Effect of Geometrically Different Graphitic Nano-fillers on the Electrical Properties
of Polycarbonate Composites
Santiago Caceres
Cal Poly, San Luis Obispo - WSU - REU Program
Dr. Sandeep Kumar (Project Supervisor), Dr. Katie Zhong (Faculty Advisor)
School of Mechanical and Materials Engineering Washington State University, Pullman, WA 99164
This work was supported by the National Science Foundation’s REU program under grant number NSF GOALI 0758251
Motivation
Scanning Electron Microscope (SEM)
Many applications require electrical conductivity in
polymers to provide electrostatic or electromagnetic
interference protection. Conductive composites are
generally made by incorporating conductive particles in
the insulating matrix. In most cases, highly conductive
fillers are added to the matrix to provide a threedimensional network of filler particles throughout the
polymer matrix.
The composite
material often
exhibits a
percolative
behavior with
respect to particle
loading, with a
well defined
insulatorconductor
transition point.
This situation is
known as the
percolation
threshold
and
is
Figure 1. Image Showing the different levels of
characterized by
resistivity required for a variety of specific
applications
a sharp drop of
several orders of magnitude in resistivity.
Polycarbonate (PC) is essentially an amorphous
polymer with very low conductivity (σ ≈ 10 15 Ω·cm), but
good mechanical properties and processability. E.g., in
electronics, polycarbonate components of computer
hard drives have been reinforced with conductive
nanofillers to render them smooth and conductive.
Multi-walled carbon nanotubes (MWCNTs) have
been used as a nanofillers to modify many polymers,
but suffer a detriment in their relatively high cost. In this
study, we attempt to mitigate those costs without
sacrificing properties by utilizing and verifying an
alternative nanomaterial approach based on blends of
MWCNTs and the much less expensive graphite
nanoplatelets (GNPs).
Fig. 2 (left):
SEM image of a
binary 3.0 wt%
MWCNT
Composite
showing strong
interfacial
interaction
between the
MWCNTs and
the PC matrix
along with
great net work
formation .
Resistivity Data
The graph in Fig. 5 Shows a clear percolation for
MWCNTs and GNPs. Further research is required to find
the exact loading, but at a loading of 0.5 wt% of
MWCNTs and GNPs alone, electrical resistivity of PC
composites decreased to 6.73 x 108 Ω·cm and 9.34 x107
Ω·cm, respectively, from 1.84 x 10 16 Ω·cm (for pure PC).
Figure 5. Graph of resistivity for binary nano filler
composites.
The hybrid system 0.25/0.25 wt% (MWCNT/GNP)
showed a resistivity drop to 1.08 x 108 Ω·cm. This means
that for a total loading of 0.5 wt%, a MWCNT/GNP hybrid is
just as effective as 0.5 wt% binary MWCNT composite (if
not more so) in creating a conductive network for
Polycarbonate.
Fig. 3 (right):
SEM image of a
binary 3.0
wt% GNP
Composite
showing good
dispersion and
interfacial
interactions.
Method
Bath Sonication
Nanofiller Dissolved in 5 ml Chloroform and
Bath sonicated for 1 hour.
Horn Type Sonication
15 Minutes of Horn-type (High Power)
sonification on Nanofiller.
45 Minutes more Horn type
sonication for PC/Nanofiller
solution.
Nano
filler
Nectar
1.8g PC
Dissolved
in 10 ml
Chloroform.
PC/Nanofiller solution stirred for 30 minutes.
Cast Solution into 10 Micron thick
films for characterization.
Fig. 4 (left):
SEM image of a
ternary
.75/.25 wt%
(GNP/MWCNT)
Composite
showing
synergistic
interaction
between the
GNPs and
MWCNTs
Figure 6. Graph of resistivity for ternary hybrid
composites.
Conclusion
In this study we introduced the concept of using two
geometrically dissimilar fillers, GNPs and MWCNTs, to
form a co-supporting network of both fillers to realize
synergistic effect for further improving the properties of
nano composites. This has been achieved with the
formation of a hybrid net structure in which the platelet
geometry shields the tube fillers from fracture and
damage during processing whilst still allowing full
dispersion of both during high power sonication. This
has been verified using morphological studies of the
film samples.
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