Impacts of polymer/surfactant interactions on spray drift

Polymers and surfactants are commonly used as adjuvants in agrochemical spray solutions. In this study, we probe the effects of changes in steady state polymer chain conformation (as a result of surfactant addition) on the physical properties of dilute polymer solutions and the resulting spray performance when such solutions are processed through a commercial spray nozzle. To create a panel of model adjuvant formulations for spraying, we added either an associative (sodium dodecyl sulfate (SDS)) or non-associative (Tween20 (polysorbate20)) surfactant, over a range of concentrations, to a base dilute Poly(ethylene oxide) (PEO) solution. The addition of the associative SDS to the PEO solution decreased the dynamic surface tension, slightly increased the zero shear viscosity and substantially increased the extensional properties of the solutions, with a strong dependency on SDS concentration. Under the high deformation processes experienced in a spray nozzle, the addition of SDS shifted the droplet size distribution to larger droplet sizes, and substantially reduced the spray drift. No such changes were seen for the non-associative PEO/Tween20 system. The changes in the dynamics of extension of the PEO chains induced through the association of a surfactant were found to be the dominant effector dictating spray performance.