Page 520 - Polymer-based Nanocomposites for Energy and Environmental Applications

Polypyrrole-based nanocomposite adsorbents 473

17.7.5 Other demonstrated methods

In recent time, various other methods beside those discussed above have been inves-
tigated by researchers to incorporate nanofillers into polymer matrixes, among
which are self-assembly, phase separation, electrospinning, template synthesis,
emulsion polymerization, etc. The self-assembly method is a process in which indi-
vidual preexisting components organize themselves into desired patterns and func-
tions [36]. Molecule-mediated one is a well-known self-assembly technique, and it
is commonly used for the construction of nanocomposite films with desired thick-
ness [38]. In this case, nanofillers are often linked by weak hydrogen bond, van der
Waals, and magnetic/electric pole interactions instead of chemical bonds [36]. The
method is a time-consuming process. The phase-separation method of preparing
polymer nanocomposites consists of dissolution, gelation, and extraction using dif-
ferent solvents, and freezing or drying results in nanoscale porous foams [36]. Sim-
ilar to self-assembly method, phase-separation method usually takes relatively long
period of time to transfer the solid polymer into the nanoporous foam [39].The
electrospinning method has been widely used for the production of nonwoven mem-
branes of nanofibers from a variety of functional materials [39,40]. By this method,
a polymer solution was introduced into the electric field, and the polymer filaments
were formed from the solution between two electrodes bearing electric charges of
opposite polarity. But the feasibility of this process depends on a number of param-
eters, including the type of polymers, conformation of polymer chains, viscosity of
solution, polarity, surface tension of the solvents, electric field strength, and dis-
tance between spinnerets and collectors [36]. The method seems to be the only
method that can be further developed for mass production of one-by-one continuous
nanofibers from various polymers [39]. The template synthesis method of polymer
nanocomposites uses a nanoporous material as a template to direct the growth of
polymer into a desired shape and size. The most important feature of this method
may lie in that nanometer tubules and fibrils of various raw materials such as elec-
tronically CPs, metals, semiconductors, and carbons can be fabricated [39]. Previ-
ously, TiO 2 tubules were synthesized within the pores of a 60 mm-thick alumina
template membrane to make a semiconductor-conductor tubular nanocomposite
[41]. The TiO 2 tubules were first synthesized by the sol-gel process on the pores
of the aluminate template prior to thermal treatment. Furthermore, polypyrrole
wires were grown inside the semiconductor tubules via chemical polymerization
method. The TiO 2 -polypyrrole nanocomposite demonstrated to be an efficient
photocatalyst due to its enhanced electric property contributed mainly by the pres-
ence of the conductive polypyrrole. The emulsion polymerization method is a rel-
atively new approach, and it involves the addition of surfactants with unmodified
nanofillers under stirring conditions [42]. The polymerization via this method
begins by feeding a monomer with an initiator, and the process is allowed under
vigorous agitation. This is followed by allowing cooling of the reaction mixture
to room temperature, and the final product is obtained after filtration, washing,
and drying under reduced pressure. This method has been investigated mainly
for nanocomposite of polymer and silicate clay [43].