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%