Quantifying the effect of extensional rheology on the retention of agricultural sprays

In pesticide and fertilizer applications, retention of spray droplets after they reach the target surface can be limited by droplets splashing, rebounding, or rolling off of the surface. In this study, a novel approach is presented for quantifying the retention efficiency. This approach enables testing of the influence of polymer additives for enhancing the retention efficiency of both real and model agricultural sprays. The results demonstrate that increasing the extensional rheology of the spray solution can increase the retention efficiency by up to 20% and in some cases achieve a total efficiency greater than 95%. The results are consistent on both synthetic surfaces and plant surfaces and suggest that for a particular polymer and surface, the extensional relaxation time alone is sufficient to predict the retention efficiency.