Agricultural spray drift control via extensional rheology and viscoelastic pinching*

Controlling the drop size distribution of agricultural sprays is a long-standing challenge that has economic, environmental and health implications due to phenomena such spray drift and retention. Despite the growing utilization of polymer additives as rheology modifiers, the role of viscoelasticity on sprayability is not well understood. Here, we examine the relationship between spray drift and the shear and extensional rheology of aqueous solutions containing ultrahigh molecular weight neutral and charged polymer adjuvants. We characterize the viscoelastic behavior of these solutions using Dripping-onto-Substrate (DoS) rheometry, which allows us to quantify extensional rheology even at very low concentrations. We investigate the link between polymer physics, rheological properties of their solutions, and the resultant spray attributes to achieve smart design of chemical additives for spray applications