Page 186 - Polymer-based Nanocomposites for Energy and Environmental Applications

Polymer-based nanocomposites 159

host materials [32]. Surface functionalization was also employed to check particle
agglomeration within the polymer matrix by improving the particle-polymer matrix
interaction. Wang et al. got some nice results when they incorporated surface
functionalized TO into the ferroelectric copolymer PVDF-TrFE-CTFE [32]. Rod-
shaped TO nanoparticles (20 70 nm) were synthesized via a hydrothermal reaction
of titanium(IV)tetraisopropoxide and hydrogen peroxide. The hydrogen peroxide
facilitated the surface functionalization of the rods with Ba-OH surface groups
through a simple reflux reaction of the TO nanorods with CO 2 -free barium hydroxide
solution under an inert atmosphere. These nanocomposites showed a much better
energy density as compared with the neat polymer. For 10 vol% modified-TO, the
1
3
energy density was 6.9 J/cm at 200 MV m , which shows a 45% increase relative
to the neat polymer matrix with an energy density of only 4.7 J cm 3 at that same field.
They found highest energy density at 10 vol% and any further addition of filler
resulted in lowering of the energy density. This can be attributed to the interfacial
effects in the nanocomposites. A maximum interfacial area can be obtained for a given
particle size on adding a filler, beyond which additional filler can generate interfacial
polarization that can be detrimental to the dielectric response of the composite
[41,238,239].
Nanosized TO was introduced in polyvinyl alcohol (PVA) by Tuncer et al. for cryo-
genic grid applications [29,240]. An approximate 25% increase in breakdown strength
of the nano-TO filled PVA was observed. However, they found uniform distribution of
TO particles unlike the previous investigators. They concluded this uniformity in the
filler dispersion was responsible for the consistent breakdown strength of the filler-
embedded polymers.

5.3.4 Biopolymer cellulose

Energy storage devices have found great applications in many portable devices.
Hence, the eco-friendly materials replace the conventional acid battery metallic stor-
age devices that require more recharge time, acid utilization and have less abundance.
The presence of a big number of hydroxyl groups on cellulose along with the GO skel-
eton leads to the formation of comprehensive networks of intra- and intermolecular
hydrogen bonds with the cellulose matrix, thus creating both the crystalline and amor-
phous structural regions in the same polymer [241]. When the polar fillers are uni-
formly distributed over cellulose, flexible biomaterials are being formed [242-244].
However, the facile aggregation of graphene during synthesis degrades the material
performance of such composites. However, aggregation can be minimized by modi-
fying the GO sheets with selective functional groups so as to enhance the interactions
with the cellulose matrix [245].

5.3.5 MoS 2 nanosheet superstructures
Recently, molybdenum disulfide (MoS 2 ) nanosheets were explored for the dielectric
properties because of their semiconducting properties, appreciable bandgap [246-
251], and electric field tunable dielectric constant [252]. Ferroelectric polymer