(562g) Agrochemical Microcapsule Placement Following Fixed Contact Line Sessile Drop Evaporation

Microcapsules containing a pesticide are delivered to the target site using water as a carrier. Droplets containing microcapsules are placed on target surfaces such as leaves, soil, or building structures, and following evaporation, microcapsules are left behind via the ?coffee stain? phenomena. However, droplet evaporation rates, humidity, surface tension, microcapsule size and densities, and proximity to other drops can affect the final deposition patterns of microcapsules. Microcapsules can be uniformly distributed throughout the original wetting area of the drop, concentrated at the wetted area edge as an annular ring of clustered material, or something in between post water evaporation. Microcapsule placement impacts the pesticide release rate from the microcapsule arrays since clustered microcapsules have a net slower release rate than individual microcapsules. This work focuses on insight and quantifying the microcapsule arrays and clusters that remain following the drying process. Microcapsule annular clustering along with more uniform capsule placement can be attained within the constraints of current agricultural nozzles having known initial droplet size distributions. Geometry of resulting microcapsule clusters is a function of the initial contact angle of the drop (e.g. surface tension and choice of surfactants), capsule number density, and the initial size of the droplet. Therefore, the physics of microcapsule transport following spraying must be accounted for to address exposure and biological efficacy for microcapsule formulations since release rate of active (and thus biological efficacy) is a function of capsule clustering in addition to conventional parameters such as the capsule polymer membrane, membrane thickness, and pesticide loading within the capsule.