Effect of silane coupling agent on the morphology, structure, and properties of poly(vinylidene fluoride-trifluoroethylene)/BaTiO3 composites

Micron- and submicron-sized barium titanate (BaTiO3) particles, untreated and surface modified with aminopropyl triethoxy silane, were incorporated in poly(vinylidene fluoride-trifluoroethylene) to fabricate composites with up to 60 vol% of ceramic phase. The morphology and structure of solvent cast and compression-molded films, and their thermal, viscoelastic, and dielectric properties were investigated. When surface-modified BaTiO3 was used, it was possible to decrease both the viscoelastic and the dielectric losses of highly filled solvent cast films, while their storage modulus and relative permittivity either increased or remained equal, owing to reduced porosity and improved matrix-filler compatibility. The effect of BaTiO3 surface modification on the morphology of compression-molded films was less marked, leading to unchanged viscoelastic properties, and lower permittivity and dielectric losses. For all composites the frequency dependency of the dielectric properties at low frequencies was suppressed with modified BaTiO3.

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Sara Dalle Vacche, Dragan Damjanovic, Yves Leterrier, Jan-Anders Månson, Véronique Michaud
Springer Verlag, 2014
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https://infoscience.epfl.ch/record/198988?ln=fr

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Interface-Dominated Time-Dependent Behavior of Poled Poly(Vinylidene Fluoride–Trifluoroethylene)/Barium Titanate Composites

Sara Dalle Vacche, Dragan Damjanovic, Yves Leterrier, Véronique Michaud

Composites in which particles of ferroelectric ceramic phase are randomly dispersed in a polymeric matrix are of interest because of flexibility, conformability, and ease of processing. However, their piezoelectric properties are rather low, unless very high volume fractions of ceramics are used. This brings agglomeration and porosity issues due to the large mismatch between the surface energies of the ceramics and of the polymer. Particle surface modification is a common approach for better dispersion; however, it may bring other effects on the properties of the composites, which are usually concealed by the huge improvement in performance due to the more homogenous microstructure. In this work, we compared poly(vinylidene fluoride–trifluoroethylene)/barium titanate composites containing 15 vol.% and 60 vol.% of pristine ceramic particles or particles modified with an aminosilane or a fluorosilane. Similar morphology, with good particle dispersion and low porosity, was achieved for all composites, owing to an efficient dispersion method. The materials were poled with two different poling procedures, and the piezoelectric coefficient d33, the relative permittivity, and the poling degree of barium titanate were followed in time. We highlighted that, although similar d33 were obtained with all types of particles, the nature of the particles surface and the poling procedure were associated with different charge trapping and influenced the evolution of d33 with time.

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Surface modified microfibrillated cellulose‐poly(vinylidene fluoride) composites: β‐phase formation, viscoelastic and dielectric performance

Dragan Damjanovic, Yves Leterrier, Véronique Michaud, Mohammed Arif Poothanari

The effect of silylation of microfibrillated cellulose (MFC) surfaces on β‐phase formation in poly(vinylidene difluoride) (PVDF) and the resulting viscoelastic and dielectric performance of MFC‐PVDF composites is investigated. Two different organosilanes, namely aminated (A) and fluorinated (F), were used. Composites of PVDF and MFC at concentrations up to 10 wt%, both untreated and silylated, were prepared by solvent casting. The two different surface modifications did not markedly change the melting and crystallization enthalpy of the polymer. However, only A‐MFC was found to promote β‐phase compared to the untreated MFC and the F‐MFC, which was attributed to the formation of hydrogen bonds at the interface between the amine groups of A‐MFC and the fluorine groups of PVDF. The elastic modulus and the permittivity of all composites increased with the amount of MFC up to a maximum value, depending on the MFC modification, and then decreased. This effect was due to the formation of MFC aggregates and porosity, as further confirmed by a comparison of experimental moduli with a classical composite mechanical model. The highest elastic modulus and highest permittivity were obtained for the untreated MFC and A‐MFC composites with 5 and 1 wt%.

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Effect of interfacial interactions on the electromechanical response of poly(vinylidene fluoride-trifluoroethylene)/BaTiO3 composites and its time dependence after poling

Sara Dalle Vacche, Dragan Damjanovic, Yves Leterrier, Jan-Anders Månson, Véronique Michaud

Solvent cast and compression molded composite films based on poly(vinylidene fluoride-trifluoroethylene), containing pristine and silylated BaTiO3 particles, were poled, and their electromechanical response (d(33)), their dielectric properties, and the crystalline structure of the embedded BaTiO3 particles, probed by X-ray diffraction, were recorded during one week. Their d(33) was also measured after long-term aging (>3 years). During this time the d(33) decreased for all composites. The d(33) of solvent cast composites was higher when surface modified particles were used, both immediately after poling and after aging, while for compression molded composites only slight differences in the initial and aged d(33) of materials containing pristine versus modified particles were found. However the decay rate of d(33) in the short time after poling was highly affected by the surface modification of the particles for both the solvent cast and the compression molded composites. The results suggest that other phenomena besides the polarization of the ceramic particles and of the polymer matrix contribute to the measured electromechanical response of the composites. Charge accumulation and differences in the charge distribution due to the presence of the silane layer on the surface of BaTiO3 may play an important role. (C) 2015 Elsevier Ltd. All rights reserved.

Elsevier2015

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