Transition to the viscoelastic regime in the thinning of polymer solutions

In this study, we investigate the transition between the Newtonian and the viscoelastic regimes during the pinch-off of droplets of dilute polymer solutions and discuss its link to the coil-stretch transition. The detachment of a drop from a nozzle is associated with the formation of a liquid neck that causes the divergence of the local stress in a vanishingly small region. If the liquid is a polymer solution, this increasing stress progressively unwinds the polymer chains, up to a point where the resulting increase in the viscosity slows down drastically the thinning. This threshold to a viscoelastic behavior corresponds to a macroscopic strain rate. In the present study, we characterize the variations of with respect to the polymer concentration and molar weight, to the solvent viscosity, and to the nozzle size, i.e., the weight of the drop. We provide empirical scaling laws for these variations. We also analyze the thinning dynamics at the transition and show that it follows a self-similar dynamics controlled by the time scale (epsilon)over dot(c)-1. This characteristic time is different and always shorter than the relaxation time of the polymer.

Automated summary

This study investigates the transition from Newtonian to viscoelastic behavior during the pinch-off process of droplets in dilute polymer solutions and explores its connection to the coil-stretch transition in polymer chains. The detachment of a droplet from a nozzle leads to the formation of a liquid neck, causing a localized increase in stress. In polymer solutions, this stress gradually unwinds the polymer chains until the viscosity increases significantly, resulting in a slowdown of the thinning process. This threshold for viscoelastic behavior corresponds to a macroscopic strain rate. The study characterizes the variations of this transition with respect to polymer concentration, molar weight, solvent viscosity, and nozzle size. Empirical scaling laws are provided for these variations. The thinning dynamics at the transition are also analyzed, revealing a self-similar behavior controlled by a characteristic time which is different and shorter than the relaxation time of the polymer.