Effect of Geometrically Different Graphitic Nano-fillers ...reu.mme.wsu.edu/2010/files/26.pdf¢  geometrically

Effect of Geometrically Different Graphitic Nano-fillers ...reu.mme.wsu.edu/2010/files/26.pdf¢  geometrically

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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


    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


    behavior with

    respect to particle

    loading, with a

    well defined



    transition point.

    This situation is

    known as the


    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


    in 10 ml





    45 Minutes more Horn type

    sonication for PC/Nanofiller


    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



    Scanning Electron Microscope (SEM) 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


    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


    Figure 6. Graph of resistivity for ternary hybrid


    several orders of magnitude in resistivity.