Abstract
A nanoemulsion is a colloidal dispersion that contains very small particles with size in the range of 20-200 nm, which may be of the oil-in-water (O/W) or water-in-oil (W/O) types depending on whether the oil is dispersed as droplets in water or vice versa. Pesticides play a critical role in controlling agriculture and ensuring food safety. In the future, the utilization of pesticides will become even more important to solve food security problems associated with providing an adequate food supply for the growing world population. Hence, development of new techniques for nanoemulsions formulation in the field of agriculture and forestry are necessary. In this chapter, the synthesis, characterization, and application of nanoemulsion in pesticides formulation are reviewed. In addition, the effect of antifungal or insecticidal and antimicrobial enhancement activity of nanoemulsions with size, composition, and stability are also discussed.
Top1. Introduction
Emulsion is a non-equilibrium heterogeneous colloidal dispersion consisting of two immiscible liquids. Nanoemulsions are isotropic, thermodynamically unstable, kinetically stable transparent colloidal dispersions with particle size in the range, 20-200 nm. It is commonly prepared by using oil, water, surfactant and a co-surfactant as the starting materials. This type of emulsion is thermodynamically unstable due to the effect of large positive interfacial tension between the oil and water phases. The smaller size of the droplets in nanoemulsions typically gives them better stability to gravitational separation and droplet aggregation than other emulsions (Gutierrez et al., 2008, McClements, 2012).
Pesticides play a critical role in reducing yield loss and ensuring food safety (Cooper and Dobson, 2007). In the future, the pesticides utilization will become very important to solve food security problems associated with providing an adequate food supply for the growing world population (Carvalho, 2006). Pesticides are synthetic or natural substances which are used to prevent, destroy or control microorganisms, insects, weeds and other pests that endanger agriculture and forestry. It also helps in regulating the growth of certain plant species. Pesticides are classified based on the biological species that they are used to control: insecticides, fungicides, nematicides, herbicides and plant growth regulators. They can be used for agricultural, forestry, hygiene and nonagricultural purposes (Silva et al., 2012; Weaver et al., 2009, Pavela, 2013, Badawi et al., 2016). Commercially, pesticides are not typically used directly in their pure chemical form. Instead, they are usually incorporated into a suitable delivery system by adding an appropriate dosage of the pesticide into a suitable solvent or colloidal dispersion, which may be used in a solid, liquid, or gaseous form (Rodham, 2000). Thus, commercial pesticide formulations can be divided into solid forms (such as granules or powders), liquid forms (such as solutions or suspensions) and gaseous forms (such as vapours). The liquid forms include solutions, emulsifiable concentrates, oil-in water emulsions and soluble concentrate (Wang et al., 2004). In addition, used of these agrochemical pesticides is also polluting the environment which is hazardous to living being. Hence, the development of suitable formulation technologies is important for efficient delivery systems for hydrophobic pesticides as well as shifting to water based pesticides system is necessary for better results and safety.
In this chapter, synthesis, characterization and application of nanoemulsion in pesticides formulation is reviewed. The effect of antifungal or insecticidal and antimicrobial enhancement activity of nanoemulsion with size, composition and stability are also discussed. This book chapter would be useful as reference for the synthesis of new nanoemulsion based system and its application in pesticides for agriculture and forestry sector.
Key Terms in this Chapter
Hydrophilic-Lipophilic Balance (HLB): A higher and lower value of HLB surfactants favours O/W and W/O type pesticide nanoformulations respectively.
Oil Phase: Essential oils are concentrated and volatile compound that usually comes from different parts of plant materials which are biodegradable and eco-friendly while non-essential oils are carrier oil that does not evaporate.
Nanoemulsion: A nanoemulsion is a colloidal dispersion that contains very small particles with size in the range, 20-200 nm which may be of the oil-in-water (O/W) or water-in-oil (W/O) types depending on whether the oil is dispersed as droplets in water or vice versa.
Emulsifiers: Emulsifiers is important components of nanoemulsion which help in controlling its size and stability.
Ostwald Ripening: Ostwald ripening is a physical instability in nanoemulsions that occurs due to a particle size dependence of the local solubility of the oil phase in the surrounding water phase.
Critical Micelle Concentration (CMC): CMC value is a point at which self-assembly of surfactants occurs and the addition of surfactant after this point is no longer reduces the surface tension which is crucial for the formation of nanoemulsions.
Pesticides: Pesticides are synthetic or natural substances used to control microorganisms, insects, weeds, and other pests that endanger agriculture and forestry and to regulate the growth of certain plant species.