Carboxyl-functionalized MWCNT doped poly(o-toluidine) nanohybrids: Synthesis, characterization with AC electrical and dielectric properties

Nanohybrids of protonic acid doped poly(o-toluidine) (POT) with carboxyl-functionalized multi-walled carbon nanotubes (MWCNT-COOH) were synthesized by in situ chemical oxidation polymerization in the absence of any added acid. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) showed that carboxylic groups had been introduced onto the surface of MWCNT. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that a thin layer of POT is well coated on the surface of MWCNT-COOH with a thickness of ∼19 nm. Based on π–π* electron and H-bonding interactions between functional groups of o-toluidine monomer and those of MWCNT-COOH, o-toluidine molecules were adsorbed and polymerized on the surface of nanotubes. AC conductivity and dielectric properties of POT/MWCNT-COOH nanohybrids were measured at 100 Hz–1 MHz and a temperature range of 25–125 °C. Upon increasing the concentration of MWCNT-COOH an increase in the AC conductivity, dielectric permittivity and loss tangent of host POT are observed. The presence of polarons and bipolarons are responsible for the frequency dependence of AC conductivity in these nanohybrids. The variation of AC conductivity with frequency has been described by the power law. The decrease in activation energy is observed with increasing concentration of MWCNT-COOH in the nanohybrids. The incorporation of 4 wt% MWCNT-COOH into POT matrix resulted in around ten-fold increase in dielectric permittivity with a negligible effect on loss tangent at 100 Hz. The permittivity is found to be stable up to 75 °C and then increase gradually with increasing temperature.