Viscoelastic and conductivity properties of thermoreversible polyaniline-DNNSA gel in m-cresol

Abstract

The rheological behavior of polyaniline (PANI)-dinonylnaphthalene sulfonic acid (DNNSA) in m-cresol is studied for different weight percent (w/v) of PANI-DNNSA_0.5. From rheological viewpoint the sample behaves like viscous fluid at low concentration (2 wt%) and gel at the concentration ≥8 wt%. The 4 wt% PANI-DNNSA_0.5 in m-cresol is at typical viscoelastic percolation region which is sol in the absence of shear but show invariant storage modulus with frequency at 30 °C. SEM picture indicates fibrillar network structure in the gel and the doped polyaniline remain as nanofiber at ≤2 wt% concentrations. The complete doping of PANI in all the systems is confirmed from UV-vis spectra. The dc conductivity of the gel increases with increasing the concentration of PANI-DNNSA_0.5 in m-cresol showing a jump at ~4% concentration (percolation threshold). ac-Conductivity increases with increase in PANI-DNNSA_0.5 concentration studied here for each frequency. At lower frequency (< 10⁵ Hz) ac-conductivity increase slowly with frequency but at higher frequency (> 10⁵ Hz) the increase is large having a curve like behavior. The gel state shows an increase of module by ~5 orders and also an increase of ~3 orders in ac-conductivity at the same frequency. The impedance spectroscopy results suggest the formation of combined resistance and capacitance (R-C) circuits in the gel and the increase of PANI-DNNSA_0.5 in the gel increases the capacitive feature more dominantly though the path becomes less resistive. The process also signifies the preparation of DNNSA doped PANI nanofiber in the gel medium.