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Effect of Geometrically Different Graphitic Nano-fillers on the Electrical Properties

of Polycarbonate Composites

This work was supported by the National Science Foundation’s REU program under grant number NSF GOALI 0758251

School of Mechanical and Materials Engineering Washington State University, Pullman, WA 99164

Santiago Caceres

Cal Poly, San Luis Obispo - WSU - REU Program

Dr. Sandeep Kumar (Project Supervisor), Dr. Katie Zhong (Faculty Advisor)

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).

Figure 1. Image Showing the different levels of

resistivity required for a variety of specific

applications

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 three-

dimensional 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

insulator-

conductor

transition point.

This situation is

known as the

percolation

threshold and is

characterized by

a sharp drop of

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.

Nanofiller Dissolved in 5 ml Chloroform and

Bath sonicated for 1 hour.

Bath Sonication Horn Type Sonication

15 Minutes of Horn-type (High Power)

sonification on Nanofiller.

PC/Nanofiller solution stirred for 30 minutes.

1.8g PC

Dissolved

in 10 ml

Chloroform.

Nano

filler

Nectar

45 Minutes more Horn type

sonication for PC/Nanofiller

solution.

Cast Solution into 10 Micron thick

films for characterization.

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 .

Fig. 3 (right): SEM image of a binary 3.0 wt% GNP Composite showing good dispersion and interfacial interactions.

Fig. 4 (left):SEM image of a ternary .75/.25 wt% (GNP/MWCNT) Composite showing synergistic interaction between the GNPs and MWCNTs

Motivation

Method

Scanning Electron Microscope (SEM) Resistivity Data

Conclusion

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.

Figure 6. Graph of resistivity for ternary hybrid

composites.

several orders of magnitude in resistivity.