8.4.3 Nanorod–Nanowire Dispersed Polymer
Nanocomposites
As a lot of reports are available on the dispersion of nanofiller in the polymer
electrolyte matrix which provides in hand the superior properties as compared to
the micro fillers there are three fundamental mechanisms which dominate here:
(i) creation of percolation pathways, (ii) reduction of polymer reorganization tendency, and (iii) aspect ratio or shape of the nanoparticle. As nanofiller surface has
acidic and basic sites which play an effective role in the ion transport or mobility in
case of polymer electrolytes, these sites support the formation of conducting pathways for the ion transport. These paths are termed as percolation pathways. As the
nanofiller surface groups alter the existing interaction between the polymer chains
and the polymer–ion, this lowers the chain reorganization tendency and provides
smoother transport. Another key role is played by the aspect ratio of the nanoparticle.
As it is well known that the nanofiller have a high aspect ratio as compared to the
micro fillers, the aspect ratio is in inverse relation with the percolation threshold.
Also, the optimum or critical concentration is lower for the nanoparticles with high
aspect ratio due to increased size distribution (Celzard et al. 1996; Liu et al. 2015,
2016, 2017; Do et al. 2012).
The mechanism behind the improved conductivity on the addition of nanofiller
highlights the interaction electron-rich group of host polymer with the surface group
of nanofiller. This supports the salt dissociation, and more free charge carriers are
available for conduction. Another important role played by nanofiller is the disruption of the recrystallization tendency of the polymer chain arrangement, and hence
the amorphous content is increased which favors the smoother and faster ion
migration. So, the percolation pathways created by the nanofiller are beneficial for
the faster ion transport. It can be concluded from here that the larger the percolation
path, the faster will be the ion migration due to the long continuous path. This will
depend on the coordinating sites (acidic–basic) available to favor the ion mobility
and sufficient salt dissociation. Another remarkable point here is that the suitable
control over the acidic–basic sites of nanofiller can lead to the improved electrical
properties. Also, the alignment of the nanorod and nanowire is important as the
aligned nanoparticle parallel to the electrodes limits the perpendicular ion migration.
The nanoparticles with the different aspect ratio and shape also alter the mechanical
properties that are further altered by the alignment of nanorod–nanowire–nanotube.
Beyond the active–passive nanoparticle, one another attractive approach is the
use of 1 D nanofiller for enhancing the electrical properties. So, regarding this, Liu
et al. (2015) reported the dispersion of LLTO (Li 0.33 La 0.557 TiO 3 ) nanowire in the
PAN–LiClO 4 -based polymer–salt matrix. XRD analysis provides no alteration in the
peak of pure PAN with the addition of nanowire, and SEM micrograph displays the
uniform distribution of NW and is fully embedded in the polymer matrix evidenced
by TEM (Fig. 8.20a–f). The highest ionic conductivity was 2.4 Â 10
À4 S cm
À1
(15 wt. % LLTO) and is three orders higher than the polymer–salt matrix without
NW. AT high NW, content lowering of conductivity is observed and may be
8 Polymer Nanocomposites: Synthesis and Characterization
301
Nanocomposites
As a lot of reports are available on the dispersion of nanofiller in the polymer
electrolyte matrix which provides in hand the superior properties as compared to
the micro fillers there are three fundamental mechanisms which dominate here:
(i) creation of percolation pathways, (ii) reduction of polymer reorganization tendency, and (iii) aspect ratio or shape of the nanoparticle. As nanofiller surface has
acidic and basic sites which play an effective role in the ion transport or mobility in
case of polymer electrolytes, these sites support the formation of conducting pathways for the ion transport. These paths are termed as percolation pathways. As the
nanofiller surface groups alter the existing interaction between the polymer chains
and the polymer–ion, this lowers the chain reorganization tendency and provides
smoother transport. Another key role is played by the aspect ratio of the nanoparticle.
As it is well known that the nanofiller have a high aspect ratio as compared to the
micro fillers, the aspect ratio is in inverse relation with the percolation threshold.
Also, the optimum or critical concentration is lower for the nanoparticles with high
aspect ratio due to increased size distribution (Celzard et al. 1996; Liu et al. 2015,
2016, 2017; Do et al. 2012).
The mechanism behind the improved conductivity on the addition of nanofiller
highlights the interaction electron-rich group of host polymer with the surface group
of nanofiller. This supports the salt dissociation, and more free charge carriers are
available for conduction. Another important role played by nanofiller is the disruption of the recrystallization tendency of the polymer chain arrangement, and hence
the amorphous content is increased which favors the smoother and faster ion
migration. So, the percolation pathways created by the nanofiller are beneficial for
the faster ion transport. It can be concluded from here that the larger the percolation
path, the faster will be the ion migration due to the long continuous path. This will
depend on the coordinating sites (acidic–basic) available to favor the ion mobility
and sufficient salt dissociation. Another remarkable point here is that the suitable
control over the acidic–basic sites of nanofiller can lead to the improved electrical
properties. Also, the alignment of the nanorod and nanowire is important as the
aligned nanoparticle parallel to the electrodes limits the perpendicular ion migration.
The nanoparticles with the different aspect ratio and shape also alter the mechanical
properties that are further altered by the alignment of nanorod–nanowire–nanotube.
Beyond the active–passive nanoparticle, one another attractive approach is the
use of 1 D nanofiller for enhancing the electrical properties. So, regarding this, Liu
et al. (2015) reported the dispersion of LLTO (Li 0.33 La 0.557 TiO 3 ) nanowire in the
PAN–LiClO 4 -based polymer–salt matrix. XRD analysis provides no alteration in the
peak of pure PAN with the addition of nanowire, and SEM micrograph displays the
uniform distribution of NW and is fully embedded in the polymer matrix evidenced
by TEM (Fig. 8.20a–f). The highest ionic conductivity was 2.4 Â 10
À4 S cm
À1
(15 wt. % LLTO) and is three orders higher than the polymer–salt matrix without
NW. AT high NW, content lowering of conductivity is observed and may be
8 Polymer Nanocomposites: Synthesis and Characterization
301