Electromagnetic shielding effectiveness and mechanical properties of N,S co-doped carbon/PVDF nanocomposite films
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摘要: 日益严重的电磁辐射迫切需要高性能的电磁干扰屏蔽材料。杂原子掺杂的碳材料能够通过电荷密度的重新分布感应产生电偶极子，改善极化损耗和传导损耗，增强电磁屏蔽效能(EMI SE)。以亚甲蓝(MB)为氮、硫及碳源，多壁碳纳米管(MWCNTs)为导电骨架及加热层，通过微波炭化制备了N, S共掺杂碳，并与聚偏氟乙烯(PVDF)复合制备了PVDF纳米复合膜。考察了MWCNTs与MB的质量比、复合膜厚度及N, S共掺杂碳填充量对屏蔽性能的影响，由于纳米复合膜具有较好的阻抗匹配性及极化损耗和传导损耗共同作用的电磁干扰屏蔽机制，当MWCNTs和MB的质量比为1∶1时制备的复合膜(厚度为0.9 mm，填充量为20 wt.%)在X波段(8.2-12.4 GHz)具有43.21 dB-45.20 dB的屏蔽性能。此时，通过纳米压痕系统在应变率0.05 s−1下测得复合膜的硬度和弹性模量分别为0.25 GPa和3.60 GPa。Abstract: High performance EMI shielding materials are urgently needed for the increasing electromagnetic radiation. Heteroatom-doped carbon materials are capable of inducing the generation of electric dipoles through the redistribution of charge density, improving polarisation loss and conduction loss, and enhancing electromagnetic shielding effectiveness (EMI SE). N, S co-doped carbon was prepared by microwave carbonization using methylene blue (MB) as nitrogen, sulphur and carbon source, and multi-walled carbon nanotubes (MWCNTs) as conductive backbone and heating layer, and PVDF nanocomposite film was prepared by composite with polyvinylidene fluoride (PVDF). The effects of the mass ratio of MWCNTs to MB, the thickness of the composite film and the filling amount of N, S co-doped carbon on the shielding performance were investigated. Due to the nanocomposite film's good impedance matching and the electromagnetic interference shielding mechanism of polarisation and conduction losses, the composite film prepared when the mass ratio of MWCNTs to MB is 1∶1 (thickness of 0.9 mm, filling amount of 20 wt.%) had a shielding performance of 43.21 dB-45.20 dB in the X-band (8.2-12.4 GHz).At this point, the hardness and modulus of elasticity of the composite film were measured to be 0.25 GPa and 3.60 GPa, respectively, by a nanoindentation system at a strain rate of 0.05 s−1.
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Key words:
- N /
- S co-doped /
- electromagnetic shielding /
- mechanical properties /
- microwave carbonization
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图 1 N, S共掺杂碳/PVDF纳米复合膜的制备流程图
Figure 1. Flow chart of N, S co-doped carbon/PVDF nanocomposite membrane preparation
图 2 (a) 不同微波功率和时间条件下N,S共掺杂碳的FTIR; (b) PVDF纳米复合膜的FTIR
Figure 2. FTIR of (a) all microwave time powers of N,S co-doped carbon and (b) PVDF nanocomposite films
图 3 不同投料比、微波功率和时间条件下的N, S共掺杂碳样品的SEM图: (a) MWCNTs; (b) MWCNTs∶MB=1∶1, 800 W 90 s; (c) MWCNTs∶MB=1∶1, 1000 W 90 s; (d) MWCNTs∶MB=1∶1, 1000 W 120 s; (e) MWCNTs∶MB=2∶1, 1000 W 90 s; (f) MWCNTs∶MB=1∶2, 1000 W 90 s; (c1) c的局部放大图; (c1’-c1’’’) c1的元素映射图像
Figure 3. SEM images of N, S-codoped carbon samples with different feeding ratios, microwave power and time conditions: (a) MWCNTs; (b) MWCNTs∶MB=1∶1, 800 W 90 s; (c) MWCNTs∶MB=1∶1, 1000 W 90 s; (d) MWCNTs∶MB=1∶1, 1000 W 120 s; (e) MWCNTs∶MB=2∶1, 1000 W 90 s; (f) MWCNTs∶MB=1∶2, 1000 W 90 s; (c1) a locally enlarged image of c; (c1’-c1’’’) the elemental mapping image of c1
图 4 (a) PVDF; (b) PVDF2-10; (c)PVDF2-20; (d)PVDF2-25分别为PVDF纳米复合膜的表面SEM图像; (e-l)分别为相应截断面的SEM图像及局部放大图像
Figure 4. (a) PVDF; (b) PVDF2-10; (c) PVDF2-20; and (d) PVDF2-25 are the surface SEM images of the PVDF nanocomposite film, respectively; (e-l) are the SEM images of the corresponding truncated surfaces and the local magnification images, respectively
图 5 当MB与MWCNTs的质量比为1∶1时所得N, S共掺杂碳的(a) XPS测量光谱和(b) C 1s; (c) N 1s; (d) S 2p高分辨率光谱
Figure 5. (a) XPS survey spectrum and high-resolution scan for (b) C 1s; (c) N 1s; (d) S 2p of N, S co-doped carbon obtained when the mass ratio of MB to MWCNTs is 1∶1
图 6 PVDF纳米复合薄的EMI SE(a)不同微波条件；(b)不同投料比；(c)不同填充量和(d)不同厚度；PVDF2-20(厚度0.9 mm)纳米复合膜的(e) SER、SEA和SET和(f) R,A
Figure 6. EMI SE of PVDF nanocomposite films (a) different microwave conditions; (b) different feeding ratios; (c) different filler amounts and (d) different thicknesses.PVDF2-20 (thickness 0.9 mm) nanocomposite films of (e) SER, SEA and SET and (f) R,A
图 7 PVDF纳米复合膜的(a) 代表性载荷-位移曲线; (b) 弹性模量-硬度
Figure 7. (a) Representative load-displacements; (b) Elastic modulus and hardness of PVDF nanocomposite films
表 1 不同投料比、微波功率和时间条件下的N, S共掺杂碳/PVDF纳米复合膜样品
Table 1. The samples of N, S co-doped carbon/PVDF nanocomposite films under different feed ratios, microwave power and time conditions
Samples MWCNTs:MB MWCNTs/mg MB/mg Microwave power/W Microwave
time/sPVDF1-Y 1∶1 20 20 800 90 PVDF2-Y 1∶1 20 20 1000 90 PVDF3-Y 1∶1 20 20 1000 120 PVDF4-Y 1∶2 10 20 1000 90 PVDF5-Y 2∶1 20 10 1000 90 Notes：MWCNTs—Multi-walled carbon nanotubes; MB—Methylene blue; PVDF—Polyvinylidene fluoride; The prepared composite membranes were named PVDFx-Y (x is the corresponding sample label under different conditions in Table 1, and Y is the mass filling amount of N, S co-doped carbon in the PVDF matrix), e.g., PVDF2-20 denotes the composite membranes prepared when Sample 2 was filled with 20 wt.% in the PVDF matrix. 
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