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

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 degrees 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 similar to 4% concentration (percolation threshold). ac-Conductivity increases with increase in PANI-DNNSA0.5 concentration studied here for each frequency. At lower frequency (<10(5) Hz) ac-conductivity increase slowly with frequency but at higher frequency (>10(5) Hz) the increase is large having a curve like behavior. The gel state shows an increase of module by similar to 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. (C) 2010 Elsevier B.V. All rights reserved.