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1. Toward improved PVDF-BaTiO 3 composite dielectrics: mechanical activation of the filler versus filler content

   https://doi.org/10.1088/1402-4896/acff4d  

   Djoković, Vladimir ; Dudić, Duško ; Dojčilović, Radovan ; Marinković, Filip S ; Pavlović, Vera P ; Pavlović, Vladimir B ; Vlahovic, Branislav ( October 2023 , Physica Scripta)

   Barium titanate (BT) perovskite particles were surface modified by means of mechanical treatment and used as inorganic component in polyvinylidene fluoride (PVDF) based composites. The changes in electrical properties of the composite films with increasing in filler content were followed by dielectric spectroscopy, breakdown strength andD-Emeasurements. A comparison of the properties of the composites prepared with untreated and mechanically activated particles revealed that there is a significant difference in their performances at low filler concentrations (<20 wt%). Introduction of the surface modified ceramic particles into PVDF matrix led to an increase of the dielectric constant without affecting significantly the electrical breakdown strength. In contrast, when as received BT particles were used a filler, both dielectric constants and breakdown strengths of the composite films were lower than the corresponding values observed for the pure PVDF. At higher concentrations, however, the influence of pre-treatment of the filler on the effective electrical properties becomes less significant. The obtained results were discussed in terms of the pronounced crystallization of polarβandγcrystal phases of PVDF in the presence of surface modified BT fillers, which is confirmed by Raman spectroscopy.

    

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2. Multifunctional SENSING using 3D printed CNTs/BaTiO 3 /PVDF nanocomposites

   https://doi.org/10.1177/0021998318800796  

   Kim, Hoejin ; Wilburn, Bethany_R ; Castro, Edison ; Garcia_Rosales, Carlos_A ; Chavez, Luis_A ; Tseng, Tzu-Liang_Bill ; Lin, Yirong ( September 2018 , Journal of Composite Materials)

   This research studied multifunctional sensing capabilities on nanocomposites composed of poly(vinylidene) fluoride (PVDF), BaTiO₃(BT), and multiwall carbon nanotubes (CNTs) fabricated by fused-deposition modeling 3D printing. To improve the dielectric property within BT/PVDF composites, CNTs have been utilized to promote ultrahigh polarization density and local micro-capacitor among BT and polymer matrix. The 3D printing process provides homogeneous dispersion of nanoparticles, alleviating agglomeration of nanoparticles, and reducing micro-crack/voids in matrix which can enhance their dielectric property. In this research, we demonstrated that by utilizing unique advantages of this material combination and a 3D printing technique, sensing capabilities for temperature and strain can be engineered with different content variations of included BT and CNTs. It is observed that the sensing capability for temperature change with respect to a 25–150℃ range can be improved as both BT and CNTs’ inclusions increase and is maximal with 1.7 wt.% CNTs/60 wt.% BT/PVDF nanocomposites, while the sensing capability for strain change in a 0–20% range is maximal with 1 wt.% CNTs/12 wt.% BT/PVDF nanocomposites. In addition, it is found that the best combination for mechanical toughness is 1 wt.% CNTs/12 wt.% BT/PVDF with 24.2 MPa and 579% in ultimate tensile strength and failure strain, respectively. These results show the technique to 3D print multifunctional nanocomposites with temperature and strain sensing capabilities as well as increased mechanical property. Furthermore, this research demonstrated the feasibility for large-scale multifunctional sensor device manufacturing with freedom of design, low-cost, and an accelerated process.

    

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3. Fabrication and magnetoelectric investigation of flexible PVDF-TrFE/cobalt ferrite nanocomposite films

   https://doi.org/10.1088/2053-1591/ac6151  

   Sapkota, Bedanga ; Hasan, Md Tanvir ; Martin, Alix ; Mahbub, Rifat ; Shield, Jeffrey E. ; Rangari, Vijaya ( April 2022 , Materials Research Express)

   Flexible nanocomposite films, with cobalt ferrite nanoparticles (CFN) as the ferromagnetic component and polyvinylidene fluoride–trifluoroethylene (PVDF-TrFE) copolymer as the ferroelectric matrix, were fabricated using a blade coating technique. Nanocomposite films were prepared using a two-step process; the first process involves the synthesis of cobalt ferrite (CoFe₂O₄) nanoparticles using a sonochemical method, and then incorporation of various weight percentages (0, 2.5, 5, and 10%) of cobalt ferrite nanoparticles into the PVDF-TrFE to form nanocomposites. The ferroelectric polarβphase of PVDF-TrFE was confirmed by x-ray diffraction (XRD). Thermal studies of films showed notable improvement in the thermal properties of the nanocomposite films with the incorporation of nanoparticles. The ferroelectric properties of the pure polymer/composite films were studied, showing a significant improvement of maximum polarization upon 5wt% CFN loading in PVDF-TrFE composite films compared to the PVDF-TrFE film. The magnetic properties of as-synthesized CFN and the polymer nanocomposites were studied, showing a magnetic saturation of 53.7 emu g⁻¹at room temperature, while 10% cobalt ferrite-(PVDF-TrFE) nanocomposite shows 27.6 emu/g. We also describe a process for fabricating high optical quality pure PVDF-TrFE and pinhole-free nanocomposite films. Finally, the mechanical studies revealed that the mechanical strength of the films increases up to 5 wt% loading of the nanoparticles in the copolymer matrix and then decreases. This signifies that the obtained films could be suited for flexible electronics.

    

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4. Negative dielectric permittivity of PVDF nanocomposites induced by carbon nanofibers and polymer crystallization

   https://doi.org/10.1002/app.49582  

   Sun, Lili ; Wu, Nan ; Peng, Rui ( June 2020 , Journal of Applied Polymer Science)

   Negative permittivity is a key characteristic of the distinctive metamaterials, a novel class of artificial materials with particular electromagnetic properties. Negative permittivity has been realized in metallic structures with special designs, but rarely achieved in polymer nanocomposites. Our recent studies discover that negative permittivity can be attained from randomly distributed carbon nanofiber (CNF) filled poly(vinylidene fluoride) (PVDF) composites over a wide frequency range, and the negative permittivity values are strongly influenced by CNF and PVDF crystalline structures. The effects of CNF on the crystallization of PVDF, and the resultant negative dielectric permittivity of CNF/PVDF composites influenced by crystallization of PVDF and CNF, are investigated. It is revealed that the introduction of CNF not only affects the dielectric permittivity directly, but also causes indirect effects to the dielectric permittivity through influencing the crystallization of PVDF. In particular, due to addition of more CNF, a α‐ to β‐phase transformation in PVDF is found to affect permittivity of the nanocomposites. Furthermore, the permittivity of CNF/PVDF composites are increased considerably (“more negative”) with more CNF, and is affected noticeably by crystalline structures of PVDF. The lowest negative permittivity achieved is −2,500 for the nanocomposite with 5 wt% CNF at 5 kHz.

    

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5. Fabrication of bulk piezoelectric and dielectric BaTiO 3 ceramics using paste extrusion 3D printing technique

   https://doi.org/10.1111/jace.16242  

   Kim, Hoejin ; Renteria‐Marquez, Anabel ; Islam, Md Didarul ; Chavez, Luis A. ; Garcia Rosales, Carlos A. ; Ahsan, Md Ariful ; Tseng, Tzu‐Liang Bill ; Love, Norman D. ; Lin, Yirong ( December 2018 , Journal of the American Ceramic Society)

   A simple and facile method was developed to fabricate functional bulk barium titanate (BaTiO₃,BT) ceramics using the paste extrusion 3D printing technique. TheBTceramic is a lead‐free ferroelectric material widely used for various applications in sensors, energy storage, and harvesting. There are several traditional methods (eg, tape casting) to process bulkBTceramics but they have disadvantages such as difficult handing without shape deformation, demolding, complex geometric shapes, expansive molds, etc. In this research, we utilized the paste extrusion 3D printing technique to overcome the traditional issues and developed printable ceramic suspensions containingBTceramic powder, polyvinylidene fluoride (PVDF), N,N‐dimethylformamide (DMF) through simple mixing method and chemical formulation. ThisPVDFsolution erformed multiple roles of binder, plasticizer, and dispersant for excellent manufacturability while providing high volume percent and density of the final bulk ceramic. Based on empirical data, it was found that the maximum binder ratio with good viscosity and retention for desired geometry is 1:8.8, while the maximumBTcontent is 35.45 vol% (77.01 wt%) in order to achieve maximum density of 3.93 g/cm³(65.3%) for 3D printedBTceramic. Among different sintering temperatures, it was observed that the sinteredBTceramic at 1400°C had highest grain growth and tetragonality which affected high performing piezoelectric and dielectric properties, 200 pC/N and 4730 at 10³ Hz respectively. This paste extrusion 3D printing technique and simple synthesis method for ceramic suspensions are expected to enable rapid massive production, customization, design flexibility of the bulk piezoelectric and dielectric devices for next generation technology.

    

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