Rheological Behaviour of Polyacrylonitrile in an Ionic Liquid Solution

The ionic liquid of 1-butyl-3-methyl-imidazolium bromide ([BMIM]Br) was used asa good solvent to dissolve polyacrylonitrile (PAN). In order to systematically studythe rheological properties of PAN/[BMIM][Br] solutions, the shear rheology ofPAN/[BMIM][Br] solutions with a concentration range of 3.0-6.0 wt% was investigatedby measuring the complex and dynamic moduli at different temperatures. The effectsof solution concentration and temperature on the complex viscosity of PAN/[BMIM][Br]solutions were studied. The solutions exhibited shear-thinning behaviours. Thecomplex viscosity of solutions increased with increase in solution concentration. Theheightening of solution temperature lowers the complex viscosity of the solution. Thenthe storage modulus, G′, and loss modulus, G′′, influenced by the PAN concentrationare 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 isincreased. Master curves are generated for complex viscosity by employing Carreauand Cross models to fit the experimental data. Both Carreau and Cross models yieldgood shifted curves for the complex viscosity. The activation energy for each solutionconcentration was calculated from the Arrhenius plots of the shift factors with respectto temperature. The activation energy for PAN/[BMIM][Br] solutions varies between4.79 and 8.88 kJ/mol, being slightly higher for the Cross model. The activation energyis 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, inwhich PAN molecules are independent of each other without any intermolecularentanglement.