. Resistivity of ECAs-changing trend image under different content of GNs.
Then calculated atomic ratio of C and O is approximately 1.8. However, after the hydrothermally method treated. The spectrum of GNs exhibits the C 1s peak at 284 eV and the O 1s peak at 533 eV. The binding energy of GNs and GO shows some deviations. That is because bond lengths and crystal potentials may vary significantly leading to a range of C 1s and O 1s binding energies (BEs) [30]. This may also account for variable BE positions of XPS spectra. Some researcher consider that the move of BEs is caused by contamination from the vacuum system [31]. Both of factors are caused the shift of BEs. the intensity of the O 1s peak of GNs significantly decreased compared to GO and C: O atomic ratio of GNs reached 2.8, indicating a reduction of GO. The oxygen-containing functional groups on the surface of GNs are identified by deconvolution the C 1s peak into three different regions. High resolution X-ray photoemission C 1s spectra of the GNs show a significant decrease of oxygen-containing functional groups after dehydration, confirming that most of the epoxide, hydroxyl and carboxyl functional groups were successfully removed compared to prior reported GO and the effective recovery of the π-electron system of GNs.
4. Electrical properties The electrical conductivity of ECAs closely relates to the electrical conductive fillers, to explore the content of the conductive fillers, GNs were added in an amount of 30% by weight of the epoxy matrix. As can be seen from Fig. 3, resistivity of ECA decreased trend with increasing content of GNs conductive filler. The resistivity of ECA reach the minimum when the content of GNs conductive filler reached 0.5%. With GNs conductive filler added, resistivity of ECAs increases gradually and conductive fillers becomes no-uniform and the cross-section morphology of ECA becomes rough. As is well known, electrically conductive channels were formed from the contact points and contact areas of conductive fillers. It observed that resistivity decreases at first and then increases when the content of GNs exceed 0.5%. The lowest resistivity of ECA was obtained, which contribute to small amount of GNs can formed effective conductive network. When the content of GNs is over 0.5%, redundant conductive fillers get together so that an aggregation and agglomeration phenomena emerges, then fewer effective conductive network will be formed in this case, and at the same time the contact points among conductive fillers was increased, then deteriorated electrical properties of ECA [32]. In summary, the optimum amount of the GNs conductive filler is 0.5%.
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As mentioned above, optimum content of electrically conductive fillers led to high electrical conductivity. Fig. 3 shows the resistivity of ECAs depending on the conductivity fillers total content was 70%. The resistivity value was decreased with the increasing GNs content. The ECAs displayed the resistivity of 2.2 10 4 Ω cm, 6.7 10 5 Ω cm, 5.0 10 5 Ω cm and 8.0 10 5 Ω cm at the microsilver flakes content of 70%, 69.8%, 69.5% and 69.2%, which corresponding to the GNs content of 0.0%, 0.2%, 0.5% and 0.8%, respectively. With the increasing GNs electrically conductive fillers, the contact points and contact areas among them increased, from which more electrically conductive networks were formed. To understand the mechanism of electrical conductivity improvement via addition of GNs, SEM images of cross-section morphology of ECA (Fig. 3(S)) visually displayed the increasing contact areas and contact points between electrically conductive fillers. From Fig. 3(A), a large portion of silver flakes are separated by epoxy matrix, so there were many gaps and voids among them and caused the electrical network is not fully formed, as evidenced by electrical resistivity measurements. However, the high aspect-ratio of GNs helps to construct new electrical pathways for electron transportation inside the network. Under the observation of the surface morphology of GNs, the arrangements of GNs gradually changed from loose to dense, the gaps and voids among them gradually changed from large to small and many to few, as the GNs filler content increased from 0.0–0.5%. However, as can be seen in Fig. 3(D), a large amount of GNs was not well dispersed inside the epoxy matrix and GNs agglomerated formed, which explains the resistivity of ECA filled with 0.8% GNs was increased.
5. Conclusions In this study, the highly electrical conductive GNs had been successfully prepared by a simple hydrothermal method. The effects of the GNs on resistivity of ECAs were discussed under different content. The results of SEM, TEM, XRD, Raman and XPS showed that the morphology and structure, SEM images of crosssection morphology of ECA show that the conductive fillers are well dispersed in the epoxy matrix without obvious agglomeration. The small content GNs applied in ECAs decreased the resistivity and when the content of GNs was reached to 0.5%, the electrical properties were excellent. The resistivity was 5.0 10 5 Ω cm. It was an effective method to get different GNs content of ECAs which can be advantageous to be used in the electronic packing and other fields.
Acknowledgements This work was financially supported by the Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT, No. IRT1161) and the Program of Science and Technology Innovation Team in Bingtuan (No. 2011CC001).
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Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Hydrothermal synthesis of graphene nanosheets and its application in electrically conductive adhesives Hongru Ma a, Mingze Ma a, Jinfeng Zeng a, Xuhong Guo a,b, Yanqing Ma a,n a School of Chemistry and Chemical Engineering, Shihezi University/Key Laboratory for Green Processing of Chemical Engineering of XinJiang Bingtuan/ Engineering Research Center of Materials – Oriented Chemical Engineering of Xinjiang Bingtuan, Shihezi 832003, PR China b State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 29 March 2016 Received in revised form 28 April 2016 Accepted 1 May 2016 Available online 2 May 2016
A highly electrical conductive adhesive based on graphene nanosheets (GNs) was developed. In this study, we prepared highly electrical conductive GNs via a green and efficient method and investigated the influence of graphene materials on the properties of electrically conductive adhesives. Primarily aimed at improving the electrical conductivity properties of electrically conductive adhesives (ECAs), graphene nanosheets was dispersed into an epoxy matrix to play a role as a network for providing a carrier transfer pathway. The results demonstrate that filling graphene nanosheets and microsilver flakes obviously decrease the resistivity of electrically conductive adhesives. Further, with increasing the graphene nanosheets content, resistivity sharply decreases. With a filling ratio up to 0.5% and the filling of 69.5% with microsilver flakes, the lowest resistivity has been reached 5.0 10 5 Ω cm. & 2016 Elsevier B.V. All rights reserved.
Keywords: Hydrothermal Graphene nanosheets Electrically conductivity adhesives
1. Introduction Electrical conductive adhesives (ECAs) is always consist of conductive fillers and polymeric resin, which can achieve low cure temperature, high line resolutions, environment friendly and meet the development on the miniaturization of electronic products and high integration of chip interconnection techniques on printed circuit boards or substrate [1–5]. In addition to this, the process of prepared ECAs is simple and also can improve the processability distinctly. Despite many advantages of ECAs compared with Sn/Pb solders, they have some limitations, such as low electrical conductivity properties [6]. The electrical conductivity properties of ECAs are mainly determined by electrical conductive fillers. Many kinds of electrical conductive materials were used as electrical conductive fillers, such as silver [7–10], silicone [11], gold, copper [12,13], carbon black and carbon nanotubes [14]. Silver is used most widely during these materials due to low cost and high electrical conductivity properties. In recent years, carbon black and carbon nanotubes as conductive fillers applied in ECAs become popular, because these materials is low cost and stable performance. However, these carbon materials have lower electrical conductivity properties than that of metals fillers. Therefore, in n
Corresponding author. E-mail address: [email protected] (Y. Ma).
http://dx.doi.org/10.1016/j.matlet.2016.05.008 0167-577X/& 2016 Elsevier B.V. All rights reserved.
order to improve the electrical conductivity properties of ECAs, graphene as a charming material are introduced into ECAs. Graphene nanosheet (GNs) is a two-dimensional planar form of carbon with a thickness of a single atom or few atoms and graphene nanosheets (GNs) has a theoretical specific surface area is 2630 m2/g [15,16]. This is much larger than that reported to date for carbon black (smaller than 900 m2/g) or for carbon nanotubes (about 100–1000 m2/g) and unique thermal, optical and mechanical properties [17] that are different from those of carbon black and carbon nanotubes. The large theoretical specific surface area of GNs combined with its high electrical conductivity make it applied in many areas such as conductive membrane [18–20], catalytic [21], solar cells [22] and super capacitor [23]. But there were seldom researches using graphene as conductive filler in the ECA. In this paper, a simple hydrothermal route to convert GO to highly electrical conductive GNs is explored. The hydrothermal conversion method has several advantages over the common chemical reduction processes. First is the process requires very simple setup, just need an autoclave. Second is the whole process is intrinsically pure and environment friendly because it utilizes only water and glucose. Last but not least, is the closed system of relative high temperature and internal pressure promotes the recovery of π-conjugation after dehydration, which is favorable for minimum defects. So we added reduced GO via hydrothermal method into electrical conductive adhesive to display distinct
182
H. Ma et al. / Materials Letters 178 (2016) 181–184
electronic properties.
2. Experiment Graphene oxide (GO) was prepared from natural graphite flakes through a modified Hummers method. The typical procedure of prepared GNs as follows, the glucose was added to graphene oxide water solution under stirring. Then the mixture solution was transferred into a stainless steel autoclave with a Teflon liner of 100 ml capacity, and heated in an oven at 180 °C for 18 h. The detail is described in the support information.
3. Results and discussion The purpose of this study is to prepare highly electrical conductive GNs via a green and efficient method. In this work, GO is synthesized by oxidation by modified Hummers method. A large number of oxygen-containing functional groups at the edge of GO sheet and on the basal planes of GO sheet, which makes GO strongly hydrophilic. These oxygen-containing functional groups were able to reduce the interplanar forces and promote complete exfoliation of GO in water. During the reduction process, the color of the suspension shifts from brown to black, which indicates the change from GO to GNs. The proposed reduction mechanism of GO by glucose as follows, first mechanism probably involves hydride transfers from the 6-membered ring of the GO, yielding water molecules [24]. The second mechanism probably is the closed system of relation high temperature and internal pressure can promote the reduction ability of glucose and the recovery of πconjugation after dehydration [25]. Fig. 1 shows the SEM (Fig. 1(A)) image and TEM (Fig. 1(B)) image of GNs treated with hydrothermally method, the images demonstrate that the 2D molecular sheets were well preserved for hydrothermal reactions. The GNs were thin enough to be flexible and restack to some degree after drying. The surface of GNs were smooth. Also, a large number of GNs may be generated much restack and decrease conductivity, so the conductivity is established at lower GNs concentrations due to the formation of conductive channels which act as paths for charge propagation. Fig. 2 shows the XRD pattern of GNs (a) and GO (b). GO has a sharp peak at 11.05° which proved inter-planer spacing (0.83 nm) of typical feature of GO (d002). The XRD pattern of GNs (a) indicated the presence of two peaks at 25.0° and 43.5° which corresponded to the inter-layer spacing (0.34 nm) of GNs (d002) and the d(101) reflecting of the carbon atoms, respectively. After hydrothermal reduction, all of the intensities of the related oxygen peaks were clearly decreased in the GNs (a) compared to GO (a), indicating that the delocalized p conjugation is restored in GNs.
Fig. 2. XRD patterns of GNs (a) and GO (b).
The result demonstrates that the formation of GNs from GO. Besides, the broad nature of the reflection indicates poor ordering of the sheets along the stacking direction, implying that the sample is composed mostly of few layers of GNs [26]. Raman spectroscopy was used to characterize the GNs (a) and GO (b). The typical features in the Raman spectra are the D band at 1341.4 cm 1 and the G band at 1589.2 cm 1 (Fig. 1(S)). The D band is a breathing mode of κ-point phonons of A1g symmetry, while the G band is usually assigned to the E2g phonon of C sp2 atoms [27]. A prominent D band is an indication of disorder in the Raman of the GO, originating from defects associated with vacancies, grain boundaries, and amorphous carbon species. The intensity ratio (ID/IG) of D band to G band of the GO is about 1.27. Hydrothermal treatment at 180 °C for 18 h decreased the ID/IG to 0.96. This suggests that the hydrothermal reaction, besides reducing the GO, is also able to recover the aromatic structures by repairing defects [28]. It is instructive to note that for prior paper about chemical-reduced graphene oxide, the ID/IG ratio increased to 1.356 after treatment [29], and this is due to the presence of unrepaired defects that remained after the removal of oxygen moieties. Therefore, we can conclude that the hydrothermal reduction route is more effective than the chemical-reduced process in repairing sp2 network. To further investigate the chemical composition on the surface of GNs. XPS spectra are presence in Fig. 2(S). XPS wide scan of the surface of the hydrothermally method treated GO (a) and GO (b) showed that it was very pure and had no impurities, and the only two elements present were oxygen and carbon. The spectrum of GO exhibits the C 1s peak at 289 eV and the O 1s peak at 535 eV.
Fig. 1. FESEM image of the GNs (A) and HRTEM images of the GNs.
H. Ma et al. / Materials Letters 178 (2016) 181–184
Fig. 3. Resistivity of ECAs-changing trend image under different content of GNs.
Then calculated atomic ratio of C and O is approximately 1.8. However, after the hydrothermally method treated. The spectrum of GNs exhibits the C 1s peak at 284 eV and the O 1s peak at 533 eV. The binding energy of GNs and GO shows some deviations. That is because bond lengths and crystal potentials may vary significantly leading to a range of C 1s and O 1s binding energies (BEs) [30]. This may also account for variable BE positions of XPS spectra. Some researcher consider that the move of BEs is caused by contamination from the vacuum system [31]. Both of factors are caused the shift of BEs. the intensity of the O 1s peak of GNs significantly decreased compared to GO and C: O atomic ratio of GNs reached 2.8, indicating a reduction of GO. The oxygen-containing functional groups on the surface of GNs are identified by deconvolution the C 1s peak into three different regions. High resolution X-ray photoemission C 1s spectra of the GNs show a significant decrease of oxygen-containing functional groups after dehydration, confirming that most of the epoxide, hydroxyl and carboxyl functional groups were successfully removed compared to prior reported GO and the effective recovery of the π-electron system of GNs.
4. Electrical properties The electrical conductivity of ECAs closely relates to the electrical conductive fillers, to explore the content of the conductive fillers, GNs were added in an amount of 30% by weight of the epoxy matrix. As can be seen from Fig. 3, resistivity of ECA decreased trend with increasing content of GNs conductive filler. The resistivity of ECA reach the minimum when the content of GNs conductive filler reached 0.5%. With GNs conductive filler added, resistivity of ECAs increases gradually and conductive fillers becomes no-uniform and the cross-section morphology of ECA becomes rough. As is well known, electrically conductive channels were formed from the contact points and contact areas of conductive fillers. It observed that resistivity decreases at first and then increases when the content of GNs exceed 0.5%. The lowest resistivity of ECA was obtained, which contribute to small amount of GNs can formed effective conductive network. When the content of GNs is over 0.5%, redundant conductive fillers get together so that an aggregation and agglomeration phenomena emerges, then fewer effective conductive network will be formed in this case, and at the same time the contact points among conductive fillers was increased, then deteriorated electrical properties of ECA [32]. In summary, the optimum amount of the GNs conductive filler is 0.5%.
183
As mentioned above, optimum content of electrically conductive fillers led to high electrical conductivity. Fig. 3 shows the resistivity of ECAs depending on the conductivity fillers total content was 70%. The resistivity value was decreased with the increasing GNs content. The ECAs displayed the resistivity of 2.2 10 4 Ω cm, 6.7 10 5 Ω cm, 5.0 10 5 Ω cm and 8.0 10 5 Ω cm at the microsilver flakes content of 70%, 69.8%, 69.5% and 69.2%, which corresponding to the GNs content of 0.0%, 0.2%, 0.5% and 0.8%, respectively. With the increasing GNs electrically conductive fillers, the contact points and contact areas among them increased, from which more electrically conductive networks were formed. To understand the mechanism of electrical conductivity improvement via addition of GNs, SEM images of cross-section morphology of ECA (Fig. 3(S)) visually displayed the increasing contact areas and contact points between electrically conductive fillers. From Fig. 3(A), a large portion of silver flakes are separated by epoxy matrix, so there were many gaps and voids among them and caused the electrical network is not fully formed, as evidenced by electrical resistivity measurements. However, the high aspect-ratio of GNs helps to construct new electrical pathways for electron transportation inside the network. Under the observation of the surface morphology of GNs, the arrangements of GNs gradually changed from loose to dense, the gaps and voids among them gradually changed from large to small and many to few, as the GNs filler content increased from 0.0–0.5%. However, as can be seen in Fig. 3(D), a large amount of GNs was not well dispersed inside the epoxy matrix and GNs agglomerated formed, which explains the resistivity of ECA filled with 0.8% GNs was increased.
5. Conclusions In this study, the highly electrical conductive GNs had been successfully prepared by a simple hydrothermal method. The effects of the GNs on resistivity of ECAs were discussed under different content. The results of SEM, TEM, XRD, Raman and XPS showed that the morphology and structure, SEM images of crosssection morphology of ECA show that the conductive fillers are well dispersed in the epoxy matrix without obvious agglomeration. The small content GNs applied in ECAs decreased the resistivity and when the content of GNs was reached to 0.5%, the electrical properties were excellent. The resistivity was 5.0 10 5 Ω cm. It was an effective method to get different GNs content of ECAs which can be advantageous to be used in the electronic packing and other fields.
Acknowledgements This work was financially supported by the Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT, No. IRT1161) and the Program of Science and Technology Innovation Team in Bingtuan (No. 2011CC001).
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