Eswaraiah et al. Nanoscale Research Letters 2011, 6:137 http://www.nanoscalereslett.com/content/6/1/137 Page 4 of 11 Figure 2 X-ray diffractograms of f-MWCNTs, MNTs, and PVDF. 20.09°. The sharp peak at 20.09° can be attributed to the presence of b-polymorph. Fourier transform infrared analysis Figure 3 shows the FTIR spectra of purified and functio- nalized MWCNTs (f-MWCNTs). The broad absorption band at 3,438 cm-1 is attributed to the hydroxyl group (νOH). The asymmetric and symmetric stretching of CH bonds are observed at 2,927 and 2,853 cm-1, respectively and the stretching of C = O of the carboxylic acid (-COOH) group is observed at 1,734 cm-1. The stretch- ing of C = C, O-H bending deformation in -COOH and CO bond stretching in the f-MWCNTs are observed at 1,635 cm-1; 1,436 cm-1; and 1,073 cm-1; respectively indicating that carboxyl and hydroxyl functional groups were attached to the surface of MWCNTs. Raman spectra analysis Figure 4 shows the Raman spectra of purified and func- tionalized MWCNTs. The spectra consists of three main peaks. The peak at 1,343 cm-1 is assigned to the defects and disordered graphite structures, while the peaks at 1,586 cm-1 and 2,693 cm-1 are attributed to the graphite band which is common to all sp2 systems and second- order Raman scattering process, respectively. Intensity ratio of defect band and graphite band is a signature of the degree of functionalization of the MWCNTs. As seen from Figure 4, ID/IG of pure carbon nanotubes is 0.868 whereas that for functionalized carbon nanotubes is 0.928 indicating the more defective nature of f- MWCNTs. Morphology and composition analysis Morphology is an important factor which affects the EMI SE of the composites. Figure 5a, b, c, d, e, f shows the FESEM images of polymer, nanofillers and nanofiller reinforced polymer composites. The corresponding images are (a) pure PVDF, (b) f-MWCNTs, (c) pure MNTs, (d) 1 wt.% MNTs-PVDF composite, (e) 2 wt.% MNTs-PVDF composite, and (f) high resolution image of 2 wt.% MNTs-PVDF composite. As shown in the Figure 5b andc, MWCNTs are 30 to 40 nm in diameter and approximately 10 μm in length and MNTs are 50 to 70 nm in diameter and in micron length. It can be observed that MWCNTs are entangled with each other because of Van der Waals interactions, whereas manga- nese dioxide nanotubes were straight and rigid and PVDF shows smooth surface as shown in the Figure 5a. f-MWCNTs and MNTs were homogeneously distributed and embedded in the PVDF matrix as shown in Figure 6a, b, c, d, e, f due to ultrasonication and shear mixing of the solutions at high rpm in the formation of compo- site films. Figure 6d, e, f indicates that the space between filler aggregates in carbon nanotube-PVDF composites is much smaller than that of MNTs-PVDF composites. Figure 6e shows the FESEM image of 5 wt.