Eswaraiah et al. Nanoscale Research Letters 2011, 6:137 http://www.nanoscalereslett.com/content/6/1/137 fluorine. Figure 7 shows the EDX spectra of PVDF- based MNTs and f-MWCNTs composite. It confirms the presence of manganese and oxygen from MnO2, car- bon from f-MWCNTs, and fluorine from the PVDF polymer. Figure 8 shows the elemental mapping of the 5 wt.% MNTs-1 wt.% f-MWCNTs-PVDF composite. As can be seen from the figures, all the elements were dis- tributed homogeneously in the polymer matrix. Chemical resistance of the polymer composites The percentage of chemical resistance of the composites in different acids, bases, organic solvents, and alkanes are shown in the Table 1. It indicates that all the poly- mer composites are highly resistant towards the chemi- cals. The MNT-MWCNTs-PVDF composite shows 95% to 100% resistance towards chemicals which indicates the potentiality of the present composite. For compari- son, the chemical resistances of MWCNT-PVDF, PVDF, and MNT-PVDF composites were also measured. Electrical conductivity analysis Electrical conductivity is of utmost importance for effec- tive EMI shielding material. As shown in the Figure 9, the conductivity of the PVDF is about 10-16S/m. As the concentration of the MNTs increases in the PVDF matrix, electrical conductivity increases, and it follows percolation behavior. Conductivity of the 1 wt.% MNTs/ PVDF composite was found to be approximately 10-6S/ m, which indicates that there is a drastic improvement in electrical conductivity. An increase of about ten Page 7 of 11 orders of magnitude of electrical conductivity was observed which can be attributed to the high aspect ratio and efficient dispersion of the MNTs in the PVDF matrix. Similar trend is observed in the case of electrical conductivity of the f-MWCNTs/PVDF composites as shown in Figure 9b. The possible mechanism for the increment in the electrical conductivity of the compo- sites can be the tunneling effect of the electrons from one nanotube to the other. The effect of f-MWCNTs content on the electrical conductivity of the MNTs/ PVDF composites was studied. Incorporation of 1 wt.% f-MWCNTs in 5 wt.% MNT/PVDF composites increases the conductivity from 10-5S/m to approximately 10-1S/m which can be attributed to the high aspect ratio, homo- geneous dispersion, and high electrical conducting nat- ure of the f-MWCNTs. Electromagnetic interference shielding effectiveness The EMI SE of MNTs/PVDF composites with various mass fractions of MNTs as a function of frequency are presented in Figure 10a. The results show that EMI shielding effectiveness of pure PVDF is almost 0.3 dB indicating that it is transparent to the electromagnetic radiation throughout the measured frequency. This is probably due to its electrically insulating nature. It is observed that EMI SE starts increasing with the addition of MNTs to the insulating PVDF matrix. The EMI SE for 1 wt.% MNTs filled PVDF composite is found to be 2.27 dB and it increases further to 5.14 and 11 dB at higher loading of MNTs of 3 and 5 wt.%, respectively. Figure 7 Energy dispersive X-ray spectra of MnO2 nanotubes and its composites.