Rheology and molecular interactions in polyacrylonitrile solutions: Role of a solvent

Abstract

We examined the rheological properties of polyacrylonitrile (PAN) solutions in seven solvents over a wide range of shear rates. These solutions were characterized using the Hansen solubility parameter. The viscosity of these dilute solutions was primarily determined by this parameter. However, above the crossover point (at c[η] > 0.7) not only viscosity but also nature of the solvents was found to be an important factor. At high polymer concentrations, certain solutions showed gelation tendency.This study aims to determine a correlation between the rheological properties of the solutions and the affinity of the solvent with PAN. These correlations are present for an intrinsic viscosity (or the Huggins constant), a second virial coefficient, and solubility parameter. However, in certain cases, experimental points do not correspond to general dependence. This is also observed for these solutions when presenting the data of viscoelastic measurements in G′–G″ coordinates: certain points deviate from the general dependence.A detailed infrared spectroscopy analysis has been used for examining these experimental results. It has been shown the water presence in the solvents and polymer solutions even than anhydrous solvents were used. Water presence tend to a solvent–water associate formation in the solutions. The solubility of PAN in these solvents and the gelation tendency depends on the polymer concentration, in addition to the structure and stability of the polymer–water associates. The experimental results obtained and the reported correlation made it possible to develop a subsequence of solvents used as per their affinity with PAN. The charactristics of dilute solutions were compared with the rheological properties of moderately concentrated solution.