Macromolecular Engineering of Rheology and Pinching Dynamics of Formulations

Formulations for personal care products, paints and coatings, and food products are common examples of multicomponent fluids containing a mixture of polymer, amphiphiles, and particles as additives. Hydrophobic stickers, charged micelles, and charged particles provide hydrophilic, flexible polymers with temporary, dynamic junctions that change with polymer concentration and deformation. Macromolecular engineering of formulations typically relies on the characterization of response to shear flow, with velocity gradients perpendicular to flow direction, emulating processing flows through channels and drag flows near moving solid surfaces. However, extensional rheology characterization has remained a longstanding challenge, even though streamwise velocity gradients associated with extensional flows, often arise during processing, especially during dispensing and liquid transfer (e.g., dripping, jetting, or spraying). In this contribution, we examine the influence of dynamic associations on macromolecular dynamics and formulation rheology in response to both shear flows and extensional flows using torsional rheometry and dripping-onto-substrate (DoS) rheometry, respectively. We find that dynamic associations help to tweak the rate-dependent rheological response, to facilitate easier dispensing and coating, and better sagging, leveling, and storage while reducing misting and stringiness.