Silver (Ag)-Graphene oxide (GO) - Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanostructured composites with high dielectric constant and low dielectric loss

Accepted Manuscript Research paper Silver (Ag)-Graphene Oxide (GO) - Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanostructured composites with high dielectric constant and low dielectric loss Srikanta Moharana, R.N Mahaling PII: DOI: Reference:

S0009-2614(17)30456-6 http://dx.doi.org/10.1016/j.cplett.2017.05.018 CPLETT 34807

To appear in:

Chemical Physics Letters

Received Date: Revised Date: Accepted Date:

28 January 2017 4 April 2017 4 May 2017

Please cite this article as: S. Moharana, R.N Mahaling, Silver (Ag)-Graphene Oxide (GO) - Poly (vinylidene fluorideco-hexafluoropropylene) (PVDF-HFP) nanostructured composites with high dielectric constant and low dielectric loss, Chemical Physics Letters (2017), doi: http://dx.doi.org/10.1016/j.cplett.2017.05.018

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Silver (Ag)-Graphene Oxide (GO) - Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanostructured composites with high dielectric constant and low dielectric loss

Srikanta Moharana and R.N Mahaling*

Laboratory of Polymeric and Materials Chemistry, School of Chemistry, Sambalpur University, Jyoti Vihar, Burla-768019, Odisha, India *Corresponding author: E-mail addresses: [email protected] or [email protected] Tel: +91 663 2430114 (office); Fax: +91 663 2430158 (office)

Abstract:

The Silver (Ag)-Graphene oxide (GO)-Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) composites were prepared by solution casting techniques and their dielectric properties were measured. Field emission scanning electron microscopy (FESEM) and X-ray analysis (XRD) confirmed that Ag layers were formed on the surface of the Graphene oxide sheets and homogeneously dispersed into the PVDF-HFP matrix. The result showed that the incorporation of Ag-GO nanoparticles greatly improved the dielectric constant value nearly about 65 at 100 Hz, which is comparatively much higher than that of pure PVDF-HFP. Furthermore, the dielectric loss of the composite remained at a low level (< 0.1 at 100 Hz). A percolation threshold of 1.5 vol% of Ag-GO was calculated and explained accordingly. The composite having high dielectric constant and low dielectric loss might be used as dielectric materials for electronic capacitors.

Keywords:

Composites;

Dielectric

properties;

hexafluoropropylene); Morphology; X-ray diffraction.

1

Poly

(vinylidene

fluoride–co-

1. Introduction Recently, polymer composites (PCs) with high dielectric constant have drawn considerable attention for applications in energy storage devices, integrated capacitors and actuators due to their several advantages, including high breakdown strength, flexibility, low cost, easy processing and economical efficiency [1-2]. To meet the miniaturization and low cost requirements for electronic devices, dielectric materials with both high dielectric constant and low dielectric loss are strongly needed. The relative dielectric constants of common polymers are very low (<10), which limits their commercial applications. Ferroelectric polymers such as poly(vinylidene fluoride) (PVDF) and its respective copolymers [poly(vinylidene trifluoroethylene) [PVDF-TrFE], poly(vinylidene fluoride–co-hexafluoropropylene) [P(VDF-HFP] and poly(vinylidene fluoride-co-chlorotrifluoroethylene) [P(VDF-CTFE)] is one of the fluorous polymeric material that attracted much interest due to its relatively high dielectric constants is approximately 10, good mechanical, thermal, ferroelectric and piezoelectric properties [3-5]. To improve the dielectric constants of polymers by introducing high dielectric constants ceramic particles such as BaTiO3 (BT) (~1800), Pb(Zr,Ti)O3 (PZT) (515) and CaCu3Ti4O12 (CCTO) (approximately 10,000) into the polymer matrix [6-8]. Therefore, the higher volume fraction of ceramic filler loading (>50 vol%) in the polymer composite results in poor process-ability and badly affect the mechanical flexibility of the resulting composites [9-10]. The strategy to overcome these problems is to incorporate conductive fillers e.g., metal particles such as silver, copper, zinc and nickel into the polymer matrix to prepare percolative composites. Usually, a high dielectric constant can be obtained when the volume fraction of conductive fillers approaches the percolation threshold [6, 11]. Among the conductive fillers silver and carbon nanofibers have aroused significant interest due to their good electrical, thermal and optical properties. Silver (Ag) is a metallic material having high thermal, electrical conductivity and surface raman scattering [12]. However, the dielectric losses of these composites increase with an increase in volume fraction of conductive fillers. The presence of interlayer or shell on the surface of the conductive fillers is used to reduce the dielectric loss of the composite by preventing the fillers from direct contact with each other. Thus, Ag acts as metal ion and a shell is an insulating material expected to be ideal fillers for the development of the composites [12, 13]. Recently, some attempts have been made for making insulating layers of graphene and carbon nanotube composites [14-19]. Dang et al [14] have reported that 12.5 vol% of Ag content in polyimide composite showed high dielectric constant value ~400 at 1 kHz. Devaraju [15] and Dang [16] have fabricated 2

Ag/BaTiO3/PI and Ni/BaTiO3/polyvinylidene fluoride (PVDF) composite which have high dielectric constant value i.e., ~1500 and ~800 while the dielectric loss value about 0.23 and 0.5 at the percolation threshold. Wu [17] prepared graphene-TiO2 based polystyrene composite which shows a high dielectric constant and low dielectric loss value at 102 Hz. Similarly, Xu et al [18] have reported that MWCNT@AC-PVDF composite film exhibits high dielectric constant and the dielectric loss value is ~ 2. These results show that the insulating layers of graphene based composite materials having high dielectric constant can have a low dielectric loss value as far as possible. Graphene has aroused enormous interest because of its excellent electrical, thermal, mechanical properties and monolayer structure of carbon atoms having two dimensional honeycomb lattice [14, 19]. Graphene shows the large aspect ratio, especially large electrical conductivity, high mechanical strength and high thermal conductivity. Therefore, it is used as an ideal filler material for polymers. The graphene based polymer composites show much improved electrical and mechanical properties than the CNT based polymer composites. The dependence of dielectric constant, dielectric loss, AC conductivity and microstructure of Ag-GO-PVDF-HFP composites has been studied. In the present work, we have made a strategy to study the dilelectric behaviour of Ag-GO-PVDF-HFP composites in which Ag nanoparticle as the conductive phase, are persistently incorporated on the surface of graphene oxide (GO). The resultant Ag-GO particles are used to fill PVDF-HFP because the Ag nanopartcles attached to the GO a conductive pathway caused by aggregation of conductors has been effectively suppressed in the composite. The result showed that the resulting composites with high dielectric constant (65 at 100 Hz) which is 6 times higher than that of the pure PVDFHFP, high conductivity (110-7S/cm-1) and low dielectric loss values(<0.15) when compared to previous literature reports. These findings provide a new insight into prepared, high dielectric and low loss composite as might be a promising material for energy storage applications. 2. Experimental Materials:

Natural flake graphite was provided by mk NANO, USA and Poly(vinylidene

fluoride-co-hexafluoropropylene) (PVDF-HFP) was purchased from Sigma-Aldrich. Potassium permanganate (KMnO4), sulphuric acid (H2SO4), hydrogen peroxide (H2O2) (30 wt %), hydrochloric acid (HCl) and silver nitrate (AgNO 3) were purchased from Merck, India. The solvent N, N-dimethyl formamide (DMF) were purchased from Himedia Laboratories Pvt. Ltd, India. All chemicals were used as received without any further purification.

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2.1. Preparation of Graphene oxide (GO) GO was prepared from purified natural graphite powder as per modified Hummers method [11]. In this experiment graphite (1.0 g), NaNO3 (0.5 g) and KMnO4 (3.0 g) were slowly added to a H2SO4 solution (30 ml) and stirred in an ice bath. The reaction mixture was stirred at 35 C for 1 hour. After the reaction was completed water (90 ml) was added, while keeping the temperature at 98C for 15 min and then warm water was added slowly followed by the addition of 30 % H2O2 (10 ml) with continuous stirring for 2 h. The obtained reaction mixture was filtered and washed with distilled water, until the pH of the supernatant was neutral. Finally, the purified sample was dispersed in deionised water and centrifuged to obtain graphene oxide. 2.2. Preparation of Ag deposited GO: In this part of the experiment, 20 mg of graphene oxide (GO) was dispersed in water under ultra sonication for 2 h at room temperature to form a homogeneous solution. 0.78mM of AgNO3 (silver precursor) was dissolved in 30 ml of deionised water and then cetyltriammonium bromide (CTAB) was put into the solution. After the resultant solution was stirred for 20 min, 1mM of hydrazine hydrate (reducing agent) was added drop wise into the solution. Immediately, the AgNO3 solution was added into the GO solution. Then the resulting solution was stirred at 140 C in the oil bath. Then, the Ag-GO suspension was washed with ethanol and water three times and then dried at 80C for 24 h. 2.3. Fabrication of Ag-Graphene oxide (GO)-PVDF-HFP composite films The Ag-GO-PVDF-HFP composite films were prepared via a solution casting technique. The obtained Ag-GO particles were dispersed in DMF by using an ultrasonic bath for 2.5 hours. Meanwhile, the PVDF-HFP was dissolved in N, N dimethyl formamide (DMF) and then previously prepared Ag-GO-DMF suspension was added into the PVDF-HFP solution. The resulting mixture was sonicated and stirred for several hours to enhance the dispersion of Ag-GO and eliminate the air bubbles simultaneously. Subsequently, the resultant solutions were cast on a petridish and dried in an oven at 800C for 4 hours to remove any traces of the solvent to produce the Ag-GO-PVDF-HFP composite films. The schematic representation of the process is shown in the Fig.1(a).

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2.4. Characterization The structure and morphology of the GO, Ag-GO and Ag-GO -PVDF-HFP composite films were examined by using an X-ray diffractometer (XRD) (Mini Flex II, Rigaku, Japan), Fouriertransform infrared spectrometer (FT-IR) (5700 FTIR, Nicolet), Field emission scanning electron microscopy (FE-SEM, Carl Zeiss SUPRA), Ultraviolet-visible absorption spectra were recorded in a Shimadzu UV-2450 spectrophotometer and Raman Spectroscopy of the GO and Ag-GO composites was analyzed by using Raman Scattering Spectrometer (LABRAM HR 800). Frequency dependent dielectric measurements of prepared composte films at room temperature using an impedance analyzer (HIOKI 3532 LCR Hi-TESTER) at a frequency range (100 Hz–1 MHz). 3. Results and discussion 3.1. FESEM Study Field emission scanning electron microscopy (FE-SEM) is used to study the morphological evolution of Ag-GO nanoparticle and its respective composite films as shown in figure 1(b-c). It is clearly observed that the Ag nanoparticles are well seated on the roof of GO sheets and the particles were homogeneously placed. As shown in Fig.1 (d-e), it reveals the clear distribution of naoparticle throughout the PVDF-HFP matrix.

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Fig.1 (a) Schematic illustration of Ag-GO-PVDF-HFP, FE-SEM images for (b) GO (c) Ag-GO nanosheets and (d-e) Ag-GO-PVDF-HFP composite film. 3.2.FTIR study The FTIR spectra of GO and Ag-GO-PVDF-HFP composite films are shown in Fig. 3. The spectrum of GO [Fig.3(a)] shows the characteristic peak for the C=O stretching of carboxylic acid group appears at 1721 cm-1, while the absorption peak at approximately 1644 cm-1 is assigned to the stretching vibration of aromatic C=C bands. The oxygenated functional group – OH shows the absorption peak at 3421 cm-1 and C-O absorption peak is observed approximately at 1143 cm-1. As shown in Fig. 3 (b), the bands appearing at 2821 and 1350 cm-1 are assigned to the C-H and C-F stretching vibration of PVDF-HFP matrix. However, after the addition of Ag to the surface of the GO sheet in the composites the characteristic peak of the C=O band disappears. This may be due to the deposition of Ag on the surface of GO in PVDF-HFP matrix.

Fig.2: FTIR spectra of (a) Graphene oxide and (b) Ag-GO-PVDF-HFP composites

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3.3. UV-Vis spectroscopy As shown in fig. 3(a), the UV-visible spectrum of GO and the Ag-GO nanoparticles. It is observed that the GO exhibits two characteristic peaks at 230 and 300 nm, corresponding to the π–π* transitions of aromatic C–C bands and n–π* transitions of C=O bands, respectively. A new absorption peak at 410 nm is observed after the deposition of Ag on the surface of graphene oxide sheets. The band at 410 nm in the absorption spectrum of the Ag-GO nanoparticles is attributed to surface plasmon resonance (SPR) and shows the presence of Ag nanoparticles [20]. 3.4. XRD Analysis Fig.3 (b) shows the powder XRD patterns of the prepared Ag-GO nanoparticles and pure graphene oxide were recorded. In the XRD patterns, the four diffraction peaks (2θ) of Ag-GO contents appear at around 38.1, 44.3, 64.4 and 77.4 corresponds to the (111), (200), (220) and (311) planes of the face centred cubic silver phase according to the standard value (JCPDS Card No. 65-2871) [11]. The characteristic amorphous peaks of Ag-GO nanoparticles may be due to the presence of Ag on the GO sheets.

Fig.3: Ultraviolet-visible (UV-Vis) spectra of (a) Ag-GO, pure GO and (b) X-ray diffraction (XRD) patterns of Ag-GO nanoparticles.

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Fig.4: Raman spectra of the pure GO and Ag-GO composites

The pure GO and Ag encapsulated GO composites were further characterized by Raman spectroscopy and the results are depicted in Fig. 4. It is observed that the Raman spectrum of typical graphene oxide (GO) are an intense D band at 1356 cm-1 and a G band at 1600 cm-1, respectively. The D band is attributed to the edge planes and disordered structures and G band is due to the E2g symmetry and in plane vibration of sp2 bonded carbon atoms [21-22]. Furthermore, the Raman spectra of Ag-GO composites are very similar to that of the GO with slight shift in the peak position of D and G bands. This peak shift which may be due to the SP 2 hybridized carbon atoms indicates the existence of some interaction between GO and Ag particles and contributes to enhance the dielectric constant and relatively lower dielectric loss of the PVDF-HFP composites. 3.5. Dielectric and electrical properties of Ag-GO-PVDF-HFP composite films High dielectric constant and low dielectric loss composites comprising of polymers as a matrix and inorganic nanopartcles as fillers are highly desirable for a modern electrical and electronic systems because of their unique dielectric properties, flexibility and easy processing. In the present study,the dielectric properties of Ag-GO-PVDF-HFP composite were investigated. Fig. 5(a) shows the frequency dependence measurements of dielectric constant for Ag-GO-PVDFHFP composite films at room temperature. A comparative enhancement of dielectric constant has been measured for all the composites with a minimum value of 10 to maximum value of 65 at all volume fractions of Ag-GO contents. The dielectric constant reaches around 65 when the volume fraction of Ag-GO content is 3.0 vol% at 100 Hz, which is much higher than that of the 8

pure PVDF-HFP matrix. The enhancement of the dielectric constant for the Ag-GO-PVDF-HFP composites are due to the polarization effect such as Maxwell–Wagner–Sillars (MWS) or interfacial polarization effect [23, 6]. Furthermore, the charge can be accumulated at the interfaces between GO, Ag and the P(VDF-HFP) matrix due to their enhanced dielectric constant at low frequency region [6]. Thus, the dielectric constant of the composite significantly increases with an increase in the volume fraction of Ag-GO content over the entire frequency range. Besides, the dielectric constant decreases with increase in frequency and it is the result of the slow dielectric relaxation effect of the polymer matrix [13]. Dielectric loss is also a another crucial role of dielectric properties that measure the energy dissipation when the external magnetic field is an applied. So, the magnitude of the dielectric loss can be used to estimate the interfacial attachment between the fillers and the polymer matrix. Fig. 5(b) shows the frequency dependence of dielectric loss of Ag-GO-PVDF-HFP composite films. It is observed that the dielectric loss of the composite decreases with the increase in frequency. Meanwhile, the dielectric loss increases with the increase in the volume fraction of Ag-GO content. The dielectric loss value of Ag-GO-PVDF-HFP composites remain at low levels (< 0.2) when the volume fraction of Ag-GO content is below 1.5 vol% at 100 Hz. Furthermore, when the volume fraction of Ag-GO content increases to 2.5 vol% the dielectric loss value increases to ~ 0.14. The low dielectric loss can be attributed to the presence of Ag layers on the surface of GO sheets, which prevents the leakage current caused b0y the direct contact of GO and the matrix, while the Ag layers show good compatibility between the GO and the polymer matrix [13]. As the volume fraction of Ag-GO content increases, the interfacial polarization is improved whereas the dipole polarization of PVDF-HFP is weakened resulting high dielectric loss at low frequency region and low loss at high frequency region. Also, the dispersion and the spatial distribution of fillers into the polymer matrix is the crucial factor for the enhancement of dielectric properties of composites. Thus, the low dielectric loss value compared to the dielectric constant of composites which might be used for the application in composites in advanced technological fields such as embedded capacitors. Fig.5(c) shows the AC electrical conductivity (σac) of Ag-GO-PVDF-HFP composite films with different volume fractions of Ag-GO contents as a function of frequency at room temperature. The values of electrical conductivity are obtained by using dielectric data and the following relation, σac = εrε0ω tan δ. It is observed that the composite shows a strong frequency dependence due to their insulating property and almost linearly with the increase in frequency and it is lower than 10 -7 Scm-1 at 100 Hz, when the volume fraction of Ag- GO content reaches 3.0 vol%. The result shows that there is no formation of conductive paths in the composites. This may be due to the low dielectric loss in the presence 9

of Ag on the surface of GO sheets in the PVDF-HFP matrix as shown in Fig.5(b) [11]. Thus, these insulating layers can prevent the direct contact of GO sheets and results in lower conductivity. However, the electrical conductivity of the composite increases with an increase in Ag-GO contents at entire frequency region. In addition, the electrical conductivity of entire composites containing Ag-GO nanoaparticles is only slightly higher than that of the pure PVDFHFP matrix. Furthermore, the addition of Ag on the surface of the GO sheets made an important contribution maintain the low conductivity and it is in good agreement for the dielectric performance of the resultant composites as described in Fig. 5(a).

Fig.5: Frequency dependence of (a) dielectric constant (b) dielectric loss and

(c) AC

conductivity of Ag-GO-PVDF-HFP composite films. Room temperature dielectric constant of Ag-GO-PVDF-HFP composites on the volume fractions of Ag-GO measured at 100 Hz (d). The inset figure shows the best fits of the dielectric constant to Eq.(1).

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A detailed investigation of the percolation threshold was performed and the dependence of dielectric constant on the volume fraction of Ag-GO is shown in Fig. 5(d). The dielectric constant increases slowly with increase in volume fraction of Ag-GO contents from 0.2 to 1.5 vol%, but the dielectric constant rapidly increased from 41.10 to 64.44, when Ag-GO content increased from 1.5 vol% to 3.0 vol%, which represents the percolation threshold is nearer to 2.0 vol%. However, the enhancement of dielectric constant can be explained by percolation theory which follows the relation[24-25]; ε =εm (fc-fAg-GO)-s for f < fc, ------------------------- Eqn. (1) where ε and εm is the dielectric constant of the Ag-GO-PVDF-HFP composites and matrix, fc is the percolation threshold and f is the volume fraction of Ag-GO in Ag-GO-PVDF-HFP composites and s is the corresponding critical exponent related to the materials properties. The inset Fig.5(d) shows that the the best fits of the experimental data which perform in good agreement with the dielectric constant to Eq.(1). The calculated value for percolation threshold fc =1.5 and S=0.989 according to the power law. Further, it is found the value of fc is in good agreement with the calculated and experimental results, shows the feasibility of controlling the volume fraction of Ag-GO contents to achieve high dielectric constant and low dielectric loss values. If Ag particles are homogeneously distributed and that to in lower concentration the electronic wave function are localized within the grains of Ag, this may be due to the fact, at higher inter-particle distance, the energy level differences between the nearer grains of Ag will be more and there may be possibility of no coupling between Ag particles [26]. Hence by slightly higher concentration of Ag the distance between arbitrarily placed Ag particles get compact show that energy difference is minimized to delocalized the electron wave which promotes tunneling of electrons [26-27]. If the volume fraction of Ag is sufficiently high it forms a tunneling network favoring conductivity, which may be attributed to the abrupt enhancement in the conductivity at the percolation [28-29]. It also true that with the addition of Ag particles which destabilize the force among the molecules of PVDF-HFP matrix and GO by creating an interface under applied field. The charges move and get accumulated at the interface which may create a polarizing zone of the matrix by an interfacial double layer of Ag particles [30]. It is well understood that at percolation threshold, interparticle distance get reduced. So that the double layer around each and every individual particle gets overlapped resulting to electromagnetic coupling of higher magnitude [31-32], within the neighboring particle, this may be reason for enhancement of dielectric constant and conductivity of the composites. Furthermore, it is also observed that the increase in Ag-GO contents represents the formation of 11

conductive network and increase in the dielectric loss values refers to the insulator-conductor transition near the percolation threshold. Table-1. Comparison of the dielectric properties of Graphene Oxide (GO)-Ag/PVDF-HFP Composite films at 100 Hz present study and its related literature; Composites

Dielec tric loss (tan ) 0.1 2.5 <1 <1 102

AC conductivity

Vol%

Ref.

TiO2-GO-PVDF-HFP PVDF-GO GO/Au-PVDF GO/Cu-PVDF PVDF/HTPB-rGO

Dielectri c constant (r) 18 30 39 50 ~103

10-10 S/cm -

2.0 0.1% 5.0

23 33 34

10-4

35

GNS/PVDF Ag-GO-PVDF-HFP

63 65

1.4 0.12

10-5 10-7

1.02wt % 1.2 3.0

24 Our work

Table 1 gives the comparison of the dielectric properties of GO/PVDF and its copolymer composites filling with different volume fraction of graphene, here in this report, the dielectric constant is as high as 65 and the dielectric loss values is relatively less (< 0.15) at 100 Hz, for Ag-GO-PVDF-HFP composite. 4. Conclusions In this work, an attempt has been made for deposition of Ag particle on the roof of the GO sheets and then the respective Ag-GO-PVDF-HFP composites were prepared by solution casting techniques. The results exhibited significantly improved dielectric properties of the Ag-GOPVDF-HFP composites. The dielectric constant of the resulting composite increased with an increase volume fraction of Ag-GO contents due to their polarization effect. The dielectric loss of the composite remained at a low value at 100 Hz. The Ag layers deposited on the surface of the GO sheet played a crucial role in the enhancement of dielectric properties. Furthermore, the improvement in dielectric properties was explained by the percolation theory, which give a percolation threshold of about 1.5vol% of Ag-GO contents. This high dielectric constant, low dielectric loss of the composite system might be used for embedded capacitor applications in electronic industries.

Acknowledgements The authors gratefully acknowledge the financial support obtained from the DST-FIST and UGC-DRS grant for the development of research work in the School of Chemistry, Sambalpur 12

University, UGC-MRP under the grant head F. No. 42 – 277/2013 (SR), New Delhi, India, and also DST Govt. of Odisha, India. We also thanks UGC, New Delhi for financial support through BSR Research fellowship. References 1. Shen Y, Lin Y.H, Nan C.W. Adv. Funct. Mater. 2007; 17: 2405. 2. Yong L, Xingyi H, Zhiwei H, Pingkai J, Shengtao L, Toshikatsu T. ACS Appl. Mater. Interfaces 2011; 3 (11): 4396. 3. Yang L, Qiu J, Ji H, Zhu K, Wang J. Compos Part A Appl. Sci Manuf.2014; 65: 125. 4. Wang G, Huang X, Jiang P. ACS Appl. Mater. Interfaces 2015; 7 (32): 18017. 5. Yu D, Xu N-X, Hu L, Zhang Q. I, Yang H. J. Mater. Chem. C, 2015; 3: 4016. 6. Xiao X, Yang H, Xu N, Hu L, Zhang Q. RSC Adv., 2015; 5: 79342. 7. Xie L, Huang X, Yang K, Li S, Jiang P. J. Mater. Chem. A, 2014; 2: 5244. 8. Yang Y, Sun H, Yin D, Lu Z, Wei J, Xiong R, Shi J, Wang Z, Liu Z, Lei Q. J. Mater. Chem. A, 2015; 3: 4916. 9. Huo X, Li W, Zhu J, Li L, Li Y, Luo L, Zhu Y. J. Phys.Chem. C, 2015; 119 (46): 25786. 10. Zhu J, Li W, Huo X, Li L, Li Y, Luo L,Zhu Y. J. Phys. D: Appl. Phys. 2015; 48: 355301. 11. Luo S, Yu S, Sun R, Wong C.P. ACS Appl. Mater. Interfaces, 2014; 6 (1): 176.. 12. Kuang X, Liu Z, Zhu H. J. App. Polym. Sci.2013; 6: 3411. 13. Liu Z.D, Feng Y, Li W.L. RSC Adv. 2015, 5: 29017. 14. Dang Z.M, Peng B, Xie D, Yao S.H, Jiang M. J, Jinbo B. J. Appl. Phys. Lett. 2008; 92: 112910. 15. Devaraju N.G, Lee B. I. J. Appl. Polym. Sci. 2006; 99: 3018. 16. Dang Z.M, Shen Y, Nan C.W. Appl. Phys. Lett. 2002; 81: 4814. 17. Wu C, Huang X, Xie L, Wu X, Yu J, Jiang P. J. Mater Chem. 2011; 21: 17729. 18. Guo Q.K, Xue Q.Z, Sun J, Dong M.D, Xia F.J, Zhang Z.Y. Nanoscale, 2015; 7(8): 3660. 19. Wageh S, He L, Ghamdi A. A. A, Turki Y.A.A, Tjong S. C. RSC Adv., 2014; 4: 28426. 20. Gurunathan S, Han J.W, Park J.H, Kim E, Choi Y.J, Kwon D.N, Kim J.H. Int. J. Nanomedicine 2015; 10: 6257. 21. Adhikari A.D, Oraon R, Tiwari S. K, Lee J.H, Kim N.H, Nayak G.C. New J. Chem., 2017; 41: 1704-1713. 22. Deshmukh K, Ahamed M.B, Deshmukh R.R, Pasha S.K.K, Sadasivuni K.K, Ponnamma D, Chidambaram K, Eur. Polym. J., 2016; 76: 14–27 23. Tong W, Zhang Y, Yu L, Lv F, Liu L, Zhang Q, An Q. Chem. Phys. Lett. 2015; 638: 43. 24. Shang J, Zhang Y, Yu L, Shen B, Lv F, Chu P.K. Compos. Sci. Technol. 2014; 91:1-7. 25. Wang L, Dang Z.M. Appl. Phys. Lett., 2005, 87, 042903-3. 26. Ambegaokar V, Halperin B.E, Langer J.S. Phys. Rev. B 1971; 4, 2612 13

27. Sheng P, Abeles B, Arie Y, Phys. Rev. Lett. 1973; 31, 44 28. Toker D, Azulay D, Shimoni N, Balberg I, Millo O. Phys. Rev. B 2003; 68, 041403 29. Deepa K.S, Nisha S.K, Parameswaran P, Sebastian M.T, James J Appl. Phys. Lett. 2009; 94, 142902-3 30. Lewis T.J. J. Phys. D 2005, 38, 202. 31. Claro F, Brouers F, Phys. Rev. B 1989; 40, 3261 32. Rojas R, Claro F, Phys. Rev. B 1986; 34, 3730 33. Rahman M. A, Lee B. C, Phan D.T, Chung G.S. Smart Mater. Struct., 2013; 22: 08501710. 34. Fakhria P, Mahmood H, Jaleha B, Pegoretti A. Synthetic Metals, 2016; 220: 653-660. 35. Wang J, Wu J, Wei X, Zhang Q, Fu Q. Compos. Sci. Technol., 2014; 91: 1–7. Figure captions Fig.1 (a) Schematic illustration of Ag-GO-PVDF-HFP, FE-SEM images for (b) Ag-GO nanosheets and (c-d) Ag-GO-PVDF-HFP composite film. Fig.2: FTIR spectra of (a) graphene oxide and (b) Ag-GO-PVDF-HFP composites Fig.3: Ultraviolet-visible (UV-Vis) spectra of (a) Ag-GO, pure GO and (b) X-ray diffraction (XRD) patterns of Ag-GO nanoparticles. Fig.4: Raman spectra of the pure GO and Ag-GO composites Fig.5: Dependence of (a) dielectric constant (b) dielectric loss, (c) AC conductivity on the frequency for Ag- GO-PVDF-HFP composite films and (d) Dependence of the dielectric constant of Ag-GO-PVDF-HFP composites on the volume fractions of Ag-GO measured at 100 Hz and room temperature. The inset figure shows the best fits of the dielectric constant to Eq.(1).

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Graphical Abstract

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Highlights The incorporation of Ag on to the surface of the GO and its resultant composites prepared via solution casting technique by the use of PVDF-HFP as matrix, exhibits significant improvement in the dielectric constant value and relatively low dielectric loss.These findings provide a new insights to prepare novel graphene based polymer composites with high dielectric constant and low dielectric loss may be useful for the development of embedded capacitor applications .

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