Emergent Interpolymer Interactions in Flowing Polymer Solutions

Polymer solutions are ubiquitous across biological, healthcare, and industrial processes. When subjected to sufficiently high deformation rates, polymer chains transition from their equilibrium coiled state to a flow-induced stretched configuration, giving rise to distinctive flow behaviors often associated with stringiness, sliminess, and stickiness. While interactions between coiled polymers at equilibrium are relatively well understood, those between flow-stretched chains continue to raise fundamental questions, introducing uncertainty in how they should be accounted for. Despite decades of research, experimental efforts to infer these emergent interactions under flow have proven challenging, often yielding contrasting interpretations of their role. In this Viewpoint, we revisit classical experiments through the lens of recent studies. We outline the principal frameworks used to describe the onset of interpolymer interactions under flow and offer a unified perspective on the conditions under which such interactions are likely to emerge.