Improved mechanical dispersion or use of coupling agents? Advantages and disadvantages for the properties of fluoropolymer/ceramic composites

The aim of this work is to investigate the influence of interfacial chemistry on the properties of fluoropolymer composites, independent of effects derived from changes in morphology, in particular particle dispersion state. A comparative study of solvent cast composites of poly (vinylidene fluoride – trifluoroethylene) with barium titanate particles, at concentrations up to 60 vol%, was carried out using pristine hydrophilic particles, and particles hydrophobized with three organosilanes, bearing different functional groups (eCH3, eCH2NH2 and eCF3). For each filler concentration, composites with good particle dispersion and comparable amount of porosity with all types of particles were prepared and characterized. While pristine particles provided higher permittivity, all silanes decreased the dielectric losses due to Maxwell-Wagner-Sillars dispersion, although to different extents. Moreover, only the aminosilane provided better thermomechanical stability to the highly filled composites. These results provide useful insights into the advantages and disadvantages of the use of different approaches to improve the dispersion of hydrophilic particles in poly (vinylidene fluoride) copolymer based composites.

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Sara Dalle Vacche, Dragan Damjanovic, Yves Leterrier, Jan-Anders Månson, Véronique Michaud
2018
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https://infoscience.epfl.ch/record/256897?ln=en

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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

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.

2020

High Breakdown Field Dielectric Elastomer Actuators Using Encapsulated Polyaniline as High Dielectric Constant Filler

Jan-Anders Månson, Martin Molberg

A novel method allowing rapid production of reliable composites with increased dielectric constant and high dielectric strength for dielectric elastomer actuators (DEA) is reported. The promising approach using composites of conductive particles and insulating polymers generally suffers from low breakdown fields when applied to DEA devices. The present publication shows how to overcome this deficiency by using conductive polyaniline (PAN I) particles encapsulated into an insulating polymer shell prior to dispersion. PANI particles are encapsulated using miniemulsion polymerization (MP) of divinylbenzene (DVB). The encapsulation process is scaled up to approximately 20 g particles per batch. The resulting particles are used as high dielectric constant (e) fillers. Composites in a polydimethylsiloxane (PDMS) matrix are prepared and the resulting films characterized by dielectric spectroscopy and tensile tests, and evaluated in electromechanical actuators. The composite films show a more than threefold increase in epsilon', breakdown field strengths above 50 V mu m(-1), and increased strain at break. These novel materials allow tuning the actuation strain or stress output and have potential as materials for energy harvesting.

Wiley-Blackwell2010

Composite material

A composite material (also called a composition material or shortened to composite, which is the common name) is a material which is produced from two or more constituent materials. These constituent

Polyvinylidene fluoride

Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic fluoropolymer produced by the polymerization of vinylidene difluoride. Its chemical formula is (C2H2F

Barium titanate

Barium titanate (BTO) is an inorganic compound with chemical formula BaTiO3. Barium titanate appears white as a powder and is transparent when prepared as large crystals. It is a ferroelectric, pyroe