Page 187 - Polymer-based Nanocomposites for Energy and Environmental Applications

160 Polymer-based Nanocomposites for Energy and Environmental Applications

composites were fabricated by introducing the MoS 2 superstructures into a ferroelec-
tric polymer, namely, PVDF. Nanosheet superstructures were used as filler rather than
individual nanosheets because of their facile large-scale production and excellent
recyclability of the products. It was reported for the first time that the MoS 2
superstructure-based composites can exhibit significantly improved dielectric proper-
ties. More interestingly, the composites show significantly enhanced electric energy
storage capability when the loading of MoS 2 superstructures was low. This may open a
new way to fabricate flexible high-dielectric-constant polymer nanocomposites for
efficient energy storage applications [253].

5.3.6 PVA based nanocomposites
Polyvinyl alcohol (PVA) is an attracting insulating material with low conductivity;
hence, it is very handy in microelectronic industry [254]. The electric conductivity
dependsonthethermallygeneratedcarriersandalsoontheadditionofsuitabledopants.
PVA is a semicrystalline material with many interesting physical properties, which are
explored in many technical applications [255]. Different additives have been intro-
duced in PVA to modify and enhance its dielectric properties [256]. Inorganic additives
such as transition metal salts have a considerable influence on the optical and electric
properties of the PVA polymer [257]. The perovskite family of ferroelectric materials
along with PVA is being exploited in the fabrication of various devices like sensors,
actuators, transducers, and capacitors, which are widely applied in many electronic
components of the modern technology [258,259]. Barium zirconium titanate,
Ba(Zr 0.1 Ti 0.9 )O 3 (BZT) ceramic along with its composites with PVA has found poten-
tial applications for the microwave technology and piezoelectric devices due to their
highdielectricconstant,lowdielectricloss,andlargetunabilitybecausethesubstitution
of Zr 4+ for Ti 4+ ions has a benefit to the stability of the system [260–262].

5.4 Grafting techniques: Methods for synthesis
of polymer nanocomposites

To tune and control the surface properties, the synthesis of a dense film of polymer
chains covalently bound to the surfaces can be studied. The most straight forward
techniques are the “grafting to” and “grafting from” techniques for understanding
well-defined polymer layers (Fig. 5.8). Mansky et al. first used the “grafting to” pro-
cess and involves the condensation of end-functionalized polymers with the reactive
groups on the substrate [263].
This technique generally does not produce highly dense polymer brushes because
chemisorption of the initially added chains poses hindrance to the diffusion of subse-
quently added chains to the surface by forming a macromolecular barrier. However,
this limitation can be overcome by employing the “grafting from” approach where we
can exhibit higher grafting densities. A monolayer of small initiator molecules is cova-
lently attached to a solid surface in this method. After initiating the polymerization,
the chains grow from the surface, and the only obstacle to the propagation is the