*2.2.2.2 Phase inversion composition*

Phase inversion composition is performed when the surfactant properties changes due to dilution of one of the phases. It involves dilution of oil phase with water or vice versa which causes an increase or decrease in hydration degree of surfactant. In phase inversion composition, phase transition takes place at constant temperature. At one point in the dilution process the affinity of the surfactant becomes equal for both the phases that is it exhibits both hydrophilic and lipophilic properties. This point is known as the emulsion inversion point [4]. At this stage a layer of microemulsions is formed. A slight change in the proportion of oil and water causes instability of the microemulsion layer which disintegrates to form nanoemulsion that are kinetically stable. It was found out that with further

**73**

*An Update on Nanoemulsions Using Nanosized Liquid in Liquid Colloidal Systems*

dilution the droplet size does not change [28]. The properties of the nanoemulsion obtained depends on conditions such as shear rate and the addition rate [30]. Heat sensitive compounds can be encapsulated by using this fabrication method for

To obtain an O/W nanoemulsion, initially a W/O microemulsion (consisting of surfactant) is required to which aqueous phase is added in a controlled manner. The resulting system is stirred for breakdown of the residues and for homogeneity [24].

A great attention is given towards the use of nanoemulsions in research, dosage form design and pharmacotherapy owing to their optical clarity, ease of preparation, thermodynamic stability and increased surface area. Some of the problems associated with conventional drug delivery systems such as low bioavailability and noncompliance which can be overcome by nanoemulsions are discussed here

It is the most effective form of drug delivery system usually adopted for active ingredients with low bioavailability and narrow therapeutic index. Here the therapeutic peptides or drugs prepared in the form of solutions or suspensions, are given as injections. Intravenous, intramuscular and subcutaneous drug delivery systems

Dissolution of enormous amounts of hydrophobic compounds coupled with mutual compatibility and ability to safeguard drugs from hydrolysis and enzymatic degradation make nanoemulsions ideal vehicles for parenteral transport [32]. Nanoemulsions help in sustained and controlled drug delivery through parenteral routes. Since nano emulsions are cleared more slowly (more residence time) than the coarse particles, they are advantageous over macroemulsion systems when

Nanoemulsions loaded with thalidomide have been synthesized. A dose as low as 25 mg leads to plasma concentrations which can be therapeutic when delivered

*DOI: http://dx.doi.org/10.5772/intechopen.84442*

*Shows the process of phase inversion by dilution with aqueous phase [4].*

nanoemulsions.

**Figure 5.**

**3.1 Drug delivery**

(**Figure 6**).

*3.1.1 Parenteral delivery*

delivered parenterally [33].

through this system [34].

This process is depicted in **Figure 5**.

**3. Applications of nanoemulsions**

are the most commonly used parenteral routes.

*An Update on Nanoemulsions Using Nanosized Liquid in Liquid Colloidal Systems DOI: http://dx.doi.org/10.5772/intechopen.84442*

**Figure 5.**

*Nanoemulsions - Properties, Fabrications and Applications*

inversion composition (PIC) method [29].

*2.2.2.1 Phase inversion temperature*

*2.2.2.2 Phase inversion composition*

volume ratio, giving rise to phase inversion temperature (PIT) method and phase

the emulsification process, especially if they have high viscosity [27].

the surfactant is equally soluble in the oil and aqueous phase [16, 17].

of its chain which in turn depends on temperature [16, 17] (**Figure 4**).

In these emulsification methods it is very important to know the behavior of the surfactant as it plays a significant role in minimizing both droplet size and polydispersity of the nanoemulsion formed. Its properties also depend on the kinetics of

The Phase inversion temperature (PIT) method is used when the surfactants are sensitive to changes in temperature. The principle of this method is based on the changes in surfactant spontaneous curvature (molecular geometry) with temperature. For example, in poly(oxyethylene)-type non-ionic surfactant, increase in temperature causes dehydration of the poly(oxyethylene) chains whereas at low temperature these chains are hydrated and hence are hydrophilic in nature. At one temperature the surfactant exhibits both hydrophilic and lipophilic properties, this temperature is known as HLB temperature (Hydrophilic–Lipophilic Balance) [17, 27]. So, at this temperature

Using PIT very small sizes of droplets can be obtained. At the HLB temperature due to the low interfacial tension the surfactant forms a layer but as soon as the temperature is changed by quick cooling or heating, the surfactant molecules move from one phase into another resulting in the formation of small oil droplets. The movement of the surfactant molecules depends on its hydrophilicity or lipophilicity

Phase inversion composition is performed when the surfactant properties changes due to dilution of one of the phases. It involves dilution of oil phase with water or vice versa which causes an increase or decrease in hydration degree of surfactant. In phase inversion composition, phase transition takes place at constant temperature. At one point in the dilution process the affinity of the surfactant becomes equal for both the phases that is it exhibits both hydrophilic and lipophilic properties. This point is known as the emulsion inversion point [4]. At this stage a layer of microemulsions is formed. A slight change in the proportion of oil and water causes instability of the microemulsion layer which disintegrates to form nanoemulsion that are kinetically stable. It was found out that with further

*Shows the curvature of surfactant and the favorable emulsion formed by heating and cooling [16].*

**72**

**Figure 4.**

*Shows the process of phase inversion by dilution with aqueous phase [4].*

dilution the droplet size does not change [28]. The properties of the nanoemulsion obtained depends on conditions such as shear rate and the addition rate [30]. Heat sensitive compounds can be encapsulated by using this fabrication method for nanoemulsions.

To obtain an O/W nanoemulsion, initially a W/O microemulsion (consisting of surfactant) is required to which aqueous phase is added in a controlled manner. The resulting system is stirred for breakdown of the residues and for homogeneity [24]. This process is depicted in **Figure 5**.
