Executive Summary : | Despite extensive research in polymer solutions, several observations in flows remain unsolved. One such observation was made by sridhar and coworkers two decades ago, who found that polymer chains are not fully stretched and that the stretch decreases with increasing extensional rates. This contradicts theoretical and computational expectations from bead-spring models. Researchers believe that the origins of these observations lie in the presence of self-entanglements and knots in the polymer chains, which may become tighter in extensional flows instead of relaxing and prevent chains from reaching maximum extension. The uncrossability of chain segments may also play a significant role. Additionally, more knots may be generated when an equilibrium ensemble is subjected to flow fields. The current state-of-the-art polymer chain simulations are the bead-spring model, which is not sufficient to capture the effect of tight knots. Researchers have advocated for finely resolved chain models, down to a single Kuhn step, to better understand the effects of self-entanglements and knots on polymer chains and rheology in different flow fields. |