Mechanism Study on the Alcoholysis and Polymerization Degree of Poly(vinyl alcohol) to Regulate Droplet Impact Behavior on Hydrophobic Surfaces

How to restrain the bounce behavior of droplets on hydrophobic surfaces is a problem in daily life, especially during pesticide spraying. Adding polymer is a constructive strategy to enhance the ability of pesticide deposition on plant leaves, but it lacks guidance about the relationship between molecular structure and regulation capacity. This study selected poly(vinyl alcohol) (PVA) with different degrees of alcoholysis and polymerization to explore physicochemical properties in different dimensions affecting the bounce behavior. The results revealed that PVA-1788 had the best regulatory ability according to suitable phase viscosity, good surface activity, high adhesion force, and tensile viscosity. Based on statistical analysis, breaking distance at the solid-gas-liquid three-phase line is quantitative sustainability metrics to promote droplet adhesion. Namely, the solution containing PVA-1788 were embedded in the micronano structures on the hydrophobic surfaces to form claw structures and then produced the pinning effect for enhancing energy consumption so as to inhibit the droplet retraction. This mechanism was verified by SEM and fluorescence microscopy, and the higher the release height, the faster the initial rate, resulting in the significant pinning effect, because of obvious bordered deposition and permeation. This study provides the mechanism into guiding polymer adjuvants added in pesticides in view of quantitative sustainability metrics, which can lead to economic and environmental benefits in the future.