(607e) Influence of Flexibility, Extesibility, Segmental Disymmetry and Charge on Pinching Dynamics, Coil-Stretch Transition, and Rheology of Polymer Solutions

We elucidate the influence of chemical structure on macromolecular hydrodynamics, rheological response and pinching dynamics underlying drop formation/ liquid transfer using polyethylene oxide (PEO), and 2-hydroxyethyl cellulose (HEC) as two neutral polymers with distinct Kuhn length and matched overlap concentrations. We contrast the filament pinching dynamics and extensional rheology response using Dripping-onto-Substrate (DoS) rheometry protocols. Even though dilute aqueous solutions of both polymers at matched concentrations diplay comparable shear viscosity, the PEO solutions exhibit distinctively higher values of extensional relaxation time, extent of strain hardening, and transient extensional viscosity, as well as an overall delay in pinch-off. We critically analyze the radius evolution for a pinching filament to posit that the solutions of flexible PEO macromolecules exhibit signatures of underlying coil-stretch transition and hysteresis manifested as a discontinuous, non-monotonic variation in extensional rate. In contrast, the solutions of semi-flexible HEC show a monotonic increase in extensional rate in response to rising interfacial stress in pinching filament, implying that the macromolecules undergo progressive stretching and orientation without coil-stretch transition or hysteresis. We show that the chemistry-dependent contrast in macromolecular dynamics and extensional rheology response can be characterized a prioriin terms of three ratios: contour length to Kuhn length (flexibility), contour length to unperturbed coil size (extensibility), and packing length to Kuhn length (a parameter we term as segmental dissymmetry). Additionally, we probe the pinching dynamics and rheology response of two model polyelectrolyte solutions to eludiate the influence of electrostatic-induced stretching on polymer dynamics and processability.