Search

Nanocomposite films comprising of ion-conducting polymer electrolyte, multi-walled carbon nanotubes (MWCNT) as the electron-conducting network and ceramic (BaTiO3) as ferroelectric nanofiller have been synthesised for electromagnetic shielding application. XRD and dielectric studies of the synthesised BaTiO3 nanoparticles show a tetragonal structure and ferroelectric nature. The incorporation of nanofillers (MWCNT and BaTiO3) in the polymer electrolyte enhances the conductivity and dielectric property of the nanocomposites. Polymer nanocomposites with 7.5 wt% of BaTiO3 nanoparticles have exhibited the highest shielding effectiveness (SET) ~ 81 dB in the X-band (8–12 GHz). This enhancement in SE can be attributed to the (1) formation of micro-capacitors and interconnected network provided by MWCNTs, (2) spontaneous polarisation of BaTiO3 and its volumetric effect on the polymer nanocomposites and (3) leakage current due to the ions of the electrolyte which results in dielectric loss.

Electromagnetic interference shield materials which are multicomponent polymer nanocomposites consisting of insulating polymer matrix of poly (vinylidene fluoride-hexafluoropropylene) (PVdF-HFP), organic/inorganic salts, electron-conducting nanofillers (MWCNTs), and insulating superparamagnetic nanoparticles (Fe3O4), have been studied. It has been found that the introduction of the salts and nanofillers in PVdF-HFP not only improves the conducting nature and skin depth of the polymer nanocomposites but also keeps the composite films thermally stable up to ~ 200 °C. Changes in the surface morphology on addition of each individual constituent have been evidenced by scanning electron microscopy. The rheological study shows the plasticization effect of organic/inorganic salts as well as provides a good estimation of the polymer–particle interaction in the polymer nanocomposites. Furthermore, effect of organic/inorganic salts and interaction between the polymer and the fillers (MWCNTs and Fe3O4) has also been observed in differential scanning calorimetry in terms of lowering of glass transition temperature (leading to enhanced flexibility). The stress versus strain behavior has shown specific interactions among different constituents of the shield material.

Polymer nanocomposites consisting of poly(vinylidenefluoride-co-hexafluoropropylene) PVdF-HFP, inorganic salt (LiBF4), organic salt (EMIMBF4), multiwalled carbon nanotubes (MWCNTs), and Fe3O4 nanoparticles were prepared as electromagnetic shield material. Improvement in conductivity and dielectric property due to the introduction of EMIMBF4, LiBF4, and MWCNTs was confirmed by complex impedance spectroscopy. The highest conductivity obtained is ∼1.86 mS/cm. This is attributed to the high ionic conductivity of the ionic liquids and the formation of a connecting network by the MWCNTs facilitating electron conduction. The total electromagnetic interference (EMI) shielding effectiveness has a major contribution to it due to absorption. Although the total shielding effectiveness in the Ku band (12.4-18 GHz) of pure ion-conducting system was found to be ∼19 dB and that for the polymer composites which are mixed (ion + electron) conductors is ∼46 dB, the contributions due to absorption are ∼16 and ∼42 dB, respectively.

Fenugreek ( Trigonella foenum-graecum ), an important spice crop belongs to the family Fabaceae. India is the largest producers as well as the largest exporter of fenugreek. Five common fenugreek varieties of India were included in this study for molecular analysis. For randomly amplified polymorphic DNA (RAPD) analysis, a total of 47 bands in the size range of 200 to 5000 bp were produced by examining across genotypes with 9 RAPD primers, with an average polymorphism of 62.4%. Total numbers of bands ranged from 3 (U407) to 7 (OPB-15). With 17 fluorescently labeled amplified fragment length polymorphism (AFLP) primer combinations (PCs), a total of 669 peaks in the size range of 50 to 538 bp were amplified. Total numbers of bands ranged from 21 (E-AAC/M-CT) to 60 (E-AAC/M-CAC). The mean genetic diversity (Nei's 1973) across all loci was found to be 23.83 and 2.1% with RAPD and AFLP markers, respectively. In all the fenugreek varieties, a total of 25 variety-specific AFLP markers were found. Phylogenetic trees among 5 plant varieties were constructed based on Nei's coefficient standard genetic distances using unweighted pair group method with arithmetic mean (UPGMA) method. For RAPD and AFLP analysis, Gujarat Methi-1 (GM-1) and Gujarat Methi-2 (GM-2) clustered together showed more similarities than other varieties. In fenugreek, RAPD markers were found more polymorphic than AFLP markers. RAPD markers also showed more diversity in comparison to AFLP markers, although the data generated for AFLP markers were more authenticated and reproducible than RAPD markers. Key words : AFLP, RAPD, genetic diversity, automated genetic analyzer, polymorphism.