Dielectric properties of polyvinylidene fluoride based thin films and electrospun mats have been studied. Frequency dependences of samples capacity and tangent of dielectric losses have been obtained. The influence of trifluoroethylene presence in copolymer on dielectric properties has been investigated. Efficiency of using deposited contacts instead of pressed contacts was considered. © Published under licence by IOP Publishing Ltd

Glasmacher, B.

Gryshkov, O.

Kapralova, V.

Sudar, N.

Tretiakov, A.

English

Institutionelles Repositorium der Leibniz Universität Hannover

Journal of Physics: Conference SeriesPAPER • OPEN ACCESSDielectric properties of PVDF based thin films andelectrospun matsTo cite this article: A Tretiakov et al 2019 J. Phys.: Conf. Ser. 1236 012009 View the article online for updates and enhancements.Recent citationsChange of sign in the Casimir interactionof peptide films deposited on a dielectricsubstrateE. N. Velichko et al-This content was downloaded from IP address 194.95.157.34 on 05/11/2020 at 07:06Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing LtdETACP 2019IOP Conf. Series: Journal of Physics: Conf. Series 1236 (2019) 012009IOP Publishingdoi:10.1088/1742-6596/1236/1/0120091      Dielectric properties of PVDF based thin films and electrospun mats  A Tretiakov1, V Kapralova1, N Sudar1, O Gryshkov2 and B Glasmacher2 1 Peter the Great St. Petersburg Polytechnic University, Russia 2 Institute for Multiphase Processes, Leibniz Universität Hannover, Germany E-mail: kapralova2006@yandex.ru Abstract. Dielectric properties of polyvinylidene fluoride based thin films and electrospun mats have been studied. Frequency dependences of samples capacity and tangent of dielectric losses have been obtained. The influence of trifluoroethylene presence in copolymer on dielectric properties has been investigated. Efficiency of using deposited contacts instead of pressed contacts was considered. 1.  Introduction Polyvinylidene fluoride (PVDF) and its co-polymer with trifluoroethylene (PVDF-TrFE) have wide spectrum of applications in biomaterials. Proven piezoelectric property and biocompatibility make these polymers one of the most promising biomaterials [1] in tissue engineering and regenerative medicine. Exemplarily, they can be used to support peripheral nerve system regeneration process, especially in case of deep wounds with nerve fibre avulsions, so relevance of the study is due to the need to develop new nerve tissue implants with improved characteristics based on combined materials. Dielectric spectroscopy is a powerful instrument of a research into molecular dynamics and relaxation processes in complex materials [2], so the main aim of this work was to characterize and compare dielectric properties of PVDF-TrFE fiber mats, PVDF and PVDF-TrFE films. 2.  Materials and methods Electrospinning is a common method for production of polymer fibers. PVDF-TrFE fiber scaffolds have been produced by using electrospinning method [3]. Polymer solutions were based on N,  N-dimethylformamide (DMF) and acetone as mixed solvents. SEM photographs of the fibrous samples structure are presented in figure 1. Before measurements, a sample of a 15 % PVDF-TrFE fiber mat with deposited graphite contacts was prepared. For the deposition of contacts onto the surface of the fibrous structure, a special mixture from graphite powder with ammonia was prepared. Also, a sample of the fiber mat of 15 %  PVDF-TrFE without deposited contacts had been prepared which was measured using pressed contacts. Surfaces of the films were studied using a microinterferometer. It turned out that the films consist of the micron-sized bubbles. This circumstance was the reason why the films have matte appearance. Further calculation of the dielectric constant showed that it is close to one. ETACP 2019IOP Conf. Series: Journal of Physics: Conf. Series 1236 (2019) 012009IOP Publishingdoi:10.1088/1742-6596/1236/1/0120092        Figure 1. SEM images of elecrtrospun PVDF-TrFE fiber mat.  Casting method was used for PVDF-TrFE and PVDF films production. Dissolving PVDF in DMF/acetone took more than 10 days at 23 °C and 1.5–3 hours at 90–100 °C. The characteristics of films are given in table 1.  Table 1. Characteristics of PVDF and PVDF-TrFE samples. Composition Type of sample Production method Appearance Thickness (µm) PVDF Film Casting Matte, opaque 11 ± 2 by optometer PVDF-TrFE Film Casting Matte, opaque 10 ± 1 by optometer PVDF-TrFE with deposited contacts Fiber mat Electrospinning White porous fiber 150 ± 10 PVDF-TrFE with pressed contacts Fiber mat Electrospinning White porous fiber 140 ± 10 3.  Results and discussion A measuring cell was also designed to study the dielectric properties of the polymer films and fiber structures. At the first stage, the dependence of the sample capacity (Cp, pF) on the uniaxial pressure was measured. Loads of different masses m1 <m2 <m3 were placed on a special piston in the chamber to prevent surge voltage due to piezoelectric effect. The results of the experiment are presented in table 2. All experiments were carried out at a constant frequency of 1 kHz.  Table 2. Dependence of sample capacity on the value of uniaxial pressure for samples. Load mass Capacitance, pF PVDF film PVDF-TrFE fiber with deposited contacts PVDF-TrFE film PVDF-TrFE fiber with pressed contacts 0 166 11 63 33 m1 190 20 62 37 m2 238 20 59 41 m1 + m2 — 21 — — m3 — — 63 —  ETACP 2019IOP Conf. Series: Journal of Physics: Conf. Series 1236 (2019) 012009IOP Publishingdoi:10.1088/1742-6596/1236/1/0120093      The results given in table 2 were used to establish the measuring procedure for the fibrous and porous samples of piezoelectric polymers. In the next step, the frequency dependence of the capacitance and tangent of the dielectric loss angle (tg() for the samples at a constant uniaxial pressure (m2) was measured. After each measurement cycle, a reference measurement was performed at a frequency of 1 kHz. The measurement results are presented in figures 2–3.  Figure 2. A plot of capacitance (Cp) vs frequency.   Figure 3. A plot of tangent of the dielectric loss angle (tg( vs frequency. ETACP 2019IOP Conf. Series: Journal of Physics: Conf. Series 1236 (2019) 012009IOP Publishingdoi:10.1088/1742-6596/1236/1/0120094      Figure 2 evidences that the capacity of the PVDF sample significantly exceeds the values of the capacity for the PVDF-TrFE samples. Hence, the addition of TrFE substantially reduces the value of the dielectric constant. It can be noted that value of fibrous samples capacitance is less then value for films. The reason for this decrease in the capacitance value is the presence of air pores in the fiber samples [4, 5]. Besides, capacity does not depend on frequency for all samples. The type of contacts did not demonstrate a significant impact on the value of the capacitance. Figure 3 shows the increase of dielectric losses with frequency for all samples. In TrFE-containing samples, there is a sharp increase in dielectric losses at low frequencies, while PVDF film sample has low losses at low frequencies. This fact allows us to suppose that in TrFE-containing materials, conduction occurs at low frequencies. In addition, the use of deposited contacts improves conductivity, while the character of dependence does not change. 4.  Conclusion In conclusion, we can emphasize the following:  the presence of TrFE in copolymer significantly reduces the value of the samples capacitance;  the capacitance of fibrous samples is much lower than that of films due to the presence of air pores;  TrFE-containing samples demonstrate high dielectric losses at low frequencies.  So, the combination of special dielectric and morphological properties of fibrous materials based on PVDF copolymers makes them highly prospective for tissue engineering, e.g. biocompatible artificial nerve conduits.   References [1] Al Halabi F,  Gryshkov O, Kuhn A, Kapralova V and Glasmacher B 2018 The International journal of artificial organs 41(11) 811-822 [2] Koroleva E, Kumzerov Y, Sysoeva A, Vakhrushev S, Burdin D and Filimonov A 2017 Physics of the Solid State 59(10) 2036-2044 [3] Gulyaev A,  Rykonov V,  Tenchurin T and  Filatov Yu 2018 International Polymer Science and Technology 38 41-46 [4] Belova V, Borodzyulya V, Ivanova T, Kapralova V and Sudar N 2015 Technical Physics 60(4) 588-591 [5] Sapurina I, Sudar’ N and Kapralova V 2018 Semiconductors 52(6) 816–819 

Dielectric properties of PVDF based thin films and electrospun mats

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Dielectric properties of PVDF based thin films and electrospun mats

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