Exploring rheological properties of aqueous polyaniline-PVP dispersion

Abstract

Stable aqueous dispersion of polyaniline (PAn) stabilized by a hydrophilic polymer poly(vinyl pyrrolidone) (PVP) exhibits interesting rheological properties different from its components. Shear thinning observed for both PVP and PAn-PVP colloid (PP) indicates partially entangled nature of the later. Linear viscoelastic response of PVP solution exhibit strong frequency dependence of elastic (G') and viscous (G) modulus over the whole frequency range (0.1-100 ras/s) where G' never exceeds G indicating the applicability of the Rouse-Zimm model to this system. On the other hand, there is a crossover of G' and G in the rheological profile of PP dispersion so that a single relaxation time model can be applicable. Therefore, PVP presents an entangled polymeric system and supposed to have a spectrum of relaxation times, whereas PP resembles to a physically crosslinked system with a single relaxation time. Increasing the extent of hydrogen bonding within the system (by raising the fraction of PAn or by leaving the solution undisturbed for long) relaxation time also becomes longer. The large difference in values of steady and complex shear viscosity (η and η*) within LVE regime reflects that original Cox-Merz rule is obviously inapplicable to these systems. But at larger strain amplitude, η and η* are satisfactorily coincident that indicates a broader applicability of the modified Cox-Merz rule.