Enhanced Dielectric Performance of Polymer Nanocomposites Based

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Enhanced Dielectric Performance of Polymer Nanocomposites Based on CNT/MnO Nanowire Hybrid Nanostructure 2

Ali Shayesteh Zeraati, Seyyed Alireza Mirkhani, and Uttandaraman Sundararaj J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b01539 • Publication Date (Web): 27 Mar 2017 Downloaded from http://pubs.acs.org on April 1, 2017

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The Journal of Physical Chemistry

Enhanced Dielectric Performance of Polymer Nanocomposites Based on CNT/MnO2 Nanowire Hybrid Nanostructure

Ali Shayesteh Zeraati, Seyyed Alireza Mirkhani, Uttandaraman Sundararaj*

Department of Chemical and Petroleum Engineering, University of Calgary, 2500 University Dr NW, Calgary, Canada T2N 1N4 Abstract In this study, we report a new highly efficient polymer nanocomposite for charge storage applications based on carbon nanotube (CNT) and MnO2 nanowire (MnO2NW). Our study suggested that combination of conductive filler (CNT) and ferroelectric filler (MnO2NW) is an effective method to fabricate nanocomposite with outstanding dielectric permittivity and low dielectric loss if two fillers share similar length and geometry. This strategy leads us to fabricate a hybrid nanocomposite (CNT: MnO2NW (3.0:4.5wt%)) with a high dielectric permittivity (50.6) and low dielectric loss (0.7), which are among the best-reported values in the literature in the X-band frequency range (8.2-12.4 GHz). We postulated that superior dielectric properties of the new hybrid nanocomposites were attributed to (i) better dispersion state of CNT in the presence of MnO2NW, which increases the effective surface area of CNTs, as nanoelectrodes, (ii) dimensionality match between the nanofillers, which increases their synergy, and (iii) barrier role of MnO2NWs, cutting off the contact spots of CNTs and leading to lower dielectric loss. Comparison of the dielectric properties of the developed hybrid nanocomposites with the literature highlights their great potential for flexible capacitors.

*Corresponding Authors: Tel: +1 403 2106549. Email: [email protected] (Uttandaraman Sundararaj) ACS Paragon Plus Environment


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Introduction High-k polymer nanocomposites have attracted much attention recently owing to their superior properties in high-tech applications such as fabrication of advanced electronics, film capacitors

1-3

and artificial muscles

4-6

, etc. These excellent properties originate from the

synergism of filler and polymer matrix properties. There are two primary approaches to obtain a high dielectric permittivity for polymer nanocomposites: The first method involves incorporation of high-k ceramic ferroelectric materials, such as BaTiO3

7-10

, SrTiO3

11-12

, TiO2

10, 13

, into the

polymer matrix to prepare a high-k polymer composite. The main shortfall of this strategy is the high loading of ceramic materials required to achieve high-k ceramic/polymer nanocomposites, which deteriorates the flexibility of the polymer nanocomposites and hampers their practical application. High-k polymer nanocomposite can also be fabricated by dispersion of conductive fillers e.g. graphene

14-16

, carbon nanotube

17-20

or metal particles

21-24

in the polymer matrix. In

these conductive filler/polymer nanocomposites (CPNs), high dielectric constant can be achieved owing to ‘insulator–conductor’ transition occurring at the percolation threshold. The excellent processability and flexibility of the polymer nanocomposite can be retained since much lower filler content can be used. However, this is achieved at the expense of a significant increase of dielectric loss. So, the current challenge in CPNs is to achieve high dielectric constant with low dielectric loss, which are critical properties for many practical applications such as charge storage. Furthermore, the geometry of the conductive filler plays a crucial role in the dielectric properties of composites. Fillers with higher aspect ratios can improve the dielectric constant of the composites more efficiently as compared to spherical particles because of their lower percolation threshold compared to that of spherical particles

2 ACS Paragon Plus Environment

25-28

. Several studies have also

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demonstrated that among high aspect ratio fillers, one-dimensional nanostructures such as nanotube and nanowires are more efficient in enhancing the dielectric properties of nanocomposites at low concentrations 9-10, 26, 28-29. Carbon nanotubes (CNTs) are promising options to fabricate high-k CPNs, owing to their large aspect ratio and high electrical conductivity 20, 30-32. The main issue with this type of CPN is its high dielectric loss at percolation threshold. Formation of a 3D conductive network by direct contact between CNTs at the percolation threshold facilitates charge transfer, and consequently generates high leakage current and very high dielectric loss. To alleviate this, several approaches have been proposed to hamper contact between CNTs, with the aim of suppressing the dielectric loss. One strategy is to form a “barrier” between CNTs by depositing another material on the external surface of CNTs i.e. a core-shell structure. In this method, the electrical conductivity of CNTs dramatically decreased by forming shell structure. However, a high loading of core-shell filler is also required to gain acceptable dielectric properties 33-37. Another approach is alignment of CNTs to reduce their effective contacts

34, 38-40

. This strategy leads to anisotropic properties,

which limits its practical application. Hybrid structures formed by combining secondary fillers with CNT is a promising option to reduce dielectric loss 41-47. In this method, the contact between neighboring CNTs can be suppressed by inserting a second filler. Furthermore, by choosing a ferroelectric material, a desirable high-k CPN can be expected due to the simultaneous increased permittivity and reduced loss 41, 44. To this end, we have used MnO2 nanowire (MnO2NW) as the secondary ferroelectric nanofiller to design and fabricate CNT/MnO2NW/PVDF to obtain a promising dielectric hybrid polymer nanocomposite. This method is expected to have outstanding properties based on the following reasons: 3 ACS Paragon Plus Environment


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(i)

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A better dimensionality match can be achieved if both fillers share the same geometry and length. It is postulated that incorporation of 1D secondary filler (MnO2NW) are more effective in disrupting conductive network formation of CNTs in comparison with nanoparticles. When nanoparticles are used as secondary filler with CNTs, high loading of nanoparticles is required to achieve high dielectric constant and low dielectric loss. This can be attributed to the poor performance of nanoparticles to disrupt formation of CNT conductive network 43-45

(ii)

41,

;

MnO2 is known for its high theoretical specific capacitance, low cost, natural abundance, and environmentally friendly nature 48-49. So, by employing MnO2NW we expect not only to reduce the dielectric loss since its barrier role between CNTs, but also to increase dielectric constant owing to its properties.

So, a hybrid structure of CNT/MnO2NW in a polymer matrix is exploited as active and promising high dielectric polymer nanocomposite by taking the advantages of individual fillers and their synergistic effect. 2. Experimental 2.1. Materials Synthesis MnO2 nanowire synthesis: In this study, MnO2 nanowires were synthesized by hydrothermal method. First, 0.608g KMnO4 (Sigma-Aldrich, ACS reagent ≥99.0%) was dissolved in 70ml distilled water and agitated vigorously for 30min. Then, 1.27ml HCl (EMD Chemicals, 37%) was added to the solution and mixed for additional 10minutes. The solution was transferred to a 100mL Teflon-lined stainless steel autoclave and kept at 140°C for 12h in oven. Then autoclave was cooled down overnight to room temperature. After cooling, 4 ACS Paragon Plus Environment

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precipitates were collected, filtered and rinsed several times with distilled water to reach neutral pH 7. Finally, the obtained powder was dried for 4h at 80°C. Nanocomposite Preparation: PVDF (3M Canada, PVDF 11008/0001) was selected as polymer matrix owing to its high dielectric constant, ferroelectricity and high breakdown strength. The industrially available multi-wall carbon nanotubes (CNTs), Nanocyl™ NC7000, with a tube diameter of approximately 9.5nm and a length of 1.5µm was used as the conductive filler. To fabricate nanocomposite samples, APAM (Alberta Polymer Asymmetric Minimixer) was used to melt mix PVDF with fillers at 240°C and 235rpm. To prepare nanocomposite samples for dielectric studies, two types of samples were fabricated: first, binary nanocomposites of CNT/PVDF (concentrations: 0.2, 0.4, 0.5, 1.0, 1.5, 2.0, and 3.0 wt%) and MNO2NW/PDVF (concentrations: 0.5, 1.0, 1.5, 2.0, and 3.0 wt%) were prepared with 15 min mixing. Second, for CNT/MnO2NW/PVDF hybrid nanocomposites, at each CNT concentration (0.5, 1, 1.5, 2, and 3), four samples with different MNO2NW/CNT weight ratios (0.5, 1, 1.5 and 2) were fabricated. To do this, PVDF was masticated for 3min, followed by addition of CNTs and mixing for 7min. Finally, MnO2NW were added and mixed for additional 8min for CNT/MnO2NW hybrid nanocomposites. A Carver compression molder (Carver Inc., Wabash, IN) was used to make disc-shaped samples at 240°C and 35MPa for 10min. The diameter and thickness of the samples are 25mm and 0.2mm respectively. 2.2. Materials Characterization Transmission Electron Microscopy: The structure of MnO2NW was studied by highresolution transmission electron microscopy (HRTEM). The TEM used in this study was Tecnai TF20 G2 FEG-TEM (FEI, Hillsboro, OR) at 200kV acceleration voltage with a standard single tilt-holder. The images were captured by a Gatan UltraScan 4000 CCD Camera (Gatan, 5 ACS Paragon Plus Environment


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Pleasanton, CA). To prepare a TEM sample, a small amount of nanopowder (< 1 ) was suspended in 10 mL of acetone and bath-sonicated for 3 min. Then, small drop of the suspension was placed on the carbon side of a standard TEM copper grid covered with a ∼ 40 nm thin holey carbon film (EMS, Hatfield, PA), and then placed on a filter paper to dry quickly. For the TEM analysis of the nanocomposites, Cryo-Ultramicrotome (Cryo Leica EM UC7) was used to prepare sections with 70nm thickness. Light Transmission Microscopy: The state of microdispersion of fillers within the PVDF matrix was analyzed using light transmission microscopy (LM) on thin cuts (2µm thickness) of the compression molded samples, prepared with a Leica microtome RM2265 (Leica Microsystems GmbH, Wetzlar, Germany) equipped with a diamond knife. An Olympus microscope BH2 equipped with a CCD camera DP71 (both from Olympus Deutschland GmbH, Hamburg, Germany) connected to the software Stream Motion (Olympus) was used to capture images with dimensions of 600 × 800µm2 from different cut sections. X-ray Diffraction: Rigaku ULTIMA III X-ray diffractometer with Cu K-alpha radiation was used to record XRD spectra. The scans were recorded in the range of 2θ = 0.92–90 degrees using a 0.02 degree step and a counting time of 1.0 degree per min at 40kV and 44mA . Electrical Conductivity and Dielectric Properties: To measure electrical conductivity of nanocomposite samples with conductivity less than 10-6 S·cm-1, Keithley 6517A electrometer was used. The Keithley 6517A electrometer was connected to a Keithley 8009 test fixture and equipped with Keithley 6524 high resistance measurement software. I-V characteristics were also measured by the same device. For conductivities greater than 10-6 S·cm , Loresta GP resistivity meter (MCP-T610 model, Mitsubishi 48 Chemical Co., Japan) connected to an ESP four-pin probe (MCP-TP08P model, Mitsubishi Chemical Co., Japan) was used. Dielectric 6 ACS Paragon Plus Environment

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properties were measured in the X-band frequency range (8.2-12.4GHz) with E5071C network analyzer (ENA series 300 kHz to 20 GHz). The samples were sandwiched between two waveguides of the network analyzer. 3. Results and Discussion 3.1. Characterization of Nanowires The XRD pattern of as-synthesized MnO2NWs is shown in Figure 1. The diffraction peaks can be finely assigned to the pure tetragonal α-MnO2

50-51

. α-MnO2 has higher specific

capacitance and lower electrical conductivity compared to other crystallographic forms of MnO2 52

. Therefore, incorporation of α-MNO2NW into polymer matrix could increase the dielectric

permittivity of the CNT/PVDF nanocomposite, and it also works as a non-conductive barrier

10

20

30

40

50

60

541 70

312

002

521 600

411 510

330 420

220

400

301

200

310

110

211

between CNTs to decrease the dielectric loss.

Intensity

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80

2θ (°)

Figure 1: XRD patterns of synthesized MnO2NW.

TEM micrographs of MnO2NW are shown in Figure 2a-b. The length and diameter of MnO2NW were obtained by averaging the dimensions of more than 100 isolated NWs. The measured length and diameter of synthesized NWs were about 2.0 µm and 57 nm, respectively 7 ACS Paragon Plus Environment


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(aspect ratio = 35). Furthermore, TEM images reveal the high purity of synthesized nanowires and also the comparable length and geometry of CNT and synthesized MnO2NW.

Figure 2: TEM images of MnO2NW at (a) low magnification and (b) high magnification.

3.2. Microstructural Characterization of Nanocomposites Images of light microscopy (LM) depicted in Figure 3 show that addition of MnO2NW improves the dispersion state of CNTs in the PVDF matrix. For these images, quantitative comparison of the agglomerate area ratio is also provided as Table S1 in supporting information. More homogeneous dispersion of CNTs and fewer agglomerates can be observed for all CNT/MnO2NW/PVDF nanocomposites (Figure 2.b-e) compared with the CNT/PVDF nanocomposite (Figure 2a). This improvement can be attributed to (i) an increase in viscosity of polymer matrix; and (ii) decrease in interfacial excess energy in the presence of MnO2NW

53-54

.

Addition of MnO2NW restricted the motion of PVDF chains hence viscosity of the polymer matrix increases. Breakage of large CNT agglomerates to smaller ones and also single nanotubes facilitated in this condition owing to higher applied shear force. Additionally, the addition of


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MnO2NW might lower the interfacial excess energy and hinder the aggregation of CNT during the mixing procedure 54. These resulted in better dispersion of CNT in the CNT/MnO2NW/PVDF nanocomposites as verified by TEM analysis of polymer nanocomposites (Figure 4 a-d).

Figure 3: LM images of fabricated nanocomposites. Dispersion state of (a) 2.0wt% CNT/PVDF; (b) 2.0wt% CNT/1.0wt% MnO2NW/PVDF; (c) 2.0wt% CNT/2.0wt% MnO2NW/PVDF; (d) 2.0wt% CNT/3.0wt% MnO2NW/PVDF; (e) 2.0wt% CNT/4.0wt% MnO2NW/PVDF nanocomposites.



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Figure 4: TEM images of fabricated nanocomposites. (a, b) 2.0wt% CNT/PVDF and (c, d) 2.0wt% CNT/2.0wt% MnO2NW/PVDF at low and high magnification.

3.3. Dielectric properties The frequency dependence of dielectric permittivity and imaginary permittivity at room temperature over the X-band for PVDF/CNT, PVDF/MnO2NW and PVDF/CNT/MnO2NW hybrid nanocomposites are shown in Figure 5a-b. For better understanding of the effectiveness of hybrid nanocomposite over frequency range, the dielectric permittivity and imaginary


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permittivity for pure PVDF, PVDF/2.0wt% MnO2NW, PVDF/2.0wt% CNT and PVDF/2.0wt% CNT/MnO2NW nanocomposites are depicted in Figure S1. Pristine PVDF shows an average dielectric permittivity around 3.0; and addition of CNT increases dielectric permittivity to e.g. 18.2 and 23.3 for 2.0 and 3.0wt% CNT, respectively. On the other hand, addition of 2.0 and 3.0wt% MnO2NW only marginally increased dielectric permittivity to 3.7 and 4.0, respectively. The increase in the dielectric permittivity of CNT/PVDF nanocomposites is due to the formation of so-called nanocapacitor structure 15, 55-56. The nanocapacitor structure is formed by considering each of the two neighboring CNTs as the electrodes and the very thin PVDF layer in between as nanodielectric. Nanocapacitors will substantially increase the intensity of local electric field around CNTs, which subsequently leads to the electronic polarization of the PVDF matrix as the nanodielectric layer. At very low concentrations of CNT, the chance of formation of nanocapacitor network is almost zero owing to large gaps between CNTs. As the CNT concentration increases, the gap between the neighboring fillers is continuously reduced (nanodielectric thickness decreases), resulting in a formation of a network of nanocapacitors. In contrast to CNT, addition of MnO2NW into neat PVDF slightly enhanced dielectric properties of nanocomposite revealing that MnO2NW polarization is active over the X-band.

100

Imaginary Permittivity (ε˝)

60

Dielectric permittivity (ε´)

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


PVDF-CNT PVDF-MnO2NW CNT:MnO2NW; 2:1 CNT:MnO2NW; 1:1 CNT:MnO2NW; 2:3 CNT:MnO2NW; 1:2

50 40 30 20 10 0 0

0.5

1 1.5 2 CNT Concentration (wt%)

2.5


80 60 40 20 0

3

0

0.5


2.5

3

Figure 5: (a) Dielectric permittivity (ε´) and (b) imaginary permittivity (ε˝) of PVDF/CNT, PVDF/MnO2NW and PVDF/CNT/MnO2NW. 11 ACS Paragon Plus Environment


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As suggested by Figure 5, increasing the ratio of MnO2NW/CNT enhanced the dielectric permittivity of the hybrid nanocomposite. For instance, dielectric permittivity of CNT/PDVF nanocomposite at 3.0wt% of CNT was 23.3. However, by adding of MnO2NW as secondary ferroelectric filler, its value increased up to 50.6. The best result achieved in this study was for hybrid nanocomposite with MnO2NW/CNT ratio of 1.5 at CNT concentration of 3.0wt%. We postulated two factors come into play to improve the dielectric permittivity of the hybrid system: first, better dispersion of CNT in the presence of MnO2NW and second, positioning of MnO2NW among CNTs. It is well established that the dielectric properties of CPNs strongly rely on the dispersion state of the fillers in the nanocomposite 2, 26. LM and TEM analysis (Figure 3 and 4) vividly revealed that adding MnO2NW into the nanocomposites improved the dispersion state of CNTs; hence, the larger number of isolated CNTs with polymer matrix become available. So, higher dielectric permittivity is expected (see Figure 6). Moreover, based on the nanocapacitor model, permittivity and capacitance ( ) are related based on = / ; where is the vacuum permittivity, is the relative permittivity of polymer matrix, is the area of the electrical electrode, and is the distance between two electrical electrodes that are CNTs here. By replacing the PVDF medium with MnO2NW/PVDF, the permittivity ( ) of the nanodielectric layer increased, enhancing the dielectric permittivity of the CNT/MnO2NW/PVDF hybrid nanocomposite (see Figure 6). Surprisingly, by increasing the ratio of MnO2NW/CNT to 2, the dielectric constant was decreased as seen in figure 5. It was postulated that at high concentration of MnO2NW, the tendency to form agglomerates was increased and consequently reduced dielectric constant.


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+++++++ + + + + +++++++

+ + + +

CNT MnO2NW

Figure 6: Schematic showing impact of MnO2NW addition on CNT/PVDF nanocomposites.

Imaginary permittivity originated from ohmic loss which signifies the dissipation of electrical energy by free charge carriers moving across a dielectric in phase with the applied electric field. Low imaginary permittivity is desired for charge storage applications

18, 21

. Figure

5 shows that addition of MnO2NW into the PVDF matrix even at high concentration (3.0%wt) has little effect on imaginary permittivity of nanocomposite owing to non-conductive nature of α-MnO2. In contrast, addition of small amounts of CNT at concentrations higher than the percolation threshold, can drastically increase imaginary permittivity owing to formation of conductive network. The percolation curves of the studied nanocomposites with different ratios of MnO2/CNT are shown in Figure 7. Employing the percolation theory, electrical percolation threshold of 13 ACS Paragon Plus Environment


CNT/PVDF nanocomposite was 0.3wt% . By increasing CNT concentration higher than 0.3wt% the conductivity increases sharply because a conductive network has formed and more contact between fillers occur at higher concentrations. On the other hand, MnO2NW/PVDF nanocomposites presented a non-conductive behavior spanning the whole concentration range and this is attributed to the non-conductive nature of α-MnO2.

1.00E+00

Conductivity (S/cm)

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1.00E-04


1.00E-08

1.00E-12

1.00E-16 0

0.5


2.5

3

Figure 7: Percolation curves of the studied nanocomposites with different ratios of MnO2NW/CNT.

The addition of MnO2NW has adverse effect on conductivity of the hybrid nanocomposite samples. MnO2NW not only serves as a dielectric but also acts as a non-conductive barrier layer, hindering the formation of conductive paths and thus efficiently decreasing the leakage current. To study this effect, voltage sweep test was performed on samples with 2.0wt% CNT and different MnO2NW/CNT ratio and the current-voltage plot is given in Figure 8. As it is shown in this figure, addition of MnO2NW can successfully suppress electric current in a given DC voltage. In other words, MnO2NWs function as a barrier to disrupt conductive pathways between CNTs resulting in reduction of electric current. This behavior could be responsible for the decrease of the dielectric loss seen for these systems. It is worth noting that the comparative 14 ACS Paragon Plus Environment

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dimensionality of the employed nanofillers i.e. similar length and geometry plays a significant role in their synergistic effect towards reducing dielectric loss. For a sake of comparison, we fabricated nanocomposite contain CNT and MnO2 nanorod, and the results showed that dielectric performance is less than CNT/MnO2NW nanocomposites (see the supplementary information, Figure S2).

2 2.0wt%CNT+1.0wt%MnO2NW 1.6

2.0wt%CNT+2.0wt%MnO2NW

1.2

2.0wt%CNT+4.0wt%MnO2NW

2.0wt%CNT+3.0wt%MnO2NW Current (mA)

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


0.8

0.4

0 0

10

20 Voltage (V)

30

40

Figure 8: Current-voltage characteristics of PVDF/2.0wt%CNT/1.0-4.0wt%MnO2NW.

Figure 9 presents the dielectric loss ( =

!"##

) of the hybrid

nanocomposites developed in this study. Low is desired for charge storage applications i.e. high dielectric permittivity and low dielectric loss. As shown, adding CNT as conductive filler to the PVDF matrix increases tan δ especially for concentrations higher than the percolation threshold because of conductive network formation. On the other hand, addition of MnO2NW to the polymer matrix decreases the tan δ value by increasing dielectric permittivity, while not significantly changing the imaginary permittivity. For hybrid nanocomposites, by adding more MnO2NW to CNT, tan δ decreases. For instance, tan δ of PVDF/3.0wt% CNT is 3.7 while for PVDF/3.0wt% CNT/4.5wt MnO2NW it is 0.7. These results show the positive effect of MnO2NW on reducing the dielectric loss. This makes the hybrid nanocomposites appropriate for 15 ACS Paragon Plus Environment


charge storage application by simultaneously increasing dielectric permittivity and reducing dielectric loss. Table 1 presents a comparison of the dielectric permittivity and dielectric loss of the hybrid nanocomposites in this study with various hybrid nanocomposites reported in the literature. Hybrid nanocomposites filled with carbonaceous materials, such as multi-walled CNT (MWCNT) and graphene, and high amount of ferroelectric particles showed moderate dielectric properties

57-60

, but adding high amount of ferroelectric materials leads to relatively low

mechanical flexibility. Nanocomposites that contain metallic fillers and ferroelectric particles have been produced with limited success, however, significant amounts of conductive fillers had to be incorporated into the polymer to obtain sufficiently high dielectric permittivity

61

. The

hybrid CNT:MnO2NW (3.0:4.5wt%) nanocomposite in the present work delivered high dielectric permittivity (50.6) and low dielectric loss (0.7), and these are among the best values for the hybrid nanocomposites reported in the literature in X-band frequency. More importantly, the nanofiller content in the current work is much lower than those reported in the literature, providing a great potential for application in flexible capacitors, e.g. embedded capacitors in printed circuit boards.

4


3.5

Dielectric loss (Tan δ)

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3 2.5 2 1.5 1 0.5 0

0

0.5


2.5

3

Figure 9: Dielectric loss (tan δ) of PVDF/CNT, PVDF/MnO2NW and PVDF/CNT/MnO2NW. Best 16 ACS Paragon Plus Environment

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results of dielectric performance achieved for PVDF/CNT/MnO2NW with MnO2NW/CNT ratio of 1.5.

Table1: Dielectric Properties of Various Hybrid Polymer Nanocomposites Reported in the Literature Total Filler Frequency Dielectric Dielectric Fabrication Nanofiller Matrix Conc. (GHz) Permittivity Loss Method 1 2 SC+CM PVDF AgNP :BT NP (15:20vol%) 35.0vol% 10.0 31 -

Polymer

Ref. 61

PVDF

CB3:BTNP (20:10wt%)

30.0wt%

2.0

~35

1.10

SC+CM

57

Epoxy

MWCNT4:Al2O3NP (0.4:40vol%)

40.4vol%

12.4

24

0.70

Compressio Casting

58

Epoxy

MWCNT:BTP5 (0.2:40vol%)

40.2vol%

12.4

23

0.46

Casting

58

Epoxy

MWCNT:TiB2P (0.2:40vol%)

40.2vol%

12.4

17.5

0.68

Casting

58

Epoxy

MWCNT:MoSi2P (0.2:40vol%)

40.2vol%

12.4

32.5

0.46

Casting

58

Wax

Graphene@MoS2 (15wt%)

15.0wt%

2.0

14

0.55

Casting

59

PVDF

Graphene@MoS2 (15wt%)

25.0wt%

2 GHz

51.1

~1.4

Casting

60

PS

MWCNT

10.0wt%

8.2-12.4 GHz

15.5

2.75

M+In.

40

PVDF

MWCNT (3.0wt%)

3.0wt%

23.3

3.74

M+CM

PVDF

MWCNT:MnO2NW (3.0:4.5wt%)

7.5wt%

50.6

0.70

M+CM

1

Nanoparticle Barium Titanate 3 Carbon Black 4 Multi-walled Carbon Nanotube 5 Microparticle 2

8.2-12.4 GHz 8.2-12.4 GHz

PVDF: Polyvinylidene Fluoride SC: Solution Casting CM: Compression Molding In: Injection Molding M: Melt Mixing

4. Conclusion: In this study, novel hybrid nanocomposites containing CNT/MNO2NWs were investigated for charge storage application. PVDF was selected as the polymer matrix owing to its good dielectric properties. The good improvement in dielectric permittivity was achieved with CNT/MnO2NW/PVDF hybrid nanocomposites. Matched length and geometry between CNT and MnO2NWs, and enhanced dispersion of CNT at the presence of MNO2NWs, are responsible for higher dielectric permittivity. Also, the introduction of the MnO2NWs can hinder the formation 17 ACS Paragon Plus Environment

This Work

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of conductive network by interrupting conductive pathways between CNT agglomerates and between individual CNTs, and thus significantly decrease dielectric loss. The best obtained dielectric permittivity and dielectric loss in this study were 50.6 and 0.7, respectively in the Xband frequency range (8.2-12.4 GHz), which are among the best-reported values in the literature. The outstanding dielectric properties of hybrid nanocomposites at low nanofiller contents make them promising materials for flexible capacitors, such as embedded capacitors in printed circuit boards. Acknowledgements Financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC) is highly appreciated. We would like to acknowledge Ms. Amy Liang and Mr. Areeb Mohammed for helping with sample preparation and Ms. Ivonne Maritza Otero Navas for preparation of the nanocomposite sections for TEM. Supporting Information Agglomerate area ratio for nanocomposites containing 2.0wt% CNT, frequency dependent plots for dielectric permittivity and imaginary permittivity for pure PVDF, PVDF/2.0wt% MnO2NW, PVDF/2.0wt%

CNT,

and

PVDF/2.0wt%

CNT/MnO2NW

nanocomposites,

dielectric

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TOC Graphic

23.3 : 50.6

3.7 : 0.7



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TOC (Graphical abstract) 195x125mm (300 x 300 DPI)

ACS Paragon Plus Environment

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Enhanced Dielectric Performance of Polymer Nanocomposites Based

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