Unusual rheological effects observed in polyacrylonitrile solutions
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Unusual rheological effects have been revealed during the deformation of polyacrylonitrile (PAN) solutions in DMSO. The effects are observed during the study of rheological properties in a wide range of PAN concentrations and are explained by the structuring occurring at low polymer concentrations. At concentrations of at most 0.1%, the solutions exhibit the behavior of soft gels, which are characterized by yield stresses and frequency-independent storage moduli. As concentration is increased, both effects gradually vanish and the solutions are almost transformed into Newtonian liquids. The results have been explained by the formation of a supramolecular spatial structure at low polymer concentrations. As concentration is increased, the role of structuring is suppressed by the formation of a network of intermacromolecular entanglements. The ability of dilute PAN solutions to exist in two states, i.e., with destroyed structuring and in the form of a physical polymer gel, leads to stress self-oscillations and thixotropic effects. The addition of a precipitant (water) to the PAN-DMSO solutions leads to the formation of a gel throughout the concentration range.
KeywordsShear Rate Storage Modulus Polymer Science Series Apparent Viscosity Itaconate
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