7
Available online at www.sciencedirect.com Colloids and Surfaces A: Physicochem. Eng. Aspects 311 (2007) 48–54 Conductive coatings and composites from latex-based dispersions Lorraine F. Francis a,, Jaime C. Grunlan b , Jiakuan Sun c , W.W. Gerberich a a Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, MN 55455, United States b Department of Mechanical Engineering, Texas A; M University College Station, TX 77843-3123, United States c Rohm and Haas (China) Holding Co. Ltd., China Research and Development Center 1077, Zhang Heng Road, Zhangjiang Hi-tech Park, Shanghai, 201203, China Available online 24 August 2007 Abstract Electrically conductive coatings and composites are prepared from aqueous dispersions of conducting particles and polymer latex particles. Relatively small amounts of conductive particles are needed to develop electrical conductivity, because the particulate nature of the latex leads to a segregated network that lowers the percolation threshold. Several nanosized conductive fillers have been studied: carbon black, antimony-doped tin oxide, indium tin oxide and carbon nanotubes. The latex chosen for most studies was either a poly(vinyl acetate-co-acrylic) polydisperse latex, a poly(vinyl acetate) polydisperse latex, or monodisperse poly(vinyl acetate) latex. This paper reviews the effect of particle size, aggregation and aspect ratio on the microstructure and properties of conductive composites and coatings. © 2007 Elsevier B.V. All rights reserved. Keywords: Composite; Latex; Conductivity; Coating 1. Introduction Composites containing conductive particles in a noncon- ductive polymer matrix have been used for many years for applications such as electromagnetic shields, thermally sensi- tive resistors, and sensors [1]. In recent years, the development of flexible electronic devices and large area “macroelectronics” [2] has led to a demand for coatings with tailored electrical prop- erties and functions. In this paper, a common base for liquid applied coatings – a latex dispersion – is combined with elec- trically conductive nanoparticles to create functional materials and coatings for a variety of applications. To impart electrical conductivity to a composite, the quantity of conductive particles must be high enough for the particles to form an interconnected network [3,4]. The formation of the network is commonly described as a percolation phenomenon in which the conductivity (σ ) follows a power law and jumps by orders of magnitude when the volume fraction of conductive particles (V) surpasses a critical percolation threshold (V c ): σ = σ 0 (V V c ) s (1) In Eq. (1), σ 0 is a proportionality constant, and s is the criti- cal conductivity exponent (1.5–2.0 for a 3D random system). Corresponding author. Tel.: +1 612 625 0559; fax: +1 612 626 7246. E-mail address: [email protected] (L.F. Francis). The formation of an interconnected conductive particle network depends both on the morphology of the conductive particles and the characteristics of the matrix and resulting composite microstructure. A variety of theories and models have been proposed to account for the conductivity of composites and the effect microstructure on conductivity [5 and references therein]. For random addition of conductive particles to a con- tinuous nonconductive matrix, the critical conductive particle content needed to establish the network is roughly 16 vol% [3,4]. Lowering the percolation threshold requires altering the con- ductive particles, the matrix or both. For example, particles with asymmetric morphologies create percolating networks at lower contents than do spherical particles [5]. The microstructure of the matrix can force percolation to occur at a lower value by seg- regating the conductive particles to a restricted volume within the microstructure. For example, conductive particles that segre- gate to one phase in a polymer blend form a percolating network selectively in that phase and therefore at a lower overall particle content [6 and references therein]. The magnitude of the conduc- tivity past the threshold strongly depends on the properties of the conductive particles themselves and the connections between the particles [7]. In this paper, latex particles are used to construct a segre- gated network of conducting particles, as shown schematically in Fig. 1. Conductive particles are mixed with nonconductive latex particles in an aqueous dispersion. On drying, latex under- goes a sequence of microstructure changes [8 and references 0927-7757/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2007.08.026

Conductive coatings and composites from latex-based dispersions

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Page 1: Conductive coatings and composites from latex-based dispersions

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Available online at www.sciencedirect.com

Colloids and Surfaces A: Physicochem. Eng. Aspects 311 (2007) 48–54

Conductive coatings and composites from latex-based dispersions

Lorraine F. Francis a,∗, Jaime C. Grunlan b, Jiakuan Sun c, W.W. Gerberich a

a Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, MN 55455, United Statesb Department of Mechanical Engineering, Texas A; M University College Station, TX 77843-3123, United States

Rohm and Haas (China) Holding Co. Ltd., China Research and Development Center 1077, Zhang Heng Road, Zhangjiang Hi-tech Park, Shanghai, 201203, China

Available online 24 August 2007

bstract

Electrically conductive coatings and composites are prepared from aqueous dispersions of conducting particles and polymer latex particles.elatively small amounts of conductive particles are needed to develop electrical conductivity, because the particulate nature of the latex leads to

segregated network that lowers the percolation threshold. Several nanosized conductive fillers have been studied: carbon black, antimony-doped

in oxide, indium tin oxide and carbon nanotubes. The latex chosen for most studies was either a poly(vinyl acetate-co-acrylic) polydisperse latex,poly(vinyl acetate) polydisperse latex, or monodisperse poly(vinyl acetate) latex. This paper reviews the effect of particle size, aggregation and

spect ratio on the microstructure and properties of conductive composites and coatings. 2007 Elsevier B.V. All rights reserved.

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eywords: Composite; Latex; Conductivity; Coating

. Introduction

Composites containing conductive particles in a noncon-uctive polymer matrix have been used for many years forpplications such as electromagnetic shields, thermally sensi-ive resistors, and sensors [1]. In recent years, the developmentf flexible electronic devices and large area “macroelectronics”2] has led to a demand for coatings with tailored electrical prop-rties and functions. In this paper, a common base for liquidpplied coatings – a latex dispersion – is combined with elec-rically conductive nanoparticles to create functional materialsnd coatings for a variety of applications.

To impart electrical conductivity to a composite, the quantityf conductive particles must be high enough for the particleso form an interconnected network [3,4]. The formation of theetwork is commonly described as a percolation phenomenonn which the conductivity (σ) follows a power law and jumpsy orders of magnitude when the volume fraction of conductivearticles (V) surpasses a critical percolation threshold (Vc):

s

= σ0(V − Vc) (1)

n Eq. (1), σ0 is a proportionality constant, and s is the criti-al conductivity exponent (∼1.5–2.0 for a 3D random system).

∗ Corresponding author. Tel.: +1 612 625 0559; fax: +1 612 626 7246.E-mail address: [email protected] (L.F. Francis).

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927-7757/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.colsurfa.2007.08.026

he formation of an interconnected conductive particle networkepends both on the morphology of the conductive particlesnd the characteristics of the matrix and resulting compositeicrostructure. A variety of theories and models have been

roposed to account for the conductivity of composites andhe effect microstructure on conductivity [5 and referencesherein]. For random addition of conductive particles to a con-inuous nonconductive matrix, the critical conductive particleontent needed to establish the network is roughly 16 vol% [3,4].owering the percolation threshold requires altering the con-uctive particles, the matrix or both. For example, particles withsymmetric morphologies create percolating networks at lowerontents than do spherical particles [5]. The microstructure ofhe matrix can force percolation to occur at a lower value by seg-egating the conductive particles to a restricted volume withinhe microstructure. For example, conductive particles that segre-ate to one phase in a polymer blend form a percolating networkelectively in that phase and therefore at a lower overall particleontent [6 and references therein]. The magnitude of the conduc-ivity past the threshold strongly depends on the properties of theonductive particles themselves and the connections between thearticles [7].

In this paper, latex particles are used to construct a segre-

ated network of conducting particles, as shown schematicallyn Fig. 1. Conductive particles are mixed with nonconductiveatex particles in an aqueous dispersion. On drying, latex under-oes a sequence of microstructure changes [8 and references
Page 2: Conductive coatings and composites from latex-based dispersions

L.F. Francis et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 311 (2007) 48–54 49

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herein]. Conductive particles are trapped as the latex forms theolymer matrix. In these systems, several materials and process-ng variables influence composite microstructure and properties.he focus here is on the effects of the characteristics of the parti-les. Examples are taken from the authors’ recent papers [9–15]nd Ph.D. theses [16,17].

. Experimental

.1. Materials

The characteristics of the conductive particles and latex dis-ersions used in the research are given in Tables 1 and 2.he following abbreviations will be used throughout the paper:arbon black (CB), antimony doped tin oxide (ATO), indium

in oxide (ITO) and single walled carbon nanotubes (SWNT),oly(vinyl acetate) (PVAc), poly(vinyl acetate co-acrylic)PVAc-co-acrylic), and poly(methyl methacrylate co-butyl acry-ate) (MMA-BA).

iuta

able 1haracteristics of conductive particles

article chemistry Abbreviation Manufacturer (product name)

arbon black CB 1 Columbian Chem. (Conductex 976Ultra)

arbon black CB2 Columbian Chem. (Raven 1170)

ntimony-tin oxide ATO Nanophase Technologies (Nanotek®)ndium–tin oxide ITO Nanophase Technologies (Nanotek®)ingle-walled carbonnanotube

SWNT Carbon Nanotechnologies

dry particle coating.*from Ramasubramaniam et al. [29]; measured on a polymer-free coating of SWNT

able 2haracteristics of latex dispersions

atex chemistry Abbreviation Manufacturer (product n

oly(vinyl acetate) PVAc Air Products (Vinac 21)

oly(vinyl acetate co-acrylic) PVAc-co-acrylic Air Products (Flexbond

oly(vinyl acetate) PVAc-M H.B. Fuller (PD 202)oly(methyl methacylateco-butyl acrylate)

MMA-BA Custom [12]

minimum film formation temperature.

omposite containing conductive particles. Adapted from [17].

.2. Preparation of composites and coatings

The general procedure for composite preparation has twoteps. First, an aqueous dispersion containing conductive parti-les and latex is prepared. Second, the dispersion is convertednto a bulk composite by drying at room temperature (CB1/latex)r a coating by application with a wire wound rod onto a substrateollowed by drying at 50 ◦C (CB2/latex, ATO/latex, ITO/latex).oating thickness is increased by repeating the deposition andrying. Details of the preparation procedures are given elsewhereor the CB/latex [9–12], ATO/latex and ITO/latex [14,15], andWNT/latex [13].

.3. Characterization

Composite microstructures and properties were character-

zed by several techniques. Scanning electron microscopy wassed to characterize the cross-sectional and surface microstruc-ures. Direct current electrical conductivity was measured using

commercial 4-point probe instruments (Veeco FPP-5000 or

Characteristics

Dry powder, 20 nm diameter spherical primary particles in open clusters

Dry powder, 20 nm diameter spherical primary particles in closed clusters,σ ∼= 1 S/cm*Dry powder, 15 nm (ave) diameter spherical primary particles, σ ∼= 0.l S/cm*Dry powder, 20 nm (ave) diameter faceted primary particles, σ ∼= 0.01 S/cm*Dry powder, 1–2 nm diameter and 100+ nm long, σ ∼= 510 S/cm**

’s.

ame) Characteristics

Aqueous dispersion; Tg = 35 ◦C, MFFT* = 15 ◦C; polydisperse (vol.ave size, Dv = 2.6 �m, num. ave. size, Dn = 108 nm)

325) Aqueous dispersion; Tg = 19 ◦C, MFFT* = 10 ◦C; polydisperse(Dv = 333 nm and Dn = 60 nm)Aqueous dispersion; Tg = 34 ◦C, monodisperse (Dv = Dn = 116 nm)Aqueous dispersion; Tg = 19 ◦C, monodisperse (Dv = 1.087 �m,Dn = 0.929 �m)

Page 3: Conductive coatings and composites from latex-based dispersions

5 A: Physicochem. Eng. Aspects 311 (2007) 48–54

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oresta AP [MCP-T4000]) or a home built apparatus consistingf a Keithley 220 current source, a K&S 4-point probe, and aeithley 6517A electrometer.

. Results and discussion

.1. Effect of latex particle size

As shown in Fig. 1, conductive particles are forced to thepaces between the compacting latex particles during drying. Asconsequence, the microstructure and properties of the compos-

tes are affected by the relative sizes of the latex particles andonductive particles (or clusters). Because of the availability ofommercial latex and synthetic methods to make latex of variousizes, particle size effects are most easily explored by varyinghe size of the latex particles and keeping the conductive particleize constant.

In the CB/latex system, the effect of latex particle size wasrobed using a custom monodisperse latex [12] and a commer-ial monodisperse latex [16]. Fig. 2 compares the conductivity ofomposites prepared with CB1 and two different sizes of latex.omposite preparation involved high shear mixing of disper-

ion and drying at room temperature. The data fit the percolationower law (Eq. (1)) and the percolation thresholds for both com-osites are below that expected for a random 3D microstructure.onductive particles are forced to occupy the spaces between

he larger latex particles and therefore prevented from adoptingrandom spatial distribution. This segregation effect is stronger

or larger size latex particles; the conductive particles adopt aess random configuration. This result is consistent with theo-etical models of size effects, which take into account the effectf size on packing of particles (i.e., the arrangement of smaller,pherical conductive particles in connected layers around larger,pherical insulating particles) [5,18]. Fitting the data to the

odels quantitatively, however, is not possible because the CB

articles are clusters, not monodisperse spheres. In addition, theormation of aggregates of either CB or latex influences packing,icrostructure, and therefore percolation [16].

ig. 2. Effect of latex on the conductivity in CB1/latex composites. Lines rep-esent fits to percolation power law. Adapted from [16].

cCtpttPttrmrtlSuBvc

td

TO/P VAc coatings. Lines are fits to percolation power law; fits apply above theercolation threshold. From [17]. With kind permission from Springer Sciencend Business Media.

In studying effects of particle size, variations in glass tran-ition temperature (Tg) and film formation behavior of theatex should be considered. In a systematic study [16] withonodisperse latex of nearly identical size and varying Tg, the

ercolation threshold of CB/latex coatings was found to increases the latex Tg decreased for a given drying temperature. The coa-escence of the latex, which is enhanced at lower Tg, disruptsonnections between the conductive particles. In the presentomparison, the larger latex has the lower Tg and hence willoalesce to a greater degree. Hence, the size effect appears haveore influence over the percolation threshold as compared with

he Tg effect.The effect of latex size was also probed in the ATO/latex

ystem [17]. Fig. 3 shows the effect of ATO content on theonductivity of ATO/PVAc and ATO/PVAc-co-acrylic coatings.oatings were prepared from stable dispersions and using drying

emperatures above the glass transition temperatures of the latexarticles. The percolation threshold drops from around 0.06 forhe coatings prepared with PVAc-co-acrylic (smaller latex par-icles on average) to around 0.03 for the coatings prepared withVAc (larger latex particles on average). Both ATO/latex sys-

ems demonstrate reduction of percolation threshold relative tohe expected result for a random composite (0.16). Figs. 4 and 5eveal the effect of latex particle size on segregation in theicrostructure. Both coating microstructures display the seg-

egated network of the smaller ATO particles packed betweenhe larger latex particles. The images show networks fully estab-ished with an ATO loading of 0.15 in the final microstructure.EM images of ATO/PVAc-co-acylic coatings with an ATO vol-me fraction 0.05 contain disconnected ATO-rich regions [14].y contrast the image of the PVAc-based coating with an ATOolume fraction of 0.03 reveals connectivity, consistent with the

onductivity results.

Since both latexes in this comparison are polydisperse, par-icle size effects are less clearly evaluated; however, the largeifference in the average size appears to provide the same effect

Page 4: Conductive coatings and composites from latex-based dispersions

L.F. Francis et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 311 (2007) 48–54 51

Fig. 4. SEM image (backscattered electron, BE, imaging mode) of cross-s0F

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ection of ATO/PVAc-co-acrylic coating with ATO volume fraction of.15. In BE mode, ATO-rich phase is brighter than polymer-rich phase.rom [17].

s in the monodisperse case. That is, PVAc latex particles arearger on average and therefore provide greater spatial segrega-ion, less randomness and lower percolation threshold. Duringhe segregation, the latex particles on the small end of the sizeistribution are also expected to be forced to the spaces betweenhe larger latex particles, and hence the ATO-rich phase, at leastn the case of the PVAc-co-acylic latex, contains some poly-

er [14]. This polymer likely influences the magnitude of theonductivity.

.2. Effect of aggregation

Aggregation can occur at several stages during the process-ng of composites. First, the conductive particles themselvesay be created as aggregates during their synthesis. Theanufacture of CB particles, for example, creates clusters

omposed of small primary particles linked together intopen or closed structures [19]. Second, aggregation can occurn the dispersion if the repulsive interactions between par-icles are not strong enough to overcome van der Waalttraction. Both latex particles and conductive particles are sus-eptible to aggregation in the suspension. Lastly, aggregatesay be generated during drying as particles approach one

nother and the composition of the remaining aqueous mediumhanges.

The effect of the addition of a dispersant [Disperbyk®,n alkanolammonium salt of poly(carboxylic acid)] on theicrostructure and properties of CB1/PVAc composites was

tudied [10]. CB1 particles are open clusters of 20 nm primary

wCsw

ig. 5. SEM images (BE mode) of cross-section of ATO/PVAc coating withTO volume fraction of (a) 0.15 and (b) 0.03. From [17].

articles. These clusters can further aggregate in aqueous disper-ions and on drying. Results from sedimentation tests with CB1ispersed in water or in latex dispersion demonstrated that theddition of dispersant increased the stability of dispersions andence cut down on aggregation in the dispersion. CB1 dispersedith PVAc latex was less prone to sedimentation compared with

B1 dispersed in water, indicating that the latex either hindered

ettling of the CB aggregates or that the aggregation processas affected by the latex or perhaps free poly(vinyl alcohol),

Page 5: Conductive coatings and composites from latex-based dispersions

52 L.F. Francis et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 311 (2007) 48–54

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ig. 6. SEM micrographs of cross-sections of CB1/PVAc latex composites con-aining 8 vol% CB: (a) with 1 wt% dispersant and (b) with 5 wt% dispersant.

hich is used to stabilize the PVAc particles. The effect of dis-ersant on microstructure of CB-PVAc microstructure is shownn Fig. 6. Composites prepared with more dispersant tended toontain smaller aggregates though there was some variability innal microstructures.

Fig. 7 shows the effect of dispersant on the conductivity ofB/PVac composites. The percolation threshold was increasedy the addition of the dispersant. By forming connectionsetween conductive particles, aggregation brings the systemloser to having the interconnected network needed for con-

uction in the final composite. That is, fewer connections needo form between conductive particles as the final microstructureevelops during drying. By preventing aggregation, the disper-ant stopped the formation of connections between conductive

tnf[

ig. 7. Effect of dispersant on the conductivity of CB/PVAc composites. From10].

articles. Fig. 7 shows a positive effect of aggregation—a lowerercolation threshold. The negative consequence of aggrega-ion for CB/PVAc composites was a reduction in the breaktrength in composites prepared with greater than 10 vol%B.

The role of particle–particle interactions and aggregationn the microstructure and properties on ATO/PVAc-co-acrylicnd ITO/PVAc-co-acrylic coatings was also studied [15]. ATOnd ITO particles used in this study were delivered in thery state. Aggregates in the dry powder do not completelyreak up in aqueous dispersions; aggregates on the order of0–100 nm have been observed in cryogenic SEM studies of sta-le aqueous dispersions [20]. In these systems, particle–particlenteractions are easily changed by altering the dispersion pH.or ATO/PVAc-co-acrylic, dispersions are stable at pH of 3 orore due to the generation of negative surface charges on bothTO and latex particles. Aggregation was induced by lowering

he pH, which decreases repulsive interactions. Microstructuretudies showed large ATO-rich clusters formed in the coating.onsistent with the CB1/PVAc result, aggregation lowered theercolation threshold from 0.06 volume fraction ATO for thetable suspensions to 0.03 volume fraction ATO for unstableuspensions prepared at pH 1.5. The negative consequence ofggregation in this system was a decrease in the optical trans-arency of the coatings.

Fig. 8 compares the conductivity of coatings prepared withifferent fillers and PVAc-co-acrylic latex as the polymer matrix.he percolation threshold of the ITO/latex coatings is higher

han for CB2/latex or ATO/latex. As explored in detail else-here [15], this difference is due at least in part to the tendency

or ITO to be attracted to the surface of the latex, which restrictsts ability to form a connected network. Comparing the fillers,he conductivity past the percolation threshold correlates wellith the conductivities of the dry, polymer-free particle coatings

hemselves (See Table 1). Hence, the composite conductivityast the percolation threshold depends on the conductivity ofhe individual particles and the particle–particle contacts. In

his aspect, the nanosize of the fillers creates a challenge: theumber of particle–particles contacts, which are frequently sitesor of increased resistance, increases as the particle size drops7].
Page 6: Conductive coatings and composites from latex-based dispersions

L.F. Francis et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 311 (2007) 48–54 53

Fig. 8. Effect of filler content and type on conductivity of PVAc-co-acrylicc4r

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oatings. Coating thicknesses were 15 �m, 4 �m, and 4 �m for CB2/latex (pH), ATO/latex (pH 3) and ITO/latex (pH 3) CB2/latex, ATO/latex and ITO/latex,espectively. From [17].

.3. Effect of filler aspect ratio

The conductive fillers used in the preceding studies (CB,TO, ITO) have little or no aspect ratio. When these rela-

ively spherical fillers are replaced with single-walled carbonanotubes (SWNTs) the percolation threshold of the latex-ased composite is dramatically reduced due to the combinationf conductive particle segregation and high aspect ratio. Tra-itional, non-segregated carbon nanotube-filled compositesypically have percolation thresholds of 0.2 vol% or more21–24], which is much lower than that of carbon black-basedomposites. The high aspect ratio of the nanotubes [25] reduceshe number of contacts required to create a conductive path andeduces the percolation threshold. Only a few researchers haveaken the additional step of creating a formal segregated net-ork to achieve even greater percolation threshold reductions

13,26,27]. Fig. 9 shows electrical conductivity as a function ofller concentration for the polydisperse PVAc filled with car-on black or SWNT. Segregated nanotube networks createdith polymer latex produce percolation thresholds as low as

tcco

ig. 10. Freeze-fractured cross-sections of PVAc latex films containing (a) 1.3 and (beproduced with permission.

ig. 9. Effect carbon filler content and type on conductivity of PVAc coatings.ata from [13] was plotted assuming a density of 1.8 g/cm3 for raw SWNT

27 wt% iron impurity) and 1.17 g/cm3 for PVAc.

.02 vol% [13,26,27]. Changing from carbon black to nanotubesroduces an order of magnitude reduction in the percolationhreshold, from 2.5 to 0.02 vol%. Fig. 10 shows cross-sectionalmages of the poly(vinyl acetate) films containing 1.3 and 2 vol%arbon nanotubes. These images provide visual evidence of theegregated network concept, in which the solid polymer par-icles have effectively squeezed the smaller nanotubes into aetworked structure.

. Summary

The electrical conductivity of composites prepared fromqueous dispersions of conductive nanoparticles and latexepends as much on the composite microstructure as it does onhe properties of the individual components. Several microstruc-

ure tailoring mechanisms for decreasing the quantity ofonductive particles needed to establish a network (i.e., the per-olation threshold) have been identified. First, the segregationf conductive particles to the interstitial space between the latex

) 2 vol% SWNT. From [28]. Copyright Wiley-VCH Verlag GmbH; Co. KGaA.

Page 7: Conductive coatings and composites from latex-based dispersions

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articles is enhanced and the percolation threshold drops ashe size disparity between the small conductive particles andhe larger latex particles increases. Second, aggregation of con-uctive particles in the dispersion also lowers the percolationhreshold. Third, high aspect ratio conductive particles createn interconnected network at much lower volume fractions thanore spherical particles. With low percolation thresholds, other

roperties, such as optical transparency (e.g., in case of ATO-nd ITO-based composites) and mechanical strength can bemproved relative to highly loaded composites, and the costssociated with incorporating higher priced nanoparticles intoomposites is reduced. Enhancing the electrical conductivityeyond the percolation threshold, however, remains a challenge.he results summarized in this paper show a correlation between

he conductivity of the conductive particles, as measured in aolymer-free particulate coating, and the composite conduc-ivity. Hence, future improvements in composite conductivityequire nanoparticles with higher conductivity and perhaps moremportantly, particle–particle contacts engineered to have loweresistance.

cknowledgements

The authors are grateful to the industrial sponsors of the Coat-ng Process Fundamentals group for supporting this research.CG thanks Eastman Kodak and the graduate school of the Uni-ersity of Minnesota for fellowships, and JS thanks the Industrialartnership in Interfacial and Materials Engineering (IPRIME)or a fellowship. JCG thanks Carbon Nanotechnologies for sup-lying carbon nanotubes and Avery Dennison for funding theWNT-latex research.

eferences

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[2] R.H. Reuss, B.R. Chalamala, A. Moussessian, M.G. Kane, A. Kumar,D.C. Zhang, J.A. Rogers, M. Hatalis, D. Temple, G. Moddel, B.J. Elias-son, M.J. Estes, J. Kunze, E.S. Handy, E.S. Harmon, D.B. Salzman, J.M.Woodall, M.A. Alam, Y.J. Murthy, S.C. Jacobsen, M. Olivier, D. Markus,P.M. Campbell, E. Snow, Macroelectronics: perspectives on technologyand applications, Proc. IEEE 93 (2005) 1239–1256.

[3] S. Kirkpatrick, Percolation and conduction, Rev. Mod. Phys. 45 (1973)574–588.

[4] R. Zallen, The Physics of Amorphous Solids, Wiley, New York, 1983.[5] F. Lux, Models proposed to explain the electrical conductivity of mix-

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[6] J. Huang, Carbon black filled conducting polymers and polymer blends,

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[

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10] J.C. Grunlan, F.L. Bloom, W.W. Gerberich, L.F. Francis, Effect of dispers-ing aid on electrical and mechanical behavior of carbon black-filled latex,J. Mater. Sci. Lett. 20 (2001) 1523–1526.

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12] J.C. Grunlan, Y. Ma, M.A. Grunlan, W.W. Gerberich, L.F. Francis,Monodisperse latex with variable glass transition temperature and particlesize for use as matrix starting material for conductive polymer composites,Polymer 42 (2001) 6913–6921.

13] J.C. Grunlan, A.R. Mehrabi, M.V. Bannon, J.L. Bahr, Water-based single-walled nanotube-filled polymer composite with an exceptionally lowpercolation threshold, Adv. Mater. 16 (2004) 150–153.

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