(195m) Macromolecular Engineering of Rheology and Pinching Dynamics of Formulations

The current state-of-the-art practice in macromolecular engineering of formulations is to rely on the characterization of response to shear flow, with velocity gradients perpendicular to flow direction, for evaluating and understanding the influence of macromolecules on stability, rheology and processability, and applications. Understanding shear rheology response has direct relevance to control of flows through channels as well as drag flows near moving solid surfaces. However, streamwise velocity gradients associated with extensional flows often arise during processing of formulations, but unlike shear rheology, measurement of extensional rheology response has remained a longstanding challenge. In particular, dispensing and liquid transfer to substrates by dripping, jetting, or spraying involve capillarity-driven pinching of liquid necks with strong extensional flows, and most conventional techniques fail to emulate the deformation history and strain rates, or are unsuitable for characterizing low viscosity, low elasticity fluids. In this contribution, we show dripping-onto-substrate (DoS) rheometry protocols that we recently developed help to address these characterization challenges. We demonstrate that characterization of pinching dynamics and extensional rheology response allows a comprehensive examination of interactions between macromolecules in presence of associative groups/molecules or particles, and consequently better understanding of material properties that must be controlled or optimized formacromolecular engineering of formulations.