**Abstract**

Microemulsion formulation is among the most suitable carrier for the delivery of bioactive and, therefore, has excellent potential for industrial applications. The microemulsion system is thermodynamically and kinetically stable. Due to the smaller droplet size of the microemulsion system, the bioactive covers a larger surface of the target pest. Botanicals and essential oils, in particular, are green options to control various soil and seed-borne pathogens. Each oil contains several bioactive constituents that practically avoid microbe-resistance against it. Nevertheless, to improve the handling and shelf-life of botanicals, microemulsion formulation is the best option available. The current chapter provides the insight of a microemulsion system and explores the possibility of botanical oil-based biopesticides for a sustainable agroecosystem. We believe that botanical oil microemulsion could be a better alternative to synthetic pesticides and opens a new corridor for the promotion of the greener way of plant protection in India and across the globe.

**Keywords:** botanicals, essential oil, microemulsion, pathogen, formulation

### **1. Introduction**

Essential oils from aromatic plants are a competent source of pesticides that have a diverse role in pest management like insecticides, fungicides, growth-regulators, deterrent, and repellent activities [1]. Essential oils' role in pharmacology or therapeutic activities and cosmetics is quite known. In recent years, the essential oil is being used in pest management applications and regularly used by the farmers to promote organic farming in an environmentally friendly way [2]. Essential oils of aromatic plants are rich in bioactive compounds viz., terpenes, terpenoids, flavonoids, phenolics, etc. These constituents have different physicochemical properties and stability, but their utilization in pure form is not feasible. Hence, a suitable delivery system is needed to enhance its bio-efficacy and stability during the application.

Various formulations of bioactive compounds are available in the market, but they have certain limitations like un-stability, high in cost, complex compositions, non-targeted delivery, and post-application wastage. It is, therefore, compelling to look upon the carrier system that overcomes the limitations mentioned above. In recent years, researchers have reported that microemulsion (ME) formulation is the most suitable carrier for the delivery of bioactive constituents of essential oils and has excellent potential for industrial applications. The microemulsion system is not only thermodynamically and kinetically stable but also possesses a small droplet size (preferably below 100 nm). It means the formulation can incorporate a large amount of bioactive essential oil in the disperse phase. Due to these characteristic features, essential oil-based ME favors a stabilized and intelligent approach for the delivery of their active ingredients into the targeted site and results in enhanced bio-efficacy. In this chapter, we will discuss the essential oil-based ME and their role in pest management.

a. Oil in water (o/w) microemulsion: In this system, oil is dispersed in a water medium, and the surfactant is in high concentration in water medium and

*Microemulsion Formulation of Botanical Oils as an Efficient Tool to Provide Sustainable…*

b. Water in oil (w/o) microemulsion: In this system, water is dispersed in oil medium. The surfactant is a high concentration in the oil phase and

c. Bicontinuousmicroemulsion (transition state from o/w to w/o): A three-phase system where a surfactant-rich middle-phase coexists with both water and

d. Single-phase homogeneous mixture: single-phase isotropic micelle solution

The microemulsion system is a competent and stabilized carrier system for all types of active constituents. The characteristic features of microemulsion are:

low surfactant concentration in oil medium.

*DOI: http://dx.doi.org/10.5772/intechopen.91788*

**2.2 Characteristics features of ME**

• Thermodynamically stable

• Transparent colloidal system

• Isotropic

• Easily penetrate

• Long shelf-life

• Easy to prepare

• Zero interfacial tension

between oil and water.

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• Droplet size is tiny, i.e., 1–100 nm

**2.3 Theories of micro emulsion formation**

Three theories explain the microemulsion formation and stability. i. **Interfacial or Mixed film theory**: According to this theory, the

reduction of interfacial tension and expressed as [Eq. (1)]:

structures solubilized and form the monophasic system.

microemulsion is formed due to the formation of oil and water complex interface reduction by surfactant and co-surfactants. This theory depends on the

Ψ = spreading pressure; ϒ<sup>i</sup> = interfacial tension; ϒo/w = interfacial tension

ii. **Solubilization theory:** According to this theory, oil or water reverse micelle

iii. **Thermodynamic theory:** According to this theory, microemulsion formation is a spontaneous process that depends upon the lowering of interfacial tension on the addition of surfactants and co-surfactants, and mixing of one

Interfacial of oil and water reduced to zero and increases the spreading pressure.

ϒ**<sup>i</sup>** ¼ ϒ**<sup>o</sup>***=***<sup>w</sup>** � **ψ** (1)

surfactant-low in the aqueous phase (Winsor II).

surfactant (Winsor III or middle-phase microemulsion).
