polymethylmethacrylate nanocomposites with excellent microwave-absorption performance

polymethylmethacrylate nanocomposites with excellent microwave-absorption performance

Materials Letters 253 (2019) 222–225 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/mlblue S...

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Materials Letters 253 (2019) 222–225

Contents lists available at ScienceDirect

Materials Letters journal homepage: www.elsevier.com/locate/mlblue

Swift heavy-ions irradiated nano-magnetite/exfoliated-nanographite/ polymethylmethacrylate nanocomposites with excellent microwaveabsorption performance Prachi Yadav a, Sunita Rattan a,⇑, Ambuj Tripathi b, Sandeep Kumar c,d a

Amity Institute of Applied Sciences, Amity University, Noida, Uttar Pradesh 201303, India Inter-University Accelerator Centre (IUAC), Aruna Asaf Ali Marg, New Delhi 110067, India Magnetics and Advanced Ceramics Lab, Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India d Department of Physics, Bhaskaracharya College of Applied Sciences, University of Delhi, Delhi 110075, India b c

a r t i c l e

i n f o

Article history: Received 28 May 2019 Received in revised form 12 June 2019 Accepted 15 June 2019 Available online 17 June 2019 Keywords: Polymer nanocomposites Swift heavy-ion irradiation Complex permeability Complex permittivity Reflection loss

a b s t r a c t In this work, a new method (swift heavy-ion (SHI) irradiation) has been adopted to develop the lightweight nano-magnetite/exfoliated-nanographite/polymethylmethacrylate (Fe3O4/NG/PMMA) nanocomposites with strong and broadband MW absorbing characteristics. The effects of SHI [C6+(80 MeV) and O7+(100 MeV)] irradiation on MW-absorbing properties of Fe3O4/NG/PMMA nanocomposites were investigated in 2–18 GHz frequency range. Irradiated nanocomposites demonstrated better homogenization of nanofillers, lower saturation magnetization, higher coercivity, stronger MW-absorption and higher effective bandwidth of absorption. Nanocomposites irradiated with O7+(100 MeV) ions at fluence of 1  1012 ions/cm2 exhibited a minimum reflection loss (RLmin) of 32.4 dB (99.94% MW-absorption) and broad bandwidth (for RL  10 dB) of 6.8 GHz. Ó 2019 Published by Elsevier B.V.

1. Introduction The extensive use of microwaves (MWs), both in civilian and military applications, has generated the serious problems of MW pollution and electromagnetic interference (EMI) [1,2]. MWabsorbing materials have received tremendous attention because of their ability in curbing unwanted MW radiation and shielding against EMI. Moreover, MW-absorbers are critical for military applications in reducing radar signatures [3–7]. The low-cost light-weight polymer nanocomposites (NCs) with strong and broadband absorptions are in great demand for highperformance MW-absorbing applications. Nanoscale magnetite (Fe3O4) is an excellent filler in polymer matrices owing to its strong magnetic properties [1–5]. The low-cost, low-density, easyprocessing, large dielectric loss, and high mechanical strength of exfoliated nanographite (NG) makes it a promising dielectric MW-absorber [1,8]. The concurrent dielectric and magnetic losses through compositing of Fe3O4 nanoparticles and NGs in polymethylmethacrylate (PMMA) matrix can produce excellent MWabsorption results [1,8]. It is hard to achieve strong and wideband MW-absorption performances simultaneously due to impover⇑ Corresponding author. E-mail address: [email protected] (S. Rattan). https://doi.org/10.1016/j.matlet.2019.06.053 0167-577X/Ó 2019 Published by Elsevier B.V.

ished solubility of nanofillers in polymer matrices and poor impedance matching of NCs. In literature, swift heavy-ion (SHI) irradiation technique has been successfully implemented in modification of material properties (i.e., dielectric, magnetic, sensing etc.) by inducing controlled defects, stress and structural disorders [9,10]. In this work, we report influences of SHI irradiation on MW-absorbing properties of melt-blended Fe3O4/NG/PMMA NCs for the first time. This unique and effective technique (SHI irradiation) attains strong (32.4 dB) and broadband (6.8 GHz) MW-absorption in irradiated NCs. 2. Material and methods Exfoliated NGs were prepared through a three-step process as described in literature [8]. Fe3O4 nanoparticles were processed through a solution combustion method using Fe(NO3)39H2O as starting raw material [11]. After dissolving Fe(NO3)3 in deionized water, citric acid was added to solution for preventing precipitation of metal-cations. Glycine was added to precursor solution, after pH neutralization, to fuel the reaction. Solution was then heated at 180 °C under magnetic stirring to produce a brownish and fluffy product. As-obtained product was calcined at 600 °C for 2 h to acquire Fe3O4 phase. To prepare Fe3O4/NG/

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PMMA NCs, optimized loadings of Fe3O4 (20 wt%) and NG (2 wt%) were dispersed in PMMA matrix through twin-screw melt-blending technique [8,12]. The resulting melt-mixture was compressed into toroidal-shaped pellets (ID-3.04 mm and OD-7.00 mm) through a specially designed die. As-prepared NCs were irradiated with SHI [C6+(80 MeV) and O7+(100 MeV)] beams at varying fluences (1  1010, 1  1011, and 1  1012 ions/cm2) using 15 UD tandem pelletron accelerator at IUAC, New Delhi, India. The energy of SHI beam was estimated using Stopping and Range of Ions in Matter (SRIM) module that was designed to estimate projected range of ions in matter [9,10]. Nanocomposite before irradiation is labelled as pristine. The labelling of all irradiated NCs and various important parameters of SHI beams are presented in Table 1. Surface microstructures of neat-PMMA, NGs, Fe3O4 nanoparticles, and NCs were studied using field-emission scanning electron microscopy (FE-SEM, MIRA II LMH). Transmission electron microscopy (TEM, FEI Tecnai TF20) recorded the distribution of Fe3O4 and NGs (in representative pristine NC). MH data of NCs was measured on SQUID magnetometer (Quantum Design MPMS XL7). Complex permittivity (e ¼ e0  ie00 ) and permeability (l ¼ l0  il00 ) spectra were recorded on vector network analyser (VNA, Agilent PNA-L N5230A). Schematic representation of synthesis, SHI irradiation and various MW-absorption mechanisms of NCs is illustrated in Fig. 1(a).

3. Results and discussion Fig. 1(b)–(d) illustrate XRD patterns of pristine, C6+(80 MeV) irradiated and O7+(100 MeV) irradiated Fe3O4/NG/PMMA NCs. The diffraction peaks at 26.5° and 53.1° can be assigned to (0 0 2) and (0 0 4) planes of NGs, respectively. All other peaks can be indexed to planes of Fe3O4 (JCPDS No.19-0629). For irradiated NCs (Fig. 1(c)–(d)), monotonic decrease in intensity of XRD peaks with an increase of irradiation dose can be caused by induced structural disordering, stress and defects [9,10]. Roomtemperature MH curves of NCs before and after SHI irradiation are shown Fig. 1(e). Table 1 lists saturation magnetisation (Ms) and coercivity (Hc) values for all NCs. Ms of 14.6 emu/g and Hc of 244 Oe are noted in pristine NC. The structural disorders and defects induced by SHI irradiation can increase number of grain boundaries, impede domain-wall motion and complicate magnetization reversal in Fe3O4 nanoparticles. Consequently, a monotonic fall in Ms and rise in Hc with an increase of irradiation dose can be recorded (Table 1) [13–15]. SEM micrographs of neat-PMMA, NGs, Fe3O4 nanoparticles, pristine and irradiated NCs are shown in Fig. 2. SEM and TEM images (Fig. 2(d)–(e)) observe heterogeneous distribution of aggregated NGs and Fe3O4 nanoparticles in pristine NC. SEM images of irradiated NCs (Fig. 2(f)–(k)) clearly demonstrate a monotonic

Table 1 Various important parameters of SHI beams, room-temperature magnetic properties, and MW absorbing properties of all NCs. Ion-beam with energy

Electronic energy loss (Se) (keV/lm)

Nuclear energy loss (Sn) (eV/lm)

Projected range of ion-beam (lm)

Fluence (ions/cm2)

Sample

Ms (emu/g)

Hc (Oe)

RLmin (dB)

tm (mm)

fm (GHz)

Bandwidth of RL  10 dB (GHz)

– C6+ (80 MeV)

– 247.3

– 133.9

– 198.9

O7+ (100 MeV)

443.7

246.7

148.1

– 1  1010 1  1011 1  1012 1  1010 1  1011 1  1012

Pristine C10 C11 C12 O10 O11 O12

14.6 14.2 12.7 11.4 13.9 12.5 10.9

244 273 361 448 296 394 472

11.5 16.5 18.9 26.2 15.1 21.1 32.4

2.0 2.0 2.2 2.3 2.0 2.1 2.3

14.2 14.5 12.5 11.9 14.5 13.8 12.9

2.5 4.4 4.6 5.5 4.2 5.1 6.8

Fig. 1. (a) Schematic representation of synthesis, SHI irradiation, and various microwave-absorption mechanisms of Fe3O4/NG/PMMA NCs. XRD patterns of (b) Pristine, (c) C6+(80 MeV) and (d) O7+(100 MeV) ions irradiated NCs. (e) MH loops for all NCs (inset shows enlarged MH loops).

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Fig. 2. SEM of (a) neat-PMMA (b) NGs (c) Fe3O4 nanoparticles. (d) SEM and (d) TEM of pristine NC. SEM of irradiated (d) C10 (e) C11 (f) C12 (g) O10 (h) O11 (i) O12 NCs.

improvement in distribution of nanofillers with an increase of irradiation dose (1  1010–1  1012 ions/cm2) for both SHI beams. According to thermal-spike model, projectile-ions create a nanometric cylindrical molten-zone (track) for few picoseconds, causing a steep rise in local temperature [9,10,13]. As a result, PMMA chains can effectively diffuse into galleries of NGs and Fe3O4 nanoparticles, generating a significant improvement in homogenization of nanofillers in irradiated NCs [9]. Fig. 3(a)–(c) show variation of complex permittivity and dielectric loss tangents (e00 =e0 ) with MW frequency for all NCs. SHI irradiated NCs demonstrate a monotonic increase of e0 , e00 and dielectric loss (Fig. 3(a)–(c)) with an increase in fluence from 1010–1012 ions/ cm2. Improved homogenization of nanofillers, delamination of NGs and evolution of defect centres, induced by SHI irradiation, can decrease electrical resistivity and increase e0 , e00 and dielectric loss of irradiated NCs [9,15]. Moreover, various electric dipoles (i.e., Fe3+, Fe2+, delocalised p-electrons, defect centres etc.) in NCs cannot follow the oscillations of applied MW signal, resulting in decrease of e0 (increase of e00 and dielectric loss) with MW frequency. Fig. 3(d)–(f) illustrate frequency dependent complex permeability and magnetic loss tangents (l00 /l0 ) for all NCs. After irradiation,

l0 decreases monotonically with an increase in irradiation dose from 1010–1012 ions/cm2, whereas opposite trend is noted in l00 (Fig. 3(d)–(e)). Consequently, the obvious monotonic rise in magnetic loss (Fig. 3(f)) can be assigned to induced structural disordering and pinning sites (defects) in irradiated Fe3O4 nanoparticles [13,14]. Frequency (f) dependent C 0 ¼ lðlÞ2 f curves (Fig. 3(g)) confirm that peaks in l‘‘ and magnetic loss spectra can be linked to natural magnetic resonance of Fe3O4 nanoparticles [7]. Moreover, the peak becomes broader and stronger with an increase of irradiation dose, suggesting greater magnetic energy loss in irradiated NCs [15]. The reflection loss (RL) of a single-layered NC is calculated by transmission-line theory using following equations [1–4,15]: 1

RL ðdBÞ ¼ 20log 10 rffiffiffiffiffiffi Z in ¼ Z 0

  Z in  Z 0 Z in þ Z 0



ð1Þ

pffiffiffiffiffiffiffiffiffiffi

l 2pjft l e tanh   c e

ð2Þ

where Zin, Z0, t and c are input impedance, free-space impedance, absorber thickness, and speed of MW, respectively.

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Fig. 3. (a) Real and (b) imaginary complex permittivity, (c) dielectric-loss, (d) real and (e) imaginary complex permeability, (f) magnetic-loss, (g) C0-f curve; (h), (i), (j) frequency and thickness dependent reflection loss for all NCs.

The frequency and thickness dependent RL of all NCs are presented in Fig. 3(h)–(j). The minimum reflection loss (RLmin) in pristine NC reaches 11.5 dB (92.9% MW-absorption). In contrast, RLmin of C6+ and O7+ SHI irradiated NCs reaches 26.2 dB (99.7% MW-absorption) and 32.4 dB (99.94% MW-absorption), respectively at irradiation dose of 1  1012 ions/cm2. Also, a significant improvement in effective bandwidth of absorption (for RL  10 dB) can be noted in irradiated NCs (Table 1). The excellent MW-absorption performance in irradiated NCs can be attributed to improved impedance matching, enhanced and synergistic effects between dielectric and magnetic losses. Impedance matching curves of all NCs, and a comparison of MW-absorption performances between this and previous reported works are presented in supplementary material. Table 1 lists various important parameters i.e., RLmin, RL  10 dB bandwidths, matching thickness (tm) and frequencies (fm) for all NCs. 4. Conclusions In summary, melt-blended Fe3O4/NG/PMMA nanocomposites were irradiated with SHI beams of C6+(80 MeV) and O7+(100 MeV) ions at varying fluences (1  1010–1  1012 ions/cm2). SHI irradiation improved the distribution of nanofillers as well as induced the structural disorders and defects in NCs. Nanocomposite irradiated at 1  1012 ions/cm2 fluence of O7+(100 MeV) SHI beam demonstrated strong (32.4 dB) and broadband (6.8 GHz) MWabsorption. The result suggest that SHI irradiation can be used as an effective technique to attain strong and broadband MWabsorption in light-weight Fe3O4/NG/PMMA NCs. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements Author, Prachi Yadav, acknowledges IUAC, New Delhi for SHI irradiation, SEM and XRD facilities. Prachi Yadav is thankful to Magnetics and Advanced Ceramics Laboratory, IIT Delhi, Delhi for measurements on VNA and SQUID magnetometer. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2019.06.053. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]

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