Phase Change Material Particles and Their Application in Heat Transfer Fluids - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 457

(a) (b)

(c) (d)

Fig. 7 Schematic illustrating the formation of metallic PCM nanoparticles. a PAO and molten
metal are in the reaction vessel. These two liquids are immiscible and phase separate. b The
polymer surfactant is soluble in PAO and preferentially adsorbs at the interface. c The mixture is
stirred using a magnetic stirrer and the bulk molten metal breaks into microscale droplets. d The
microscale emulsion is exposed to high-intensity ultrasonication until the PCM nanoparticles are
formed [ 5 ]

4.1.1 Synthesis of Low-Melting-Point Metallic Nanoparticles

A one-step, nanoemulsification technique has been developed to prepare suspen-
sions of metallic PCM nanoparticles [ 5 ]. The fabrication process of metallic PCM
nanoparticles is illustrated in Fig. 7 . Briefly, this technique exploits the extremely
high shear rates generated by the ultrasonic agitation and the relatively large
viscosity of the continuous phase-PAO, to rupture the molten metal down to
diameter below 100 nm. As an example, the preparation of Indium (melting point:
156.6 C) and Field's metal (melting point: 63.2 C) metallic PCM fluids is dis-
cussed below.
A large number of factors can affect the metallic particle size in the emulsifi-
cation process. These include selecting an appropriate composition, controlling the
reaction temperature, choosing the order of addition of the components, and
applying the shear in an effective manner. However, the fundamental relationship