**2.1 High energy methods for emulsion formation**

In contrast to the low energy methods for nanoemulsion formation, high energy methods require the use of many devices which uses mechanical or chemical energy as input to form small droplets because they are non-equilibrium systems which cannot be formed spontaneously [17]. These devices often entail a huge initial cost as well as expenses to maintain throughout use. The purpose of these devices in high energy methods is to provide intense mechanical energy that helps to break up macroscopic phases or turn larger droplets into smaller droplets [18]. These devices provide forces so strong that it disrupt water and oil phases to form nanoemulsions. In high energy methods, input energy density is about 108–1000 W/kg. The required energy supplied is in very shortest duration of time to the system in order to obtain homogeneous small sized particles. In addition to this, the high energy methods for 55 nanoemulsion formation are not limited by the types of oil and emulsifiers that can be used like the low energy methods are. At present high energy methods are more frequently utilized in the food industry than low energy methods with high pressure valve homogenization, microfluidization, and sonication being the most common [19]. All this high energy methods are impacted by emulsion component characteristics (i.e. oil, type, surfactant type, surfactant concentration, viscosity, etc.) and equipment characteristics (i.e. size of the equipment, pressure used, number of passes/time in equipment, design, etc.). The input energy density is about 108–1010 W/kg [20]. These parameters should be optimized for each and every system and high energy method.

**69**

*2.1.2 Sonication*

**Figure 1.**

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

HPVH is the most popular method used for the production of nanoemulsions. The most common use is in applications from ketchup processing to milk homogenization and to manufacture nanoemulsions that particle sizes are up to 1 nm [18]. When using a HPVH, a coarse emulsion is initially made using a high-speed mixer, fed into the input valve of the HPVH, and then flowed between the valve seat and valve at a high velocity. The macroemulsion is forced to pass through a small orifice at an operating pressure between 500 and 5000 Psi [18]. Since several forces like hydraulic shear, intense turbulence and cavitation act together extremely small droplet sized nanoemulsions are achieved. The process is repeated till the final product reaches our desired droplet size and polydispersity index (PDI). Lower the PDI means higher uniformity of droplet size in nanoemulsions. Mono-disperse samples have PDI lesser than 0.08, narrow size distribution range is 0.08–0.3 and

With an increase in velocity, the pressure decreases causing an instantaneous pressure drop and encouraging the coarse emulsion to impinge on the impact ring [21]. Sometimes HPVH passes through two valves and thus emulsion production will break up into two stages: in the first stage the droplets are broken up and in the second stage a lower pressure is utilized to disrupt any 'flocs' formed by the initial valve [22]. Obtaining submicron levels requires large amount of energy and high temperature which can deteriorate the components. Thermolabile compounds like proteins, enzymes and nucleic acids may be damaged easily [18] (**Figure 1**).

Emulsions produced by sonication use ultrasonic homogenizers (UH) to provide high intensity of ultrasonic waves to the sample. The frequency of the waves (29 kHz or larger) is higher than the maximum audible frequency of human ear (16–18 kHz) [17]. These waves provide around 56 disruptive forces to breakup oil and water phases thus forming small droplets on the principle of cavitation. Input energy comes from a sonicator probe which can be directly placed in the sample. There are two mechanisms which take part in sonication [17]. Firstly, acoustic field creates interfacial waves which makes oil phase to disperse in the continuous phase as droplets. Secondly, ultrasound provokes acoustic cavitation which provides formation and collapse of microbubbles respectively since there is a pressure fluctuation

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

*2.1.1 High pressure valve homogenizer (HPVH)*

PDI greater than 0.3 indicates broad size distribution [18].

*Schematic representation of high pressure valve homogenizer [18].*

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