Eswaraiah et al. Nanoscale Research Letters 2011, 6:137 http://www.nanoscalereslett.com/content/6/1/137 Characterization The direct current (DC) volume electrical conductivity of the composites was measured at room temperature using homemade resistivity setup with the help of Keith- ley 2400 sourcemeter and 2182 nanovoltmeter. The high resistance of the films was measured with a 617 pro- grammable electrometer and a 6517B high-resistance electrometer. The EMI shielding measurement was per- formed with an Agilent E8362B vector network analyzer using a 201-point averaging in the frequency range of 8 to 12 GHz (X-band). Figure 1 shows the pictorial repre- sentation of the experimental setup for measuring the shielding effectiveness of the composite materials. Here, we followed the transmission line technique using an X- band waveguide sample holder for measuring scattering parameters of the composites. Samples of dimensions 22.84 × 10.16 mm2 were prepared and kept inside the waveguide. The EMI shielding effectiveness is defined as the ratio of incoming (Pi) to outgoing power (Po) of radiation. Shielding effectiveness (SE) = 10 log (Pi/Po) and is defined in decibels (dB). The higher the value in decibels, the less energy passes through the material. When electromagnetic radiation falls on the shielding material, reflection, absorption, and transmission are observed. The corresponding reflectivity (R), absorp- tivity (A), and transmissivity (T) are according to the equation A + R + T = 1. R and T can be calculated from the measured scattering coefficients, from the rela- tions S12 = 10 log T and S11 = 10 log R. The cross-sec- tional morphology of the composites were observed using field emission scanning electron microscope (FESEM, QUANTA 3 D, FEI) and transmission electron Page 3 of 11 microscope. X-ray elemental mapping was also per- formed using EDX genesis software. Powder X-ray dif- fraction (XRD) studies were carried out using X’Pert PRO, PANalytical diffractometer with nickel filter Cu Ka radiation as the X-ray source. The samples were scanned in steps of 0.016° in the 2θ range 10 to 80. For the determination of functional groups, a Fourier trans- form infrared spectrum was acquired using Perkin Elmer FTIR spectrometer from 400 to 4,000 cm-1. The chemical resistance of the composites in different acids, bases, alkanes and organic solvents was estimated by measuring the weight of the sample before and after treatment with these chemicals using METTLER TOLEDO XS 105 weighing balance. Results and discussion X-ray diffraction analysis The crystal structure of polymer, MNTs, and f- MWCNTs has been investigated by powder X-ray dif- fraction. Figure 2 shows the XRD pattern of the PVDF, f-MWCNTs, and MNTs. Figure 2a shows the XRD pat- tern of f-MWCNTs in which the peaks are indexed to the reflections of hexagonal graphite. The absence of additional peaks corresponding to the catalytic impuri- ties confirms that the impurities have been removed by the acid treatment. The XRD spectrum of the as-synthe- sized MNT is shown in Figure 2b. All the diffraction peaks can be indexed according to the a-MnO2 phase, and no other characteristic peaks from any impurity are observed. This establishes the high purity of the sample. In Figure 2c, it can be seen that pure PVDF membrane is crystalline in nature with visible peaks at 18.65° and Figure 1 Experimental setup for EMI shielding characteristic measurements of polymer composites.