*2.1.1.2 Particle size*

As mentioned above, microemulsions have tendency to form single narrow size distribution, ought to its maturity in terms of fabrication methods. Adding to its thermodynamic stability, the size of a microemulsion will not undergo changes once it is formed by a specific approach. This is different from nanoemulsions where they tend to have multiple peaks in its size distribution. This


**Table 1.**

*Summary of microemulsion and nanoemulsion common facts and common differences.*

**7**

mankind.

sion formation.

**Figure 2.**

**3. Conclusion**

*Introductory Chapter: From Microemulsions to Nanoemulsions*

is not surprising due to its unstable thermodynamic as discussed previously. Therefore, if an emulsion system has multiple peaks formation in its size distribution, it can possibly be considered as a system that has both microemulsions and nanoemulsions. However, the noticeable approach to be used in this scenario is to undergo proper physical characterization such as Zetasizer or using scanning electron microscope for proper size measurement, as well as storing it for a period of time, i.e., 1 year to observe the change of emulsion structure. These approaches might provide other significant evidence to validate the type of emul-

*state despite the assistance of surfactants. Reprinted with permission from Ref. [3].*

*Schematic illustration between microemulsions and nanoemulsions, with its separated phase state, respectively. Microemulsions have a relative lower free Gibbs energy than the phase-separated state; therefore, it is unlikely to break down even after a long storage period provided the storage condition remains unchanged. Meanwhile, nanoemulsions have a higher free Gibbs energy, leading to breakdown and revert back to its original separated* 

This chapter is a timely content of nanoemulsion development as this research field has shown significant publication output for the past decade due to growing interest as a result of nanotechnology development as seen in **Figure 3** using Web of Knowledge (Thomson Reuters) online search engine [15]. Presently, microemulsionrelated publication is dominating in terms of publications output per year. This is in line with the history of microemulsion for the past seven decades which covers a comprehensive research range from science (i.e., chemistry, biology, physics, etc.) to engineering (chemical, biomedical, environmental, etc.). On the contrary, nanoemulsions received much lesser focus until the mid-1990s. It has relative incomplete fundamental knowledge understanding in terms of properties, characterizations and fabrication methods, and it also has limited applications presently. Therefore, this book is important in attempting to mend the knowledge gap and form the trend. As nanotechnology matures gradually, the outlook of nanoemulsion looks bright and it aims to stretch its capability to apply across different fields that will benefit

*DOI: http://dx.doi.org/10.5772/intechopen.87104*

*Introductory Chapter: From Microemulsions to Nanoemulsions DOI: http://dx.doi.org/10.5772/intechopen.87104*

#### **Figure 2.**

*Nanoemulsions - Properties, Fabrications and Applications*

Tend to have single narrow peak for size distribution

Composition An oil phase, an aqueous phase, a surfactant and possibly a co-surfactant [1]

> Opaque or semitransparent [3]

Kinetically stable for indefinitely

spherical, subject to fabrication method used [14]

Principally, it can form spontaneously due to its thermodynamic stability. In practical, external force will be exerted to emulsion formation

*Summary of microemulsion and nanoemulsion common facts and common differences.*

Size 1 nm (1 × 10<sup>−</sup><sup>9</sup>

Particle size distribution

Water-in-oil/ oil-in-water formation

Optical properties

Thermodynamic stability

Gravitational stability

Fabrication methods

Particle structure Spherical or non-

**Descriptions Microemulsion Nanoemulsion Remarks**

m) to 100 nm (1 × 10<sup>−</sup><sup>6</sup>

Have multiple peaks for size distribution

Transparent when the size is ≤30 nm [12]

Unstable system that will break down over

time [3]

to gravitational separation (creaming/ sedimentation) increases significantly for particle size ≤90 nm due to dominance of Brownian motion [3]

External energy must be applied to overcome positive free Gibbs energy to form emulsion. Common fabrication approaches are high energy, low energy, and phase inversion [3, 16]

Not reported Colloidal dispersion

Possible Both microemulsion and

m) The difference between

distribution

difference

energy, ΔG)

Spherical The governing equation is used to

(∆*PL* <sup>=</sup> <sup>2</sup>γ\_\_ *<sup>r</sup>* ). The small radius of nanoemulsions has relative large Laplace pressure, thus sphere sharp has lowest interfacial area

this area of research

microemulsions and nanoemulsions cannot be distinguished merely from size

Normally, the combination of micro- and nanoemulsions exists in multiple peaks colloid

nanoemulsion can form water-inoil and oil-in-water emulsion type

Microemulsions will not undergo breakdown provided the storing condition remains unchanged Nanoemulsions will breakdown and revert back to separated phase, subject to energy barrier between nanoemulsions and separated phase (Gibbs free

Limited work has been to validate

determine particle size, thus the structure Laplace pressure,

Difficult to distinguish based on

fabrication methods

A greater surfactant-to-oil ratio is required to prepare a microemulsion than a nanoemulsion due to size

**6**

**Table 1.**

*Schematic illustration between microemulsions and nanoemulsions, with its separated phase state, respectively. Microemulsions have a relative lower free Gibbs energy than the phase-separated state; therefore, it is unlikely to break down even after a long storage period provided the storage condition remains unchanged. Meanwhile, nanoemulsions have a higher free Gibbs energy, leading to breakdown and revert back to its original separated state despite the assistance of surfactants. Reprinted with permission from Ref. [3].*

is not surprising due to its unstable thermodynamic as discussed previously. Therefore, if an emulsion system has multiple peaks formation in its size distribution, it can possibly be considered as a system that has both microemulsions and nanoemulsions. However, the noticeable approach to be used in this scenario is to undergo proper physical characterization such as Zetasizer or using scanning electron microscope for proper size measurement, as well as storing it for a period of time, i.e., 1 year to observe the change of emulsion structure. These approaches might provide other significant evidence to validate the type of emulsion formation.
