Rheological Behaviour of Polyacrylonitrile in an Ionic Liquid Solution

The ionic liquid of 1-butyl-3-methyl-imidazolium bromide ([BMIM]Br) was used as a good solvent to dissolve polyacrylonitrile (PAN). In order to systematically study the rheological properties of PAN/[BMIM][Br] solutions, the shear rheology of PAN/[BMIM][Br] solutions with a concentration range of 3.0-6.0 wt% was investigated by measuring the complex and dynamic moduli at different temperatures. The effects of solution concentration and temperature on the complex viscosity of PAN/[BMIM][Br] solutions were studied. The solutions exhibited shear-thinning behaviours. The complex viscosity of solutions increased with increase in solution concentration. The heightening of solution temperature lowers the complex viscosity of the solution. Then the storage modulus, G', and loss modulus, G", influenced by the PAN concentration are discussed. Both G' and G" are increased with the increasing in PAN concentration. The crossover frequency of G' to G" is shown to decrease as the concentration is increased. Master curves are generated for complex viscosity by employing Carreau and Cross models to fit the experimental data. Both Carreau and Cross models yield good shifted curves for the complex viscosity. The activation energy for each solution concentration was calculated from the Arrhenius plots of the shift factors with respect to temperature. The activation energy for PAN/[BMIM][Br] solutions varies between 4.79 and 8.88 kJ/mol, being slightly higher for the Cross model. The activation energy is increased with the increase in PAN concentration. It can be summarized that 3-5 wt% range of PAN/[BMIM][Br] solution concentrations are considered as dilute solutions, in which PAN molecules are independent of each other without any intermolecular entanglement.