GNP Nanocomposite Direct current volume

resistivity Alternating Current

relative permittivity

Direct current surface resistivity

SEM imaging

Characterization Methods

Soy protein coated graphite nanoplatelets in polycarbonate composite for improved static dissipation rate

Michelle Tsui1, Bin Li2, Jianying Ji2, Michael Robert Pierce2 and Wei-Hong Zhong2 1Department of Materials Science and Engineering, University of California-Berkeley

2School of Mechanical and Materials Engineering, Washington State University

Electrostatic Discharging Electrostatic discharging (ESD) occurs when an electrically charged object attempts to neutralize through a sudden flow of electric charge, resulting in a spark. Although most human encounters with ESD do not cause serious injury, a spark can inflict latent and catastrophic damage to electronic parts as well as cause fires or explosions.

Introduction

Electrical Properties

Investigate the effect of SPI concentration on dispersion and interfacial interaction

Probe sonication- effect of power, time, and temperature on GNP size during sample preparation

This work was supported by the National Science Foundation’s REU program under grant number DMR-1062898

Figure 1. Electrostatic discharging damage to a circuit capacitor

• Probe sonication for 1 hour: Disperse aggregated graphite platelets

GNP Exfoliation

• Stir on hotplate for 6 hours: Denature SPI and let denatured SPI coat GNP

Surface Treatment

• Dissolve and mix PC with suspension for 6 hours: Achieve uniform composite solution and thorough contact between GNP and Polymer

Compounding

• Bath sonicate for 1 hour: Ensure homogeneous dispersion of GNP

Further Dispersion

• Solution cast on glass panel

• 0.03-0.05 mm thickness for testing

Casting

Sample Preparation

Polycarbonate (PC)

Exfoliated Graphite Nanoplatelets (xGNP)

Soy Protein Isolate (SPI)

C16H14O3

Applications in industry include: Electronic components, construction, transportation, data storage (CDs, DVDs…)

Diameter of 25 micrometers

Width of 5-10 micrometers

Graphite also in pencils, superconductors, batteries, lubricant

Applications include: adhesives, asphalts, cosmetics, polyesters, textile fibres

Food applications : cereal, dietary supplement, pasta, infant formulas

Rate of static dissipation, τ:

ESD protection requires quick dissipation rate

Want low electrical resistivity and low relative permittivity

The Polymer Composite:

Polymers used in engineering applications for lightness, processability and high specific strength, but are strong insulators and prone to ESD

Conductive filler added to polymer decreases static dissipation rate. Effectiveness depends strongly on:

• dispersion of particles in polymer • interfacial bonding between filler and polymer

Carbon nanoparticles are highly conductive and shape and size make them attractive choice, but agglomeration occurs due to attractive forces (i.e. Van Der Waals) between particles

Surface treatment of filler improves dispersion and interfacial bonding. Surfactants usually toxic, but hypothesize soy protein isolate (SPI)— edible,

abundant, easily produced—is economical alternative with competitive results

Figure 2. Direct current (DC) surface resistivity of SPI treated and non-treated composites at different concentrations of GNP.

Figure 3. DC volume resistivity of SPI treated and non-treated composites versus concentration of GNP.

1.E+06

2.E+08

4.E+10

8.E+12

2.E+15

0.0 1.0 2.0 3.0 4.0 5.0

Vo

lum

e r

esi

stiv

ity

(oh

m*c

m)

Concentration of GNP (wt%)

SPI

no SPI

0.05 wt% 1.0 wt%

SPI improves dispersion, allowing a conductive network of GNP (percolation threshold) to form at 0.05 wt%, compared to 1 wt% without SPI

1E+03

2E+05

4E+07

8E+09

2E+12

3E+14

0 1 2 3 4 5 6

Surf

ace

re

sist

ivit

y (O

hm

s/Sq

)

Concentration GNP (wt%)

SPI

no SPI

Results

GNP reduces both volume and surface resistivities of PC, while SPI further reduces resistivity of composite through improved dispersion

SPI prevents permittivity from increasing with increasing GNP concentration—a desirable property to static dissipation.

Facile SPI surface treatment improves interfacial interaction between GNP and PC

Scanning Electron Microscopy (SEM) Imaging

Figure 5. SEM images of fractured surface along thickness of composite. A. SPI treated specimen at X20,000-

good dispersion and many well-bonded interfaces of smaller particles

B. Untreated specimen at X20,000- poor dispersion leading to agglomerates (circled) and poor interfacial interaction

C. Large agglomerate of small GNP particles in untreated specimen at X50,000

Dielectric properties\

Conclusions

Future Work

Acknowledgements

PC

Good Interface

GNP

PC

GNP Agglomerate

Poor Interface

A. SPI Treated B. Untreated

C. Untreated

1.E+00

1.E+01

1.E+02

1.E+03 1.E+04 1.E+05 1.E+06

Re

lati

ve P

erm

itti

vity

Frequency (Hz)

SPI Treated GNP 4.5%

3%

1%

1.E+00

1.E+01

1.E+02

1.E+03 1.E+04 1.E+05 1.E+06

Re

lati

ve P

erm

itti

vity

Frequency (Hz)

Untreated GNP 4.50%

3%

1%