preparation and characterization of polymer nanocomposites based on pvdf pvc doped with graphene nanoparticles

Elsayedd,e,⇑ Spectroscopy Department, Physics Division, National Research Centre, Cairo, Egypt Physics Department, Faculty of Science at Al-Ula, Taibah University, Madinah, Saudi Arabia

5

6

7 I.S Elashmawia,b, Naifa S AIatawiac, Nadia H Elsayedd,e,⇑

Spectroscopy Department, Physics Division, National Research Centre, Cairo, Egypt

Physics Department, Faculty of Science at Al-Ula, Taibah University, Madinah, Saudi Arabia

10 c

Physics Department, Faculty of Science, University of Tabuk, Tabuk 71421, Saudi Arabia

11 d

Chemistry Department, Faculty of Science, University of Tabuk, Tabuk 71421, Saudi Arabia

12 e Department of Polymers and Pigments, National Research Centre, Cairo 12311, Egypt

13

17 Article history:

18 Received 27 October 2016

19 Received in revised form 13 January 2017

20 Accepted 14 January 2017

21 Available online xxxx

22 Keywords:

23 Nanocomposites

24 Graphene oxide

25 FT-IR

26 X-ray

27 AC conductivity

28

2 9

a b s t r a c t

30 Novel nanocomposites based on PVDF/PVC blend containing graphene oxide nanoparticles (GO) were

31 prepare using sonicator IR analysis revealed that the addition of GO prompts a crystal transformation

32

ofa-phase of PVDF The change of the structural before and after adding GO to PVDF/PVC were studied

33

by X-ray diffraction A decrease in activation energy gap from UV data was observed with increasing GO

34 content, implying a variation of reactivity as a result of reaction extent The variation ofe0with frequency

35

is nearly the same as that ofe00 At higher frequencies, the decrease of bothe0ande00becomes nearly

con-36 stant The dispersion at lower frequenciese0ofe0polarization is of Maxwell–Wagner interfacial

polariza-37 tion but at higher frequencies, it levels off The behavior of conductivity (rAC) tends to acquire constant

38 values approaching it DC values The values ofrAC was increased after doped GO with exponential

39 increase after the critical value of frequency All nanocomposites behaved the same fashion revealing that

40

a higher number of polarons were getting added to conducting pool in composites as graphene content

41 was increased Conduction mechanism appeared to be getting expedited with increasing frequency due

42

to fact that increase in frequency enhances polaron hopping frequency

43

Ó 2017 The Authors Published by Elsevier B.V This is an open access article under the CC BY-NC-ND

44 license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

45 46

47 Introduction

48 Polymer blend give effective trends to make new properties in

49 polymeric materials The polymer blend is conceivable to create a

50 scope of materials with properties that are better than individual

51 segment polymers[1] Fundamental preferences of the blend are

52 easy to preparation and simplicity of controlling for physical

prop-53 erties Furthermore, it normally requires little or no additional

54 compared to new polymer synthesis[2] In any case, the miscibility

55 between the constituents of polymer blend on the molecular scale

56 is responsible for material with prevalent and superior properties

57 [3]

58 Polyvinylidene fluoride (PVDF) is a semi-crystalline polymer

59 that has been broadly researching for its piezoelectric properties

60 because its polar b phase[4] PVDF has well physical and electrical

61 properties of a kind for many applications[5] PVDF have various

62 favorable of advantages, including excellent dielectric properties,

63

high mechanical strength/flexibility, thermal and chemical

stabil-64

ity[6] Generally, some reports demonstrate the crystalline

struc-65

tures of PVDF and show a minimum five possible kinds of the

66

crystal phase, namely,a, b,c,eand d phases[7] Other than the

67

most well-known, b-phase is a more attractive crystal type in

68

PVDF, which is described by all-trans planar zigzag conformation

69

with all the fluorine atoms situated on the similar side of the

poly-70

mer chains[8] This arrangement of molecular chains in b-phase

71

gives PVDF a much higher with other PVDF phases due to the net

72

dipole moment[9]

73

Polyvinyl chloride (PVC) is one of the most important and

gen-74

erally utilized thermoplastic polymers due to its notable

perfor-75

mance and properties with low cost, great processability,

76

synthetic resistance and low combustibility PVC assumes part in

77

industry of plastic, furthermore, it may be combined with fillers

78

For example thermal stabilizer and plasticizer, before preparing

79

utilizing the ideals of toughness, acid, alkali resistance and grating

80

resistance[10] It is processed by itself, so it requires consolidation

81

of various added substances, since its little thermal stability Due to

82

the unique structure and remarkable mechanical, optical, thermal

http://dx.doi.org/10.1016/j.rinp.2017.01.022

2211-3797/Ó 2017 The Authors Published by Elsevier B.V.

This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).

⇑ Corresponding author at: Department of Polymers and Pigments, National

Research Centre, Cairo 12311, Egypt.

E-mail addresses: n.helsayed@yahoo.com , nhussein@ut.edu.sa (N.H Elsayed).

Contents lists available atScienceDirect

Results in Physics

j o u r n a l h o m e p a g e : w w w j o u r n a l s e l s e v i e r c o m / r e s u l t s - i n - p h y s i c s

Please cite this article in press as: Elashmawi IS et al Preparation and characterization of polymer nanocomposites based on PVDF/PVC doped with

gra-83 and electrical properties, graphene has been studied to produce

84 high-performance polymer composites

85 The dispersion of graphene within different polymer matrices

86 has made the new class of polymer nanocomposites [11] The

87 development of nanocomposite materials speaks to a productive

88 route to enhance the exhibitions of polymer and extend their

89 application scopes

90 Advantages of graphene oxide (GO) are easy dispersibility in

91 water and other organic solvents due to the presence of oxygen

92 and hydroxyl functionalities[12] This remains a very important

93 property when mixing with polymer matrices to improve their

94 spectroscopic, electrical and mechanical properties GO is

promis-95 ing materials and it’s used in basic studies for potential

applica-96 tions such as sensors, batteries, super capacitors, hydrogen

97 storage and reinforcing agents[13] Pure GO has 2D-dimension

98 form and it is consists of sp2bonds of carbon atom[14]

99 GO can be obtained by the exfoliation of graphite yielding well

100 separated two-dimensional[15] It offers extraordinary electronic,

101 thermal and mechanical properties Many reports have been made

102 not only on graphene’s very high electrical conductivity at room

103 temperature but also its potential use as nano-sensors, transparent

104 electrodes and many other applications[16] The object of this

arti-105 cle is to develop new polymeric nanocomposites (PVDF/PVC)

106 embedded with graphene oxide (GO) nanoparticles to be used in

107 different applications X-ray diffraction, IR, UV–Vis and AC

conduc-108 tivity has been carried out to study the prepared nanocomposites

109 Experimental

110 Materials

111 The basic materials are polyvinylidene fluoride (PVDF) (–CH2

-112 CF2–)nand polyvinyl chloride (PVC) (C2H3Cl)nsupplied by

Sigma-113 Aldrich Graphene oxide (GO) nanoplatelets are one of a kind

114 nanoparticles comprising of short stacks of graphene sheets having

115 a platelet shape Graphene oxide particles have a normal thickness

116 of roughly 6–8 nm and a typical surface area around 130 m2/g was

117 also supplied by Sigma-Aldrich

118 Preparation

119 PVDF and PVC were dried before used at 50°C for 1 h to remove

120 any moisture A weight ratio of 3:1 between PVDF and PVC were

121 dissolved in tetrahydrofuran (THF) with stirring for approximately

122 4 h at 60°C until the homogenous solution was formed Graphene

123 oxide (GO) nanopowder was dissolved in THF using sonication

124 technique The obtained GO solution was added to the blend

solu-125 tion dropwise to different final GO concentrations of 0.005 and

126 0.010 wt% with continuous stirring under ultrasonic The final

127 solution was cast in Petri dishes and left in an oven at 60°C for

128 approximately 72 h to dry and remove the solvent The thickness

129 of the samples for IR and UV/Vis measurements is nearly 20lm

130 and150lm for other measurements The films were then peeled

131 from the dishes and stored in a desiccator until use

132 Measurements

133 An FT-IR spectrophotometer (Nicolet iS10, USA) was used to

134 obtain the IR spectra IR spectra were collected in the wavenumber

135 range from 4000 to 400 cm1 The XRD measurements were

car-136 ried out on an PANalytical X’Pert PRO XRD system using Cu Ka

137 radiation (where k = 0.1540 nm, the tube was operated at 30 kV

138 and the Bragg angle 2h = 5–80° The UV–Vis absorption spectra

139 were collected in the 190–800 nm wavelength region using a

spec-140 trophotometer (V-570 UV/VIS/NIR, JASCO, Japan) The AC

measure-141

ments were carried out using an LCR meter of the Hioki3531Z

Hi-142

Tester, using the two-probe method, Japan, operating at a

fre-143

quency range from 42 Hz to 1 MHz, with impedance accuracy

144

ranging from 0.15% up to 4% In the electrical measurements, the

145

films were cut into pieces of 1 cm diameter The films were coated

146

by silver paste on both sides and tested for ohmic contact The LCR

147

meter was connected to the computer through an Rs–232c

inter-148

face and the dielectric measurements were performed at room

149

temperature as well as the conductivity

150

Results and discussion

151

Fourier Transform Infrared spectroscopy (FT-IR)

152

For comparison purposes, The FT-IR spectra of pure PVDF/PVC

153

doped 0.005 and 0.010 wt.% of graphene oxide in wavenumber

154

range 4000–400 nm are included inFig 1 The assignments of IR

155

spectrum of PVDF have been reported as follows:a-phase bands

156

due to CF2 bending are observed at 482 cm1, 531 cm1 and

157

615 cm1 The main bands due to CH2wagging broad mode are

158

observed at 1062 cm1, whereas the b-phase peak due to CF2

sym-159

metric stretching is observed at 870 cm1 [17] The absorption

160

peaks appearing at 3035 cm1is assigned to CF stretching mode

161

of PVDF[18]

162

The assignments of IR spectrum of PVC shows the following

163

main bands[19]: absorption band at 2977 cm1due to CH

stretch-164

ing, a band at 2919 cm1assigned to the CH2asymmetric

stretch-165

ing mode, a sharp band at 1434 cm1 attributed to the CH2

in-166

phase vibration, a band at 964 cm1assigned to chain stretching

167

The band at 837 cm1ascribed to the C–Cl stretching mode which

168

gives a conclusion about the interaction between the two

poly-169

meric matrices and hence the complexation

170

For PVDF/PVC blend doped with 0.005 and 0.01 wt.% of

gra-171

phene oxide nanoparticles, the intensities of the a-phase PVDF

172

bands decreased with increasing of GO content This result

con-173

firms that the doping of graphene oxide prompts a crystal

transfor-174

mation for the a-phase The changes of the intensity in IR

175

absorption bands can be utilized as a measure of the quality of

176

interactions between segments in prepared nanocomposites

177

X-ray analysis

178

The X-ray diffraction was utilized to study the nature of

crys-179

tallinity with respect to study the complexation between PVDF/

180

PVC and GO The X-ray diffraction of PVDF/PVC/GO

nanocompos-4000 3500 3000 2500 2000 1500 1000 500

Wavenumber (Cm-1

) PVDF/PVC 0.005 0.010

Fig 1 FT-IR absorption spectra of PVDF/PVC/Graphene nanocomposites.

Please cite this article in press as: Elashmawi IS et al Preparation and characterization of polymer nanocomposites based on PVDF/PVC doped with

gra-181 ites is represented as shown inFig 2 The XRD diffraction of pure

182 PVDF/PVC blend indicate the semicrystalline nature as the main

183 hump (hallow peak) centered at 2h = 18.38° and a sharp peak at

184 2h = 39.07° In the doped samples by graphene oxide nanoparticles,

185 No impurity-related ripples or small peaks were observed in all

186 spectra, demonstrating the purity and good dispersion of graphene

187 in PVDF/PVC polymeric matrices The shifts of the peak position

188 were observed from 2h = 18.38° to 2h = 20.04° indicating that the

189 crystal structure of GO was altered by its incorporation into

190 PVDF/PVC The decrease in the broadness of the apparent peak at

191 18.38o of the doped samples has been observed when compared

192 with the pure blend This can be interpreted as far as the Hodge

193 et al.[20], which has established a correlation between the

inten-194 sity of the peak and the degree of crystallinity So, the increase in

195 the broadness of this peak reveals the increase of these amorphous

196 regions in the samples From all previously mentioned results, the

197 interaction between the PVDF/PVC blend and GO results in

198 decreasing crystallinity with rich amorphous phase The

amor-199 phous nature is responsible for higher conductivity and affirms

200 the complexation between GO and the PVDF/PVC blend From all

201 previously mentioned results, the interaction between the PVDF/

202 PVC blend and GO results in decreasing crystallinity with rich

203 amorphous phase The amorphous nature is responsible for higher

204 conductivity and confirms the complexation between GO and the

205 PVDF/PVC blend

206 UV–Vis analysis

207 The UV–Vis spectra of the prepared nanocomposites in the

208 wavelength range 190–800 nm are shown inFig 3 These spectra

209 are used to describe the shape of the optical absorption edge

210 The absorption edges attributed to the semicrystalline behavior

211 of the nanocomposites were observed at 277 nm for all of the

sam-212 ples The intensity of the absorption edge decreased with

increas-213 ing GO content, indicating that reactions between all components

214 occurred because of the addition of GO The absorption bands

215 observed in the 233–238 nm range were assigned to thep?p⁄

216 transition originating from unsaturated bonds (C@O and C@C)

217 Other small bands at 284 and 297 nm were observed A new band

218 was seen at 309 nm after adding GO

219

Determination of the optical energy band gap

220

Polymers doped fillers are categories into direct and indirect

221

band gap For direct band gap, the highest of the valence band

222

and the bottom of conduction band lie at zero crystal momentum

223

If the bottom of the conduction band does not relate to zero crystal

224

momentum, then it is called indirect While, in indirect band gap

225

materials, the transition from valence to conduction band should

226

be associated with phonon of the right magnitude of crystal

227

momentum Near the fundamental band edge, both direct and

228

indirect transitions occur and can be obtained by plot the relations

229

betweena1/2,a2and energy (E = hm)[21]

230

The absorption coefficient (a) from the original UV–Vis spectra

231

was calculated using the equation:

232

a¼ 2:303 A

235

where A is the absorbance and d is the thickness of the sample

236

The relation between absorption coefficient and the photon

237

energy (hm) can be obtained by the Thutpalli and Tomlin method

238

[22]:

239

hm¼ ðahmÞs

242

where Egis energy band gap, h is Planck’s constant and s is order

243

describe the model used (direct or indirect transition) The s

con-244

stant has different values for different types of transitions: s = 2

245

for direct transmission and s =½ for indirect transmission The

val-246

ues of energy band gap (Eg) in indirect transitions are obtained by

247

plotting the relation between (ahm)1/2 and the energy (hm), as

248

shown inFig 4 Extrapolation of linear regions in the figure onto

249

x-axis provided calculated values of indirect band gap energy (Eg)

250

dependence on GO content

251

AC conductivity

252

Dielectric properties

253

The values of the real part of the dielectric constant (e0) at 30°C

254

at different frequencies for all the PVC/PVDF doped graphene oxide

255

nanocomposites were calculated from the relation[23]:

256

e0¼ Cpd

259

where Cpis the measured capacitance, d is the thickness and A is

260

the cross-section area of the sample.Fig 5shows the variation of

261

dielectric constant e0 with frequency for all the nanocomposites

262

From this figure, we can note that the dielectric constante0 of all

263

measured samples is found to decrease rapidly with frequency

2 theta (degree)

blend 0.005 0.010

Fig 2 The X-ray diffraction scan of PVDF/PVC/Graphene nanocomposites.

2.0 2.2 2.4 2.6 2.8 3.0

Wavelength (nm)

PVDF/PVC

0.005 0.010

Fig 3 UV–Vis spectra of PVDF/PVC/Graphene nanocomposites.

Please cite this article in press as: Elashmawi IS et al Preparation and characterization of polymer nanocomposites based on PVDF/PVC doped with

gra-264 The values of the imaginary part of the dielectric loss (e00Þ were

265 calculated from the relation:

266

268

269 where, tan d is the loss angle or dissipation factor The dielectric loss

270 factore00variation with frequency for all the samples is plotted in

271 Fig 6 The behavior of variation ofe00 with frequency is nearly the

272 same as that ofe0 with frequency The behavior of dielectric loss

273 e00decreases with increase in frequency At the higher frequencies

274 (>105Hz), the decrease ofe00becomes nearly constant

275 The small dispersion was observed at lower frequencies of the

276 behavior ofe0but at higher frequencies, it levels off The dispersion

277 in the dielectric loss at the lower frequency may be according to

278 the procedure of polarization due to Maxwell–Wagner interfacial

279 polarization[24] And because the grain boundaries of lower

con-280 ductivity are effective and at the higher frequency, graphene grains

281 of moderate conductivity are prominent

282 Graph of dielectric loss tangent (tan d) versus Log F was plotted

283 and typical is shown inFig 7 From the graph, it is seen that, the

284 values of tan d decreases with increase in frequency for these

285 nanocomposites attribute to that the hopping frequency of charge

286 carriers maybe follow the changes of externally applied electric

287 field beyond a certain frequency limit All samples have the higher

288

value ofe0in the low range of frequencies may be due to smaller

289

resistivity

290

Electrical conductivity

291

The AC electrical conductivity of the samples was estimated

292

from the following relation[25]:

293

296

whereeois the permittivity of free space (eo¼ 8:85  1012Fm1),

297

x= 2pf is the angular frequency and tan d is the dielectric loss factor

298

[26] The variation of AC electrical conductivity (rAC) variation with

299

different frequencies of all the samples at 30°C is shown inFig 8

300

For all the nanocomposites, it can be seen that at the lower

frequen-301

cies, conductivity (rAC) tends to acquire constant values (i.e an

302

increase in frequency is not appreciable at low frequencies)

303

approaching it DC values, and the values of the electrical

conductiv-304

ity was increased from 5.6 102m1 to 1.2 104

X1m1 after

305

doped graphene, while after a critical value of frequency, varies

306

exponentially increase with increasing frequency The type of this

307

behavior is common in disordered solids, appears to be in

accor-308

dance with the AC universal law and is considered as a strong

indi-309

cation for charge migration via the hopping mechanism All the

310

present nanocomposites behaved in the same fashion This result

Fig 4 The relation between (ahm) 1/2

and the energy (hm) for PVDF/PVC/Graphene nanocomposites.

Fig 5 The variation of dielectric constant ðe0 Þ with Log frequency for PVDF/PVC/

Graphene nanocomposites at room temperature.

Fig 6 The variation of dielectric loss factor ðe00 Þ with Log frequency for PVDF/PVC/

Graphene nanocomposites at room temperature.

Fig 7 The variation of dielectric loss tangent (tan d) versus Log frequency for PVDF/ PVC/Graphene nanocomposites at room temperature.

Please cite this article in press as: Elashmawi IS et al Preparation and characterization of polymer nanocomposites based on PVDF/PVC doped with

gra-311 reveals that a higher number of polarons (electrons) are getting

312 added to the conducting pool in the composites as graphene

con-313 tent is increased Also, conduction mechanism in these composites

314 appeared to be getting expedited with increasing frequency This

315 could be due to the fact that increase in frequency enhances polaron

316 hopping frequency The behavior of variation ofe00with frequency is

317 nearly the same as that ofe0with frequency The dielectric losse00

318 decreases with increase in frequency At higher frequencies

319 (>105Hz), the decrease ofe00becomes nearly constant

320 Conclusion

321 Nanocomposites films consists of polyvinylidene fluoride

322 (PVDF)/polyvinyl chloride (PVC) blend doped 0.005 and 0.010 wt

323 % of graphene oxide nanoparticles (GO) The films were prepared

324 and studied by different techniques IR analysis revealed that the

325 addition of GO prompts a crystal transformation from the a

-326 phase of PVDF The change of the structural before and after adding

327 GO to PVDF/PVC blend were studied by X-ray technique The

328 behavior of variation ofe00 with frequency is nearly the same as

329 that ofe0with frequency The decrease ofe00 becomes nearly

con-330 stant at the higher frequency The dispersion at lower frequencies

331 ofe0proposes that procedure of polarization is related to Maxwell–

332 Wagner interfacial polarization while at higher frequencies it

333 levels off The values of tan d decreases with increase in frequency

334 due to hopping frequency of charge carriers follow the changes of

335 applied electric field beyond a certain frequency limit The

conduc-336 tivity (rAC) tends to acquire constant values approaching itrDC

val-337 ues The values ofrAC were increased after doped graphene All

338 nanocomposites behaved in the same fashion which reveals that

339 a higher number of polarons (electrons) are getting added to

con-340 ducting pool in the composites as graphene content is increased

341 Acknowledgement

342 The author would like to acknowledge University of Tabuk for

343 the financial support under research project number S1437-0136

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Fig 8 The variation of AC conductivity (rAC ) with Log frequency for PVDF/PVC/

Graphene nanocomposites at room temperature.

Please cite this article in press as: Elashmawi IS et al Preparation and characterization of polymer nanocomposites based on PVDF/PVC doped with