Contrasting Role of Defect Induced Carbon Nanotubes in

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C: Physical Processes in Nanomaterials and Nanostructures

Contrasting Role of Defect Induced Carbon Nanotubes in Electromagnetic Interference Shielding Kunal Manna, and Suneel Kumar Srivastava J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b04813 • Publication Date (Web): 02 Aug 2018 Downloaded from http://pubs.acs.org on August 11, 2018

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The Journal of Physical Chemistry

Contrasting Role of Defect Induced Carbon Nanotubes in Electromagnetic Interference Shielding Kunal Manna† and Suneel Kumar Srivastava†,* †

Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur, India -

721302 *Corresponding Author: Email: [email protected] Tel: +91-3222-283334

1 ACS Paragon Plus Environment

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ABSTRACT: Tuning of the defect is critical for specific application of a material worth exploring and researching. In view of this, additional defects have been incorporated in single-walled carbon nanotubes (SWCNTs) by subjecting them to camphor mediated combustion and characterized by x-ray diffraction (XRD), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and electron paramagnetic resonance (EPR). Subsequently, we compared electromagnetic interference (EMI) shielding performance of SWCNTs vis-à-vis multi-walled carbon nanotube (MWCNT) filled polystyrene (PS) nanocomposites. Interestingly, induced defects in SWCNT played contrasting role with respect to MWCNT in their performance as EMI shielding materials. These findings have been correlated with the aspect ratio and percolation threshold of carbon nanotubes (CNTs) as well as dc conductivity of PS/CNT nanocomposites in the light of electromagnetic (EM) theory.


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INTRODUCTION Physical properties of materials are largely influenced by the nature and extent of the defects present in their atomic arrangements.1 In this regard, SWCNTs possess different types of intrinsic defects, such as vacancies, metastable atoms, pentagons, heptagons, Stone-Wales defects, discontinuities of walls, heterogeneous and dangling bonds at open ends.1-2 In addition, defects in pristine SWCNTs could be further induced externally by means of post synthetic treatment.3 Such induced defect in SWCNTs enable anchoring of multiple functionalities acting as nucleating sites in directing them for their specific applications.4 Electromagnetic interference (EMI) of radio frequency radiation continues to be a grim disquiet in modern civilization. Therefore, lightweight EMI shielding material is desirable to protect the workspace and environment from radiation. In this regard, SWCNTs, MWCNTs and their polymer nanocomposites offer a new arena in the development of advanced EMI shielding materials. According to Watts et al.5 defective CNTs act as high radiation absorber due to generation of polarizing centre accounting for its enhanced interaction with incident EM waves. Accordingly, defects have been introduced in CNT by physical as well as chemical methods.3,6 Recently, MWCNTs filled polystyrene (PS) has been successfully used as EMI shielding materials due to its high conductivity and low density.7-12 However, contemporarily, no significant work has been reported on SWCNT filled polymers. Eklundet al., observed significant enhancement in EMI shielding efficiency (SE) of annealed SWCNT filled epoxy composites due to higher aspect ratios and reduction of wall defects.13 In view of this, exploring and researching EMI SE performance of SWCNT filled polymer nanocomposites remain more exciting. Motivated by our earlier findings on MWCNT1, we hereby report a simple, facile, mild and straight forward method consisting in achieving additional defects in intrinsically defective pristine SWCNT by camphor mediated combustion (SWCNT-CM) while avoiding excessive



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interruption in its basic structure and property followed by their characterization (S1). It is anticipated that defects (intrinsic/induced) and aspect ratio of CNT could play important role in their EMI SE performance in corresponding polymer nanocomposites needs to be explored. Considering this, we have fabricated conductive polymer nanocomposites using earlier prepared defective MWCNTs and SWCNTs filled in PS. Subsequently, we focused our work on investigating role of additional defects in camphor mediated SWCNT/PS and MWCNT/PS nanocomposites on their EMI SE performance. The choice of PS in this work has been mainly guided by its insulating nature.14 To the best of our knowledge, present work is the first systematic study demonstrating experimental validation of the contrasting role of induced additional defects in SWCNT and MWCNT for a series of most important CNT/PS nanocomposites.

EXPERIMENTAL SECTION

Materials. Single walled Carbon Nanotubes (SWCNTs) Main range of Diameter (< 2 nm), Length (5-15 µm) and Camphor were purchased from Shenzhen Nanotech Port Co. Ltd. And Sigma Aldrich respectively. Ethanol, Methanol and Acetone were procured from SRL Pvt.Ltd. Mumbai. All the reagents were used without any further purification. Fabrication of Camphor Mediated Defective SWCNTs. A mixture of 20:1 (w/w) camphor and SWCNT was thoroughly mixed with the help of spatula and kept in a porcelain pot and ignited with a burning matchstick. The combustion of the camphor continued until the burning stopped automatically. The products of SWCNT/Camphor left after combustion was referred as SWCNT-CM. Fabrication

of

SWCNT-CM/PS

and

MWCNT-CM/PS

Nanocomposites.

SWCNT/PS, SWCNT-CM/PS, MWCNT/PS and MWCNT-CM/PS composites were prepared following dry grinding and mixing of CNT and PS15 in 4:1 weight ratio. In order to make 4 ACS Paragon Plus Environment

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comparison of its EMI SE performance, SWCNT/PS, SWCNT-CM/PS, MWCNT/PS and MWCNT-CM/PS composites were also prepared consisting of CNT and PS in the weight ratio of 50/50, 60/40 and 70/30 respectively. Accordingly, these samples have been designated as SWCNT/PS-50, SWCNT/PS-60, SWCNT/PS-70, SWCNT-CM/PS-50, SWCNT-CM/PS-60, SWCNT-CM/PS-70, MWCNT/PS-50, MWCNT/PS-60, MWCNT/PS-70, MWCNT-CM/PS50, MWCNT-CM/PS-60, MWCNT-CM/PS-70.

RESULTS AND DISCUSSION

XRD of pristine SWCNT and SWCNT-CM, are exhibited in Figure 1. The 002 diffraction peak appeared at 2θ ~ 260 corresponding to d002 values of 0.3506 and 0.3473 nm due to hexagonal carbon in pristine SWCNT and SWCNT-CM respectively.16 In addition, other peaks appeared at ~430 and ~440 corresponding to (100) and (101) plane of SWCNT.16 Full width at halfmaximum (FWHM) calculation showed the following order: SWCNT-CM (3.22°) > SWCNT (2.61°). The higher intensity of (002) peak in SWCNT in comparison to SWCNT-CM could be ascribed to relatively lower alignment of nanotubes.16 The microstrain (ε) in the SWCNT and SWCNT-CM was also calculated17 and follow the order: SWCNT-CM (3.54) > SWCNT (2.89).

Figure 1. XRD pattern of pristine SWCNT and SWCNT-CM. ACS Paragon Plus Environment

5


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The increase in microstrain in SWCNT-CM could be attributed to the inclusion of substantial defects in SWCNT through camphor mediated combustion.18 The degree of graphitization has also been calculated according to the reported literature.19It is noted that degree of graphitization of pristine SWCNT and SWCNT-CM correspond to ~ 87% and ~51% respectively. This further strengthened our earlier contention based on maximum deformation observed in SWCNT-CM.1,19 The inclusion of structural defect induced in pristine SWCNT through camphor mediated combustion has also been investigated by field emission scanning electron microscopy (FESEM) study of pristine SWCNTs and SWCNT-CM and findings are displayed in Figure 2 (a) and (b) respectively. It is noted that, pristine SWCNTs appears more or less smooth, clean, long, straight, well aligned and uniformly distributed indicating less defective wall of SWCNTs.20 In contrast, discontinuity irregularity, twisting and fragmentation was clearly evident on the surfaces of the SWCNT-CM through high

(a)

(b)

(c)

(d)

Figure 2. (a) FESEM images of SWCNT (scale bar = 200 nm), (b) FESEM images of SWCNT-CM (scale bar = 100 nm), (c) High resolution FESEM image of twisted SWCNT-CM (scale bar = 100 nm) and (d) High resolution FESEM image of ACS Paragon Plus Environment

fragmented SWCNT-CM (scale bar = 100 nm).

6

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resolution FESEM images as depicted in Figure 2(c) and 2(d).21 This could be ascribed to the damage extended to the underlying sidewalls leading to the bending, twisting and curling of the SWCNTs during combustion of camphor.21 Figure 3(a) exhibits high resolution transmission electron microscopy (HRTEM) image of pristine SWCNT. Deposition of disordered carbon layers on the outer side walls of SWCNT has been evidently validated in SWCNT-CM through HRTEM image as shown in Figure 3(b). It is also established segmentation of pristine SWCNTs could lead to formation of relatively shorter nanotubes having more open ends.22 Further, twisting of SWCNT tube kinks and disintegration of nanotubes in SWCNT-CM has also been prominently observed through transmission electron microscopy (TEM) images in Figure 3(c) and 3(d) respectively.

(a)

(c)

(b)

(d)

Figure 3. (a) HRTEM image SWCNT, (b) HRTEM image of SWCNT-CM, (c) 7 TEM images of twisted and (d) TEM image of disintegrated SWCNT-CM. ACS Paragon Plus Environment


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The straight rectilinear fringes in pristine SWCNT as depicted in Figure S1 accounts for its relatively less defective structure.23 Further, insignificant distortions are observed in the inner walls of the pristine SWCNTs and a majority of planes stay aligned.24 In all probability, this could be ascribed to the interlayer interactions, change in helix angle, and defect mediated structural stabilization.25 The defect density generated in pristine SWCNT and camphor treated samples follow the order SWCNT-CM > SWCNT and in agreement with the findings reported on MWCNT.1 Such, additional defects (fragmentation, rehybridization) induced in pristine SWCNT with intrinsic defects (vacancies, dislocations) could not be removed by annealing.1 Raman spectra of pristine SWCNT and SWCNT-CM in Figure 4 (a) shows presence of characteristic D and G bands at ~1340 and ~1570 cm-1 respectively. These G and D bands appeared a result of doubly degenerate phonon Raman active mode of crystalline graphitic sp2 carbon systems and imperfect lattice arrangement predominantly at the edges/defects of the sp2 hybridized carbon network respectively.26-27 It is noted that intensity of the G band decreased and that of D band increased in SWCNT-CM compared to SWCNT. This is clear evidence about the intense defects induced in SWCNT-CM as a result of camphor mediated combustion. This has been further reaffirmed our earlier contention on enhanced defect concentration supplemented by comparing intensity ratio of D to G peaks (ID/IG) in both the samples. It is observed that the ID/IG value of pristine SWCNT (0.001) is significantly increased in SWCNTCM (0.054). This further in SWCNT-CM due to the energy transfer through camphor mediated combustion.1 Further, SWCNT-CM showed no significant shifting of D and G bands with respect to pristine SWCNT unlike that observed in camphor mediated MWCNT.1 Typical X-ray photoelectron spectroscopy (XPS) wide scan spectra of the pristine SWCNT and SWCNT-CM are displayed in Figure S2. A distinct carbon peak at ~ 284 eV in the spectra clearly signified carbon as major constituent.28 Further, Figure 4(b) showed appearance of a broadened C1s envelope in camphor mediated combustion of SWCNTs.


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(b)

(a)

Figure 4. (a) Raman and (b) XPS of SWCNT and SWCNT-CM.

(a)

(b)

Figure 5. Deconvoluted C 1s XPS of (a) pristine SWCNT and (b) SWCNT-CM. The shifting of binding energy corresponding to C 1s signal follows the order: SWCNT-CM (284.2 eV) > pristine SWCNT (284.0 eV). It may be noted that higher binding energy C1s peak appeared in SWCNT-CM was similar to that observed in MWCNTs treated with camphor mediated combustion.1Additionally, shifting of binding energy in SWCNT-CM noticed in our case is well supported as reported on defect generated SWCNT prepared by treating it with conc. HNO3.21Figure 5 (a) and (b) displayed HR-XPS fitting of the C1 s peak of SWCNT and SWCNT-CM respectively. It is noted that deconvoluted C1s spectrum in either case consist of five components (SI-2).29 The peaks appeared at ~284.04 eV (C=C : sp2), ~284.5 eV (C=C : 9 ACS Paragon Plus Environment


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sp2 with defects, C–C : sp3), ~285.5 eV (C–OH), ~286.2 eV (C=O) and ~290.3 eV (π-π*).30 Figure 5 (b) also shows decrease in relative width and intensity of C=C sp2 peaks in SWCNTCM (284.26 eV), whereas intensity of C-C sp3 peaks in SWCNT-CM (283.3 eV) increased and slightly shifted to lower energy compared to pristine SWCNT.31 All these observations reveal the inclusion of relatively more intense additional defects in terms of rehybridization in SWCNT-CM. According to available literature, satellite peak (Binding energy : 290.3 eV, FWHM~3.52°) appear in pristine SWCNTs corresponding to the π−π* shakeup satellite and sensitive to aromatic nature.32 We observed broadening of this peak (FWHM∼5.33°) in SWCNT-CM similar to that reported in MWCNT-CM earlier. These findings clearly indicated presence of sp3 defects in SWCNT-CM in the form of amorphous carbon as earlier shown in HRTEM.1 Electron paramagnetic resonance (EPR) measurements are very sensitive to impurities and dangling bond defects.33 Therefore, EPR studies has been made to unfold role of induced defects and impurities in pristine carbon nanotubes and corresponding findings are displayed in Figure 6. It is noted that pristine SWCNT as well as MWCNT displayed a very weak and wide resonance EPR signal as shown in inset of Figure 6 (a) and (b).33

(a)

(b)

Figure 6. EPR spectra of (a) SWCNT (inset) and SWCNT-CM; (b) MWCNT (inset) and MWCNT-CM.


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In the case of SWCNT-CM and MWCNT-CM, appearance of broad U-spectrum is typical characteristics of defects induced in pristine carbon nanotubes.34,35 In addition, increased amplitude of the broad line also indicated significantly enhanced defect density in both SWCNT-CM and MWCNT-CM compared to their pristine counterparts. The ‘g’ values were also calculated based on Lorentzian line shape fitting of asymmetric Dysonian line shape experimental data using equation below: ℎ𝜐 = 𝑔𝜇𝐵 𝐵

(1)

where, h= Planck’s constant (6.626×10-34 J.s), ν = Frequency (9.66×109 Hz), µB = Bohr Magneton (9.274×10-24 JT-1) and B = magnetic field in Tesla. The calculated ‘g’ values in SWCNT (MWCNT) correspond to 1.998 and 4.313 (2.132 and 4.544) compared to 2.316 and 4.792 (2.355 and 5.189) in case of SWCNT-CM (MWCNT-CM) respectively. It is anticipated that observed higher ‘g’ values in SWCNT-CM and MWCNT-CM could be assigned to the interaction between the conducting electrons in the nanotubes trapped at defects and impurities.35,36 Further, deviation of ‘g’ values in pristine as well as defective CNTs compared to the theoretical free electron g-value (2.0013)35 further strengthened our contention on articulation of enhanced defects in pristine CNTs through camphor mediated combustion. Figure S3(a) shows isotherm adsorption/desorption curve plotted against relative partial pressure for SWCNT and SWCNT-CM. The superior N2 adsorption in pristine SWCNTs could be ascribed to higher micropore density, i.e. lower micropore volume compared to SWCNTCM. Brunauer-Emmett-Teller (BET) surface area of pristine SWCNT and SWCNT-CM were found to be 538.4 and 377.7 m2g−1 respectively. The lower surface area of SWCNT-CM fits well with the observed reduction in micropore density as depicted in the plots of differential pore volume distribution with average pore diameter using Barrett–Joyner–Halenda (BJH) desorption data in Figure S3(b). Further, our finding on reduced surface area of SWCNT-CM could also be correlated with its lower aspect ratio as a result of distortion, kinking and



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ultimately segmentation upon burning with camphor.37,38 Such induced defects are expected to diminish supramolecular interactions responsible for the aggregation between the nanotubes in the solid state and lead to higher degree of deaggregation.18 EMI shielding can be expressed as the logarithm of the ratio of incident power (P I) to transmitted power (PT) in decibels as 𝑃

𝑆𝐸𝑇 (𝑑𝐵) = 10 𝑙𝑜𝑔 (𝑃 𝐼 )

(2)

𝑇

Further, total EMI shielding effectiveness (SET) is the sum of contributions of reflection (SER), absorption (SEA) and multiple internal reflections (SEM) expressed as:, SET = SER + SEA + SEM

(3)

When SET > 15 dB, contribution of SEM considered to be negligible13 i.e. SET = SER + SEA

(4)

In a vector network analyzer, EMI SE is represented in terms of scattering parameters which are S11 (forward reflection coefficient), S12 (forward transmission coefficient), S21 (backward transmission coefficient), and S22 (reverse reflection coefficient). The SET can be evaluated from the S parameters by using the following equations, 39,40 1

1

12

21

1

𝑆𝐸𝑇 (𝑑𝐵) = 10𝑙𝑜𝑔10 (𝑆2 ) = 10𝑙𝑜𝑔10 (𝑆2 ) = 10𝑙𝑜𝑔10 (𝑇) 1

1

𝑆𝐸𝑅 (𝑑𝐵) = 10𝑙𝑜𝑔10 (1−𝑆2 ) = 10𝑙𝑜𝑔10 (1−𝑅)

(5) (6)

11

2 1−𝑆11

𝑆𝐸𝐴 (𝑑𝐵) = 10𝑙𝑜𝑔10 (

2 𝑆12

1−𝑅

) = 10𝑙𝑜𝑔10 (

𝑇

)

(7)

The absorptivity (A), reflectivity (R) and transmissivity (T) of EM wave incident on a slab of material must sum to the value “one”, that is, T + R + A=1.

(8)

Figure 7(a) and 7(b) shows variation of SER and SEA values for pristine SWCNT/PS and SWCNT-CM/PS respectively, as following the trend:


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(b)

(a)

(c)

Figure 7. (a) Plots of frequency vs SET and (b) frequency vs SER, and (c) frequency vs SEA of of SWCNT/PS and SWCNT-CM/PS nanocomposites at 20 wt % loading.

SER: SWCNT/PS (16-10 dB) < SWCNT-CM/PS (18-12 dB). SEA: SWCNT/PS (12-18 dB) > SWCNT-CM/PS (6-10 dB). Figure 7(c) shows variation of SET with frequency (2-8 GHz) of SWCNT/PS and SWCNTCM/PS. It is noted that PS loaded with 20 wt % pristine SWCNT exhibit relatively higher SETcompared to same wt% of SWCNT-CM loaded in PS. These findings clearly reveal a dominant role of reflection in comparisonto absorption in SET. Eklundet. al.13 also studied EMI SE of epoxy filled with 10 wt % each SWCNT (long), SWCNT-annealed (material formed after annealing of SWCNT-short at 1100 0C in N2) and SWCNT (short) in the range of 10 MHz to 1.5 GHz and found following order: SWCNT (long)-epoxy > SWCNT-annealed-epoxy >



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SWCNT (short)-epoxy. These findings indicated superior performance of SWCNT (long)epoxy due to relatively higher aspect ratio and conductivity. It was concluded that relatively higher conductivity, lower percolation threshold and higher aspect ratio of SWCNT-long in epoxy composite account for superior EMI SE. According to percolation theory, conductive filler exhibiting high aspect ratio forms conductive network in the PS matrix at relatively lower percolation threshold. In our case, we noticed relatively lower dc conductivity due to reduction of aspect ratio in SWCNT-CM. As a result, formation of conducting network of SWCNT-CM in PS is achieved at higher percolation threshold. In view of EM theory, superior higher conductivity, lower percolation threshold and higher aspect ratio could account for higher EMI SE for any materials. Therefore, observed trend of SET in SWCNT-CM/PS and SWCNT/PS could also be explained in the light of these facts. The segmentation and twisting in SWCNTCM resulted in lower aspect ratio. As a result, SWCNT-CM (20 wt%)/PS nanocomposites exhibited higher percolation threshold and relatively lower conductivity (0.123 S/cm) compared to SWCNT (20 Wt %)/PS (0.233 S/cm)in accordance with percolation theory.13 As a consequence, SWCNT-CM/PS showed relatively lower EMI SE compared to SWCNT/PS nanocomposites at the same wt% loading. We further investigated the effect of 50, 60 and 70 wt% loading of SWCNT and SWCNT-CM in PS matrix on performance of EMI SE as displayed in Figure S4. The insignificant improvements in EMI SE are observed in 50-70 wt% loaded SWCNT and SWCNT-CM filled in PS matrix in comparison to 20 wt% SWCNT and SWCNT-CM loaded PS nanocomposites. Interestingly, EMI SE of SWCNT-CM/PS was found to be always lower compared to its SWCNT/PS nanocomposites at all the filler loading. This further strengthened our earlier contention, that inclusion of additional defects of SWCNT has an adverse impact on its EMI SE performance irrespective of its contents in PS.


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In addition, we also investigated EMI SE of defective MWCNT filled PS nanocomposites and compared these findings with pristine MWCNT/PS nanocomposites. Figure 8 (a) and (b) represent variation of SER and SEA of MWCNT/PS and MWCNT-CM/PS

(a)

(b)

(c)

Figure 8. (a) Plots of frequency vs SET and (b) frequency vs SER, and (c) frequency vs SEA of MWCNT/PS and MWCNT-CM/PS nanocomposites at 20 wt % loading. respectively at 20 wt% filler loading. Interestingly, SER and SEA of MWCNT/PS and MWCNT-CM/PS showed following opposite trend: SER: MWCNT/PS (9-8 dB) > MWCNT-CM/PS (3-4 dB), SEA: MWCNT/PS (18-19 dB) < MWCNT-CM/PS (25-26 dB).



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These results clearly signify that reflection as well as absorption dominates in MWCNT/PS and MWCNT-CM/PS respectively. Figure 8 (c) depicts variation of the SET for PS composites filled with pristine MWCNT and MWCNT-CM at 20 wt % filler loading over 2-8 GHz. It is noted that MWCNT-CM/PS exhibited relatively higher SET compared to MWCNT/PS over the entire frequency range.22 In all probability, such higher SET value in MWCNT-CM/PS could be ascribed to additional defects originating from rehybridization and fragmentation of MWCNTs through camphor mediated combustion. It is also anticipated that induced defects in MWCNT increase interfacial area and account for the formation of more interconnected conducting networks compared to pristine MWCNT in PS matrix.10 The room temperature dc conductivity of MWCNT/PS (0.035 S/cm) and MWCNT-CM/PS (0.287 S/cm) also supported our earlier contention. Further, defects in CNTs could also introduce localized states near the Fermi level.5 Therefore, it is most likely that incidentEM radiations on the surface could lead to absorption of the energy via contiguous states to the Fermi level and account for larger radiation absorption tendency.5 We further investigated the effect of 50, 60 and 70 wt% loading of MWCNT and MWCNT-CM in PS matrix on performance of EMI SE as displayed in Figure S5. Interestingly, all MWCNT-CM loaded PS composites exhibited higher EMI SE in comparison to corresponding pristine MWCNT/PS composites. This is in contrast to our findings observed earlier on SWCNT and SWCNT-CM filled PS composites reaffirming contrasting role of induced defect in carbon nanotubes. All these findings further reaffirm contrasting role of defect induced carbon nanotubes in their EMI shielding performance. Figure 9 schematically represents variation of frequency vs SEA, SER and SET of SWCNT/PS, SWCNT-CM/PS, MWCNT/PS and MWCNTCM/PS at 20 wt% loading. All these findings clearly suggested that additional defect inclusion following the same strategy in SWCNT as well as in MWCNT filled PS made adverse impact on the total EMI SE. Such contrasting roles of the induced defects in SWCNT and MWCNT


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could be endorsed on the basis of aspect ratio, percolation threshold and the dc conductivity of corresponding PS nanocomposites in the upshot of the EM theory.

Figure 9: Schematic presentation of variation of frequency vs SEA, SER and SET of SWCNT/PS, SWCNT-CM/PS, MWCNT/PS and MWCNT-CM/PS.

CONCLUSION: In summary, present work reports fabrication of defective SWCNT and MWCNT filled PS nanocomposites and their EMI SE performance have been studied. Our findings showed adverse role of additional defects generated in SWCNT and MWCNT through camphor mediated combustion on the EMI SE. To the best of our knowledge, this work demonstrates experimental validation of the contrasting role of induced additional defects in SWCNT and MWCNT in SWCNT/PS and MWCNT/PS nanocomposites. ASSOCIATED CONTENT



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Supporting Information: Characterization Techniques, Lattice fringes of pristine SWCNT and SWCNT-CM, BET Isotherms, differential pore volume plots, wide XPS spectra. Variation of SET with frequency for SWCNT/PS, SWCNT-CM/PS, MWCNT/PS and MWCNT-CM/PS nanocomposites with 50-70 wt% loading of filler respectively. AUTHOR INFORMATION Corresponding Author *(S.K.S.) E-mail: [email protected]. Present Addresses Department of Chemistry, Indian Institute of Technology Kharagpur, India, 721302. Author Contributions K.M. performed work under supervision of S.K.S. Equal contributions have been made in writing and review of this manuscript. Notes The authors declare no competing financial interests. ACKNOWLEDGMENT S.K.S. is grateful to DRDO, India, for providing a grant for the ENA Network Analyzer and IIT Kharagpur for providing other necessary facilities in this work. The authors would like to thank Prof.Sanjeev Kumar Srivastava of the Department of Physics for XPS analysis. K. M. gratefully acknowledges IIT Kharagpur for providing financial support.


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Contrasting Role of Defect Induced Carbon Nanotubes in

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