**1. Introduction**

In the past two decades, there has been much attention within food and beverages, pharmaceutical, biomedical, special chemicals and other industries in using colloidal as main media for process encapsulation, protection and delivery of various active components for different purposes [1–3].

This dispersion normally exists as a suspension of small particles within a liquid medium. Conventionally, particles at >1000 nm are studied due to its rising trend of research interest as a result of introduction of microfluidics [4]. Microfluidics is a concept that is defined as a branch of fluid mechanics that focuses on the understanding, design, fabrication and operation systems that convey liquids and gases inside an enclosed channel with two of the three geometry length scales are in the order of microns (10<sup>−</sup><sup>6</sup> ). The reduction in dimension had magnified the effect of some uncommon macroscale liquid properties such as surface tension, capillary effect and material hydrophilicity/hydrophobicity. The first ventures in microfluidic started in the early 1950s when dispersion methods of nano- (10<sup>−</sup><sup>9</sup> ) and pico- (10<sup>−</sup>12) litre of fluids were developed, which served as the foundation of modern day Inkjet technology [5, 6]. As microfluidics' continuous development advanced for the past 70 years, multiple cross disciplines with intersections of engineering, physics, chemistry, biology, nanotechnology and biotechnology had been developed and commercialised. In 2003, Forbes magazine named microfluidics technology as one of the most important inventions that can affect the future of humanity [7]. Meanwhile, microfluidics hold some of the key advantages that include the low manufacturing costs, economic use and disposal, shorter time of analysis, minimal consumption of reagents and samples, minimal production of potentially harmful by-products, enhancement of separation efficiency, enhancement of portability for point-of-care testing, high surface to volume ratio and small laboratory footprint [8, 9].

On the other hand, there are some colloidal applications that desire very much smaller particles (<100 nm) since they have advantages over microscale colloids, such as better stability to particles aggregation and gravitational separation [2], weak light scattering [10–12], and have novel physical properties (i.e., high viscosity and gel-like behaviour) [2, 13]. In conjunction with the new rise of nanotechnology research trend, a decent amount of research has been devoted to fabrication, characterization and application of colloidal dispersion that contains of nanometre-sized particles as delivery systems. As the research duration is merely less than two decades, much knowledge gap in this research field remains to be filled.

This chapter therefore emphasizes the most commonly used terms in this field of study, namely microemulsions (>1000 nm) and nanoemulsions (<100 nm). Using oil-in-water (O/W) system, which is widely used as delivery systems in a

range of different industries as well as many literatures, this chapter will outline the similarities and differences between microemulsions and nanoemulsions, to articulate the scientific terminology used to describe each of the terms and also to look into research progress of both microemulsions and nanoemulsions as a whole.
