Stretched Polymer Physics and Rheology for Future Foods and Sustainable Formulations

Stringiness, stickiness, and dispensing behavior of polymeric complex fluids are often assessed qualitatively by dripping from a nozzle or spoon or by stretching a liquid bridge between two surfaces (thumb and forefinger). The lifespan of pinching necks is determined by the response of polymers to extensional flows associated with streamwise velocity gradients that spontaneously arise within necks undergoing capillarity-driven pinching dynamics. In this contribution, we describe the stretched polymer hydrodynamics underlying observed rheological response and processing behavior of polymers used as rheology modifiers, focusing on designing sustainable formulations and future foods using various polysaccharides and polypeptides. In addition to dripping-onto-substrate (DoS) rheometry protocols we developed to visualize and analyze pinching dynamics of a columnar neck formed between a nozzle and a sessile drop and assess extensional rheology response, we describe recent progress in scaling theories, alternative rheometry protocols, and challenges in creating and curating a library of sustainable alternatives. We discover that our pursuit involves myriad, intertwined quests and insights into conformation-dependent hydrodynamic and excluded volume interactions, Pincus’ tension blobs, finite extensibility effects, coil-stretch transition and hysteresis, and polymer's flexibility, extensibility and segmental dissymmetry.