Studies are being carried out actively to relate the structure of polymers to rheological properties, including the complex viscosity coefficient and the normal stress difference of polymer liquids, which are the most fundamental physical quantities in rheology. Previously, Rigid Dumbbell theory was used to investigate the rheological properties of viscoelastic materials. However, as the structure of various polymers in liquids has been recently known and the discussion has been further extended, it has been found that this theory cannot accurately explain the properties related to polymer structure orientation. Therefore, we proposed a new model to overcome the drawbacks of the previous theory and take into account polymer orientation, and worked on the rotarance theory that could be applicable in various rheological flows.
Though our work on rotarance theory is motivated mainly by basic theoretical investigation, its practical implication has not escaped our attention. In polymer molding, for instance, the polymer orientation developed during flow, is frozen into plastics parts. The more rapidly the orientation relaxes before freezing, according to the results of our calculation, the less it will be frozen. Stresses frozen into plastics parts cause shrinkage and warpage and compromise the durability or longevity.
The research result has been published in "Physics of Fluids" [ 36,073110 (2024) ] under the title of "Stress Relaxation Following Sudden Cessation of Steady Shearing from Polymer Rotarance Theory"(https://doi.org/10.1063/5.0218742).
