Electrical, Morphological and Rheological Study of Melt‐Mixed Polystyrene/Copper Nanowire...

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Electrical, Morphological and RheologicalStudy of Melt-Mixed Polystyrene/CopperNanowire Nanocomposites

Bin Lin, Genaro A. Gelves, Joel A. Haber, Petra Potschke,Uttandaraman Sundararaj*

Polystyrene and copper nanowires were melt-mixed at 200 8C and 50 rpm in 5 mL and 15 mLDSM co-rotating conical micro-compounders (DSM5 and DSM15), respectively. The electrical,morphological and rheological properties of the resulting nanocomposites were studied. Theelectrical percolation of nanocomposites isbetween 1.0 and 2.0 vol.-% for the compositesprepared in DSM5 and above 2.0 vol.-% for thecomposites prepared in DSM15. SEMmicrographsshow smaller copper nanowire agglomeratesinside polystyrene from DSM15 than those fromDSM5. However, TEM micrographs reveal thatboth single copper nanowires and nanowire bun-dles coexist in the polymer matrix for thesamples prepared in both micro-compounders.No obvious microstructure transition is detectedby the dynamic rheological data at 200 8C.

Introduction

Polymer nanocomposites are usually polymers reinforced

with nanoscale fillers. To be considered nanoscale, fillers

must have at least one characteristic length scale on the

order of nanometers. Polymer nanocomposites are an

emerging new class of materials, which have attracted

B. Lin, G. A. Gelves, U. SundararajDepartment of Chemical andMaterials Engineering, University ofAlberta, Edmonton, Alberta T6G 2G6, CanadaFax: þ1 780 492 2881; E-mail: [email protected]. A. HaberInternational Solar Electric Technology, Inc., 20600 Plummer St.,Chatsworth, CA 91311, USAP. PotschkeDepartment of Polymer Reactions and Blends, Leibniz Institute ofPolymer Research Dresden, Hohe Strasse 6, Dresden D-01069,Germany

Macromol. Mater. Eng. 2008, 293, 631–640

� 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

great attention both in industry and academia. Nanocom-

posites are expected to provide better electrical, thermal

and mechanical properties than conventional composites

at lower filler contents because the nanofillers have high

aspect ratios (or surface area to volume ratios) and the

characteristic size of the nanofillers is about the size of the

radius of gyration of a polymer chain, Rg (5–20 nm).[1]

Conductive 1D nanofillers, such as carbon nanotubes[2–4]

and metal nanowires,[5] are attractive because incorpora-

tion of these nanofillers into polymers can produce

antistatic, electrostatically dissipative, and electromagne-

tically shielding and absorbing materials.[6]

Three different methods are commonly used in prepar-

ing polymer nanocomposites, namely, melt mixing, in situ

polymerization and solution processing.[7] Melt mixing is

the preferred method because it is environmental benign

(free of solvents) and it is compatible with current

industrial processes.[8] However, for initial evaluations,

it normally needs more materials (more than 50 g) than

DOI: 10.1002/mame.200800045 631

B. Lin, G. A. Gelves, J. A. Haber, P. Potschke, U. Sundararaj

Figure 1. a) SEM; and, b) TEM micrographs of the synthesizedCuNW.

632

the other methods. This amount of material is not possible

for nano-materials that are synthesized in the laboratory

scale (less than 1 g). There are several miniature mixers

with volumes of 1–15 cm3 that are commercially available,

like the MiniMAX molder and micro-compounder (or

miniature twin-screw extruder).

It has been shown that the MiniMAX is not efficient in

preparing uncompatibilized polymer blends[9,10]compared

to those prepared from the extruder and the batch mixer.

This is because the flow field generated by the MiniMAX

has only shear flow without any extensional elements or

reorientation. Therefore, it is difficult to get a good

dispersion of nanofillers inside the polymer matrix due

to the high van derWaals interactions between nanofillers.

However, it is expected that by applying appropriate shear

during the mixing, the tendency of the nanofillers to form

aggregates may be minimized.[11]

Themicro-compoundershavebeen foundtobesuccessful

in preparing polymer and carbon nanotube nanocompo-

sites.[12–14] There are several companies that provide the

micro-compounder, including DSM (Heerlen, Netherlands),

DACAInstruments (Goleta,CA,USA)andHaake Instruments

Inc. (Paramus, NJ, USA). The micro-compounders from

different sources have common features in their configura-

tions. They all are comprised of a conical twin-screw

extruder with a bypass, which allows the melt material to

recirculate so that the material can be mixed for a certain

period of time. The capacity of the micro-compounder is

approximately 5 cm3, though the DSM has also developed a

triple sized micro-compounder with 15 cm3 capacity.

We have previously reported[5,15–17] that copper nano-

wires (CuNW) with high aspect ratio (50–500) have been

synthesized by the template-directed method in our

laboratory. Nanocomposites of polystyrene/copper nano-

wire (PS/CuNW) prepared in solution have shown

enhanced electrical properties[5,17,18] as compared to the

pure polymer. The PS/CuNW nanocomposites have also

been melt mixed in the APAM,[19] a custom designed

asymmetric miniature mixer.[20] It is found that the

nanocomposites prepared in the APAM show an electrical

percolation concentration similar to the composites

prepared in solution, which is between 1.0 and 2.0

vol.-%. In this paper, polystyrene (PS) and CuNW are

directly melt mixed in two commercially available DSM

micro-compounders, with volumes of 5 and 15 cm3 (DSM5

and DSM15, respectively). Nanocomposites are extruded

from the micro-compounders and their properties are

analyzed. The electrical volume resistivity of the nano-

composite is measured to detect the electrical percolation

threshold. The overall dispersion of the copper nanowires

inside the pristine polymer is observed by scanning

electron microscopy (SEM) and the structure of the

nanowires is further examined with transmission electron

microscopy (TEM). Rheological data of the nanocomposites



at different copper nanowire contents are analyzed to

check the microstructure of the nanocomposites.

Experimental Part

Preparation of PS/CuNW Nanocomposites

CuNWs were synthesized in our laboratory by using 10� 25 cm2

aluminium oxide templates (PAO). For each batch, around 3 g of

CuNWs could be produced. Figure 1 shows the SEM and TEM

micrographs of the synthesized copper nanowires. The nanowires

had a diameter of around 25 nm and an average length of

DOI: 10.1002/mame.200800045

Electrical, Morphological and Rheological Study of Melt-Mixed . . .

1.29� 0.83 mm. A detailed description of the experimental pro-

cedures for nanowire synthesis can be found elsewhere.[5,16] PS

(Styron 666D) was kindly provided by the Dow Chemical Com-

pany. The densities at 25 8C of the copper and the PS are 8.96 and

1.04 g � cm�3, respectively. In this paper, we assume that the

CuNWs have the same density as the bulk copper. PS/CuNW

composites with CuNW concentrations at 0, 0.25, 0.5, 0.75, 1.0, 2.0

and 4.0 vol.-%, calculated from mass percentage using the den-

sities specified above, were prepared. The nanocomposite with

8.0vol.-% CuNWwas also obtained from the DSM15, whichwas used

for electrical property measurement only. The concentrations of

CuNW in this paper are expressed in volume percentage, unless

otherwise specified.

The PS pellets and CuNWs were premixed with a spatula and

then fed into the two DSM micro-compounders at 200 8C and

50 rpm. For both mixers, after a mixing time of 6 min, the sample

products were extruded as strands through a heated cylindrical

die directly into cooling water. Essentially, the DSM15 is

volumetrically triple the scale as the DSM5 and both have similar

configurations. Figure 2 shows photographs of open DSM5 and

DSM15, both consisting of two conical co-rotating screws with a

bypass. The bypass differentiates these micro-compounders from

a standard extruder. In a typical continuous flow extruder, the

residence time is determined by screw length; whereas, in the

Figure 2. Photographs of: a) DSM5; and, b) DSM15.



DSM micro-compounders, the materials circulate for a defined

time, making them more like batch mixers.

Electrical Resistivity Measurements

The volume resistivity was measured with thin circular sheets

(diameter� thickness: 67�0.60 mm) prepared by compression

molding the small strand pieces with a length between 0.5 and

1.0 mm, which were cut from the extruded strands obtained from

the micro-compounders. The amount of the small strands was

weighed according to the volume of the mold and then put

randomly into the mold for press molding, either parallel to or

perpendicular to the extrudate direction. The electrical volume

resistancewasmeasuredwith a Keithley electrometerModel 6517

and an 8009 resistivity test fixture equipped with ring electrodes.

Prior to the measurements, the surfaces of the samples were

cleaned with ethanol. According to ASTM D4496 and D257, the

measured volume resistance, Rv, was converted to volume

resistivity, rv, using

rv ¼ A

tRv (1)

where A is the effective area of the measuring electrode and t is

the average thickness of the specimen. For each specimen, the

reported data are the arithmetic average of at least four

measurements.

Scanning Electron Microscopy

The morphology of the synthesized copper nanowires and the

fracture surfaces of the composite strands were analyzed using a

JEOL 6301F field emission scanning electron microscope. Before

imaging, the samples were sputter-coated with chromium. The

backscattered SEM micrographs were taken at an accelerating

voltage of 20 kV. For the composites, the aggregates larger than

2 mmwere measured with SigmaScan Pro (version 4.01) software.

The area (Aagg) of each aggregate (or particle) was determined and

the equivalent diameter was obtained by assuming that the

particle cross-section was circular in shape:

Deq ¼ffiffiffiffiffiffiffiffiffiffiffiffi4Aagg

p

r(2)

This equivalent diameter (Deq) of more than 1000 particles per

sample was used to compare the particle size (cf. Figure 5).

The lengths of CuNW before and after melt mixing were also

measured. Pristine CuNWs were dispersed in methanol (CH3OH)

using ultrasound for 1 h after liberation from the PAO template.

For CuNW, after melt mixing, the nanocomposite was first

dissolved in methylene chloride (CH2Cl2) overnight and filtered

through Whatman PTFE paper (pore size: 0.2 mm). The solute was

washed with CH2Cl2 five times, suspended in CH2Cl2 and then put

in an ultrasonic bath for 1 h. Immediately after sonication, around

1 mL of each of the suspensions obtained before and after

processing was spin cast into a 2.5� 2.5 cm2 glass slide at

3 000 rpm for 2 min. The samples were then characterized by SEM.

www.mme-journal.de 633


634

The length of every recognizable nanowire was measured. In this

method, nanowireswith lengths greater than 0.2mmwere collected

for analysis. For each sample, at least 250 single nanowires were

counted.

Figure 3. Volume resistivity of PS/CuNW composites at differentCuNW contents.

Transmission Electron Microscopy

For the pure synthesized copper nanowires, a drop of methanol/

nanowire suspension was placed on a molybdenum grid coated

with carbon film. Immediately after the methanol was evapo-

rated, the nanowires were examined with a JEOL 2010

TEM equipped with a thin-window energy-dispersive X-ray

spectrometer at 200 kV. For the PS/CuNW composites, the

extruded strands were ultramicrotomed to provide slices that

had thickness of around 70 nmusing an Ultracut diamond knife at

room temperature. The samples were cut along the cross-section

of the strands; that is, perpendicular to the extrusion direction.

The thin sections of the nanocomposite samplewere examined by

TEM with a Philips Morgagni 268 microscope at an acceleration

voltage of 70 kV.

Rheological Characterization

Dynamic rheological characterizations were performed in a

Rheometrics RMS800 Rheometer with a 25 mm parallel plate

fixture at 200 8C under nitrogen atmosphere. Samples with a

thickness of around 1mmwere tested. Frequency sweeps from 0.1

to 100 rad � s�1 were performed at low strains, 3–10%, where the

materials showed linear viscoelastic behavior.

X-Ray Photoelectron Spectra (XPS) Characterization

For the pure copper nanowires, the suspension of the copper

nanowires in methanol was dried under reduced pressure onto a

piece of silicon wafer. The X-ray photoelectron spectra (XPS) of the

dried copper nanowires and the freshly fractured surface of the

nanocomposite were collected with a Kratos Axis 165 X-ray

photoelectron spectrometer using Al Ka (1 486.6 eV) as the

electron source and operating at 15 kV and 14 mA. The base

pressure of the instrument was about 3�10�10 mbar (1

mbar¼ 100 Pa). The XPS binding energy (BE) was internally

referenced to the aliphatic C (1s) peak (BE¼284.8 eV).

Results

Electrical Resistivity

Figure 3 shows the effect of CuNW content on the volume

resistivity of PS/CuNW nanocomposites prepared from

DSM5 and DSM15. At 0% CuNW, the data reported are

based on the pure polymer processed at the DSM5 and the

DSM15 micro-compounders, respectively. Without any

conductive nanowires filler, the polymer has a volume

resistivity in the order of 1018 V � cm. As the concentration

of the copper nanowire increases, the resistivity decreases.



A dramatic decrease in volume resistivity indicates the

formation of an electrically percolated network. The

electrical percolation is between 1.0 and 2.0% for the

nanocomposites melt mixed from DSM5, which is similar

to thepercolation threshold of the composites preparedwith

solution method[18] and melt mixed from the APAM,[19] a

miniature mixer that was custom designed in our group.[20]

However, the nanocompositesmixed inDSM15 showhigher

volume resistivity than those from DSM5 for nanowire

composition less than 2.0%. At 2.0%, the difference

between the volume resistivity data for the sample

prepared from DSM5 and DSM15 is greatest, around eight

orders of magnitude. The percolation for the nanocompo-

sites obtained from DSM15 is greater than 2.0%.

Morphology Characterization

Figure 4 shows the backscattered SEM micrographs of PS/

CuNW with 2.0% nanowires prepared from the DSM5

(Figure 4a, c and e) and DSM15 (Figure 4b, d and f)

micro-compounders. Figure 4a and b illustrate the general

dispersion of the nanowires at a low magnification, and

Figure 4c–f are the micrographs at higher magnifications.

Copper nanowires and nanowire aggregates appear as

bright spots in the backscattered micrographs. Figure 4a

contains larger aggregates compared with Figure 4b,

Figure 4c shows less tiny bright spots compared to

Figure 4d, and Figure 4e exhibits fewer single nanowires

or bundles of 2 or 3 nanowires than Figure 4f. Therefore,

the SEM micrographs indicate that the nanowires

dispersed better when they were processed in DSM15.

Figure 5 gives the size distribution of the aggregates with

sizes greater than 2 mm. It supports our observation that

the composite prepared from DSM15 has much smaller

DOI: 10.1002/mame.200800045


Figure 4. Backscattered SEMmicrographs of the PS/CuNW composite (2% CuNW) extruded from: a,c,e) DSM5; and, b,d,f) DSM15. Note scalebars. The arrows in f are pointing to the smaller nanowire bundles.

aggregates (or particles) and less large aggregates as

compared to that from DSM5. In other words, DSM15 is

more efficient in breaking up the nanowire bundles.

Figure 6 presents the TEM micrographs of PS/CuNW

with 2.0% nanowires obtained from DSM5 (Figure 6a and c)

and DSM15 (Figure 6b and d). Nanowire aggregates and

individual nanowires with long and short nanowires are

shown. It is clear that the nanowires are not well dispersed



and distributed inside the PS matrix. The lengths of CuNW

after processing are measured, and the number-average

lengths for the nanowires obtained from the DSM5 and

DSM15 are 0.86� 0.65 and 0.85� 0.70 mm, respectively.

Figure 7 gives the length distribution of CuNW before and

after melt mixing. Before mixing, the average length of the

CuNW is 1.29� 0.83 mm and 30% of the nanowires are

longer than 1.5 mm, whereas, after mixing, only 15% of the



Figure 5. Aggregate size distribution of the PS/CuNW composite(2% CuNW) extruded from DSM5 and DSM15. Note that onlyaggregates greater than 2 mm were counted.

Figure 6. TEM micrographs of PS/CuNW (2% CuNW) from: a,c) DSM5

636Macromol. Mater. Eng. 2008, 293, 631–640


nanowires have length greater than 1.5 mm. Compared

with the original copper nanowires, there is a 34%

reduction in the average length after melt processing;

however, the difference of the average length between the

micro-compounders is minor. The nanowires processed

from DSM15 have a larger standard deviation and the

composite contains 5% more nanowires with lengths

shorter than 1.25 mm compared to DSM5.

Rheological Properties

It has been shown in literature that rheological data

provide microstructure information about the nanocom-

posite.[21–23] The dynamic rheological properties of the PS/

CuNW nanocomposites at 200 8C were characterized and

the complex viscosity and the storage modulus for

nanocomposites with different CuNW compositions are

presented in Figure 8 and 9. The data for the 0% CuNW are

obtained using pure polymer that was processed for the

same period of time in the DSM5 and the DSM15

; and, b,d) DSM15. Note scale bars.

DOI: 10.1002/mame.200800045


Figure 7. Length distribution of CuNW: a) before mixing; and,b) after dissolving PS from the PS/CuNW composite (2% CuNW)extruded from DSM5 and DSM15.

Figure 8. Complex viscosity at 200 8C for the PS/CuNW compo-sites from: a) DSM5; and, b) DSM15.

micro-compounders. It should be noted that there was no

difference between the rheological data of PS before and

after processing. The complex viscosities of the nanocom-

posites with 1.0% CuNW are around 30% higher than those

of pure PS for frequencies less than 1 s�1, whereas, at

frequency higher than 10 s�1, the viscosities are greater by

10–15%. The viscosities of the nanocomposites prepared

from both micro-compounders increase with CuNW

content. The curve of the complex viscosity versus frequency

has a similar shape irrespective of the filler concentration

studied; that is, the viscosities are relatively flat at low

frequencies and decrease faster at higher frequencies

(Figure 8). No obvious yield stress at low frequencies has

been observed for the systems studied.

The storage modulus of the nanocomposites in Figure 9

increases as the nanowire composition increases. Again, all

the curves are similar in shape. No plateau at low



frequencies was detected even when the CuNW content

was 4.0%. Figure 10 compares the storage modulus of the

nanocomposites at 0.1 rad � s�1. It is demonstrated that the

storage modulus of the nanocomposites obtained from

DSM5 and DSM15 are similar and the increase in the

modulus is minor upon the addition of CuNW.

The dynamic rheological data for the nanocomposites

obtained from DSM5 and DSM15 are different from those

composites prepared in solution.[18] An obvious yield

stress[18,21–23] and/or a plateau of storage modulus[18,21–23]

at low frequencies is an indication of rheological fluid-solid

transition, or a rheological percolation. The lack of yield

stress and plateau of storage modulus of the PS/CuNW

nanocomposites melt-mixed in the micro-compounders

suggests that these nanocomposites are different from the

studies reported in the literature. For example, polymer/

carbon nanotube nanocomposites show a rheological



Figure 9. Storagemodulus at 200 8C for the PS/CuNW compositesfrom (a) DSM5 and (b) DSM15.

Figure 10. Storage modulus at 1 s�1 for the nanocompositesprepared from the micro-compounders.

638Macromol. Mater. Eng. 2008, 293, 631–640


percolation concentration, which is lower than the

electrical percolation concentration.[21–23] It is lower because

the rheological percolation threshold originates from a

combined nanotube-polymer network (including the poly-

mer-polymer entanglement network, the carbon nanotube

network and the carbon nanotube-polymer network) and

the electrical percolation threshold requires a nanotube

network. The lack of a rheological percolation threshold for

the PS/CuNW prepared from the micro-compounders

suggests that the poor dispersion of nanowires weakens

the interaction between the polymer chains and the copper

nanowires, restricting a rheological fluid-solid transition.

Discussion

The electrical percolation thresholds for PS/CuNW melt

mixed in the DSM5 and the DSM15 micro-compounders

are between 1.0 and 2.0%, and above 2.0%, respectively.

The volume resistivity data of the nanocomposites from

DSM5 have similar trend, magnitude and percolation

threshold as those for the PS/CuNW composites prepared

in solution.[18] However, the nanocomposites from DSM15

show higher volume resistivity and a higher electrical

percolation threshold, suggesting that scale-up is not a

simple task.

The SEM analysis shows that the nanocomposites pre-

pared in DSM15 have smaller copper nanowire aggregates

than those from DSM5, indicating that DSM15 is more

efficient in breaking up nanowire bundles. It is well

accepted that well dispersed nanoparticles are essential to

achieve low percolation threshold; however, the PS/CuNW

system obtained from the micro-compounders shows the

opposite effect. The aspect ratio of nanofillers is important

and can alter the percolation threshold. During the direct

melt mixing, the high shear applied tends to break up the

nanofiller bundles and also breaks the individual filler into

shorter segments. Shorter filler length results in smaller

aspect ratio, which consequently increases the percolation

threshold of the nanocomposite. Therefore, in melt pro-

cessing, appropriate mixing conditions are required, and a

longer mixing time at a lower rotation speed is preferred.

In this paper, a rotation speed of 50 rpm and amixing time

of 6 min at 200 8C are used for preparing all the nano-

composites in the DSM5 and the DSM15micro-compounders.

The lengths of the nanowires are reduced after processing

in the two micro-compounders; however, the final

nanowire length in the two mixers is very similar. If the

length distribution is examined carefully (Figure 7), it can

be seen that DSM15 has 5% more nanowires shorter than

1.25 mm compared to DSM5.

DSM15 has triple the volume of DSM5. Both micro-

compounders have similar configurations: co-rotating

conical screws and a recirculation path. For both mixers,

DOI: 10.1002/mame.200800045


Figure 11. Axial force versus time during the feeding andmixing ofPS and 2.0% CuNW in the micro-compounders.

Figure 12. XPS high resolution spectrum of Cu 2p peak for: a) thesynthesized CuNW; and, the PS/CuNW composite (2% CuNW)prepared from: b) DSM5; and, DSM15 (c).

the screw speed is 50 rpm and the mixing time is 6 min

after the materials are fed into the compounder. The

feeding time is around 3 min for DSM5 and it is around

5min for DSM15, as shown in Figure 11. Results show that

the copper nanowires dispersed better after being melt

mixed in DSM15, which may be due to the higher shear

stress applied. It is found from the experimental readings

during the processing of 2.0% CuNW in PS, the maximum

axial force in the DSM15 and the DSM5 micro-

compounders are 4 070 and 978 N, respectively; that is,

the force inside DSM15 is four times larger than that inside

DSM5 even though it only has three times the volume.

Therefore, the materials experience higher shear stresses

in DSM15 than those inside DSM5. The higher shear stress

results in higher energy dissipation and higher tempera-

ture increase in DSM15. This highermelt temperaturemay

increase the surface oxidation rate of copper nanowires

and consequently, lead to lower volume resistivity of the

nanocomposites.[24] The TEM micrograph in Figure 6d for

the nanocomposite prepared from DSM15 shows that

there is some roughness on the nanowire surfaces,

whereas, for the nanocomposite obtained from DSM5,

the surfaces of the nanowires in Figure 6c appear to be

smoother. The roughness is attributed to the copper

oxide[18,25] generated during the mixing process, which

can be detected with XPS analysis.

Figure 12 shows the high resolution XPS Cu 2p spectrum

of the synthesized copper nanowires and the nanocompo-

sites with 2.0% CuNW prepared from DSM5 and DSM15. It

has been recognized[26–28] that Cu 2p3/2 has a single peak at

932.7 eV, Cuþ has a single peak at 932.4 eV and Cu2þ has a

main peak at 933.6 eV. For CuO, there are shakeup

satellites at higher binding energies (940.3 and 943.1 eV). It

is clearly seen from Figure 12 that the magnitudes of the

main peak and shakeup satellites associated with a Cu2þ

increase from pure copper nanowires (Figure 12a) to the



nanocomposite from DSM5 (Figure 12b) and are even

higher for the nanocomposite from DSM15 (Figure 12c). It

is also observed that the combination peak (including

contributions from Cu, Cuþ and Cu2þ) gets wider with

increased oxidation (from Figure 12a to c). The XPS results

confirm our hypothesis and TEM examination that the

copper nanowires inside the nanocomposites prepared

fromDSM15 have higher copper oxide contents than those

from DSM5.

Conclusion

We studied polystyrene/copper nanowire composites at

different CuNW compositions melt mixed in two DSM

micro-compounders, with capacities of 5 and 15 cm3. The

electrical percolation threshold for the nanocomposite

prepared from DSM5 is between 1.0 and 2.0%, which is

lower than that from DSM15 (greater than 2.0%), but is

similar to that of nanocomposites prepared in solution. It

implies that scale up from DSM5 to DSM15 is not a simple

process. The SEM and TEM micrographs show that the

nanowires are still not well dispersed inside the polymer

matrix, perhaps because of the high van der Waals inter-

action between the nanowires. The dynamic rheological

characterization indicates that there is nofluid-solid transi-

tion upon the addition of nanowires, suggesting the nano-

wires are not well dispersed, resulting in a weak interaction

between the nanowires and the polymer chains.

Acknowledgements: We would like to thank the Natural Sciencesand Engineering Research Council of Canada (NSERC) for the



640

financial support of this work. B.L. is grateful for a financialassistance from the Leibniz Institute of Polymer Research Dresdenduring her stay as a guest scientist. We would like to thankH. Scheibner, S. Pegel and E. Cantergiani at the Leibniz Institute ofPolymer Research Dresden for instruction on the DSM micro-compounders. We would also like to thank Dr. D. Karpuzov,Mr. G. Braybrook and Mr. R. Mandryk at University of Alberta forhelping with XPS analysis, SEM and TEM imaging.

Received: February 14, 2008; Revised: April 28, 2008; Accepted:May 5, 2008; DOI: 10.1002/mame.200800045

Keywords: copper nanowires; electrical conductivity; mixing;nanocomposites; percolation; resistivity

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DOI: 10.1002/mame.200800045

Electrical, Morphological and Rheological Study of Melt‐Mixed Polystyrene/Copper Nanowire...

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