(716c) Extensional Relaxation Time, Pinch-Off Dynamics and Printability of Semi-Dilute Polyelectrolyte Solutions

Quantitative studies of capillary-driven thinning and pinch-off dynamics of semi-dilute polyelectrolyte solutions, and their response to extensional flows, typically encountered in drop formation applications, are relatively rare, and are the focus of this contribution. Here the pinch-off dynamics and extensional rheology of two model polyelectrolytes: poly (sodium 4-styrenesulfonate) (NaPSS) and poly(acrylic acid) (PAA) in two different solvents are characterized by using dripping-onto-substrate rheometry. Unlike shear relaxation time that decreases with increase in concentration in the unentangled, semi-dilute solutions, the extensional relaxation time of PAA solutions increases with an exponent of 1/2, and entangled solutions also exhibit a stronger concentration dependence of 3/2. In contrast, the extensional relaxation time is not measurable for the unentangled, semi-dilute aqueous NaPSS solutions, though entangled NaPSS solutions show concentration-dependent values. The experiments and analysis described herein elucidate how the interplay of stretching due to electrostatics and hydrodynamics influence extensional rheology response and printability of polyelectrolyte dispersions.