A. C. Lopes

Nanoparticle size and concentration dependence of the electroactive phase content and electrical and optical properties of Ag/poly(vinylidene fluoride) composites.

This paper describes the processing of silver-nanoparticle-doped poly(vinylidene fluoride). The effects of the concentration and size of the filler on the electroactive phase of the polymer and the optical and electrical properties are discussed. Spherical silver nanoparticles incorporated into the poly(vinylidene fluoride) polymeric matrix induce nucleation of the electroactive γ phase. The electroactive phase content strongly depends on the content and size of the nanoparticles. In particular, there is a critical nanoparticle size, below which the filler losses its nucleation efficiency due to its small size relative to that of the polymer macromolecules. Furthermore, the presence of surface plasmon resonance absorption in the composites is observed, which once again shows a strong dependence on the concentration and size of the particles. The absorption is larger for higher concentrations, and for a given concentration increases with particle size. This behavior is correlated to the electrical response and is related to the extra bands and electrons provided by the nanoparticles in the large energy band gap of the polymer.

Osteoblast, fibroblast and in vivo biological response to poly(vinylidene fluoride) based composite materials

Electroactive materials can be taken to advantage for the development of sensors and actuators as well as for novel tissue engineering strategies. Composites based on poly(vinylidene fluoride), PVDF, have been evaluated with respect to their biological response. Cell viability and proliferation were performed in vitro both with Mesenchymal Stem Cells differentiated to osteoblasts and Human Fibroblast Foreskin 1. In vivo tests were also performed using 6-week-old C57Bl/6 mice. It was concluded that zeolite and clay composites are biocompatible materials promoting cell response and not showing in vivo pro-inflammatory effects which renders both of them attractive for biological applications and tissue engineering, opening interesting perspectives to development of scaffolds from these composites. Ferrite and silver nanoparticle composites decrease osteoblast cell viability and carbon nanotubes decrease fibroblast viability. Further, carbon nanotube composites result in a significant increase in local vascularization accompanied an increase of inflammatory markers after implantation.

Influence of zeolite structure and chemistry on the electrical response and crystallization phase of poly(vinylidene fluoride)

Zeolites with framework types LTL, LTA, FAU, and MFI were synthesized and used as fillers to prepare PVDF/zeolite composites. The obtained composites showed structural and electrical dependence on the pore system and chemical content of the inorganic host. The larger polymer-zeolite electrostatic interactions of the Y and A zeolites lead the polymer to crystallize in the electroactive γ-phase, which in the case of the L zeolite is prevented due to the reduced interaction area. The solvent and water encapsulation ability of the zeolite as well as improve of the dielectric response of the composite is directly related to the Si/Al ratio, leading zeolites with lower Si/Al ratios to larger dielectric responses and encapsulation efficiencies in the composites. These effects show also some dependency on the dimensionality of the pore system; the zeolite L-containing 1D channels showing superior dielectric performance than the 3D pore system of zeolite Y.

Tailoring microstructure and physical properties of poly(vinylidene fluoride–hexafluoropropylene) porous films

This paper presents a systematic study for the production of poly(vinylidene fluoride–hexafluoropropylene) [P(VDF–HFP)], porous films using solvent evaporation (SE) and non-solvent-induced phase separation (NIPS) techniques. Parameters such as volume fraction of the copolymer solution, film thickness, time exposure to air, non-solvent, and temperature of the coagulation bath were investigated on the morphology, crystallization, and mechanical properties of the samples. Films with different porous morphologies including homogeneous pore sizes, macrovoids, and spherulites were obtained depending on the processing conditions, which in turn affect the wettability and mechanical properties of the material. Knowing that the phase content of the films also depends on the processing conditions, this paper shows that P(VDF–HFP) films with tailored porous morphology, electroactive phase content, hydrophobicity, crystallinity, and mechanical properties can be achieved for a specific application using the adequate SE and NIPS techniques conditions.

Poly(vinylidene fluoride-trifluoroethylene) Porous Films: Tailoring Microstructure and Physical Properties by Solvent Casting Strategies

A systematic study for the production of porous poly(vinylidene fluoride-trifluoroethylene), P(VDF-TrFE), films using solvent evaporation and nonsolvent induced phase separation techniques is presented. Processing parameters such as copolymer volume fraction, solvent, preset exposure time to air before immersion, and nonsolvent and temperature of the coagulation bath were varied and the corresponding sample morphology, hydrophobicity, thermal, and mechanical properties were determined. Film morphologies including homogeneous pore distributions, micropores, microvoids, spherulites, and nonporous films were obtained. The morphology variations strongly influence sample hydrophobicity and mechanical properties. All samples crystallized in the electroactive β-phase with a degree of crystallinity around 30%.

Influence of solvent properties on the electrical response of poly(vinylidene fluoride)/NaY composites

Different solvents were used for the preparation of poly(vinylidene fluoride), PVDF, and NaY zeolite composites by solvent casting and melt crystallization. Solvents like N,N-dimethylformamide (DMF), dimethylsulphoxide (DMSO) and triethyl phosphate (TEP) were chosen as they present different dielectric constants and can be encapsulated in the porous structure of NaY zeolite introduced in the PVDF/zeolite composites. The solvent molecules encapsulated induce variations in the dielectric response of the composite films according to the solvent dielectric constant. In this way, the solvent with the higher dielectric constant, DMSO, results in the composite with higher dielectric constant, while the opposite happens with TEP. The solvent molecules modify the distribution of intra zeolite cations increasing the dielectric constant of the composite. The zeolite also contribute to the increase of the d.c. conductivity, which is characterized by a double regime indicated by a breaking voltage, which value decreases when the dielectric constant of the solvent increases.