TY - JOUR
AU - Buranurak,, S
AB - Abstract The main focus of this study is to investigate the effect of gamma irradiation on the electrical properties of PVDF/BT nanocomposites. A 1.25 MeV gamma-ray was delivered to the composite films with different BaTiO3-volume fraction, ƒBT = 0–0.4, and with different absorbed doses ranged 50–2500 Gy. Dielectric properties of PVDF/BaTiO3 composites under frequencies ranged from 100 Hz to 10 MHz at room temperature were investigated using an impedance analyser. An increase of 28% in the dielectric constant and a decrease of 15% in the loss tangent were observed in the PVDF/BT 40 vol% nanocomposite film under the accumulated dose of 1500 Gy. Scanning electron microscopy provided no significant difference in microscopic structures between non-exposed and gamma-exposed materials. Fourier-transform infra-red spectroscopy provides gamma-induced transition of PVDF-crystalline forms as alpha-PVDF into beta-PVDF/gamma-PVDF which has been reported as one of the main factors affected the change of dielectric constant in polymers. UV–visible spectrophotometry has been observed gamma-induced red shift in the absorption edge of the PVDF/BT 40 vol% nanocomposite film from 400 nm to 420 nm under the accumulated dose of 1500 Gy. However, a blue shift is observed with increase the accumulated dose up to 2000 Gy. INTRODUCTION Dielectric polymer nanocomposites have gained considerable interest as a novel material in response to demands of high-performance miniaturised electronic devices for current and future advanced technologies due to a combination of ideally attractive features between good mechanical performances of the host polymers and excellent dielectric properties of the nanodispersed ferroelectric fillers(1, 2). These outstanding properties give benefits to be used in various applications; for example, using as a high-energy-density capacitor with flexible and embedded forms for modern industrial electronics, energy storage, aeronautics, telecommunications, automobiles, medical equipment and sensing devices(3–6). However, in reality, the dielectric properties of these composite materials are still unsatisfied(7, 8). Many strategies have been introduced to achieve the dielectric constant (ε′) improvement without the dielectric loss (tan δ) excessiveness(8). Among various types of polymer composites, a combination of poly (vinylidene fluoride) (PVDF) with barium titanate (BaTiO3 or BT) nanoparticles has been extensively studied due to its outstanding characteristics of PVDF polymer matrix which exhibits a high ε′ value and electro-active response and BaTiO3 filler which offers the attractive ε′ value and piezoelectric properties(2, 7–10). Basically, grain-size and content of BaTiO3 filler as well as interfacial bonding between the filler and PVDF host-polymer are experimentally remarked as three main factors influence on the ε′ value of PVDF/BT nanocomposites(7). The study by Silakaew et al.(9) confirms that preparation routes on the distribution of BaTiO3 filler in the PVDF matrix significantly affect to the different dielectric behaviours of PVDF/BT nanocomposites. The polymer nanocomposite prepared by solution processing (SP) method offers the strong dipole polarisation inside the large clusters of BaTiO3 nanoparticles and exhibits the interfacial polarisation at the large space-charge area of PVDF–BT interfaces. These factors are contributed to the enhancement of the ε′ in PVDF/BT nanocomposites. In addition to the study by Upadhyay et al.(2), fabrication of beta-crystalline phase PVDF matrix composited with BaTiO3 filler is demonstrated to achieve high ε′ and low tan δ values. Beta-PVDF presents outstanding pyroelectric, piezoelectric and dielectric properties which are utilised for diverse microelectronic applications. Radiation-induced modification of structural and chemical compositions in polymers have been studied for several decades(11, 12). Breaking down of polymer chains together with creating of free radicals occur when gamma-ray penetrate through the polymer matrix(11). Conformation changes caused by main chain scission, intermolecular crosslinking, creation of unsaturated bonds, formation of volatile fragments and creation of carbonaceous clusters induce transformation of alpha-phase into a mixture beta and gamma-phase(12). Theoretically, the electro-active phases of beta and gamma are attributed to the increment in the dielectric constant of PVDF(2). Therefore, enhancement of dielectric performance in PVDF by gamma-induced phase transition is expected. The main focus of this study is to demonstrate the effect of gamma-induced changes in structural and electrical properties of PVDF/BT nanocomposite films with different BaTiO3-volume fraction, ƒBT = 0–0.4, and different absorbed doses ranged 50–2500 Gy. EXPERIMENTAL PROCEDURE Preparation of PVDF/BaTiO3 nanocomposites using solution processing (SP) method In this study, SP method was used for fabrication of PVDF/BaTiO3 nanocomposites. PVDF (Sigma-Aldrich Co., USA) was dissolved in N,N-dimethylformamide (DMF) together with electromagnetic stirring for 30 min; or until a clear solution was obtained. BaTiO3 particles (BT, <100 nm: Sigma-Aldrich Co., USA) were used as a filler material in the polymer matrix with the BT volume fractions of 0–0.4. The PVDF/BT mixture solution was stirred under an ultrasonic action for 1 h in order to drive the dispersion of BT nanoparticles. After that it was heated to 100°C for 4–6 h. for complete evaporation of DMF solvent. For the final procedure, PVDF/BT nanocomposite sheets were cut as a disc-shape with ~2 mm in diameter and were moulded by hot-pressing at 200°C under the pressure of 10 MPa for 30 min in order to obtain a disc-shape nanocomposite film with ~1 mm in thickness. Characterisation of PVDF/BaTiO3 nanocomposite film under gamma irradiation A collimated gamma-ray beam ranged from 0 to 2500 Gy was delivered to expose each PVDF/BT film. An impedance analyser (Agilent 4294 A, Agilent Technologies Inc., USA) was used to demonstrate the dielectric constant and loss factor of the films. Scanning electron microscope (MiniSEM) (SNE-4500 M, SEC Co., Ltd., Korea) was used for characterising and revealing cross-sectional features of nanocomposite films. All samples were analysed with UV–visible spectrometer in the wavelength ranged 200–500 nm to observe the variation of energy gap with the increase of gamma irradiation dose. Finally, molecular components and structures were demonstrated using Fourier-transform infra-red spectroscopic technique (FTIR) (TENSOR-27, Bruker Technology Co., Ltd., USA). RESULTS AND DISCUSSION Physical characteristics of PVDF/BT nanocomposites under gamma irradiation Figure 1 shows the surface morphologies of (a) neat PVDF films, (b) BaTiO3 bulks and (c) fabricated PVDF/BT (0.4 vol% BaTiO3) nanocomposite films. Clearly seen in Figure 1(a) that a slight increase of BaTiO3 particle sizes from 0.88 ± 0.18 μm to 1.19 ± 0.38 μm is observed at the accumulated gamma dose of 1500 Gy, while Figure 1(b) shows no significant effect on the film thickness between irradiated and non-irradiated PVDF films. In case of PVDF/BT nanocomposite films as seen in Figure 1(c), the cross-section images provide large clusters of BT nanoparticles appeared in dried polymer nanocomposite films for both irradiated and non-irradiated nanocomposite films. Orientation of BT particles as spherical clusters is originated by the strong agglomeration of BT nanoparticles in order to reduce their surface energies(7). Figure 1. Open in new tabDownload slide SEM images of (a) BaTiO3, (b) neat PVDF and (c) PVDF/BT nanocomposites in comparison with (1) non-irradiation and (2) gamma-irradiation at 1500 Gy. Figure 1. Open in new tabDownload slide SEM images of (a) BaTiO3, (b) neat PVDF and (c) PVDF/BT nanocomposites in comparison with (1) non-irradiation and (2) gamma-irradiation at 1500 Gy. Dielectric properties of PVDF/BT nanocomposites Figure 2 provides the respective plots of (a) dielectric constant (ε′) and (b) loss tangent (tan δ) at 1 kHz under room temperature for PVDF and 0–40 vol% BaTiO3 of PVDF/BT nanocomposite films with the increase of gamma-irradiation dose ranged between 0 and 2500 Gy. An increase of 28% in the ε′ and a decrease of 15% in the tan δ are observed in PVDF/BT 40 vol% under the accumulated dose of 1500 Gy, whereas the decrease of 50% in the ε′ and the increase of 13% in the tanδ are observed at the accumulated dose increased up to 2500 Gy. This is related to the assumption that gamma irradiation induces changes in structural and chemical compositions of the polymer matrix. Transition of crystalline forms as alpha-phase to mixture of beta and gamma-phases is obtained with the increase of radiation dose. Realignment of molecular dipoles from ground into highly ordered state of chain cross-linked molecules in crystalline region of PVDF eventually results changing in electrical properties of the polymer nanocomposites(9, 12). Figure 2. Open in new tabDownload slide Dose dependence of (a) dielectric constant; ε′ and (b) dielectric loss; tan δ in neat PVDF and PVDF/BT nanocomposites with 5–40 vol% BT. Figure 2. Open in new tabDownload slide Dose dependence of (a) dielectric constant; ε′ and (b) dielectric loss; tan δ in neat PVDF and PVDF/BT nanocomposites with 5–40 vol% BT. FTIR spectroscopy of neat PVDF films Theoretically, PVDF is a semi-crystalline partially fluorinated fluoropolymers whose radiation can be induced transformation from alpha-phase to beta and gamma-phases due to newly created crystallites upon irradiation(12). This is confirmed by the FTIR spectra of the neat PVDF film as shown in Figure 3, transmittance peaks at 812, 840 and 1074 cm−1 have observed on the spectra of irradiated PVDF films under the gamma dose of 1500, 1750 and 2000 Gy. These peaks represent a mixture of beta- and gamma-phases obtained by alpha-phase transition of PVDF. The dependence of crystalline phase on dielectric properties of PVDF has been previously reported(9), alpha-phase exhibits a higher permittivity than beta and gamma-phases, whereas a larger dielectric loss has been observed in the alpha-phase than beta and gamma-phases(9). Additionally, in case of PVDF/BaTiO3 nanocomposites, Ti ions may arrest the vibration of F ions resulting in the suppression of alpha-phase and enhancement of beta-phase of PVDF(11). However, the study by Silakaew et al.(7) reports a high ε′ value of PVDF/BT 40 vol% nanocomposite prepared by SP method. This is consistent to our study. The reason is due to the high-intensity interfacial polarisation induced at the large interface area of PVDF thin layers which are sandwiched by large clusters of BaTiO3 nanoparticles. Figure 3. Open in new tabDownload slide FTIR spectra of neat PVDF films under gamma-irradiation doses of 0, 1500, 1750 and 2000 Gy. Figure 3. Open in new tabDownload slide FTIR spectra of neat PVDF films under gamma-irradiation doses of 0, 1500, 1750 and 2000 Gy. UV–visible spectrophotometry of PVDF/BT nanocomposites Figure 4(a) shows the UV–Vis spectra of PVDF/BT nanocomposite films. A red shift in the absorption edge occurs from 400 nm of non-irradiated PVDF/BT sample to 420 nm of irradiated sample at 1500 Gy. The possible explanation is due to the breaking of chain and creation of new defects(12). In addition, the optical band gap of the irradiated sample decreases as compared to the non-irradiated sample; from 3.125 eV to 3.0625 eV, as shown in Figure 4(b). This is due to the molecular interaction between BaTiO3 particles and PVDF matrix caused by radiation-induced changes from alpha to the mixture of beta and gamma phase transition. Figure 4. Open in new tabDownload slide (a) UV–Vis spectra and (b) Tauc’s plots of (αhν)½ versus hν of PVDF/BT 40 vol% nanocomposite films in comparison with non-irradiation and gamma-irradiation doses of 800, 1500, 1750 and 2000 Gy. Figure 4. Open in new tabDownload slide (a) UV–Vis spectra and (b) Tauc’s plots of (αhν)½ versus hν of PVDF/BT 40 vol% nanocomposite films in comparison with non-irradiation and gamma-irradiation doses of 800, 1500, 1750 and 2000 Gy. CONCLUSION The study has observed the insignificant changes in the dielectric constant and the loss tangent of PVDF/BT 0–40 vol% nanocomposite films within the dose range of 50–2500 Gy. An increase of 28% in the ε′ and a decrease of 15% in the tan δ are found in the PVDF/BT 40 vol% film under the accumulated dose of 1500 Gy. However, a 50% decrease in the ε′ and 13% increase in the tan δ obtained with the accumulated dose increases to 2500 Gy. SEM images show no significant differences in microscopic structures between non-irradiation and 1500 Gy gamma-irradiation of the neat PVDF films and the PVDF/BT 40 vol% nanocomposite. While a slight increase of BaTiO3 particles is observed at the accumulated gamma dose of 1500 Gy. Radiation-induced the increase of BT grain-size, which leads to a slight decrease in the ε′ of the irradiated BaTiO3 sample. FTIR spectra provides gamma-induced transition of PVDF-crystalline forms as alpha-PVDF into the mixture beta-PVDF/gamma-PVDF which has been reported as a main cause of change in dielectric properties of polymers. In case of PVDF/BT nanocomposites prepared by the SP method, gamma-induced formation of the agglomerated BaTiO3 nanoparticles is observed. This may result the existence of a large cluster of dipole moments which has been reported as an important factor contributed to electrical response in the PVDF/BT nanocomposites. Gamma-induced the red shift in the absorption edge which may attribute to molecular interaction between BaTiO3 nanoparticles and the matrix of PVDF. However, a blue shift is observed with increase the accumulated dose up to 2000 Gy. ACKNOWLEDGEMENTS The authors gratefully acknowledge the financial support from the National Research Council of Thailand and express our sincere thanks to staffs of Gems Irradiation Centre, Thailand Institute of Nuclear Technology for gamma-irradiation facility supported. The authors are also thankful Prof. Shinji Tokonami and Dr Kantaphat Kranrod, and Dr Samuk Pimanpang for their kind help and support. REFERENCES 1 Xia , W. and Zhang , Z. PVDF-based dielectric polymers and their applications in electronic materials . IET Nanodielectrics 1 ( 1 ), 17 – 31 ( 2018 ). Google Scholar Crossref Search ADS WorldCat 2 Upadhyay , R. H. and Deshmmukh , R. R. Investigation of dielectric properties of newly prepared β-phase polyvinylidene fluoride-barium titanate nanocomposite films . J. Electrostat. 71 , 945 – 950 ( 2013 ). Google Scholar Crossref Search ADS WorldCat 3 Huang , T. C. , Yeh , J. M. and Lay , C. Y. 18–Polymer nanocomposite coatings. Woodhead Publishing Series in Composites Science and Engineering . Adv. Polym. Nanocompos. 1 , 605 – 638 ( 2012 ). Google Scholar Crossref Search ADS WorldCat 4 Prateek , Thakur , V. K. and Gupta , R. K. Recent process on ferroelectric polymer-based nanocomposites for high energy density capacitors: synthesis, dielectric properties, and future aspects . Chem. Rev. 116 , 4260 – 4317 ( 2016 ). Google Scholar Crossref Search ADS PubMed WorldCat 5 Min , Y. , Olmedo , R. , Hill , M. , Radhakrishman , K. , Aygun , K. , Kabiri-Badr , M. , Panat , R. , Dattaguru , S. and Balkan , H. Embedded capacitors in the next generation processor . Electron. Compon. Technol. Conf. 13 , 1225 – 1229 ( 2013 ). WorldCat 6 Heo , S. Y. , Kim , J. , Gutruf , P. , Banks , A. , Wei , P. and Pielak , R. Wireless, battery-free, flexible, miniaturized dosimeters monitor exposure to solar radiation and to light for phototherapy . Sci. Transl. Med. 10 , 1 – 12 ( 2018 ). Google Scholar Crossref Search ADS WorldCat 7 Li , Y. C. , Tjong , S. C. and Li , R. K. Y. Dielectric properties of binary polyvinylidene fluoride/barium titanate nanocomposites and their nanographite doped hybrids . eXPRESS Polym. Lett. 5 ( 6 ), 526 – 534 ( 2011 ). Google Scholar Crossref Search ADS WorldCat 8 Zheng , P. , Zhang , J. L. , Tan , Y. Q. and Wang , C. L. Grain-size effects on dielectric and piezoelectric properties of poled BaTiO3 ceramics . Acta Mater. 60 , 5022 – 5030 ( 2012 ). Google Scholar Crossref Search ADS WorldCat 9 Silakaew , K. , Saijingwong , W. , Meeporn , K. , Maensiri , S. and Thongbai , P. Effect of processing methods on dielectric properties of BaTiO3/poly (vinylidene fluoride) nanocomposites . Microelectron. Eng. 146 , 1 – 5 ( 2015 ). Google Scholar Crossref Search ADS WorldCat 10 Sharma , M. , Quamara , J. K. and Gaur , A. Behaviour of multiphase PVDF in (1−x)PVDF/(x)BaTiO3 nanocomposite films: structural, optical, dielectric and ferroelectric properties . J. Mater. Sci. Mater. Electron. 29 , 10875 – 10884 ( 2018 ). Google Scholar Crossref Search ADS WorldCat 11 Korostynska , O. , Arshak , K. , Morris , D. , Arshak , A. and Jafer , E. Radiation-induced changes in the electrical properties of carbon filled PVDF thick films . Mater. Sci. Eng., B 141 , 115 – 120 ( 2007 ). Google Scholar Crossref Search ADS WorldCat 12 Aarya , S. , Srivastava , A. K. , Saha , A. and Wahab , M. A. Effect of 1.25 MeV gamma irradiation in α-phase PVDF . Nucl. Instrum. Methods Phys. Res., Sect. B 267 , 3545 – 3548 ( 2009 ). Google Scholar Crossref Search ADS WorldCat © The Author(s) 2019. Published by Oxford University Press. All rights reserved. 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TI - DIELECTRIC PROPERTIES OF POLY (VINYLIDENE FLUORIDE)/BARIUM TITANATE NANOCOMPOSITES UNDER GAMMA IRRADIATION
JF - Radiation Protection Dosimetry
DO - 10.1093/rpd/ncz111
DA - 2019-10-01
UR - https://www.deepdyve.com/lp/oxford-university-press/dielectric-properties-of-poly-vinylidene-fluoride-barium-titanate-dSURRaqW9Y
SP - 342
VL - 184
IS - 3-4
DP - DeepDyve
ER -