**3. Factor affecting the particle size of active entity (drug or agrochemical) in microemulsion**

The microcavities in microemulsion by surface-active agents causes a cage-like effect and check the particle agglomeration [5]. The stability of microemulsion drops depends upon the following factors.

*Microemulsion Formulation of Botanical Oils as an Efficient Tool to Provide Sustainable… DOI: http://dx.doi.org/10.5772/intechopen.91788*

**Figure 3.** *Diagrammatic representation of the titration method of microemulsion.*

I. **The viscosity of the microemulsion**: The size of particle in a microemulsion is depended upon the viscosity of the mixture after adding all the surfaceactive agents and water and expressed by the following equation [Eq. (3)]:

$$
\eta\_{\rm r} = \eta/\eta\_{\rm o} = \mathbf{1} + \mathbf{5}/2\mathbf{q} \tag{3}
$$

where, η<sup>r</sup> = relative viscosity; η = viscosity of the dispersion; η<sup>o</sup> = solvent viscosity; ȹ = volume of droplets.

In the microemulsion system, breaking up of droplets gives droplet volume fractions up to 0.2, the expected relative maximum viscosity is 1.5, which results in droplet interactions and destabilizes the microemulsion system [5].

II. **The ratio of water to surface-active agents:** The water level inside the spherical micelles gives the radius measurement by the following expression [Eq. (4)] and **Figure 4**.

$$\mathbf{r} = \mathbf{3} \,\mathrm{Vm/s} \tag{4}$$

where, Vm is the dispersed volume of water; s is the interfacial area by surfactant molecules.

As the water level is high, it lowers the stability due to less capability of surfaceactive agents to protect the more substantial drop — consequently, particles undergo coagulation and flocculation. Therefore, the size of the droplet depends upon the ration of water to surface-active agents (ώ).


phase to another contributes in enhancing the entropy which results into reduction of droplet size. The following thermodynamic equation expresses

ΔGf = free energy of formation; γ = surface tension of the oil–water interface; ΔA = change in the interfacial area after microemulsion; ΔS = change in entropy of

There are two methods to develop a microemulsion system of very low interfacial tension at the correct ratio of surfactants and co-surfactants. There are two

I.**Phase inversion method**. In this method, phase inversion occurs after the

temperature control. During phase inversion, the particle size of any drug or agrochemical reduced, which results in active release kinetics. This method is also called the phase inversion temperature method. Because after the cooling phase, inversion will occur from w/o to o/w. short chains of surfactants

addition of excess dispersed phase in the surfactant system under

II.**Phase titration method**. This method is also known as a spontaneous emulsification method and can represent with the help of phase diagrams. The phase diagram is handy in studying the various interactions that occur while mixing different components of the microemulsion. The phase diagram is constructed to find out the zones of the microemulsion, and each corner represents 100% of each element. The phase diagram is built at fixed surfactant and co-surfactant weight ratios and titrated with water at room temperature. The formation of the transparent monobasic system is

*Δ***Gf** ¼ **γ** *Δ* **A** � **T** *Δ* **S** (2)

this theory as (Eq. (2):

**2.4 Preparation methods**

**Figure 2.**

the system after mixing; T = is the temperature.

*Diagrammatic representation of the phase inversion method of microemulsion.*

*Nano- and Microencapsulation - Techniques and Applications*

methods of microemulsion preparation:

promote this inversion (**Figure 2**).

**agrochemical) in microemulsion**

drops depends upon the following factors.

**264**

established by physical appearance (**Figure 3**).

**3. Factor affecting the particle size of active entity (drug or**

The microcavities in microemulsion by surface-active agents causes a cage-like effect and check the particle agglomeration [5]. The stability of microemulsion

**4.5 Active ingredient stability**

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

**4.6 Viscosity measurement**

culation or phase separation.

**4.7 Electrical conductivity**

**4.8 In-vitro drug release**

**4.9 Advantages**

• Easy to form

• Easy to develop

**4.10 Disadvantages**

**267**

lyzed for active ingredient content.

• Enhanced bio-efficacy

• Slow-release delivery system

• Solubilize water-insoluble active constituents

• Effective in both contact as well as systemic delivery

• Protect the active constituents from hydrolysis and oxidation.

• Limiting solubilizing capacity for high melting active constituents

• Microemulsion stability influenced by temperature and ph.

• Use of high amount of surfactants and co-surfactants

• Smell masking of unpleasant active ingredients

tion development.

The active ingredient stability is quantified by suitable analytical techniques like

Viscosity is the fundamental property of the microemulsion system. If any type of viscosity change occurs, it will destabilize the microemulsion and leads to floc-

The electrical conductivity of formulated samples in microemulsion form was checked after adding a surfactant, oil, and water components. A conductometer

The bioactive content release study was carried out in Franz diffusion cell of volume 20 ml. Two compartments are present- one is a receptor compartment, and the other is the donor compartment. Receptor compartment is filled with buffer, and the donor compartment is filled with a microemulsion sample and covered by a cellophane membrane. At certain intervals of time the donor compartment is ana-

does this measurement at ambient temperature and 1 Hz frequency.

HPLC, GC–MS, LC–MS, and others. According to the active constituents after formulation development. The active constituent's stability is crucial after formula-

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

#### **Figure 4.**

*Diagrammatic representation of the effect of water on the surface-active agent on the stability of the microemulsion.*

of non-ionic surfactants due to de-hydration of hydrophilic groups at high temperature. In the oil phase, on the other hand, active agents'solubility increases in the oil phase. Therefore temperature optimization is critical in droplet size reduction and microemulsion stabilization.
