RINP 542 No of Pages 5, Model 5G 18 January 2017 Results in Physics xxx (2017) xxx–xxx Contents lists available at ScienceDirect Results in Physics journal homepage: www.journals.elsevier.com/results-in-physics Preparation and characterization of polymer nanocomposites based on PVDF/PVC doped with graphene nanoparticles I.S Elashmawi a,b, Naifa S AIatawia c, Nadia H Elsayed d,e,⇑ 10 11 12 13 14 17 18 19 20 21 22 23 24 25 26 27 28 a Spectroscopy Department, Physics Division, National Research Centre, Cairo, Egypt Physics Department, Faculty of Science at Al-Ula, Taibah University, Madinah, Saudi Arabia c Physics Department, Faculty of Science, University of Tabuk, Tabuk 71421, Saudi Arabia d Chemistry Department, Faculty of Science, University of Tabuk, Tabuk 71421, Saudi Arabia e Department of Polymers and Pigments, National Research Centre, Cairo 12311, Egypt b a r t i c l e i n f o Article history: Received 27 October 2016 Received in revised form 13 January 2017 Accepted 14 January 2017 Available online xxxx Keywords: Nanocomposites Graphene oxide FT-IR X-ray AC conductivity a b s t r a c t Novel nanocomposites based on PVDF/PVC blend containing graphene oxide nanoparticles (GO) were prepare using sonicator IR analysis revealed that the addition of GO prompts a crystal transformation of a-phase of PVDF The change of the structural before and after adding GO to PVDF/PVC were studied by X-ray diffraction A decrease in activation energy gap from UV data was observed with increasing GO content, implying a variation of reactivity as a result of reaction extent The variation of e0 with frequency is nearly the same as that of e00 At higher frequencies, the decrease of both e0 and e00 becomes nearly constant The dispersion at lower frequencies e0 of e0 polarization is of Maxwell–Wagner interfacial polarization but at higher frequencies, it levels off The behavior of conductivity (rAC ) tends to acquire constant values approaching it DC values The values of rAC was increased after doped GO with exponential increase after the critical value of frequency All nanocomposites behaved the same fashion revealing that a higher number of polarons were getting added to conducting pool in composites as graphene content was increased Conduction mechanism appeared to be getting expedited with increasing frequency due to fact that increase in frequency enhances polaron hopping frequency 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/) 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 Introduction 48 Polymer blend give effective trends to make new properties in polymeric materials The polymer blend is conceivable to create a scope of materials with properties that are better than individual segment polymers [1] Fundamental preferences of the blend are easy to preparation and simplicity of controlling for physical properties Furthermore, it normally requires little or no additional compared to new polymer synthesis [2] In any case, the miscibility between the constituents of polymer blend on the molecular scale is responsible for material with prevalent and superior properties [3] Polyvinylidene fluoride (PVDF) is a semi-crystalline polymer that has been broadly researching for its piezoelectric properties because its polar b phase [4] PVDF has well physical and electrical properties of a kind for many applications [5] PVDF have various favorable of advantages, including excellent dielectric properties, 49 50 51 52 53 54 55 56 57 58 59 60 61 62 ⇑ Corresponding author at: Department of Polymers and Pigments, National high mechanical strength/flexibility, thermal and chemical stability [6] Generally, some reports demonstrate the crystalline structures of PVDF and show a minimum five possible kinds of the crystal phase, namely, a, b, c, e and d phases [7] Other than the most well-known, b-phase is a more attractive crystal type in PVDF, which is described by all-trans planar zigzag conformation with all the fluorine atoms situated on the similar side of the polymer chains [8] This arrangement of molecular chains in b-phase gives PVDF a much higher with other PVDF phases due to the net dipole moment [9] Polyvinyl chloride (PVC) is one of the most important and generally utilized thermoplastic polymers due to its notable performance and properties with low cost, great processability, synthetic resistance and low combustibility PVC assumes part in industry of plastic, furthermore, it may be combined with fillers For example thermal stabilizer and plasticizer, before preparing utilizing the ideals of toughness, acid, alkali resistance and grating resistance [10] It is processed by itself, so it requires consolidation of various added substances, since its little thermal stability Due to the unique structure and remarkable mechanical, optical, thermal Research Centre, Cairo 12311, Egypt E-mail addresses: n.helsayed@yahoo.com, nhussein@ut.edu.sa (N.H Elsayed) 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/) Please cite this article in press as: Elashmawi IS et al Preparation and characterization of polymer nanocomposites based on PVDF/PVC doped with graphene nanoparticles Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.01.022 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 RINP 542 No of Pages 5, Model 5G 18 January 2017 I.S Elashmawi et al / Results in Physics xxx (2017) xxx–xxx 108 and electrical properties, graphene has been studied to produce high-performance polymer composites The dispersion of graphene within different polymer matrices has made the new class of polymer nanocomposites [11] The development of nanocomposite materials speaks to a productive route to enhance the exhibitions of polymer and extend their application scopes Advantages of graphene oxide (GO) are easy dispersibility in water and other organic solvents due to the presence of oxygen and hydroxyl functionalities [12] This remains a very important property when mixing with polymer matrices to improve their spectroscopic, electrical and mechanical properties GO is promising materials and it’s used in basic studies for potential applications such as sensors, batteries, super capacitors, hydrogen storage and reinforcing agents [13] Pure GO has 2D-dimension form and it is consists of sp2 bonds of carbon atom [14] GO can be obtained by the exfoliation of graphite yielding well separated two-dimensional [15] It offers extraordinary electronic, thermal and mechanical properties Many reports have been made not only on graphene’s very high electrical conductivity at room temperature but also its potential use as nano-sensors, transparent electrodes and many other applications [16] The object of this article is to develop new polymeric nanocomposites (PVDF/PVC) embedded with graphene oxide (GO) nanoparticles to be used in different applications X-ray diffraction, IR, UV–Vis and AC conductivity has been carried out to study the prepared nanocomposites 109 Experimental 110 Materials 111 The basic materials are polyvinylidene fluoride (PVDF) (–CH2CF2–)n and polyvinyl chloride (PVC) (C2H3Cl)n supplied by SigmaAldrich Graphene oxide (GO) nanoplatelets are one of a kind nanoparticles comprising of short stacks of graphene sheets having a platelet shape Graphene oxide particles have a normal thickness of roughly 6–8 nm and a typical surface area around 130 m2/g was also supplied by Sigma-Aldrich 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 112 113 114 115 116 117 118 Preparation 119 131 PVDF and PVC were dried before used at 50 °C for h to remove any moisture A weight ratio of 3:1 between PVDF and PVC were dissolved in tetrahydrofuran (THF) with stirring for approximately h at 60 °C until the homogenous solution was formed Graphene oxide (GO) nanopowder was dissolved in THF using sonication technique The obtained GO solution was added to the blend solution dropwise to different final GO concentrations of 0.005 and 0.010 wt% with continuous stirring under ultrasonic The final solution was cast in Petri dishes and left in an oven at 60 °C for approximately 72 h to dry and remove the solvent The thickness of the samples for IR and UV/Vis measurements is nearly 20 lm and %150 lm for other measurements The films were then peeled from the dishes and stored in a desiccator until use 132 Measurements 133 An FT-IR spectrophotometer (Nicolet iS10, USA) was used to obtain the IR spectra IR spectra were collected in the wavenumber range from 4000 to 400 cmÀ1 The XRD measurements were carried out on an PANalytical X’Pert PRO XRD system using Cu Ka radiation (where k = 0.1540 nm, the tube was operated at 30 kV and the Bragg angle 2h = 5–80° The UV–Vis absorption spectra were collected in the 190–800 nm wavelength region using a spectrophotometer (V-570 UV/VIS/NIR, JASCO, Japan) The AC measure- 120 121 122 123 124 125 126 127 128 129 130 134 135 136 137 138 139 140 ments were carried out using an LCR meter of the Hioki3531Z HiTester, using the two-probe method, Japan, operating at a frequency range from 42 Hz to MHz, with impedance accuracy ranging from 0.15% up to 4% In the electrical measurements, the films were cut into pieces of cm diameter The films were coated by silver paste on both sides and tested for ohmic contact The LCR meter was connected to the computer through an Rs–232c interface and the dielectric measurements were performed at room temperature as well as the conductivity 141 Results and discussion 150 Fourier Transform Infrared spectroscopy (FT-IR) 151 For comparison purposes, The FT-IR spectra of pure PVDF/PVC doped 0.005 and 0.010 wt.% of graphene oxide in wavenumber range 4000–400 nm are included in Fig The assignments of IR spectrum of PVDF have been reported as follows: a-phase bands due to CF2 bending are observed at 482 cmÀ1, 531 cmÀ1 and 615 cmÀ1 The main bands due to CH2 wagging broad mode are observed at 1062 cmÀ1, whereas the b-phase peak due to CF2 symmetric stretching is observed at 870 cmÀ1 [17] The absorption peaks appearing at 3035 cmÀ1 is assigned to CF stretching mode of PVDF [18] The assignments of IR spectrum of PVC shows the following main bands [19]: absorption band at 2977 cmÀ1 due to CH stretching, a band at 2919 cmÀ1 assigned to the CH2 asymmetric stretching mode, a sharp band at 1434 cmÀ1 attributed to the CH2 inphase vibration, a band at 964 cmÀ1 assigned to chain stretching The band at 837 cmÀ1 ascribed to the C–Cl stretching mode which gives a conclusion about the interaction between the two polymeric matrices and hence the complexation For PVDF/PVC blend doped with 0.005 and 0.01 wt.% of graphene oxide nanoparticles, the intensities of the a-phase PVDF bands decreased with increasing of GO content This result confirms that the doping of graphene oxide prompts a crystal transformation for the a-phase The changes of the intensity in IR absorption bands can be utilized as a measure of the quality of interactions between segments in prepared nanocomposites 152 X-ray analysis 177 The X-ray diffraction was utilized to study the nature of crystallinity with respect to study the complexation between PVDF/ PVC and GO The X-ray diffraction of PVDF/PVC/GO nanocompos- 178 0.010 Intenisity (a u.) 0.005 PVDF/PVC 4000 3500 3000 2500 2000 1500 1000 500 -1 Wavenumber (Cm ) Fig 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 graphene nanoparticles Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.01.022 142 143 144 145 146 147 148 149 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 179 180 RINP 542 No of Pages 5, Model 5G 18 January 2017 I.S Elashmawi et al / Results in Physics xxx (2017) xxx–xxx 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 ites is represented as shown in Fig The XRD diffraction of pure PVDF/PVC blend indicate the semicrystalline nature as the main hump (hallow peak) centered at 2h = 18.38° and a sharp peak at 2h = 39.07° In the doped samples by graphene oxide nanoparticles, No impurity-related ripples or small peaks were observed in all spectra, demonstrating the purity and good dispersion of graphene in PVDF/PVC polymeric matrices The shifts of the peak position were observed from 2h = 18.38° to 2h = 20.04° indicating that the crystal structure of GO was altered by its incorporation into PVDF/PVC The decrease in the broadness of the apparent peak at 18.38o of the doped samples has been observed when compared with the pure blend This can be interpreted as far as the Hodge et al [20], which has established a correlation between the intensity of the peak and the degree of crystallinity So, the increase in the broadness of this peak reveals the increase of these amorphous regions in the samples From all previously mentioned results, the interaction between the PVDF/PVC blend and GO results in decreasing crystallinity with rich amorphous phase The amorphous nature is responsible for higher conductivity and affirms the complexation between GO and the PVDF/PVC blend From all previously mentioned results, the interaction between the PVDF/ PVC blend and GO results in decreasing crystallinity with rich amorphous phase The amorphous nature is responsible for higher conductivity and confirms the complexation between GO and the PVDF/PVC blend UV–Vis analysis 207 The UV–Vis spectra of the prepared nanocomposites in the wavelength range 190–800 nm are shown in Fig These spectra are used to describe the shape of the optical absorption edge The absorption edges attributed to the semicrystalline behavior of the nanocomposites were observed at 277 nm for all of the samples The intensity of the absorption edge decreased with increasing GO content, indicating that reactions between all components occurred because of the addition of GO The absorption bands observed in the 233–238 nm range were assigned to the p ? p⁄ transition originating from unsaturated bonds (C@O and C@C) Other small bands at 284 and 297 nm were observed A new band was seen at 309 nm after adding GO 208 209 210 211 212 213 214 215 216 217 218 Intensity (a u.) 206 20 30 40 50 60 0.010 2.8 0.005 2.6 2.4 PVDF/PVC 2.2 2.0 200 300 400 500 600 Wavelength (nm) Fig UV–Vis spectra of PVDF/PVC/Graphene nanocomposites Determination of the optical energy band gap Polymers doped fillers are categories into direct and indirect band gap For direct band gap, the highest of the valence band and the bottom of conduction band lie at zero crystal momentum If the bottom of the conduction band does not relate to zero crystal momentum, then it is called indirect While, in indirect band gap materials, the transition from valence to conduction band should be associated with phonon of the right magnitude of crystal momentum Near the fundamental band edge, both direct and indirect transitions occur and can be obtained by plot the relations between a1/2, a2 and energy (E = hm) [21] The absorption coefficient (a) from the original UV–Vis spectra was calculated using the equation: A a ẳ 2:303 d 1ị where A is the absorbance and d is the thickness of the sample The relation between absorption coefficient and the photon energy (hm) can be obtained by the Thutpalli and Tomlin method [22]: s hm ẳ ahmị ỵ Eg 2ị 219 220 221 222 223 224 225 226 227 228 229 230 231 232 234 235 236 237 238 239 241 where Eg is energy band gap, h is Planck’s constant and s is order describe the model used (direct or indirect transition) The s constant has different values for different types of transitions: s = for direct transmission and s = ½ for indirect transmission The values of energy band gap (Eg) in indirect transitions are obtained by plotting the relation between (ahm)1/2 and the energy (hm), as shown in Fig Extrapolation of linear regions in the figure onto x-axis provided calculated values of indirect band gap energy (Eg) dependence on GO content 242 0.010 AC conductivity 251 Dielectric properties The values of the real part of the dielectric constant (e0 ) at 30 °C at different frequencies for all the PVC/PVDF doped graphene oxide nanocomposites were calculated from the relation [23]: 252 0.005 blend 10 3.0 Intenistity % 181 70 80 theta (degree) Fig The X-ray diffraction scan of PVDF/PVC/Graphene nanocomposites e Cp d ¼ eo Á A ð3Þ where Cp is the measured capacitance, d is the thickness and A is the cross-section area of the sample Fig shows the variation of dielectric constant e0 with frequency for all the nanocomposites From this figure, we can note that the dielectric constant e0 of all measured samples is found to decrease rapidly with frequency Please cite this article in press as: Elashmawi IS et al Preparation and characterization of polymer nanocomposites based on PVDF/PVC doped with graphene nanoparticles Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.01.022 243 244 245 246 247 248 249 250 253 254 255 256 258 259 260 261 262 263 RINP 542 No of Pages 5, Model 5G 18 January 2017 I.S Elashmawi et al / Results in Physics xxx (2017) xxx–xxx Fig The relation between (ahm)1/2 and the energy (hm) for PVDF/PVC/Graphene nanocomposites Fig The variation of dielectric constant ðe0 Þ with Log frequency for PVDF/PVC/ Graphene nanocomposites at room temperature 264 265 266 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 The values of the imaginary part of the dielectric loss (e00 Þ were calculated from the relation: 00 e ẳ e tan d 4ị where, tan d is the loss angle or dissipation factor The dielectric loss factor e00 variation with frequency for all the samples is plotted in Fig The behavior of variation of e00 with frequency is nearly the same as that of e0 with frequency The behavior of dielectric loss e00 decreases with increase in frequency At the higher frequencies (>105 Hz), the decrease of e00 becomes nearly constant The small dispersion was observed at lower frequencies of the behavior of e0 but at higher frequencies, it levels off The dispersion in the dielectric loss at the lower frequency may be according to the procedure of polarization due to Maxwell–Wagner interfacial polarization [24] And because the grain boundaries of lower conductivity are effective and at the higher frequency, graphene grains of moderate conductivity are prominent Graph of dielectric loss tangent (tan d) versus Log F was plotted and typical is shown in Fig From the graph, it is seen that, the values of tan d decreases with increase in frequency for these nanocomposites attribute to that the hopping frequency of charge carriers maybe follow the changes of externally applied electric field beyond a certain frequency limit All samples have the higher Fig The variation of dielectric loss factor ðe00 Þ with Log frequency for PVDF/PVC/ Graphene nanocomposites at room temperature Fig The variation of dielectric loss tangent (tan d) versus Log frequency for PVDF/ PVC/Graphene nanocomposites at room temperature value of e0 in the low range of frequencies may be due to smaller resistivity 288 Electrical conductivity The AC electrical conductivity of the samples was estimated from the following relation [25]: 290 rAC ¼ xeo e00 ¼ xeo e0 tan d ð5Þ where eo is the permittivity of free space (eo ¼ 8:85 Â 10À12 FmÀ1 ), x = 2pf is the angular frequency and tan d is the dielectric loss factor [26] The variation of AC electrical conductivity (rAC ) variation with different frequencies of all the samples at 30 °C is shown in Fig For all the nanocomposites, it can be seen that at the lower frequencies, conductivity (rAC ) tends to acquire constant values (i.e an increase in frequency is not appreciable at low frequencies) approaching it DC values, and the values of the electrical conductivity was increased from 5.6 Â 102 mÀ1 to 1.2 Â 104 XÀ1 mÀ1 after doped graphene, while after a critical value of frequency, varies exponentially increase with increasing frequency The type of this behavior is common in disordered solids, appears to be in accordance with the AC universal law and is considered as a strong indication for charge migration via the hopping mechanism All the present nanocomposites behaved in the same fashion This result Please cite this article in press as: Elashmawi IS et al Preparation and characterization of polymer nanocomposites based on PVDF/PVC doped with graphene nanoparticles Results Phys (2017), http://dx.doi.org/10.1016/j.rinp.2017.01.022 289 291 292 293 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 RINP 542 No of Pages 5, Model 5G 18 January 2017 I.S Elashmawi et al / Results in Physics xxx (2017) xxx–xxx Fig The variation of AC conductivity (rAC ) with Log frequency for PVDF/PVC/ Graphene nanocomposites at room temperature 319 reveals that a higher number of polarons (electrons) are getting added to the conducting pool in the composites as graphene content is increased Also, conduction mechanism in these composites appeared to be getting expedited with increasing frequency This could be due to the fact that increase in frequency enhances polaron hopping frequency The behavior of variation of e00 with frequency is nearly the same as that of e0 with frequency The dielectric loss e00 decreases with increase in frequency At higher frequencies (>105 Hz), the decrease of e00 becomes nearly constant 320 Conclusion 321 340 Nanocomposites films consists of polyvinylidene fluoride (PVDF)/polyvinyl chloride (PVC) blend doped 0.005 and 0.010 wt % of graphene oxide nanoparticles (GO) The films were prepared and studied by different techniques IR analysis revealed that the addition of GO prompts a crystal transformation from the aphase of PVDF The change of the structural before and after adding GO to PVDF/PVC blend were studied by X-ray technique The behavior of variation of e00 with frequency is nearly the same as that of e0 with frequency The decrease of e00 becomes nearly constant at the higher frequency The dispersion at lower frequencies of e0 proposes that procedure of polarization is related to Maxwell– Wagner interfacial polarization while at higher frequencies it levels off The values of tan d decreases with increase in frequency due to hopping frequency of charge carriers follow the changes of applied electric field beyond a certain frequency limit The conductivity (rAC ) tends to acquire constant values approaching it rDC values The values of rAC were increased after doped graphene All nanocomposites behaved in the same fashion which reveals that a higher number of polarons (electrons) are getting 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