Eswaraiah et al. Nanoscale Research Letters 2011, 6:137 http://www.nanoscalereslett.com/content/6/1/137 Table 2 Electrical conductivity and EMI SE of the polymer composites Composite 1 wt.% f-MWCNTs/PVDF 2 wt.% f-MWCNTs/PVDF 5 wt.% MNTs/PVDF 7 wt% f-MWCNTs/PVDF 5 wt.% MNTs/1 wt.% f-MWCNTs/PVDF 5 wt.% MNTs/2 wt.% f-MWCNTs/PVDF Electrical conductivity (S/m) Approximately 10-10 Approximately 10-1 Approximately 10-5 Approximately 10-1 Approximately 10-1 EMI SE (dB) Approximately 2 Approximately 7 Approximately 11 Approximately 18 Approximately 21 Approximately 10-1 Approximately 20 formulae mentioned in the experimental section. For 5 wt.% f-MWCNT-PVDF composites, the transmissivity, reflectivity, and absorptivity are 0.177, 0.601, and 0.222, respectively and the corresponding parameters for 7 wt.% f-MWCNT-PVDF composites are 0.131, 0.794, and 0.075. From these results, we can conclude that reflection is the major EMI shielding mechanism in the present f-MWCNT-PVDF composites. This may be due to the presence of conjugated π electrons on the surface of f-MWCNTs. In the case of MNTs/PVDF composites, the chances of absorbing incident radiation are more due to the presence of electric dipoles. Table 3 gives a comparison of the reflectivity and absorptivity of various composites. It is observed that f-MWCNTs/MNTs/ PVDF composites and MNTs/PVDF composites exhibit more absorption than reflection. For 5 wt.% MNTs/ 1 wt.% f-MWCNTs/PVDF composite, the absorptivity, transmissivity, and reflectivity values are respectively 0.78, 0.01, and 0.210. Based on the measured fundamen- tal properties of MNTs/PVDF, f-MWCNTs/PVDF, and MNTs/f-MWCNTs/PVDF composites, the present com- posites can be engineered for reflection to absorption of the incoming EM radiation by varying the amount of carbon nanotubes and MnO2 nanotubes in the polymer Table 3 Transmissivity, reflectivity, and absorptivity of MNTs/f-MWCNTs/PVDF composites Absorptivity Transmissivity Reflectivity Composite 1 wt.% f-MWCNTs/PVDF 2 wt.% f-MWCNTs/PVDF 5 wt.% f-MWCNTs-PVDF 7 wt.% f-MWCNTs-PVDF 5 wt.% MNT-PVDF 7 wt.% MNT-PVDF 5 wt% MNT-1 wt.% f-MWCNTs-PVDF 7 wt% MNT-1 wt.% f-MWCNTs-PVDF 0.042 0.218 0.222 0.075 0.530 0.608 0.780 0.796 0.631 0.199 0.177 0.131 0.1 0.1 0.01 0.01 0.327 0.583 0.601 0.794 0.370 0.292 0.210 0.194 Page 10 of 11 matrix. The incorporation of MNTs in f-MWCNT- PVDF composite helps in overcoming the Van der Waals forces between f-MWCNTs while utilizing the high aspect ratio of them. Another advantage of the addition of MNTs is that it could decrease the amount of f-MWCNT loading in PVDF matrix. Conclusion Novel hybrid nanofiller consisting of multiwalled carbon nanotubes and MnO2 nanotubesreinforced PVDF com- posite has been fabricated and proposed as an efficient material for EMI shielding applications. MNTs and f- MWCNTs acting as spacers in PVDF matrix helps in reducing the aggregation of the nanofillers and creates an excellent 3 D conducting network in the polymer. MNTs are acting as very good filler material when added to the entangled carbon nanotubes incorporated polymer. An EMI shielding effectiveness of approxi- mately 20 dB has been achieved with 5 wt.% MNTs and 1 wt.% f-MWCNTs in polymer matrix in X-band region. The increase in EMI shielding effectiveness with the addition of nanofillers is attributed to the enhanced electrical conductivity of the composite due to the addi- tion of f-MWCNTs and good homogeneity of the nano- fillers in the polymer. The present hybrid polymer nanocomposites are proposed as low-cost and efficient EMI shielding materials in X-band region. Acknowledgements This work was supported by IIT Madras and the authors thank the Department of Science and Technology (DST), India for financial support. One of the authors (V. ESWARAIAH) thanks Dr. Harishankar Ramachandran, professor, Microwave Lab, Department of Electrical Engineering, IIT Madras for helping in EMI shielding measurements. Author details 1Alternative Energy and Nanotechnology Laboratory (AENL), Nano Functional Materials, Technology Centre (NFMTC), Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India 2Low Temperature Physics Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India Authors’ contributions VER carried out the composites preparation, other characterizations and written the manuscript. VSN and SRP are conceived in its coordination. 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