Trifluoroethylene Copolymer Research Articles

Effect of Fe3O4 Nanoparticles Modified by Citric and Oleic Acids on the Physicochemical and Magnetic Properties of Hybrid Electrospun P(VDF-TrFE) Scaffolds.

This study considers a fabrication of magnetoactive scaffolds based on a copolymer of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE)) and 5, 10, and 15 wt.% of magnetite (Fe3O4) nanoparticles modified with citric (CA) and oleic (OA) acids by solution electrospinning. The synthesized Fe3O4-CA and Fe3O4-OA nanoparticles are similar in particle size and phase composition, but differ in zeta potential values and magnetic properties. Pure P(VDF-TrFE) scaffolds as well as composites with Fe3O4-CA and Fe3O4-OA nanoparticles demonstrate beads-free 1 μm fibers. According to scanning electron (SEM) and transmission electron (TEM) microscopy, fabricated P(VDF-TrFE) scaffolds filled with CA-modified Fe3O4 nanoparticles have a more homogeneous distribution of magnetic filler due to both the high stabilization ability of CA molecules and the affinity of Fe3O4-CA nanoparticles to the solvent used and P(VDF-TrFE) functional groups. The phase composition of pure and composite scaffolds includes a predominant piezoelectric β-phase, and a γ-phase, to a lesser extent. When adding Fe3O4-CA and Fe3O4-OA nanoparticles, there was no significant decrease in the degree of crystallinity of the P(VDF-TrFE), which, on the contrary, increased up to 76% in the case of composite scaffolds loaded with 15 wt.% of the magnetic fillers. Magnetic properties, mainly saturation magnetization (Ms), are in a good agreement with the content of Fe3O4 nanoparticles and show, among the known magnetoactive PVDF or P(VDF-TrFE) scaffolds, the highest Ms value, equal to 10.0 emu/g in the case of P(VDF-TrFE) composite with 15 wt.% of Fe3O4-CA nanoparticles.

Solution-processed ferroelectric polymer nanocrystals

Since the first demonstrations of ferro- and piezoelectricity in solution-processed ferroelectric polymer thin films research activities have been stimulated in both academia and industry. Several applications have been reported using ferroelectric polymer thin films as bistable polarization switches in memory devices or as transducers in (micro-)electromechanical devices. In light of the continuing miniaturization of such devices, nanoscaled structures of ferroelectric polymers such as nanomesas are attracting increasing interest. However, nanopatterning ferroelectrics, to develop stable and reliable ferroelectric nanomesas remains challenging. In this work, we demonstrate the fabrication of solution-processed ferroelectric polymer nanocrystals, i.e. ferroelectric nanomesas, and verify their ferroelectric activity. By using the ferroelectric copolymer of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE)), we are able to isolate crystalline domains. Morphology, molecular conformation, (nano-)mechanical and electromechanical properties of the nanocrystals are measured, yielding comparable results to those observed in uniform, continuous thin films. Therefore, synthesizing self-assembled ferroelectric polymer nanocrystals from polymer solution by spin-casting represents a promising approach for the realization of ferroelectric nanomesas.

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

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 polar β phase 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−1 at 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.

Annealing of grain-like poly (vinylidene fluoride-trifluoroethylene) membranes with a single-crystalline electroactive phase and high anti-fouling activity

Electroactive membranes are attracting attention due to their piezo-, pyro-, and ferro-electric properties. Here we report the fabrication of electroactive membranes from poly (vinylidene fluoride-trifluoroethylene) P(VDF-TrFE), i.e. co-polymers of vinylidene fluoride and trifluoroethylene. A new P(VDF-TrFE)/Polyvinylpyrrolidone (PVP)/Dimethylacetamide (DMAc)/water system was used to tailor the membranes’ structure. Since hot treatment in the air could induce defect on membrane structure (i.e., fracture, shrinkage, and rolling), the annealing was conducted in the glycerin. Thanks to the high boiling point and moderate surface tension of glycerin, the integrity of P(VDF-TrFE) membranes was preserved during the annealing process. X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy experiments revealed that the relative abundance of the β–crystalline phase increased with the annealing temperature when the latter was above the Curie temperature. P(VDF-TrFE) membranes annealed at 130 °C exhibited high crystallinity with grain-like surface, which resulted from multiple stacks of edge-on lamellae, and possessed excellent physicochemical properties of filtration. The anti-fouling performance of pristine and annealed P(VDF-TrFE) membranes was tested by dead-end filtration with a 13.5 mg/L humic acid (HA) solution. Annealed P(VDF-TrFE) membranes achieved greater fluxes and had superior anti-fouling properties, which was attributed to the weaker hydrophobic attraction between HA and the aligned β–phase crystals. This work provides a facile method for designing highly crystalline P(VDF-TrFE) membranes with potential applications in filtration systems, smart wearable devices, and medicine.

Effect of electric field assisted crystallisation of PVDF-TrFE and their functional properties

Uniform thin films of poly(vinylidene fluoride)-trifluoroethylene copolymers were spin-coated and their functional electrical properties were investigated after corona poling. The copolymers were poled in the gel state at room temperature (RT) without stretching or annealing treatment. This E-field crystallisation processing method at RT leads to the formation of improved ferroelectric and pyroelectric properties in the investigated thin films. That processing method has great potential for ferroelectric material coatings on thermally highly sensitive substrates. The selected composition (∼1 µm thick composites of 65/35 mol% PVDF-TrFE) of the copolymer produced a pyroelectric coefficient value of 36 ± 3 µC/m2K1, a dielectric constant of 9, and a dielectric loss of about 0.018 at a frequency of 1 kHz under ambient conditions.

Multi-scale characterisation of a ferroelectric polymer reveals the emergence of a morphological phase transition driven by temperature

Ferroelectric materials exhibit a phase transition to a paraelectric state driven by temperature - called the Curie transition. In conventional ferroelectrics, the Curie transition is caused by a change in crystal symmetry, while the material itself remains a continuous three-dimensional solid crystal. However, ferroelectric polymers behave differently. Polymeric materials are typically of semi-crystalline nature, meaning that they are an intermixture of crystalline and amorphous regions. Here, we demonstrate that the semi-crystalline morphology of the ferroelectric copolymer of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE)) strongly affects its Curie transition, as not only a change in crystal symmetry but also in morphology occurs. We demonstrate, by high-resolution nanomechanical measurements, that the semi-crystalline microstructure in the paraelectric state is formed by crystalline domains embedded into a softer amorphous phase. Using in situ X-ray diffraction measurements, we show that the local electromechanical response of the crystalline domains is counterbalanced by the amorphous phase, effectively masking its macroscopic effect. Our quantitative multi-scale characterisations unite the nano- and macroscopic material properties of the ferroelectric polymer P(VDF-TrFE) through its semi-crystalline nature.

The Influence of γ Radiation on the Dielectric Properties of Ferroelectric Langmuir–Blodgett Films

Dielectric relaxation of Debye type has been found for thin vinylidene fluoride‒trifluoroethylene copolymer films of different composition, fabricated by the Langmuir–Blodgett (LB) technique. The influence of γ radiation on the dielectric response of LB films is studied. It is established that the relaxation time increases after the γ irradiation, the phase transition is observed at a lower temperature, and the temperature hysteresis is reduced.

Dielectric properties of composite materials based on P(VDF-TrFE) copolymer and deuterated triglicyne sulfate crystal

The film structures on the base of soft and crystalline ferroelectrics (poly(vinylidene fluoride - trifluoroethylene) copolymer and deuterated triglycine sulfate) were produced. The volume content of the DTGS microcrystal particles embedded in the polymer matrix of the composite films was up to 10%. It was found crystalline phase changes in the polymer matrix at the DTGS inclusions presence. The DTGS crystal particles increased dielectric permittivity and electrical conductivity of the composite films. The temperature dependences of the dielectric permittivity indicated increasing the phase transition temperature of polymer matrix at the DTGS inclusions growth.

Boron Nitride Nanotube Addition Enhances the Crystallinity and Cytocompatibility of PVDF-TrFE.

Analysis of the cellular response to piezoelectric materials has been driven by the discovery that many tissue components exhibit piezoelectric behavior ex vivo. In particular, polyvinylidene fluoride and the trifluoroethylene co-polymer (PVDF-TrFE) have been identified as promising piezo and ferroelectric materials with applications in energy harvesting and biosensor devices. Critically, the modulation of the structural and crystalline properties of PVDF-TrFE through annealing processes and the addition of particulate or fibrous fillers has been shown to modulate significantly the materials electromechanical properties. In this study, a PVDF-TrFE/boron-nitride nanotube composite was evaluated by modulated differential scanning calorimetry to assess the effects of boron nitride nanotube addition and thermal annealing on the composite structure and crystal behavior. An increased beta crystal formation [f(β) = 0.71] was observed following PVDF-TrFE annealing at the first crystallization temperature of 120°C. In addition, the inclusion of boron nitride nanotubes significantly increased the crystal formation behavior [f(β) = 0.76] and the mechanical properties of the material. Finally, it was observed that BNNT incorporation enhance the adherence and proliferation of human tenocyte cells in vitro.

Direct piezoelectric response in vinylidene fluoride–trifluoroethylene copolymer films

The effective transverse piezoelectric coefficient e31,f in vinylidene fluoride–trifluoroethylene copolymer [P(VDF–TrFE), 75/25 mol %] films was investigated. 2-µm-thick P(VDF–TrFE) films were deposited by spin coating on a Pt/Si substrate at a valid annealing temperature from 100 to 160 °C. The phase development and surface morphology suggest that the films were melted by annealing at 150 °C and above, and that gauche defects increase with the annealing temperature. Although all the films have similar dielectric constants between 8 and 10, the remanent polarization Pr and coefficient e31,f show maximum values of 9.1 µC/cm2 and 140 mC/m2, respectively, at 140 °C. These results indicate that the ferroelectric and piezoelectric properties of P(VDF–TrFE) films are enhanced by annealing just below the melting point.

Resistive switching and nanoscale chemical mapping of phase separation in PVDF/PMMA/F8T2 ternary thin films

In recent years organic ferroelectric/semiconducting blend film has attracted much attention due to its integration of both resistive switching and electrical rectifying properties. In all reported blend structures, P(VDF-TrFE), the copolymer of vinylidene fluoride and trifluoroethylene, is used as the ferroelectric phase, which is blended with organic semiconductors to form phase-separated structure. As another representative ferroelectric polymer, poly(vinylidene fluoride) (PVDF) has its own advantages of even larger polarization and low cost. However, PVDF has much complicated crystalline phases in which its non-polar α phase is the most thermally stable. Effective phase transformation from the α to the ferroelectric phases is still an open question especially for PVDF thin films. Till now seldom work has been reported on PVDF-based ferroelectric/semiconducting resistive films. Here we reported the fabrication and structural and electrical characterizations of PVDF-based ferroelectric/semiconducting ternary resistive films. Poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) was used as semiconducting phase which was phase separated with PVDF phase in PVDF/F8T2 blends. Poly(methyl metacrylate) (PMMA) was introduced into PVDF to promote its ferroelectric γ and β phases. This PVDF/PMMA/F8T2 ternary film showed good resistive switching performance with ON/OFF ratio up to 103, which was comparable to and even larger than those values obtained from blends with P(VDF-TrFE) as the ferroelectric phase. However, the introduction of PMMA also complicateed the basic understanding on phase separation and thus resistive switching mechanism in this ternary film. To clarify this, nanoscale chemical mapping was conducted to distinguish the local distributions of all three phases, the results of which showed obvious nanoscale phase separation in this ternary blend film.

Influence of an Interfacial Effect on the Laser Performance of a Rhodamine 6G/Cellulose Acetate Waveguide on a Vinylidene Fluoride Copolymer Layer.

The fluorescent properties of dyes and fluorophores in condensed matter significantly affect the laser performance of organic dye lasers and fluorescent polymer lasers. Concentration quenching of fluorescence is commonly observed in condensed matter. Several approaches have been presented to suppress such quenching, such as the use of a dendrimer and the use of effective energy transfer in a guest-host system. The enhanced fluorescence of rhodamine 6G (R6G) dye on a vinylidene fluoride polymer is an alternative method for enhancing laser performance because of the roughness of the P(VDF-TrFE) surface and the interaction between polar β-crystals of P(VDF-TrFE) and R6G dye. In this paper, a significant improvement in slope efficiency (SE) is demonstrated without a significant depression in the lasing threshold for distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers fabricated using an R6G-dispersed cellulose acetate (CA) matrix spin-coated onto a copolymer of vinylidene fluoride and trifluoroethylene P(VDF-TrFE) thin film. SEs of 3.4 and 1.3% were measured for DBR and DFB laser devices with CA/R6G on a P(VDF-TrFE) thin film, respectively, whereas an SE of less than 1.0% was measured for both corresponding laser devices without a P(VDF-TrFE) thin film. From the aspect of simple fabrication procedures, repeatability in device fabrication and performance, stability of the device, time for device fabrication, the present approach is the most preferable way for industrial applications, requiring only the additional step of spin-coating of a P(VDF-TrFE) thin film.

Coalescence and split of high-entropy polymer lamellar cocrystals

The solvent evaporation has been identified able to induce the cocrystallization of dissolved polyvinylidene fluoride (PVDF) homopolymer and poly(vinylidene fluoride trifluoroethylene) (PVDF-TrFE) copolymer solutes in this research. Upon the random incorporation of either trifluoroethylene (TrFE) or vinylidene fluoride (VDF) motif during this selected route of cocrystallization, several ferroelectric crystalline phases grow concurrently. For the development of each crystalline form, there is an appropriate composition range of TrFE motif, instead of a specific composition. When the inclusion of TrFE is beyond a threshold level, the non-polar HT-form crystals were found to solely develop upon slow heating above Curie temperature, and therefore inherits various compositions of TrFE motif. During the stay above Curie temperature, stick-like HT-form lamellar cocrystals preferably associate together and coalesce into coarser crystalline lamellae. This coalescence behavior is deduced to be driven by the secondary crystallization above Curie temperature, presumably enabled by the acceptable level of lattice-packing entropy of HT-form cocrystals. During the subsequent cooling below Curie temperature, the coalesced HT-form lamellar cocrystals reversely split into thinner lamellar cocrystals with various types of ferroelectric lattice packing comprising narrower ranges of TrFE composition. The Curie transition of cocrystals is thus accompanied with the alteration of the stacking dispersion of crystalline lamellae within materials, which associates with the variation of motif composition and therefore the lattice-packing entropy.

Phase Separation in Organic Semiconducting/Ferroelectric Blend Films with Air-Stable Resistive Properties

Organic semiconducting/ferroelectric blend films integrate both resistive and rectifying properties and thus well solve the cross-talk problem usually suffered in resistive memories. Till now several kinds of semiconducting/ferroelectric blend systems have been developed with good retention and ON/OFF properties. However, seldom work concerns air stability of their electrical properties. Here we report one kind of blend resistive films with air-stable Poly[(9,9-dioctylfluorenyl-2,7-diyl) -alt-co-(bithiophene)] (F8T2) as semiconducting material and the copolymer of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE)) as ferroelectric material. We introduce AFM based nanoscale electrical measurements into the observation of phase separation in F8T2/P(VDF-TrFE) blend films. Conductive AFM measurements present discrete high-conductivity circular domains embedded in continuous low-conductivity matrix. Surface Potential Microscopy results further indicate that these discrete circular domains show lower surface potential than those from their surrounding matrix, implying the difference in chemical structures. It is reasonable to attribute those continuous surrounding matrix to ferroelectric P(VDF-TrFE) phase and those discrete circular domains to semiconducting F8T2 phase who penetrates the whole film resulting in large electrical conductivity. F8T2/P(VDF-TrFE) resistive blend films present good restive performance with high ON/OFF ratio up to 3.5×103. Such blend films show excellent electrical stability in air even after aging of 200 days.

B-doped diamond field-effect transistor with ferroelectric vinylidene fluoride–trifluoroethylene gate insulator

A B-doped diamond field-effect transistor (FET) with a ferroelectric vinylidene fluoride–trifluoroethylene (VDF–TrFE) copolymer gate insulator was fabricated. The VDF–TrFE film deposited on the B-doped diamond showed good insulating and ferroelectric properties. Also, a Pt/VDF–TrFE/B-doped diamond layered structure showed ideal behavior as a metal–ferroelectric–semiconductor (MFS) capacitor, and the memory window width was 11 V, when the gate voltage was swept from 20 to −20 V. The fabricated MFS-type FET structure showed the typical properties of a depletion-type p-channel FET and a maximum drain current density of 0.87 mA/mm at room temperature. The drain current versus gate voltage curves of the proposed FET showed a clockwise hysteresis loop owing to the ferroelectricity of the VDF–TrFE gate insulator. In addition, we demonstrated the logic inverter with the MFS-type diamond FET coupled with a load resistor, and obtained the inversion behavior of the input signal and a maximum gain of 18.4 for the present circuit.

High diffusion barrier and piezoelectric nanocomposites based on polyvinylidene fluoride‐trifluoroethylene copolymer and hydrophobized clay

ABSTRACTNanocomposites based on polyvinylidene fluoride–trifluoroethylene copolymer and up to 4 vol % of hydrophobized clay nanoparticles are investigated. The structure, piezoelectric properties, and oxygen permeability of solvent cast films are analyzed before and after annealing above the Curie temperature of the polymer. Exfoliation of the clay takes place at concentrations up to 1 vol %, beyond which it rapidly drops and is absent at a concentration of 4 vol %. The presence of clay does not change the crystallinity of the polymer, but leads to a threefold decrease of the oxygen permeability at a concentration of 0.5 vol %. Annealing at 130 °C increases the crystallinity, the proportion of β phase up to 94%, and the piezoelectric coefficient by 20–40% at clay fractions below 1 vol %. Annealing also leads to a remarkable 3‐ to 10‐fold decrease of O2 permeability and to intriguing changes of the activation energy for O2 transport, which decreases from 56 kJ/mol for the as‐cast polymer to below 10 kJ/mol for the polymer and exfoliated composite. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1828–1836

Synthesis and characterization of poly(trifluoroethylene-co-hexafluoropropylene) and the optical properties of its thin films

Copolymers of trifluoroethylene (TrFE) and hexafluoropropylene (HFP) were synthesized and characterized by various instrumental techniques. The maximum incorporation of HFP was 19.6 mol%. It was found that the reactivity ratios of TrFE and HFP were r TrFE =4.12 and r HFP ≈0, respectively, by applying Mayo-Lewis method. It was also found that the incorporation of HFP in copolymer chain influenced thermal properties. As increasing HFP content in copolymers, the melting temperature and crystallinity of copolymers were decreased and the glass transition temperature of copolymers gradually shifted to low temperature. Reduced crystallinity of copolymers was helpful to prepare coating layers having much even surface. Compared with coating layer prepared from TrFE homopolymer, the surface roughness was decreased and light transmittance through the coating layer increased when the copolymers of TrFE and HFP were used. This tendency was more appreciable as increasing HFP content in the copolymers.

Analysis of vinylidene fluoride–trifluoroethylene copolymer film for nonpolarized energy harvester

In this paper, an investigation of a vinylidene fluoride–trifluoroethylene (VDF/TrFE) copolymer film for use in a nonpolarized energy harvester is presented. The Fourier transform infrared spectroscopy and X-ray diffraction analysis of a nonpolarized VDF/TrFE copolymer film indicate that polymer crystallinity depends on film thickness. Furthermore, the growth of the polar structure (β phase) is observed upon the reduction in the thickness. However, power generation does not exhibit a linear behavior because the generation capacity increases with the thickness. These results indicate that the film thickness for a nonpolarized harvester must be optimized to obtain the maximum output.

Ferroelectric surfaces for cell release

Adherent cells cultured in vitro must usually, at some point, be detached from the culture substrate. Presently, the most common method of achieving detachment is through enzymatic treatment which breaks the adhesion points of the cells to the surface. This comes with the drawback of deteriorating the function and viability of the cells. Other methods that have previously been proposed include detachment of the cell substrate itself, which risks contaminating the cell sample, and changing the surface energy of the substrate through thermal changes, which yields low spatial resolution and risks damaging the cells if they are sensitive to temperature changes. Here cell culture substrates, based on thin films of the ferroelectric polyvinylidene fluoride trifluoroethylene (PVDF-TrFE) co-polymer, are developed for electroactive control of cell adhesion and enzyme-free detachment of cells. Fibroblasts cultured on the substrates are detached through changing the direction of polarization of the ferroelectric substrate. The method does not affect subsequent adhesion and viability of reseeded cells.

Surface topography and crystal and domain structures of films of ferroelectric copolymer of vinylidene difluoride and trifluoroethylene

The crystallization of a copolymer from a solution at room temperature is found to lead to the formation of a metastable structure, characterized by the coexistence of ferroelectric and paraelectric phases. The fraction of the latter decreases after annealing above the Curie point. Atomic force microscopy (AFM) has revealed a difference in the surface topographies between the films contacting with air and the films contacting with a glass substrate. The microstructure of copolymer chains has been investigated by 19F NMR spectroscopy. The chain fragments with “defect” attached monomeric units are ejected to the surface. The character of the ferroelectric domains formed during crystallization and their size distribution are analyzed.