(421e) Characterization of Drop Impact of Oil-in-Water Emulsions on Spinach Leaf

Synthetic pesticides have been widely used in production agriculture to control pests and protect crops from yield losses and reduction in quality. However, their overuse is polluting land and water resources and may cause food safety issues to humans and animals. Therefore, the replacement of synthetic pesticides with natural alternatives, such as biopesticides produced from phytochemicals and essential oils (EOs), is a growing trend in the food and agriculture area. Nano-emulsions have been reported to improve the stability and bioactivity of EOs. However, very little is known about the behavior of spray droplets of novel nano-emulsion-based pesticides. The goal of this research is to understand the mechanisms of individual micro-sized droplets impacting the surface of a plant leaf (spinach), which is the first step to improving spraying efficiency of novel pesticides.

Drop impact of oil-in-water emulsions with varying concentrations will be recorded using a high-speed camera. Videos will be analyzed to observe the slow-motion physics of droplets directly impacting the surface of a spinach leaf and droplets impacting pre-existing droplets on the leaf. Any physical changes to the spinach leaf will indicate the efficacy of a formulation. These physical changes will be correlated with the physicochemical properties of the droplet, characterized by dimensionless numbers such as Weber number (We) and Reynolds number (Re). Preliminary results show that various emulsion formulations will have different effects on the surface of spinach leaf. High essential oil concentrations (>0.5%) can be phytotoxic and damage the target plant. Adjusting the ratio of oil to water in an emulsion droplet will affect its physicochemical properties, such as viscosity and surface tension, which will in turn affect the physics of the droplet impact on the target surface. We find that varying the oil concentration in emulsion droplets will affect the drop impact behavior and final drop shape. Correlations between the dimensionless characterization of droplets with droplet efficacy/toxicity on the spinach leaf will be analyzed in order to determine optimal droplet parameters and oil concentration for pesticide applications.

Using pesticide sprays that can produce ideal droplets is essential for minimizing pesticide usage and therefore minimizing cost and environmental harm. This study aims to provide a better understanding of characterizing emulsion droplet impact in order to predict its retention and efficacy on plant leaf surfaces. These results are the first steps to creating improved spraying methods with controllable droplet properties and creating better and safer pesticide formulations using essential oils.