Phase Change Material Particles and Their Application in Heat Transfer Fluids - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 451

Fig. 1 Schematic illustrating the formation of the microcapsules comprising paraffin core and
melamine-formaldehyde shell [ 28 ]

It is followed by in situ polymerization of the prepolymer in acidic environ-
ment, in which the melamine-formaldehyde resin shell is formed on the surface of
the octadecane droplets,

N

N N

NH 2 N N

N

NH 2 N OH

N N N N

N N

NH NH

HN OH

H +

N N

+ O N

N

NH 2 N OH

N N

N N

N N

N NH

HN OH

N N

NH 2

(2)

The microstructure of the melamine-formaldehyde shell can be characterized
by the degree of crosslink and bridge types between two triazine rings, which can
be either methylene ether ones or methylene ones [ 29 , 30 ]. The parameters of the
encapsulation process, including surfactant concentration, F:M ratio, the pH values
of prepolymer solution, and HAc concentration in emulsion, affect significantly the
microstructure and phase changing properties of the microcapsules.