Enhancement in alternating current conductivity of polypyrrole by multi-walled carbon nanotubes via single electron tunneling

To enhance alternating current (ac) conductivity of polypyrrole (PPy), multi-walled carbon nanotubes (MWCNT) are used to prepare polypyrrole-multi-walled carbon nanotube (PMCN) composites. PPy synthesized by chemical oxidative polymerization and MWCNT prepared by arc discharge were mechanically mixed to prepare two PMCN composites of mass ratios 0.95:0.05 (PMCN-1) and 0.90:0.1 (PMCN-2) respectively. The FTIR studies confirmed strong interaction between PPy and MWCNT in the composites. Highly crystalline nature of PMCN-2 composite in which MWCNT is wrapped around by PPy confirmed from XRD, FESEM and TEM analyses. Significant increase in ac conductivity of PMCN-2 composite by four orders of magnitude due to greater increase in effective degree of electron delocalization in it confirmed. High values of real dielectric constant (epsilon') and dielectric loss (tan delta) at low frequency for PPy and the composites due to Maxwell-Wagner polarization, a semicircular complex plane impedance plot for PMCN-2 composite reminiscent of Debye model confirmed. Theoretical interpretation of charge transport mechanism in the composites as due to single electron tunneling as against that in PPy as due to hopping of polarons discussed thoroughly. Composites showing single electron tunneling type of charge transport have potential for production of multi functional semiconductor and superconducting devices.