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Colloids and Surfaces A: Physicochem. Eng. Aspects 441 (2014) 614– 622

Contents lists available at ScienceDirect

Colloids and Surfaces A: Physicochemical andEngineering Aspects

jo ur nal ho me p ag e: www.elsev ier .com/ locate /co lsur fa

heological behavior and electrical properties ofolypyrrole/thermally reduced graphene oxide nanocomposite

. Manivela, S. Kanagarajb, A. Balamurugana, N. Ponpandiana, D. Mangalaraja,

. Viswanathana,∗

Department of Nanoscience and Technology, Bharathiar University, Coimbatore 641 046, Tamil Nadu, IndiaDepartment of Mechanical Engineering, Indian Institute of Technology, Guwahati 781 039, Assam, India

i g h l i g h t s

Ppy/TRGO nanocomposites weresynthesized by in situ polymerizationmethod.Rheological behavior of Ppy/TRGOnanocomposite was analyzed bycone-plate method.The nanocomposite exhibits shearthinning behavior at lower andhigher temperature.The Ppy/TRGO nanocomposites donot deform at high shear rate andtemperature.

g r a p h i c a l a b s t r a c t

r t i c l e i n f o

rticle history:eceived 13 August 2013eceived in revised form 7 October 2013ccepted 9 October 2013vailable online 17 October 2013

eywords:olypyrroel

a b s t r a c t

Polypyrrole/thermally reduced graphene oxide (Ppy/TRGO) nanocomposites were synthesized via anin situ polymerization of pyrrole in the presence of TRGO in various proportions (1–5%). The synthesizednanocomposites were characterized by various techniques. SEM analysis clearly indicated the completedispersion of TRGO in the Ppy matrix. The nanocomposite exhibited obvious improvement in the ther-mal stability and electrical conductivity in comparison with the pure Ppy. The aim of this study was todetermine the rheological behavior of Ppy/TRGO nanocomposite at different mass ratio (100:1, 100:3 and100:5%) and temperature (25–180 ◦C) by using a rotational mode in cone-plate method. The nanocom-

anocompositeslectrical propertieseformationheology

posite was found to exhibit a non-Newtonian and shear thinning behavior at both lower and highertemperature. The rheological results showed that the Ppy/TRGO nanocomposites are stabile, and doesnot deform at high shear rate and temperature. The shear stress (�, Pa) and viscosity (�, Pa s) of thenanocomposites were increased with the addition of TRGO sheet into the Ppy. It was noted that TRGOsheets are effective material for the reinforcement of Ppy and the nanocomposite exhibit high flexibility

Ppy

compared with rigid pure

. Introduction

Conducting polymers have received much attention in recentears because of their potential applications such as in electronicevices, super capacitor, batteries, sensors and many other fields

∗ Corresponding author. Tel.: +91 422 2428422; fax: +91 422 2422387.E-mail addresses: viswanathan@buc.edu.in, jgviswa@gmail.com

C. Viswanathan).

927-7757/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.colsurfa.2013.10.031

.© 2013 Elsevier B.V. All rights reserved.

[1]. Especially five-membered ring heteroaromatic polypyrrole(PPy) is considered as one of the most important conducting poly-mers and has been studied extensively in the last decades owingto its high electrical conductivity accompanied by a high stabil-ity upon exposure to ambient conditions, easy preparation andgood environmental stability and cost effectiveness [2–5]. How-

ever, these conducting polymers usually show a poor thermal,mechanical, oxidative stability and insolubility in common solventsand infusibility that limits their commercial application [6]. In orderto overcome this problem, several processing methods have been

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tudied. Various composites of Ppy with inorganic nanoparticlesuch as insulating polymers, carbon nanomaterials have been pre-ared to improve its mechanical, electrical, thermal properties. Theelative instances include the conducting polymer nanocompositesade by incorporating conductive polymers in inorganic carbon

ased materials such as graphite oxide (GO), graphene, carbonanotubes [7–9].

Graphene, a flat monolayer of hexagonally arrayed sp2-bondedarbon atoms tightly packed into a two-dimensional (2D) honey-omb lattice, has been the major focus of recent research due to itsutstanding mechanical, electrical, thermal and optical propertiesver since its first discovery in 2004 [10]. It has been demonstratedhat graphene with zero band gap and high carrier mobility andoncentrations, shows nearly ballistic transport at room temper-ture [11]. Graphene also has other potential applications suchs in electrochemical resonators, stretchable and elastic matricesor flexible electronic devices and as filler for electrical, mechan-cal flexible nanocomposite [12]. One possible route to harnesshe remarkable properties of graphene sheets would be to inte-rate graphene sheets with other material, which would eventuallynhance its properties. Manufacturing such naocomposite wouldequire not only the graphene sheets to be produced on a sufficientcale but also they have to be properly incorporatedand homoge-eously distributed into the chosen matrices [13].

The nanocomposite based on conducting polymers and layer-y-layer structured graphene often exhibit synergistic propertieserived from both components [14]. It has been reported in severaltudies that the graphene based polymer nanocomposite’s exhib-ted enhanced thermal, mechanical, electrical properties [15–17].o utilize the unique properties of graphene and its derivatives,onsiderable efforts have been made to incorporate graphene orts derivatives into Ppy based matrix to the form the nanocompos-te, which will display good mechanical strength owing to carbon

atrix and excellent electrical conductivity due to the conductingpy [18]. Okan et al. studied the graphene coated with polypyr-ole via in situ polymerization of pyrrole (Py) monomer withifferent feeding mass ratios of Py [19]. Li et al. reported on theovalently assembled graphene/polypyrrole foams prepared by aydrothermal method [20]. Wang et al. reported the Ppy film coat-

ng on the surface of graphene/SnO2 via in situ polymerization [21].herefore, a number of studies have been performed regarding thehermal, electrical conductivity and the mechanical properties ofanocomposites. Recently only few reports are available the elec-rorheological performance of reduced graphene oxide/polypyrrolend polyaniline/graphene nanocomposite [22–24].

In the present study, we report the synthesis of polypyr-ole/thermally reduced graphene oxide nanocomposite by in situolymerization. TRGO can be delaminated into nanosheets andomogeneously dispersed in aqueous solution, and there will be–� interaction between Ppy and the domain of TRGO sheets. Thisork was aimed at obtaining a good dispersion of TRGO sheetithin the polymer matrix as well as to achieve enhancements in

hermal and electrical properties of the nanocomposites. The rheo-ogical behaviors of the nanocomposites were investigated in termsf their shear viscosity and shear stress. Furthermore, the sheartress and viscosity of the nanocomposites was increased with thencrease in mass ratios of TRGO incorporated into Ppy. The intro-uction of less amount of TRGO into Ppy was found to be effective

n the enhancement of the properties of Ppy.

. Experimental

.1. Materials

Natural graphite flakes (10 mesh) were purchased from Alfaesar. Pyrrole was purchased from Himedia chemical and was

ochem. Eng. Aspects 441 (2014) 614– 622 615

distilled under reduced pressure and kept below 0 ◦C before use.Sodium nitrate, sulfuric acid, hydrochloric acid, potassium perman-ganate, ammonium peroxydisulfate, were obtained from Himediachemicals and hydrogen peroxide obtained from Sd-fine chemi-cals. All the analytical-reagent grade chemicals are used withoutfurther purification. All the aqueous solutions were prepared withdouble-distilled water.

2.2. Synthesis of polypyrrole nanoparticles (Ppy)

Pyrrole was first distilled under vacuum to remove the oxidationimpurities. The purified pyrrole (0.2 M) was dissolved in 100 mLof 1 M HCl aqueous solution. While maintaining vigorous stirringat room temperature, the ammonium peroxydisulfate (0.25 M) in50 mL of 1 M HCl aqueous solution was slowly added drop wiseinto the pyrrole solution. Polymerization was observed after com-plete addition when the characteristic black color of polypyrroleemeraldine salt appeared. The mixture was allowed to stir at roomtemperature overnight. The precipitated polypyrrole was collectedby filtration and repetitively washed with double distilled water,ethanol and acetone successively until the filtrate became colorlessand dried in vacuum oven at 60 ◦C overnight.

2.3. Synthesis of polypyrrole/thermally reduced graphene oxidenanocomposites (Ppy/TRGO)

Polypyrrole/thermally reduced graphene oxide nanocompositewas prepared by in situ polymerization of pyrrole in a suspensionof thermally reduced graphene oxide in acidic solution. Thermallyreduced graphene oxide was synthesized by radio frequency chem-ical vapor deposition method (RF-CVD) [25]. The weight ratio ofpyrrole to graphene oxide was varied as 100:1, 100:2, 100:3, 100:4and 100:5 and the resulting composites were named as Ppy/TRGO1,Ppy/TRGO2, Ppy/TRGO3, Ppy/TRGO4 and Ppy/TRGO5, respectively.Typically, the TRGO was dispersed in 100 mL of 1 M HCl aqueoussolution by bath sonicating for 1 h. Then 0.2 M pyrrole was dis-solved in the dispersed TRGO containing acidic aqueous solution.While maintaining vigorous stirring at room temperature, ammo-nium peroxydisulfate solution, with a mole ratio to aniline of 1:2, in1 M HCl was added drop wise into the resulting mixture. After about5 min of addition, the pyrrole started to polymerize while the colorof mixture changed into black. The mixture was stirred at roomtemperature overnight. The composites were collected by filtrationand repetitively washed with double distilled water, ethanol andacetone successively until the filtrate became colorless and driedin vacuum oven at 60 ◦C overnight.

2.4. Characterization

The FT-IR spectra of the samples were recorded on a Thermon-icolet 10–ATR mode FT-IR spectrometer by using KBr pellets toconfirm the presence of functional groups. X-ray diffraction (XRD)patterns were recorded on an X-pert Pro’ PANlytical powder X-raydiffractometer. Copper K� line was used as a radiation source with� = 1.5406 A. Raman spectra were recorded at ambient temperatureon a Horiba Jobin-LabRam-HR UV spectrometer with Argon laser atan excitation wavelength of 514 nm. A QUANTA 250 field emissionscanning electron microscope (FE-SEM) was used to determine themorphology of the composites. Structures of the composite sam-ple were examined with transmission electron microscopy (TEM)using a JEM-2010 electron microscope: JEOL Co working at 200 kV.TGA was performed using a SEIKO-TG/DTA 6200 instrument in the

temperature range of 23–800 ◦C with a heating rate of 20 ◦C/minunder a nitrogen flow to study the thermal degradation of the sam-ples. The Electrical conductivity measurement was performed onpellets of the nanocomposite powder samples using a standard four

616 P. Manivel et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 441 (2014) 614– 622

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Fig. 1. FTIR spectra of (a) TRGO, (b) Ppy and (c) Ppy/TRGO nanocomposite.

robe technique using a Keithley 2182 A instrument. The pow-er was pressed into a 3 mm diameter pellet at under identicalonditions. The pellet was then vacuum dried for 1 h before mea-urement.

.5. Rheological measurements

The synthesized Ppy/TRGO nanocomposite particles weretored in vacuum desiccators prior to use. The Rheological fluid wasrepared by dispersing Ppy/TRGO nanocomposite particles (5 wt%)

n silicone oil with the help of an ultrasonicator for better disper-ion. The rheological measurements of the nanocomposite wereaken in an Anton paar rheometer (Physica MCR 101). The sheartress/shear rate and shear viscosity/shear rate rotation ramp testsere performed using a cone sensor (CP50-1-SN22160; 50 mmiameter, 1◦ angle), with 0.099 mm gap. The samples were mea-ured at different temperature (25, 100, 150, 180 ◦C). The flowurves of shear stress vs. shear rate were carried out in the rangef 1–1000 s−1. The sample was not reused after heating due to thehange in rheological properties.

. Results and discussions

.1. Characterization of Ppy/TRGO nanocomposite

FTIR spectra of pure TRGO, Ppy and Ppy/TRGO nanocompositere represented in Fig. 1. In the FTIR spectrum of TRGO, the smallntense peak 1635 and 1735 cm−1 corresponds to the C C stretch-ng mode and C O stretching vibrations of the COOH group,espectively. The broad peak corresponding to the stretching vibra-ions of O H at 3409 cm−1 indicates the water adsorbed TRGO

amples. In the spectra of Ppy, the strong absorption band obtainedt1544 cm−1 and 1455 cm−1 corresponds to the C C stretchingibration in pyrrole ring. The band at 1297 cm−1 is attributed tohe C N in-plane, and the bands at 1175 and 1031 cm−1 are related

Fig. 2. XRD pattern of (a) TRGO, (b) Ppy and (c) Ppy/TRGO nanocomposite.

to the C H bending modes while the band for C H out-of-planedeformation vibration was found at 897 cm−1. The FTIR spectrumof Ppy/TRGO nanocomposite was almost the same as that of Ppy.The absorption peaks at 1544 and 1455 were associated with theC C and C N stretching vibration in the Ppy ring. The absorptionsmall intensed peaks located at 2915 and 2841 cm−1 were ascribedto asymmetric stretching and symmetric vibration of CH2 [26,27].It was observed that the peak due to the C O group within thePpy/TRGO nanocomposite has been shifted to 1706 cm−1, whichcould be due to the �–� interaction and hydrogen bonding betweenthe TRGO sheet and aromatic Ppy rings. The characteristic peaks ofPpy at 1544 cm−1 and 1455 cm−1 suggests the presence of Ppy inthe Ppy/TRGO nanocomposite.

Fig. 2 shows the X-ray diffraction patterns (XRD) of TRGO, Ppyand Ppy-TRGO nanocomposite. For TRGO, the diffraction peaksat 2� = 24.4◦ (i.e., d = 0.38 nm) and 43◦ can be attributed to thegraphite-like structure (0 0 2) and (1 0 0), respectively. Also, thebroad diffraction peak is also indicative of a loss of the long-rangeorder in graphenes [28]. The pure Ppy, exhibit a weak and broaddiffraction peak at 2� = 15–33◦, which indicates that the Ppy isamorphous in nature. For Ppy/TRGO nanocomposite, one broad andhigh intense peak appeared at around 2� = 25.7◦ and small intensepeak appeared at 2� = 43.7◦ which is the characteristic peaks ofPpy and graphite like-structure of TRGO, respectively. Additionally,the peak ascribed to TRGO within the nanopcomposites completelyoverlapped with the Ppy diffraction peak and also the mass ratioof TRGO ranging from 1% to 5% only got incorporated into the Ppymatrix. The diffraction peaks of TRGO overlapped with Ppy aftercomplete in situ polymerization process. These XRD data revealedthat the growth of the polymer chain of pyrrole in the TRGO sheetshas resulted in an increased interlayer distance.

Fig. 3 shows, the Raman spectra for the developed Ppy/TRGOnanocomposite as well as for pure Ppy and TRGO layer. In the Ramanspectrum of TRGO sheet, the two intense bands at 1349 cm−1 and

1570 cm have been assigned to D band and G band respec-tively. The G band assigned to the first order scattering of theE2g phonon of TRGO represent the in-plane bond stretching vibra-tion of sp2-bonded carbon atoms in a 2D hexagonal lattice. The D

P. Manivel et al. / Colloids and Surfaces A: Physic

Fig. 3. Raman spectra of (a) TRGO, (b) Ppy and (c) Ppy/TRGO nanocomposite.

Fig. 4. FE-SEM images of (a) Ppy, (b) TRGO

ochem. Eng. Aspects 441 (2014) 614– 622 617

band is associated with the breathing mode of K-point phononsof A1g symmetry with vibration of carbon atoms with danglingbonds in plane terminations of disordered graphite [25,29]. Thesharp peak observed at 2700 cm−1 was assigned to 2D band andit is well known key parameter to judge both the formation andlayer numbers of the graphene sheets. In the Raman spectrum ofpure Ppy, the characteristic bands appear at 1565 and 1347 cm−1,which were assigned to the C C backbone stretching and the ringstretching vibration of Ppy, respectively. In the Raman spectrum ofPpy/TRGO nanocomposite, the D band becomes broad during thein situ polymerization process. In addition, both these D and G bandshift to 1366 and 1558 cm−1, when TRGO was introduced into thePpy matrix. This is probably due to the doping of carboxyl groupof thermally reduced graphene oxide to Ppy backbone and �–�interaction between Ppy and TRGO sheets [18].

The morphology of Ppy, TRGO and PPy/TRGO nanocompositeswas characterized using FE-SEM (Fig. 4). The pure polypyrrole pre-pared showed an irregular spherical like structure in the orderof ∼150–200 nm. TRGO prepared here exhibited a flat; multilay-ered structure with thin and flaky appearance. In the Ppy/TRGOnanocomposite, Ppy nanoaprticle was coated on the surface ofexpanded TRGO by in situ chemical oxidative polymerization ofpyrrole monomer and it was difficult to distinguish the individualphases.

The monomer and TRGO sheet mass ratio effect of Ppy/TRGOnanocomposite (Ppy/TRGO1, Ppy/TRGO3 and Ppy/TRGO5) surface

morphology are shown in Fig. 5. In all Ppy/TRGO nanocomposites,Ppy retains its spherical like morphology with similar size as thatof the pure Ppy nanoparticles, and TRGO retains its layer-like struc-ture. For Ppy/TRGO1 nanocomposite, where Ppy nanoparticles are

and (c, d) Ppy/TRGO nanocomposite.

618 P. Manivel et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 441 (2014) 614– 622

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rated into nanosheet, the �–� electron stacking between thepyrrole ring of Ppy and unoxidized domain of TRGO can trans-fer electron more effectively [14]. The electrical conductivity ofthe Ppy/TRGO nanocomposite was found to have increased in

Table 1Electrical conductivity measurements of pure Ppy and Ppy/TRGO nanocomposite.

Sample particulars Thickness of pellet(d, cm)

Resistivity(�, � cm)

Conductivity(�, S/cm)

Ppy 0.3 4.016 0.249Ppy/TRGO1 0.3 0.435 2.298

Fig. 5. FE-SEM images of TRGO mass ratio effect in Ppy/TRGO nan

n the majority, TRGO sheets are embedded in the Ppy nanoparti-les evenly distributed both on the surface and between the TRGOheets. For other Ppy/TRGO (3 & 5) nanocomposites with a reducedmount of Ppy, spherical like Ppy mainly adsorbs on the surface orntercalates between TRGO sheets and the wrinkled, folded, layer-ike morphology of TRGO was observed.

TEM characterization was also used to investigate the struc-ure and morphology of the sample. The TEM images for Ppy/TRGOanocomposite were shown in Fig. 6. The spherical like struc-ures of Ppy which are decorated at the surface or intercalatesetween the TRGO sheets. It confirms the formation nearly aggre-ated particles (∼150 nm) on the surfaces of the TRGO sheets.t is observed that the Ppy/TRGO composite sheets are folded

ith some dark edges which indicate the flexible character of theanocomposite. SEM and TEM images reveal that the thermallyodified TRGO and Ppy formed a nanocomposite with the Ppy

bsorbed on the TRGO surface and/or filled between the TRGO

anosheets.

The DC electrical conductivity of pure Ppy and Ppy/GOanocomposites are determined using a four probe resisti-ity measurement system at room temperature. The average

posite: (a, b) Ppy/TRGO1, (c, d) Ppy/TRGO3 and (e, f) Ppy/TRGO5.

conductivities are summarized in Table 1. The in situ polymer-ization of pure Ppy, with HCl as medium, shows a conductivityof 0.249 S/cm which is lower than that of Ppy synthesized bythe electrochemical method (10–50 S/cm) [30] but higher thanthat of Ppy synthesized by the chemical method using FeCl3 asthe oxidant (0.070 S/cm) [31]. However, when TRGO is incorpo-

Ppy/TRGO2 0.3 0.343 2.915Ppy/TRGO3 0.3 0.276 3.623Ppy/TRGO4 0.3 0.228 4.385Ppy/TRGO5 0.3 0.209 4.784

P. Manivel et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 441 (2014) 614– 622 619

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Fig. 6. TEM images of Ppy/TRGO nanocomposi

omparison to the pure Ppy. The nanocomposite showed anncrease in magnitude of conductivity even at a low TRGO massatio. For Ppy/TRGO1, Ppy/TRGO2, Ppy/TRGO3, Ppy/TRGO4 andpy/TRGO5, the conductivities were found to be 2.298, 2.915, 3.623,.385 and 4.784 S/cm respectively at room temperature. The struc-ure of Ppy/TRGO nanocomposite probably results in improvedlectrical conductivity, the large surface area of TRGO sheet mayerve to increase the conductivity of Ppy/TRGO nanocompos-tes.

TGA studies were carried out to investigate the thermal stabil-ty of TRGO, Ppy and Ppy/TRGO nanocomposites shown in Fig. 7.he TRGO, first starts to lose weight upon heating from 30 ◦C to50 ◦C owing to the evaporation of residuals present between the

ayers in TRGO; a second major weight loss occurs at about 450 ◦Chich is due to the decomposition of functional groups (such as

C and COOH). For the pure Ppy, the Ppy was stable in the tem-erature range up to 200 ◦C and shows only about 15% mass losshich is due to dehydration of the Ppy. However, a rapid weight loss

akes place after 300 ◦C, which corresponds to the complete degra-

ation and decomposition of Ppy at different polymerization stage.

n Ppy/TRGO nanocomposite, the slow weight loss up to 200 ◦C cane attributed to the loss of co-intercalated water molecules and

Fig. 7. TGA curve of (a) TRGO, (b) Ppy and (c) Ppy/TRGO nanocomposite.

low magnification and (b) high magnification.

pyrolysis of the liable oxygen containing functional groups. After200 ◦C, major weight loss has occurred which may be due to thedecomposition of the Ppy from nanocomposites. The Ppy/TRGO5nanocomposite shows nearly 31% weight retention at about 700 ◦Cwhich is probably due to the existence of a carbon structure in thenanocomposites.

3.2. Rheological behavior of Ppy/TRGO nanocomposite suspension

Fig. 8A shows the rheological behavior of pure Ppy andPpy/TRGO nanocomposite (5 wt%) suspension analyzed by shearstress as a function of shear rate at 25 ◦C and 150 ◦C using arotational rheometer system. For both pure Ppy and Ppy/TRGOnanocomposite shear stress curve were increased by increasingshear rate at 25 ◦C. In the Ppy/TRGO nanocomposite, shear stressvalues were high compared to pure Ppy suspension. Furthermore,both Ppy and Ppy/TRGO nanocomposite stress appeared like ina Bingham fluid behavior, when the temperature was increasedto 150 ◦C [32]. The shear stress flow curve of pure Ppy increasedsuddenly when the shear rate was in the range from 450 to1000 S−1 at high temperatures. However, the pure Ppy withstoodstress up to shear rate in the range of 450 S−1 at higher tempera-ture. Hence, the Ppy/TRGO nanocomposites withstood stress curveflow as function in the whole shear rate range without changeby temperature effect. Due to the Ppy grown in the pores andgalleries of TRGO sheet and pyrrole polymerized in the inter-face of TRGO sheets this nanocomposite suspension does notshow any deformation even at high temperature and high shearrate.

Fig. 8B shows the typical viscosity obtained for suspension ofPpy and Ppy/TRGO nanocomposite in the solution of silicone oil.This figure presents a plot of viscosity as a function of shear rateat constant volume fraction 50 mg/mL for both components at25 and 150 ◦C. There is no pronounced shear thickening behav-ior at 25 ◦C for both Ppy and Ppy/TRGO nanocomposite suspensionover the shear rate range examined. The viscosity level and shearthinning behavior of Ppy/TRGO nanocomposite was increased incomparison with the pure Ppy. It’s due to the evenly dispersionof TRGO sheets in Ppy and it serves to increase the viscosity ofthe suspension. Furthermore, the viscosity measurements for bothPpy and Ppy/TRGO nanocomposite suspension were carried out at

150 ◦C. The pure Ppy exhibited shear thinning behavior and vis-cosity rapidly decreased linearly at moderate shear rate. On theother hand, the viscosity rapidly increased and behavior transitionfrom shear thinning to shear thickening occurs at higher shear rate.

620 P. Manivel et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 441 (2014) 614– 622

Fig. 8. (A) The flow curves of shear rate and shear stress of silicone oil, Ppy, and Ppy/TRGO nanocomposite suspension for (a) 25 ◦C and (b) 150 ◦C. (B) The flow curves of shearr (a) 25

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ate and viscosity of silicone oil, Ppy, and Ppy/TRGO nanocomposite suspension for

ven though, it appears that shear thickening may be discontinuousnd accompanied by a sudden jump in the shear stress or increasen the viscosity of the system. Particulate suspensions can showhear thickening behavior if subjected to the right conditions (com-ination of interparticle forces, particle size and hydrodynamic

nteractions). The Ppy/TRGO nanocomposite suspension exhibitedigh shear thinning behavior up to 10 S−1, further increasing shearate the shear thinning was gradually decreased. The addition ofRGO sheet content in the Ppy induces a little increase in the vis-osity. However, the Ppy is grown or deposited on the TRGO sheetsith even size distribution and it can be used to avoid the free

py inter particles force in the nanocomposite. The interparticleorce and hydrodynamic interactions are removed by the presencef TRGO sheets in the nanocomposite. It can be observed that theRGO sheet has assisted to shear thinning behavior and viscos-ty.

Fig. 9A shows the shear stress flow curve of various TRGO sheetontent (1, 3 and 5%) in the Ppy/TRGO nanocomposite suspension at5 ◦C and 150 ◦C. There appears to be a trend. All shear stress curves

ncreased non-linearly (Bingham fluid behavior) with increasinghear rate at both temperatures. This is due to an internal forcef Ppy/TRGO nanocomposite to resist deformation when the sus-ension is subjected to shear force. The shear stress values were

ncreased with addition of TRGO sheet in the nanocomposite. On

he other hand, the shear stress curves increased with increasinghear rate at 150 ◦C. However, the shear stress formed as non-linearccurred at low shear rate up to 20 � S−1. This is due to temperatureffect, colloidal composite particles is agglomeration and particle

◦C and (b) 150 ◦C.

interaction force. Further transition from the non-linear to lin-ear curve occurs with increase in shear rate. There is Ppy/TRGOnanocomposite exhibited good stability both at low and high tem-perature and also does not showed deformation even at high shearrate.

Fig. 9B shows the typical viscosity profiles of various mass ratioof TRGO sheet addition in the nanocomposite at 25 and 150 ◦C.It was observed that the all curves of nanocomposite suspensionshowed shear thinning behavior for the various mass ratios TRGOchosen. High shear thinning behavior of Ppy/TRGO nanocompositewas observed at both temperatures. This is due to the TRGO sheetsbind with Ppy by H-bonding and pi–pi interaction. Therefore, thisTRGO sheet acts as a backbone for the Ppy and it also helps foreven dispersion of colloidal solution of nanocomposite and resistthe agglomeration of polymer particles at high temperature andshear rate.

Fig. 10 a and b shows the rheological behavior of Ppy/TRGO(mass ratio 3%) nanocomposite suspension analyzed by shear stressand shear viscosity as a function of shear rate at different tem-perature (25, 100, 150 and 180 ◦C). The entire shear stress curveincreased with increasing shear rate. The shear stress values weredecreased by increasing temperature with non-Newtonian process.However, this Ppy/TRGO nanocomposite showed considerable sta-bility without deformation at high temperature and shear rate.

This could be due to the TRGO sheet as a backbone of nanocom-posite suspension. From viscosity curve we observed that theshear thinning behavior was increased with increasing tempera-ture.

P. Manivel et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 441 (2014) 614– 622 621

Fig. 9. (A) The flow curve of shear rate and shear stress of various TRGO additions in Ppy/TRGO nanocomposite suspension for (a) 25 ◦C and (b) 150 ◦C. (B) The flow curve ofshear rate and viscosity of various TRGO additions in Ppy/TRGO nanocomposite suspension for (a) 25 ◦C and (b) 150 ◦C.

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ig. 10. Different temperature effect flow curve of 3% TRGO addition of Ppy/TRGO n

. Conclusion

Polypyrrole/thermally reduced graphene oxide nanocompositesave been successfully synthesized by in situ polymerization. FTIR,RD and Raman spectrum revealed the incorporation of TRGO into

he Ppy matrix. The surface morphology was observed by FE-SEM.

mposite suspension for (a) shear rate vs. shear stress and (b) shear rate vs. viscosity.

The electrical conductivity of the nanocomposite was increasedfrom 2.275 S/cm to 3.920 S/cm with increasing TRGO sheet com-

pared with the conductivity of pure polypyrrole (0.180 S/cm).The Ppy/TRGO nanocomposite showed improved thermal stabilitycompared to the pure Ppy, in the temperature range 50–700 ◦C. Therheological results showed that the shear stress (�, Pa) and viscosity

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�, Pa s) of the Ppy/TRGO nanocomposites is higher than the pureolypyrrole. This result is accompanied by an increase in elastic andhear thinning properties of the nanocomposites. Hence we suggesthat the synthesized nanocomposite with the improved rheologicalehavior, electrical conductivity, increased thermal stability coulde an ideal material for industrial applications.

cknowledgement

We thank Dr. Nikhil K Kothurkar, Department of Chemicalngineering and Material Science, Amrita Vishwa Vidyapeethamniversity for the preparation of thermally reduced graphene oxide

n Radio frequency chemical vapor deposition (RF-CVD).

eferences

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