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Colloids and Surfaces A: Physicochem. Eng. Aspects 396 (2012) 195– 202

Contents lists available at SciVerse ScienceDirect

Colloids and Surfaces A: Physicochemical andEngineering Aspects

jo ur nal homep a ge: www.elsev ier .com/ locate /co lsur fa

olyaniline effect on the conductivity of the PMMA/Ag hybrid composite

ejin Leeb, Eunhee Kimb, Kijung Kimb, Byung H. Leea, Soonja Choeb,∗

Department of Chemistry, University of Incheon, Incheon, Republic of KoreaDepartment of Chemical Engineering, Inha University, Yonghyundong 253, Namgu, 402-751 Incheon, Republic of Korea

r t i c l e i n f o

rticle history:eceived 25 August 2011eceived in revised form4 December 2011ccepted 27 December 2011

a b s t r a c t

The electroless coating of Ag on PMMA sphere pre-coated with polyaniline (PANI) was investigated. Pre-coating was carried out using in situ chemical polymerization. The extent of silver coating on PMMAand PMMA/PANI particles was studied by measuring the remaining content of Ag using TGA, in terms ofthe number of pretreatment steps, PANI content, AgNO3 concentration and the particle size. The resultsindicated that the deposition of PANI on the PMMA surface induced high efficiency of the silver plating

vailable online 2 January 2012

eywords:MMA/PANI/Ag composite particleslectroless silver platingesistivity

due to the activation effect. The resistivity of PMMA/Ag and PMMA/PANI/Ag composites varied between1014 and 10−1 � cm and between 108 and 10−4 � cm, respectively. Such increase in resistivity, along withthe relatively compact and continuous silver layer on PMMA/PANI/Ag composite particles showed thatthis method is effectively applicable on the development of conductive materials.

© 2012 Elsevier B.V. All rights reserved.

onductive material

. Introduction

Recently, the organic/inorganic composites have been attract-ng a lot of attentions due to their potential applications inarious fields such as electroluminescence [1], electromagneticnterference (EMI) shielding, sensors, catalysts, biochemistry andlectronic conducting fillers [2–4].

Many research groups that were interested in nano-sizedetals, such as silver and copper, focused their attention on

he opto-electronic application of organic/inorganic composites5]. In particular, silver (Ag) particles received more atten-ion compared to other metals due to their enhanced electricalroperty and thermal conductivity [6]. Therefore, numerous inves-igation of polymer/silver composites were carried out usingarious techniques such as physical incorporation [7], reduc-ion of polymer–metal ion complexes [8] and electroless plating9]. Among them, electroless plating appeared to be the mostonvenient and effective method in preparing polymer/metal com-osites. There are two initial steps which have to be applied beforehe electroless plating; the sensitization of PMMA using tin chlorideSnCl2) and the activation of the sensitized layer using palladiumhloride (PdCl2) [10]. However, the toxic nature of Sn and high costf Pd work as the drawbacks [11].

In order to alleviate these disadvantages, polyaniline was intro-uced. Polyaniline (PANI) is one of the most attractive conductingolymers due to its high conductivity, excellent environmental

∗ Corresponding author. Tel.: +82 32 860 7467; fax: +82 32 872 0959.E-mail address: sjchoe@inha.ac.kr (S. Choe).

927-7757/$ – see front matter © 2012 Elsevier B.V. All rights reserved.oi:10.1016/j.colsurfa.2011.12.071

stability, fast reaction and a variety of applications, especially inelectronic devices, secondary batteries, chemical sensors, catalysis,and antistatic coatings [12–14]. Despite such advantages, it is diffi-cult to synthesize the spherical PANI particle. In order to overcomethis deficiency, many research groups implemented various meth-ods to prepare PANI-coated polystyrene composite particles; themethods include chemical oxidative polymerization [15,16] andelectrochemical polymerization using different substrates [17–21].PMMA microspheres were coated with PANI, which was preparedby in situ polymerization of aniline in the presence of core particlesand sodium dodecyl sulfate (SDS) in water [22].

The reduction of Ag+ to Ag occurred while NH groups ofPANI chain were simultaneously oxidized to N through theoxidation–reduction reaction of ions [23]. Wang et al. reported thatthe PANI is an effective activator for the electroless silver coating[11], considering its intrinsic character of having different inter-convertible oxidation states. In addition, the redox chemistry ofPANI and PPY (polypyrrole) was utilized to reduce Au(III) ions fromacidic solution, thereby obtaining elemental gold [24–26].

Since PANI was used as an activator, we focused on pre-coatingPANI before the electroless silver coating, in addition to the sensi-tization and activation with SnCl2 and PdCl2, respectively. Thus, inthis study, PANI was coated on the monodisperse spherical PMMAparticles prepared through dispersion polymerization. Before theelectroless Ag coating, various steps of pretreatment were per-formed in order to achieve better silver coating. The electroless

Ag plating was applied to the PMMA or PMMA/PANI compos-ite particles using various steps of pretreatment, under differentconcentrations of AgNO3 solution, aniline contents and PMMA par-ticle sizes. We measured the remaining weight percentage and

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96 Y. Lee et al. / Colloids and Surfaces A: Ph

esistivity of Ag to compare the efficiency and the conductivity ofhe composites.

. Experimental

.1. Materials

The monomer, methylmethacrylate (MMA) (Junsei Chemicalo. Ltd, Japan), was purified using an inhibitor removal columnAldrich, USA) and stored at −5 ◦C under nitrogen prior to use.olyvinylpyrrolidone (PVP K-90) (Canto chemical, Japan) as a parti-le stabilizer and 2,2′-azobis (isobutyronitrile) (AIBN, Aldrich, USA)s an initiator were used without further purification. Methanol99%; Samchun Chemical, Korea) was used as a medium for thereparation of PMMA core spheres. Aniline (≥99.5%; Aldrich, USA)as used for the preparation of polyaniline, and ammonium persul-

ate (APS) (98%, Aldrich, USA) and polyvinylalcohol (PVA; 87–89%ydrolyze, Aldrich, USA) were used as an oxidant and a stabilizer,espectively.

Tin(II) chloride (SnCl2) (98%; Aldrich, USA) and palladium(II)hloride (PdCl2) (99.9+%; Aldrich, USA) were used as the sensi-izing and activating catalytic material, respectively. Hydrochloriccid (35 wt%; Duksan Chemical, Korea), sodium hydroxide (NaOH)Duksan, Korea) and silver nitrate (AgNO3) (99+%, Aldrich, USA)ere used as the plating agents solution. Glucose (C6H12O6)

Aldrich, USA), tartaric acid (C4H6O6) (98%, Aldrich, USA) andthanol (Duksan Chemical, Korea) were used as the reducing agentolution.

.2. Synthesis of PMMA seed particles

Various sizes of PMMA spheres, 1, 2 and 5 �m, were preparedsing the dispersion polymerization. The experimental procedurereparing micron-sized PMMA through the dispersion polymeriza-ion was described elsewhere [27].

.3. Polyaniline coating

Aniline (0.6 g) was dissolved in the PVA aqueous solution (0.5 g),n which PMMA particles (1 g) were dispersed. Chemical oxida-ive seeded dispersion polymerization was carried out with APSqueous solutions (0.6 g/10 ml) and PVA for 1 h according to theescription elsewhere [11,27]. The PMMA/PANI composite par-icles were repeatedly washed by centrifugation before furtherxperiment.

.3.1. Electroless silver platingThe wet PMMA or PMMA/PANI composite particles (1 g) were

ispersed in 50 ml water and then sensitized in 20% SnCl2 solu-ion for 60 min. After being rinsed with the distilled water, theMMA powders were activated in PdCl2 solution for 60 min. Thereated PMMA/PANI composite particles were immersed in thequeous solution of reducing agent, consisting of tartaric acidC4H6O6), ethanol and glucose (C6H12O6), and stirred for 10 min.gNO3 (99.8%) and aqueous ammonia (28–30%) were used for thereparation of silver solution. The transparent silver solution wasrepared by dissolving AgNO3 (0.6 g) in water (100 ml) with theddition of several drops of the aqueous ammonia, then NaOH0.3 g) and finally several drops of aqueous ammonia were addedntil the Ag(NH3)+ solution turned to be transparent. The mix-ure of PMMA/PANI composite and reducing agent were poured

nto the silver solution and stirred for 60 min at room temperature.uring the coating process, the pH was kept at 11. After washingnd drying, the silver plated PMMA/PANI composite powders werebtained.

hem. Eng. Aspects 396 (2012) 195– 202

2.3.2. CharacterizationFE-SEM (Field Emission Scanning Electron Microscopy, HITACH

S-4300) and optical microscopy (Olympus Optical CO.) were usedto study the morphology of the PMMA particles, and PMMA/PANI,PMMA/Ag and PMMA/PANI/Ag composites. FE-SEM images wereobtained using the samples coated with a thin layer of platinum, to adepth of approximately 20 nm, under vacuum. The weight-averagediameter (Dw) and the distribution of the particle sizes wereanalyzed using the PSA (particle size analyzer, Mastersizer2000,Malvern).

The content of silver, localized in the PMMA/Ag andPMMA/PANI/Ag composites, was measured using TGA between0 and 700 ◦C under nitrogen atmosphere at a heating rate of20 ◦C/min. The onset of the degradation temperature was deter-mined at the transition point where the curve passed the maximumnegative slope. The cross sectional morphology of the PMMA/Agand PMMA/PANI/Ag hybrid particles was observed using the fieldemission transmission electron microscopy (FE-TEM, JEOL JEM2100F). The sample was prepared by cutting to a width of approxi-mately 70 nm using the ultra-microtome (UTM, MTX) on the coppergrid.

The resistivity of the dried samples was determined using thepressed pellets at 100 ◦C by the conventional four-point-probetechnique with the low and high resistivity meter (MitsubishiChemical Co.).

3. Results and discussion

3.1. Synthesis of the monodisperse PMMA particles

The SEM images of the PMMA particles produced by the disper-sion polymerization are shown in Fig. 1(a)–(c). The PMMA particleswere monodisperse and spherical. Fig. 1(d) shows the PSA analysisof the monodisperse 1, 2 and 5 �m PMMA particles. Size distri-bution (Cv: coefficient of variance) of each particle was 7.8, 6.4and 8.1%, which meant fairly narrow size distribution. The mea-sured weight-average molecular weight of the PMMA particles was110,000 g/mol, 153,000 g/mol and 125,000 g/mol and the molecularweight distribution (PDI) was 2.5, 3.0 and 2.8, respectively.

3.2. The effect of PANI coating

Fig. 2(A) shows the SEM images of PMMA/PANI (1:0.6; weightpercentage) composite particles prepared from 2 �m PMMA. PANIwas coated on the surface of PMMA, of which the layer of PANI wasuniform at 0.25 �m thickness on average. The color of PMMA/PANIwas apparently dark brown, which was distinct from the white col-ored PMMA, suggesting that PANI was deposited on the PMMA.In addition, Fig. 2(A′) represents the optical microscopy image ofthe PMMA/PANI composites taken from the well dispersed parti-cles in aqueous media. The Fourier transform infrared spectroscopy(FTIR) of PANI, PMMA particles and PMMA/PANI composite parti-cles are shown in Fig. 2(B). Pure PANI exhibited characteristic bandscorresponding to the stretching of the C N (1245–1298 cm−1) andN H (3435 cm−1). The C N stretching bands of the benzenoid andquinonoid rings were seen at 1245 and 1298 cm−1, and the in-plane C H stretching band was observed at 1110 cm−1. The FTIRspectrum of the PMMA contained major bands; the C O stretch-ing bands of PMMA appeared at 1277, 1241, 1195 and 1150 cm−1.In addition, the C O stretching band of PMMA was assigned at1731 cm−1. Comparing the FTIR spectra of the PMMA/PANI com-

posite with those of PMMA and PANI, the vibration bands observedfrom the PMMA/PANI composite was fairly well distinguishedfrom those from PMMA and PANI. This result indicated that thePMMA/PANI composite particles were successfully produced.

Y. Lee et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 396 (2012) 195– 202 197

) 5 �m

uw(octc1a

Fc

Fig. 1. SEM images of (a) 1 �m PMMA particles, (b) 2 �m PMMA particles, (c

In order to confirm the variation of PMMA/PANI particle sizepon aniline content and particle size, various amounts of anilineas coated using the various sizes of PMMA spheres. Fig. 3(a) and

b) shows the plots of the thickness of the coated PANI as a functionf aniline contents and particle size obtained from the PSA and thealculation by using the Eq. (1), respectively. As seen in Fig. 3(a), thehickness of the PANI shell by the PSA measurement and empirical

alculation for the 2 �m PMMA was 103, 235, 392 and 500 nm, and50, 270, 432 and 520 nm upon the aniline content for 40, 60, 80nd 100%, respectively. The higher the aniline content, the thicker

ig. 2. (A and A′) SEM and Optical microscopy image of PMMA/PANI composite particlomposites using 2 �m PMMA.

PMMA particles and (d) PSA analysis of the 1, 2 and 5 �m PMMA spheres.

the PANI shell was obtained. In addition, the value from the calcu-lation was thicker than that from the PSA measurement becausethe calculation was based on the ideal sphere and uniform thick-ness. Moreover, Fig. 3(b) shows that the larger the particle size, thethicker the PANI shell was observed due to the smaller surface areafor the large particles.

The thickness of PANI shell was calculated from the following

equation made by this lab.

4�(R3 − r3)3 × A

:4�r3

3 × B= a : b

es and (B) FTIR spectra of (a) pure PANI, (b) pure PMMA, (c) PMMA/PANI (1:0.6)

198 Y. Lee et al. / Colloids and Surfaces A: Physicoc

Fig. 3. (a) Plots of the thickness of the coated PANI as a function of aniline contentsoua

wn(i

r

R

x

3

2opgasttcw

btained from 2 �m particle of PMMA/PANI composites; by PSA (�) and caculationsing the equation (�). (b) The thickness of PANI vs. PMMA particle size with 60%niline by PSA (•) and caculation (�).

here R is the thickness of (PMMA core + PANI shell); r is the thick-ess of PMMA core; A is 1.479 (specific gravity of PANI); B is 1.188PMMA specific gravity); a is PANI gravity content; b is PMMA grav-ty content.Thus,

=[

1.479b × R3

1.479b + 1.188a

]1/3

=[

r3 × (1.479b + 1.188a)1.479b

]1/3

Finally, the thickness of the PANI shell was obtained from

= R − r. (1)

.3. The effect of AgNO3 solution

The electroless silver plating of PMMA and PMMA/PANI using �m particles was carried out using 0.06 M AgNO3 solution afterne- or two-step pretreatment of sensitization and/or activationrocess. The brown color of PMMA/PANI was distinct from theray color of PMMA/PANI/Ag. The SEM images of the PMMA/Agnd PMMA/PANI/Ag composite particles were shown in Fig. 4. Theurface of PMMA/Ag showed granular morphology, and the par-

icles in Fig. 4(b) are relatively completely coated with silver byhe electroless silver plating. The size (diameter) of Ag nanoparti-le was 15–23 nm and their size distribution (Cv) was 10.5%, whichas fairly monodisperse. In addition, the thickness of silver layer

hem. Eng. Aspects 396 (2012) 195– 202

of PMMA/Ag composites and PMMA/PANI/Ag composites was uni-form with 88 and 150 nm on average, respectively. The silver layerof both PMMA/Ag and PMMA/PANI/Ag composites seemed to becompact and uniform, but the thickness of silver layer was different.As a result, the smaller the PMMA particles, the thinner the silverlayer was obtained due to the larger surface area of the smaller par-ticle sizes. In addition, the better coating of silver on PMMA/PANI (inFig. 4(b)) was observed than that of PMMA particles (in Fig. 4(a)).This may be from the better stabilization of silver ion upon thesimultaneous activation by PdCl2 and PANI on PMMA.

Fig. 4(a′) and (b′) shows the TEM images representing thesilver plating. No major difference between the PMMA/Ag andPMMA/PANI/Ag was observed except the thickness of the silverlayer. Moreover, the homogeneous distribution of silver nanopar-ticles was deposited on PANI [28], which was based on the intrinsicability of PANI to occupy the different reversible oxidation states.

Fig. 5(a) and (b) shows the TGA curves of the PMMA/Ag andPMMA/PANI/Ag composite using 2 �m PMMA particles, respec-tively. Two major weight losses were observed in the derivativecurves of TGA. The initial weight loss took place between 230 and300 ◦C due to the release of absorbed water. Subsequently, a sharpand somewhat gradual weight loss profile after 400 ◦C occurredcorresponding to the decomposition of the polymer. In addition,the remaining weight was considered as the silver content in thecomposites. In general, for polymer/inorganic hybrid composites,the thermal stability of composites increased with the increaseddecomposition temperature of polymer [29–31]. The remainingweight percentage of PMMA/Ag composites and PMMA/PANI/Agcomposites in Fig. 5(a) and (b) at 700 ◦C was 17.5 and 53.7%, respec-tively. Thus, the silver plating on PMMA/PANI was highly effectivecompared to that on PMMA solely.

3.4. The effect of the pretreatments with sensitization andactivation

In order to evaluate the quality of the electroless silver plating,three processes of pretreatment were performed; Fig. 6 showedso called 0-step, 1-step and 2-step which represent no chemicaltreatment, sensitization with SnCl2, and both sensitization and acti-vation with SnCl2 and PdCl2, respectively. The electroless silverplating was performed using 2 �m PMMA and PMMA/PANI com-posite (PMMA: PANI = 1.0:0.6). Fig. 6(a)–(c) is the representativeSEM images from PMMA/Ag and Fig. 6(d)–(f) is the SEM imagesfrom PMMA/PANI/Ag composites using the above three processes.As seen in this picture, different level of silver plating was observeddepending on the steps of pretreatment.

The TGA measurements showed the weight loss and thereforethe remaining silver content up to 700 ◦C in Fig. 7. The remainingweight percentage of the PMMA/PANI/Ag composite using 2 �mparticles upon 0-step, 1-step and 2-step was 5.02, 25.01 and 53.08%,respectively. For the PMMA/Ag composite, those upon the numberof steps from 0- to 2-step was 3.2, 8.3, and 17.5%, respectively. Thus,the higher the number of steps of chemical pretreatment, the higherthe remaining silver content was obtained. Since the electrolessplating selectively occurred on the activated sites, the pretreat-ment process induced better silver plating. Moreover, the activationeffect of PANI induced the enhancement of silver plating, resultingin twice much remaining silver content. This result showed betteradhesion in PMMA/PANI/Ag composite by the chelation reactionbetween amine/imine groups in PANI and silver ions than between

Pd and silver ion [11]. On the other hand, when the pretreatmentprocess was absent, the combination of the cathodic depositionof metal and the anodic oxidation of the reducing agent on thesurface of PMMA particles was occurred, and the efficiency of the

Y. Lee et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 396 (2012) 195– 202 199

F d b′) P2

aa

3

pcfwwimw

Fp

ig. 4. SEM and TEM images of (a and a′) PMMA/Ag composite particles and (b an �m PMMA.

ctivation was highly reduced, thus, silver contents was minimizednd showed no ‘zero’ on 0-step.

.5. The effect of aniline content

In order to verify the optimum amount of aniline on the silverlating, the PMMA/PANI composites were prepared using variousontents of aniline and the electroless silver plating was per-ormed using 0.06 M AgNO3 solution. Then, the TGA measurementsere carried out up to 700 ◦C. As seen in Fig. 8, the remaining

eight percentage of silver upon aniline contents from 0 to 100%

ncreased from 17.5, 46.9, 53.1, 54.0 to 54.3%, respectively. In sum-ary, the higher the aniline contents, the higher the silver contentas obtained, because the higher aniline concentration led the

ig. 5. Thermo-gravimetric analysis of (a) PMMA/Ag and (b) PMMA/PANI/Ag com-osite particles via the electroless plating using 2 �m PMMA particles.

MMA/PANI/Ag composite particles via electroless plating using 0.6 M AgNO3 and

formation of electrically conductive polyaniline. But no distinctiveeffect of silver plating was obtained above 60% of PANI.

3.6. The effect of AgNO3 concentrations

In order to study the effect of the AgNO3 concentration forthe electroless plating, various concentrations of AgNO3 solutionbetween 0.02 and 0.1 M were used. Although the SEM images werenot shown in the text, the silver layer was compact and uniform fol-lowing to the increasing silver concentration; however, too low ortoo high concentration of AgNO3 induced non-uniform depositionexhibiting islands and un-plated spots on the particle surface.

The remaining weight percentage of silver analyzed from theTGA of the PMMA/Ag and PMMA/PANI/Ag composites upon var-ious concentrations of AgNO3 at 700 ◦C is depicted in Fig. 9. Thesilver content in PMMA/Ag composite linearly increased from 4.6to 24.6% for 0.02–1.0 M of AgNO3, and that of PMMA/PANI/Ag com-posites increased from 19.9 to 63.3%, respectively. As a result, thehigher the AgNO3 concentration, the higher the remaining silvercontent was obtained. In addition, the activation behavior of PANIgreatly enhanced the plating efficiency of silver in the PMMA/PANIcomposite.

3.7. The effect of the PMMA particle size

The effect of the PMMA particle sizes on the silver plating wasstudied on the above PMMA and PMMA/PANI composite. As seenin Fig. 10, the remaining weight percentage of silver obtained from

the TGA at 700 ◦C was 17.5, 19.5, and 21.1% for 1, 2 and 5 �mPMMA/Ag, respectively, and that of PMMA/PANI/Ag composite was47.3, 48.2, and 53.7%, respectively. The remaining weight percent-age of two different composite systems slightly increased with the

200 Y. Lee et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 396 (2012) 195– 202

Fig. 6. SEM images of 2 �m PMMA/Ag composite with (a) in the absence of pretreatment (0-step), (b) in the presence of sensitization with SnCl2 (1-step) and (c) in thepresence of both sensitization and activation with SnCl2 and PdCl2 (2-step), respectively. The SEM images of (d), (e) and (f) are obtained from PMMA/PANI/Ag upon the abovesame pretreatments. PMMA:PANI = 1:0.6.

Step210

Ag

cont

ent i

n pr

oduc

t (%

)

0

20

40

60

80

100

Fig. 7. The plots of final silver contents as a function of pretreatment stepsobtained from thermo-gravimetric analysis of 2 �m PMMA/Ag (solid line) andPMMA/PANI/Ag composites (dotted line) prepared from various steps of pretreat-ment.

Aniline contents (%)0 40 60 80 100

Ag

cont

ent i

n pr

oduc

t (%

)

0

20

40

60

80

100

Fig. 8. Silver contents obtained from thermo-gravimetric analysis ofPMMA/PANI/Ag composites prepared from various aniline contents from 0to 100% on 2 �m PMMA.

Ag concentration (M)0.02 0.0 4 0.06 0.08 0.1

Ag

cont

ent i

n pr

oduc

t (%

)

0

20

40

60

80

100

Fig. 9. Plots of the remaining silver contents as a function of AgNO3 concentra-tion obtained from thermo-gravimetric analysis of 2 �m PMMA/Ag (solid line) andPMMA/PANI/Ag composites (dotted line) prepared with various AgNO3 concentra-tions.

Seed size (µm)

1 2 5

Ag

cont

ent i

n pr

oduc

t (%

)

0

20

40

60

80

100

Fig. 10. Plots of the final silver contents as a function of seed size obtainedfrom the thermo-gravimetric analysis of PMMA/Ag composite (solid line) andPMMA/PANI/Ag composites (dotted line) prepared from various PMMA particlesizes.

Y. Lee et al. / Colloids and Surfaces A: Physicoc

Fuc

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3

PcfProrotsiscaP

[

[

[

ig. 11. (a) Resistivity of 2 �m PMMA/Ag (—) and PMMA/PANI/Ag (. . . . .) compositespon AgNO3 concentration and (b) resistivity versus silver contents in the PMMA/Agomposites (�) and PMMA/PANI/Ag (�).

article size. Since same amounts of PMMA and same concentrationf AgNO3 were used, the total silver content would be theoreticallyame which was independent of the particle size. However, sincehe smaller particles having large surface area exhibited thinnerilver layer than the larger particles, some defects such as non-niform deposition and no-plating on the particle surface werebserved after the washing process. This would cause the increasedilver contents with the PMMA particle size. In addition, the plat-ng efficiency of silver on PMMA/PANI/Ag composites was higherhan that on PMMA/Ag particles due to the activation effect of PANI,egardless of the particle size.

.8. Comparison of the resistivity

The resistivity of the various pellets of PMMA/Ag andMMA/PANI/Ag composites was plotted as a function of AgNO3oncentration in Fig. 11. As the AgNO3 concentration increasedrom 0.02 to 1.0 M, the resistivity of the two different composites,MMA/Ag and PMMA/PANI/Ag, decreased as seen in Fig. 11(a). Theesistivity of the former varied from 1014 to 107 � cm, while thatf the latter varied from 109 to 10−4 � cm, respectively. Thus, theesistivity of PMMA/PANI/Ag composites was much lower than thatf PMMA/Ag composites, indicating that PANI strongly influencedo enhance the conductivity. This was relevant that the larger theilver content, the higher the conductivity or the lower the resistiv-ty was obtained. The resistivity was again plotted as a function of

ilver contents in Fig. 11(b). That of PMMA/Ag and PMMA/PANI/Agomposites varied between 1014 and 10−1 � cm and between 108

nd 10−4 � cm, respectively. The above two results implied thatANI was strongly supportive for silver to plate on PMMA particles

[

hem. Eng. Aspects 396 (2012) 195– 202 201

and functioned as an activator for the composites to enhance theconductivity.

4. Conclusion

Monodisperse PMMA particles were prepared by the dispersionpolymerization and PANI was then successfully coated on the sur-face of PMMA particles by the in situ chemical polymerization. Theresultant particles were electroless plating with AgNO3 solutionand the various characterizations were performed in terms of thenumber of steps of the pretreatment, aniline content, AgNO3 con-centration and particle size. The remaining weight percentage ofsilver measured by TGA was used to verify the efficiency of silverplating. Results showed that PANI coated on the PMMA particleswas evidenced by the SEM and FTIR spectra and the degree of sil-ver plating was measured using TGA analysis. The silver platingwas enhanced with the particle size, and PANI stimulated the silverplating due to the activation effect. The resistivity of PMMA/Ag andPMMA/PANI/Ag composites upon silver content varied between1014 and 10−1 � cm and between 108 and 10−4 � cm, respectively.These results implied that PANI was strongly supportive for thesilver plating on PMMA composites as an activator, resulting inenhanced conductivity. In addition, the resistivity exhibited 3 timeshigher conductivity in PMMA/PANI/Ag than in PMMA/Ag system,which indicated that the continuous deposition of PANI leads theuniform plating of the silver layer. Thus, the use of PANI as anactivator is worthwhile in enhancing the silver plating.

Acknowledgements

This work was supported by the Business for Cooperative R&Dbetween Industry, Academy, and Research Institute funded by theKorea Small and Medium Business Administration in 2011.

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