Synthesis of Nanofluids

Abstract

In this chapter we are concerned with the synthesis of a diverse variety of nanofluids. As this book is concerned with nanofluids designed for specific applications, we limit our discussion to stable nanofluids and free-standing nanosystems which may be made in the form of fluids. Although the first category of fluids may not be separable into the constituent phases (i.e., solid and liquid), the other is in the separated phases to begin with. Nanoparticles formed in porous media such as zeolites, and embedded particles in glasses are not dealt with, although in a larger sense, particles in solids may be considered as solutions.From a general perspective, a two-phase colloidal system can be classified in terms of a dispersed phase and a dispersion medium. The dispersed phase and dispersion medium can be any one of the three phases (i.e., gas, liquid, or solid) except that the first category (i.e., gas in gas) is unknown. From this, a solid nanoparticle dispersed in an amorphous solid may be considered as a colloidal system and consequently, a nanofluid. In our descriptions, fluids will be liquids at ordinary conditions of temperature and pressure, and for that reason, supercritical fluids and gases as the dispersion phase are not considered. It may be noted that the synthesis of nanoparticles in these media (i.e., solid matrices 1 and supercritical fluids 2 ) is a large and advanced area of science. From a historical perspective, it is also important to remember that some of the early applications of nanoparticles were in the form of embedded particles in glasses. 3 Supercritical fluids are a recent area of development in nanoparticle science. GENERAL ISSUES OF CONCERNThere are several factors of interest when considering a given synthetic approach:(1) thermal stability, (2) dispersability in diverse media, and (3) chemical compatibility and ease of chemical manipulation. Each of these parameters is discussed in some detail below. It should be noted that several are intimately connected to each other.