Page 34 - Polymer-based Nanocomposites for Energy and Environmental Applications

Introduction of polymer-based nanocomposites 13

of nickel oxide (NiO). In another study [95], NiFe and Fe nanoparticles were dis-
persed in epoxy as nanocomposites, through different volume fractions. Various
factors including permeability, permittivity, and loss tangents of the composites
were analyzed by an impedance analyzer. The results were correlated with the
magnetic characteristics of the particle such as saturation magnetization and field
anisotropy.

1.4 Processing of polymer nanocomposites

There are various types of synthesis of PNCs including the following:
(a) Template synthesis
Template synthesis technique is not generally carried out, even though it exhibits the
ability to produce exfoliated nanocomposites. In this process, the inorganic material is syn-
thesized in the presence of polymer matrix; therefore, the polymer leads to the nucleation
and growth of the inorganic host crystals and trapping through the layers. As the important
matters, the filler aggregation and high-temperature usage must be considered in the men-
tioned method [96].
(b) Polymer intercalation from solution
In this technique, the nanoparticles are dispersed in a solvent, while the polymer is sol-
uble too. Consequently, the polymer adsorbs onto the delaminated sheets and followed by
the solvent evaporation. After solvent evaporation, the sheets reassembling occur and trap
the polymer chains among the chains. Hence, this phenomenon ends to an ordered
multilayer structure [96].
(c) Melt intercalation
In the melt intercalation method, the high-molecular-weight polymer is melted at high
temperature, while the filler is mixed with the polymer melts under shear. Therefore, in this
method, there is no need for neither chemical synthesis nor solvent. But, due to thermody-
namic and kinetic effects on intercalation, this process may be challenging for high-
molecular-weight polymer chains in the filler interlayers. Thus, modification of fillers is
required for exfoliating in the polymer matrix under shear action, as another concern for
this process is high-temperature usage that can lead to thermal degradation of modified
fillers and polymers as well [96].
Erceg et al. [97] investigated the structure, crystallinity, thermal properties, kinetic
analysis of thermal degradation, and ionic conductivity of poly(ethylene oxide)/lithium
montmorillonite (PEO/LiMMT) nanocomposites produced by melt intercalation. Also,
Shen et al. [98] synthesized organic-inorganic hybrid nanocomposite materials of
poly(methyl methacrylate) (PMMA) and organically modified silicate (B34) systems
by melt intercalation with variation of tacticity and molecular weight as the main
molecular variable items.
(d) In situ synthesis.
Among the in situ intercalation method, the layered particle is swollen in monomer, and
the polymerization of the monomer is initiated afterward. Due to the presence of monomer
both in and out of the filler interlayers, the generated structure is significantly intercalated
or exfoliated. Also, on the basis of different polymerization rate or mechanism in and out of
the filler interlayers, reintragallery and extragallery polymerization reactions need to be
under control for uniform polymerization [96].