**1.2 Nanoemulsions**

As the name suggests, the size of the droplets in this type of emulsion is in nanometer ranges. They not only differ in size but also in the many properties and method of preparation. The main difference between nanoemulsion and conventional emulsion (macroemulsion) is the size and shape of the droplets in the continuous phase. In macroemulsion, the shape is usually spherical but in nanoemulsions a variety of shapes can be seen like swollen micelles and bicontinuous structures. Though micro and nanoemulsions are similar in their sizes the method of preparation differs between them. Both of them require energy inputs, but nanoemulsions mostly use mechanical shear while micro emulsions make use of spontaneous emulsification methods. Microemulsions also need a high surfactant concentration compared to nanoemulsions. The application of nanoemulsion in pharmaceutical, food, cosmetic, and chemical industry is comparatively more than microemulsion since moderate surfactant concentration is sufficient for their making [5].

Nanoemulsions are said to be kinetically stable and thermodynamically unstable. Their stability can be altered by their preparation methods like adding specific co-surfactants. They usually use high energy methods for their preparation but low energy based methods can also be used with the help of some special conditions using certain chemical potential of the component [6]. Nanoemulsions are said to be transparent, biodegradable, and biocompatible. Normal emulsions usually undergo sedimentation by gravity, which is overcome by nanoemulsions. Nanoemulsions exhibit Ostwald ripening phenomenon. Due to this, small


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

molecules collide and form large globules. To overcome this, co-surfactants are added or second oil is added to the dispersion phase. Proper manufacturing procedure also helps overcome Ostwald ripening [7]. Nanoemulsions provide a wide surface area and so allow active components to penetrate easily and faster. Another important characteristic of nanoemulsion is their transparent optical property. This is mainly due to their size, which is one fourth of the wavelength of visible light [8]. Nanoemulsions have the ability to solubilize both hydrophobic and hydrophilic substances, and hence enhance their permeability and bioavailability [9]. This makes them very useful as drug delivery systems for both the type

Nanoemulsions are also said to have tunable rheological properties. They are tuned by controlling the dispersed phase volume, droplet size or the addition of salt and depletion agents [4]. Hence nanoemulsions can be tuned from being a free flowing fluid to a gel like substance [10]. Addition of polymers also tunes the rheological properties. The polymers associate either with themselves or with the nanoemulsions. A thermo reversible gel was made, where a polymer gelator (with two hydrophobic end groups) was added. At temperatures greater than the gelling temperature, the polymer's two hydrophobic ends bridges with the nanoemulsion droplets making them a gel. At lower temperature, they detach and hence return to

There are three types of nanoemulsion based on the composition:

• Oil in water: oil droplets are dispersed in continuous aqueous phase.

• Bi-continuous (double): micro domains of oil and water are interdispersed

As already mentioned, nanoemulsions are being used in a wide range of fields. There is a lot of research and development work done in the field of nanoemulsions. Many bioactive substances are present in natural available substances, emulsification of these bioactive components is a trending research topic. In September 2018, water compatible form of coconut oil through nano-emulsification was developed [12]. The nanoemulsion was made successfully using PHC as a surfactant at a concentration of 5% {w/w}. Nanoemulsions have also found an important space in field of pharmaceuticals. Many of the oral drugs synthesized do not have aqueous stability almost insoluble) and have low bioavailability. A low energy method to make composite hydrogel beads encapsulated with single and multiple hydrophobic drugs was developed [13]. This makes nanoemulsions a promising carrier of hydrophobic drugs. It was shown that nanoemulsions were used to enhance the antileishmanial activity of *Copaifera* spp. oleoresins against both *Leishmania amazonensis* and

Recently a new technique for making Pickering nanoemulsions using Silica nanoparticles was developed which is highly scalable and energy efficient.

Nanoemulsions are usually stabilized using surfactants. The use of surfactants has some disadvantages which include surfactant desorption and Ostwald ripening. Hence a new interest of making nanoparticle stabilized nanoemulsion (Pickering nanoemulsions) has evolved. Nanoparticles have higher desorption energy barrier. However, the limitation of nanoparticles as stabilizing agent was obtaining the size in nano-range. In the traditional method to make Pickering emulsions (high energy

• Water in oil: water droplets are dispersed in continuous oil phase.

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

a transparent fluid like structure.

within the system [11].

*Leishmania infantum* strains [14].

**1.3 Current trends in nanoemulsions**

of drugs.

**Table 1.** *Emulsion type and its droplet size [4].*

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

molecules collide and form large globules. To overcome this, co-surfactants are added or second oil is added to the dispersion phase. Proper manufacturing procedure also helps overcome Ostwald ripening [7]. Nanoemulsions provide a wide surface area and so allow active components to penetrate easily and faster. Another important characteristic of nanoemulsion is their transparent optical property. This is mainly due to their size, which is one fourth of the wavelength of visible light [8]. Nanoemulsions have the ability to solubilize both hydrophobic and hydrophilic substances, and hence enhance their permeability and bioavailability [9]. This makes them very useful as drug delivery systems for both the type of drugs.

Nanoemulsions are also said to have tunable rheological properties. They are tuned by controlling the dispersed phase volume, droplet size or the addition of salt and depletion agents [4]. Hence nanoemulsions can be tuned from being a free flowing fluid to a gel like substance [10]. Addition of polymers also tunes the rheological properties. The polymers associate either with themselves or with the nanoemulsions. A thermo reversible gel was made, where a polymer gelator (with two hydrophobic end groups) was added. At temperatures greater than the gelling temperature, the polymer's two hydrophobic ends bridges with the nanoemulsion droplets making them a gel. At lower temperature, they detach and hence return to a transparent fluid like structure.

There are three types of nanoemulsion based on the composition:

