Droplet/leaf surface interface

Two main interfaces are involved when droplets of an agrochemical formulation are produced from a spray nozzle (i) spray solution/air interface (ii) droplet/leaf surface interface. The main factors that must be considered are solution/air surface tension and solid/liquid interfacial tension (that is determined by the contact angle of the Uq-... 

Pesticides are substances that repel, kill or otherwise control unwanted animals or plants. Examples include insecticides, fungicides and herbicides. The formulation of pesticides is significant in terms of product stability and product performance. The current trend in crop protection is towards products that are more potent, safer to user, having less impact on the environment, more convenient to use and improved efficiency of the apphed product [85]. In the case of sprayed products, colloid and interface science impacts all aspects of apphcation. First, spray droplets impact the leaf surface, creating a fohar deposit from which the pesticide moves into the leaf or contacts the pest (see Figure 13.7) [85]. The spray pattern is influenced by the applicator nozzle hydrodynamics, the physical properties of the spray fluid and the movement of sprayer vehicle. 

Several interfacial aspects must be considered when dealing with agrochemical formulations (i) Both equilibrium and dynamic aspects of adsorption of surfactants at the air/liquid interface. These aspects determine spray formation (spray droplet spectrum), impaction and adhesion of droplets on leaf surfaces as well as the various wetting and spreading phenomena, (ii) Adsorption of surfactants at the oil/water interface which determines emulsion formation and their stability. This subject is also important when dealing with microemulsions, (ill) Adsorption of surfactants and polymers at the solid/liquid interface. This is important when dealing with dispersion of agrochemical powders in liquids, preparation of suspension concentrates and their stabilization. 

Foliar application of herbicides may involve volumes ranging from high (e.g., 1000 liter/ha) to ultralow (e.g., 1 liter/ha), and maximum capture by the leaf surface depends upon such factors as droplet size, impaction, wetting, spreading, and retention. The interactions at various interfaces involved in pesticide application and their effects on transfer and performance have been reviewed by Tadros. ... 

The first interface occurs between the spray solution and the atmosphere (air) and determines the droplet spectrum, rate of evaporation, drift, etc. The second interface occurs between the liquid droplets and the leaf surface. The droplets impinging on the surface are subject to a number of processes which determine their adhesion, retention, and further spread. The nature of the deposit formed is governed by the rate of droplet evaporation and the concentration gradient of the surfactant across the droplet. 

Once the spray particle lands on the surface of a leaf, there a new interface is created, i.e. the plant surface solid-droplet interface. It is well known that... 

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