Vinylidene Fluoride-tetrafluoroethylene Copolymer Research Articles

Influence of Internal Microarchitecture on the Shape of Individual Implants Made from Vinylidene Fluoride Copolymer by 3D Printing with High-Temperature Crystallization

The healing potential of individual polymer implants for the reconstruction of extensive craniofacialdefects after cancer resection is largely determined by the internal architecture of the implant. The architectureof an implant during polymer crystallization could affect the structure and shape of the implant at themicro and macro levels. In this study, the relationship between the internal architecture (triply periodic minimumsurface structure (gyroid), cube, grid, and honeycomb) and shape changes of individual implants by3D printing with a vinylidene fluoride-tetrafluoroethylene copolymer after crystallization is examined at afilling density of 70%. Using the method of differential scanning calorimetry, it is established that crystallizationleads to the rearrangement of the crystalline structure of the implant into electrically active (ferroelectric)crystalline phases. Moreover, the type of internal architecture affects the change in the shape of theimplant after crystallization. The results of the computed tomography show that structures with a triply periodicminimum surface (gyroid) provide the minimal deformation of the implant during crystallization, whichmakes such structures optimal for manufacturing implants for replacing bone defects in the zygomatic-orbitalcomplex.

Microgel Particle Collision with Smooth and Nanofiber Hydrophobic Surfaces during Three-Dimensional Printing of a Biopolymer Layer.

The impact of microgel particles onto a wall represents an elementary process that determines the one-stage production of a biopolymer layer on a nanofiber scaffold in the framework of tissue bioengineering. The formation of a microgel layer is experimentally examined on a hydrophobic uniform surface and a nonwoven polymer membrane made of vinylidene fluoride-tetrafluoroethylene copolymer. In-air microfluidics methods, namely, an external vibration disturbance on the microflow of a cross-linkable biopolymer, make it possible to form the microstructures of "beads-on-thread" with a uniform distance between microgel particles of identical size (340-480 μm, depending on the sample). The successive particle-surface and particle-particle collisions are explored to develop the concept of technology for depositing microgel particles on surfaces for mobile one-stage production of microgel layers with a thickness of one and two particles, respectively. A physical model of successive particle-surface and particle-particle interactions is proposed. Empirical expressions are derived for predicting the diameters of maximum spreading (deformation) and the minimum heights of microgel particles on smooth and nanofiber surfaces, as well as in particle-particle collisions using a dimensionless criterion of gelation degree. The effect of microgel viscosity and fluidity on the maximum particle spreading during successive particle-surface and particle-particle collisions is elucidated. The consistent findings have made it possible to develop a predictive method for determining the growth dynamics of microgel layer area with a thickness of one or two particles on a nanofiber scaffold within a few seconds. The specific behavior of a microgel with a given gelation degree is simulated to produce a layer.

ИССЛЕДОВАНИЕ СТРУКТУРЫ И СВОЙСТВ ПОЛИМЕРНЫХ КОМПОЗИТНЫХ МЕМБРАН НА ОСНОВЕ СОПОЛИМЕРА ВИНИЛИДЕНФТОРИДА С ТЕТРАФТОРЭТИЛЕНОМ И ПОЛИВИНИЛИДЕНФТОРИДА, СФОРМИРОВАННЫХ МЕТОДОМ ЭЛЕКТРОФОРМОВАНИЯ

In the present article the results of studying the influence of polyvinylidene fluoride content (PVDF) in a mixture with vinylidene fluoride-tetrafluoroethylene copolymer (VDF-TeFE) on the properties of spinning solutions, structure, surface free energy and cocrystallization of polymers in composite membranes – obtained by electrospinning –are presented. It was established that an increase in PVDF content in a mixture with VDF-TeFE leads to an increase in electrical conductivity and a decrease in the viscosity of spinning solutions, a decrease in the diameter of the fibers forming the membrane, and a decrease in the tensile strength and relative elongation. It was shown that, regardless of the PVDF content, all the formed membranes are hydrophobic and have low free energy of the surface. It was established that an increase in the PVDF content leads to disordering of the ferroelectric β-phase, which manifests itself in a decrease in the interplanar spacing and crystallite size, and a decrease in the degree of system crystallinity.

Antibacterial Ferroelectric Hybrid Membranes Fabricated via Electrospinning for Wound Healing.

In the present study, wound healing ferroelectric membranes doped with zinc oxide nanoparticles were fabricated from vinylidene fluoride-tetrafluoroethylene copolymer and polyvinylpyrrolidone using the electrospinning technique. Five different ratios of vinylidene fluoride-tetrafluoroethylene to polyvinylpyrrolidone were used to control the properties of the membranes at a constant zinc oxide nanoparticle content. It was found that an increase of polyvinylpyrrolidone content leads to a decrease of the spinning solution conductivity and viscosity, causing a decrease of the average fiber diameter and reducing their strength and elongation. By means of X-ray diffraction and infrared spectroscopy, it was revealed that increased polyvinylpyrrolidone content leads to difficulty in crystallization of the vinylidene fluoride-tetrafluoroethylene copolymer in the ferroelectric β-phase in membranes. Changing the ratio of vinylidene fluoride-tetrafluoroethylene copolymer and polyvinylpyrrolidone with a constant content of zinc oxide nanoparticles is an effective approach to control the antibacterial properties of membranes towards Staphylococcus aureus. After carrying out in vivo experiments, we found that ferroelectric hybrid membranes, containing from five to ten mass percent of PVP, have the greatest wound-healing effect for the healing of purulent wounds.

Peculiarities of structure and dielectric relaxation in ferroelectric vinylidene fluoride-tetrafluoroethylene copolymer at different crystallization conditions

Vinylidene fluoride (VDF)/tetrafluoroethylene (TFE) 94/6 copolymer films obtained by low-temperature crystallization from acetone solution and by melt-crystallization under high pressure were studied. As shown in the X-ray diffraction patterns, β- and γ- phases coexist in the sample crystallized from a solution. At melt-crystallization, a number of γ-crystals decrease and spherulitic supramolecular structure is formed. It is accompanied by a decrease of the amorphous phase density in the intra- and inter-spherulite regions, which leads to an increase in the glass transition temperature. Differential scanning calorimetry data indicate a smaller fraction of the amorphous phase for the sample crystallized from the melt. At the same time, the relaxation strength of the mobility in the amorphous phase in this sample is higher. This contradiction is explained by the increased ratio of isomers in planar zigzag conformation, as shown by IR spectroscopy.

A low-fouling polymer surface prepared by controlled segregation of poly(ethylene oxide) and its functionalization with biomolecules

A polyethylene terephthalate polymer surface was modified by dip coating in a polymer mixture composed of methacrylate-based terpolymers containing both perfluoroalkyl (Rf) groups and poly(ethylene oxide) (PEO) side chains, vinylidenefluoride-tetrafluoroethylene copolymers ((CH2CF2)80(CF2CF2)20) and poly(methyl methacrylate). The terpolymers contained Rf groups with various numbers of carbons. After the dip coating, both the Rf groups and the PEO chains predominantly segregated on the top surface. The modified surfaces were characterized with X-ray photoelectron spectroscopy, protein adsorption, thrombogenesis and cell adhesion. The results indicate that because of the surface-segregated PEO chains, the surfaces exhibited resistance to nonspecific protein adsorption, antithrombogenicity and resistance to cell adhesion. In addition, covalent conjugation of biotin with the PEO termini enabled selective immobilization of streptavidin from a mixed protein solution on the dip-coated surface. A polymer surface was modified by dip coating a mixture of three kinds of polymers: methacrylate-based terpolymers containing both perfluoroalkyl (Rf) groups and poly(ethylene oxide) (PEO) as side chains, vinylidenefluoride-tetrafluoroethylene copolymer (CH2CF2)80(CF2CF2)20, and poly(methyl methacrylate) (PMMA). These modified surfaces showed resistance to nonspecific protein adsorption, antithrombogenicity and resistance to cell adhesion due to surface-segregated PEO chains. We also succeeded in covalent conjugation of biotin with the termini of PEO chains and demonstrated the immobilization of streptavidin on the dip-coated surface.

Effect of the structure of a ferroelectric vinylidene fluoride-tetrafluoroethylene copolymer on the characteristics of a local piezoelectric response

The surface topography and characteristics of a local piezoelectric-response signal in isotropic films of a ferroelectric vinylidene fluoride-tetrafluoroethylene copolymer with a composition of 94: 6 are studied via scanning probe microscopy. The X-ray diffraction and IR spectroscopy data indicate that crystallization occurs in a mixture of β and γ polymorphic modifications. The exposure of the original film to a dc field bipolar leads to the formation of polarized regions exhibiting low stability. Recrystallization is followed by structural transformations accompanied by conformational transitions. As a result, there is a decrease in the concentration of chain segments in the T3GT3G− conformation and, conversely, an increase in the concentration of isomers in the planar zigzag conformation. In addition, the characteristics of the local piezoelectric response after polarization become more stable, while the signal undergoes phase reversal. A second-harmonic piezoelectric response signal induced by the electrostriction effect is detected for the studied ferroelectric polymer samples. It is found that the original film has two types of regions that contribute to the measured signal. A change in the pattern of the second-harmonic piezoelectric-response signal in the recrystallized film is attributed to a change in the contribution of the electrostriction effect to the macroscopic piezoelectric response.

Shaping of the structure of vinylidene fluoride-tetrafluoroethylene copolymer membranes

A 19F NMR study revealed differences in the interaction of hard (phosphoric acid) and soft (acetic acid) precipitants with vinylidene fluoride-tetrafluoroethylene copolymer in dimethylformamide. Phase separation in solutions with additions of mixtures of phosphoric and acetic acids was examined.

The influence of structural and electrical parameters of the pyroelectric phase on the pyroelectric properties of a polymer-pyroelectric ceramic composite

The influence of structural and electrical parameters of the pyroelectric phase on the pyroelectric properties of composites based on poly(vinylidene fluoride), vinylidene fluoride-tetrafluoroethylene copolymer (F-42), and pyroelectric ceramics of the lead zirconate titanate family with different structures is investigated. It is revealed that the pyroelectric coefficient of the composite is determined by the reorientation polarization and the mobility of domains in the pyroelectric ceramic phase, which depend on the homogeneous parameter of the spontaneous strain of the perovskite cell.

Electrically controlled elasticity utilizing piezoelectric coupling

Electrical control of elasticity was performed in piezoelectric polymer films by connecting an electric circuit parallel to the sample electrodes. A polyvinylidene fluoride film and a vinylidene fluoride tetrafluoroethylene copolymer (73/27) film were used. Electrical circuits acting as a variable negative capacitor or a variable inductor were constructed using operational amplifiers. Theoretically, when the value of the external negative capacitance is increased, the observed elastic constant increases from that at an open circuit to positive infinity at around the value of the sample, turns to negative infinity, and then increases through zero to that at a short circuit. If the inductance of the external circuit is changed around the electrical resonant frequency, the elastic constant exhibits resonance and antiresonance against frequency. Experimental observations of the characteristics of the dynamic elastic constant agreed well with these theoretical predictions. By coupling the negative capacitance, the elastic constant changed between 0.5 and 2 times the original value, and the elastic loss increased to tan δ=0.7.

An equilibrium study on the distribution of structural defects between the lamellar and amorphous portions of poly(vinylidene fluoride) and (vinylidene fluoride-tetra fluoro ethylene) copolymer crystals

An equilibrium study on the distribution of structural defects between the lamellar and amorphous portions of poly(vinylidene fluoride) and (vinylidene fluoride-tetra fluoro ethylene) copolymer crystals

An equilibrium study on the distribution of structural defects between the lamellar and amorphous portions of poly(vinylidene fluoride) and (vinylidene fluoride-tetra fluoro ethylene) copolymer crystals

Samples of poly(vinylidene fluoride) (PVF2) and (vinylidene fluoride-tetra fluoroethylene) (VF2-VF4) copolymer were etched with a chromium-based etching reagent. The etching rate was lower for the VF2-VF4 copolymer samples than for the PVF2 samples. The melting point and enthalpy of fusion increased with increased etching time of the etched specimen. This was also true for the melt-quenched (etched) samples, whose values were always lower than those obtained from the direct run of the etched samples. The scanning electron micrographs of specimens etched for 24 h indicated that only the amorphous portion was etched without affecting the crystalline lamella. The sequence distribution of the PVF2 and VF2-VF4 copolymer crystals were determined by 19F NMR measurements of the samples and their etched species. The observed probabilities (Pobs), calculated from the integrated area of the NMR peaks, indicated that the crystalline lamella had a more oriented chain structure than that of the amorphous overlayer portion. The head-to-head defects calculated from the aforementioned sequence analysis indicated a greater propensity in the amorphous portion than in the crystalline lamella. The equilibrium constant (K) for the distribution of defects between the lamella and amorphous portion of the crystal varied from 0.7 to 0.9. It was higher at a higher quenching rate of the crystallization, and in the isothermal crystallization, it also had a substantially high value, indicating the equilibrium inclusion of defects in the crystal. The distribution constant increased with an increase in the defect content in the chain and decreased with an increase in the defect size. The sequence distribution data, analyzed through a suitable melting-point depression equation, indicated a defect energy of 2.25 kcal/mol for the α-phase PVF2 crystals and 0.68 kcal/mol for the β-phase VF2-VF4 copolymer. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 297–308, 2000

Cocrystallization mechanism of vinylidene fluoride-tetrafluoroethylene copolymers with different copolymer composition

Cocrystallization mechanism of vinylidene fluoride-tetrafluoroethylene copolymers with different copolymer composition

Cocrystallization mechanism of vinylidene fluoride-tetrafluoroethylene copolymers with different copolymer composition

The crystallization rate of two vinylidene fluoride(VF2)-tetrafluoroethylene(VF4) copolymers (VF2/VF4 90/10) (Cop-1), (VF2/VF4 86/14) (Cop-2) and their cocrystals of different compositions was measured by differential scanning calorimetry (DSC). At same undercooling (ΔT) the crystallization rate of cocrystals is faster than that of the pure components. The Avrami exponent varies from 1.8–0.4. Analysis of the crystallization rate using the Lauritzen-Hoffman (L-H) growth rate theory indicates that the crystallization is occurring in a single regime and the product of surface free energies (σσe) is lower for the cocrystals than those of the pure components. Assuming σe as invariant for the samples, σ values are calculated and are interpreted according to a recent theory of Hoffman et al. The chain characteristic ratio (C∝) calculated from the kinetic data indicates chain extension in the melt of the blend. The entropies of cocrystallization are also calculated from the kinetic data and amount to ca. 0.4 cal · mol−1 · K−1.

Cocrystallization of poly(vinylidene fluoride) and vinylidene fluoride-tetrafluoro-ethylene copolymer blends: 3. Structural study

The structure of poly(vinylidene fluoride) (PVF 2) and vinylidene fluoride-tetrafluoroethylene (VF 2-VF 4) copolymer blends has been investigated by wide angle X-ray scattering (WAXS) study. Blends of two PVF 2 samples (KF, HH defect = 3.5 mol% and KY, HH defect = 5.3 mol%) and two copolymers (Cop-1, Cop-2, HH defect = 15.8 and 21.3 mol%, respectively) were crystallized at 30°C, 120°C and 156°C (130°C for copolymers). From the WAXS results it has been observed that both the KF/KY PVF 2 and Cop-1/Cop-2 blends cocrystallize at all the temperatures in the α and β phases, respectively. However, in the KF/Cop-1 or in the KY/Cop-1 blends cocrystallization is not found for all the compositions of the blends. In PVF 2 rich compositions α phase cocrystals were found and in Cop-1 rich compositions both α and β polymorphs were found. The latter results indicate the absence of cocrystallization at the Cop-1 rich compositions for both the systems. The results support the theoretical prediction of crossover point composition from α to β phases, particularly for systems where cocrystallization is occurring. The spacing d hkl increases with HH defect for both the phases at all temperatures, but the rate of its increase with HH defect is maximum for crystallization at 120°C. Further the rate of increase of d hkl with HH defect is more for β phase than that for α phase and has been attributed to the more compact nature of β unit cell. The lattice parameters for zero% HH defect PVF 2 measured from the least square intercept of d hkl vs HH plots are somewhat higher than the values predicted from the theoretical calculations by Farmer et al.

Cocrystallization of poly(vinylidene fluoride) and vinylidene fluoride-tetrafluoroethylene copolymers: 2. Thermodynamic study

The phase diagrams of poly(vinylidene fluoride) (PVF 2; KF and KY) and vinylidene fluoride-tetrafluoroethylene (VF 2–VF 4) copolymers (Cop-1, Cop-2) have been reported. They are the KF/KY, Cop-1/Cop-2, KF/Cop-1 and KY/Cop-1 systems. The head to head (H-H) defect structures of KF, KY, Cop-1 and Cop-2 are 3.5, 5.3, 15.8 and 21.3 mol%, respectively. The KF/KY and Cop-1/Cop-2 blends exhibit linear variation of apparent melting points with composition but the KF/Cop-1 and KY/Cop-1 blends show a bifurcation of melting point-composition diagram at the Cop-1 rich regions. The crystallization temperature ( T c)-composition plots are linear except for the KF/Cop-1 system. The anomaly of the KY/Cop-1 system in this regard has been explained. The equilibrium melting points ( T m 0) of the blends were determined using the Hoffman-Weeks procedure. The KF/KY blends show a slightly concave upward T m 0 vs. composition curve indicating weak interaction of the components. The Cop-1/Cop-2 blends exhibit a linear plot over the same composition due to ideal mixing. Both the KF/Cop-1 and KY/Cop-1 blends exhibit a concave upward curve with some concave downward portion for the T m 0 vs. composition plots at the Cop-1 rich regions. Further, at the Cop-1 rich regions ( W Cop-1 = 0.75), three melting peaks of isothermally crystallized KF/Cop-1 and KY/Cop-1 blends were observed when melted from the T c s. Liquid-liquid phase separation in the melt for the KF/Cop-1 and KY/Cop-1 systems at Cop-1 rich compositions has been attributed to the different behaviour rather than observed from the other pairs. The cocrystallization of this system is complicated by both the crystalline phase segregation and the liquid-liquid phase segregation.

Cocrystallization of poly(vinylidene fluoride) and vinylidene fluoride—tetrafluoroethylene copolymers: 1. Effect of chain structure and crystallization conditions

Poly(vinylidene fluoride) and vinylidene fluoride-tetrafluoroethylene copolymers cocrystallize depending on the structures present in each. In the α-phase, the maximum difference in the defect concentration of the two polymers (Δ defect) equals 12.3% during isothermal crystallization, and is equal to 10.5% when the system is quenched. In the β-phase, it is 11.8% for isothermal crystallization, and ∼5.5% when quenched. Apart from isomorphic cocrystallization between components of the same polymorph, cocrystal formation between the α- and β-polymorphs was also observed. The resulting cocrystal adopts the structure of a particular polymorph, according to the results obtained from potential energy calculations. The interplanar spacings ( d hkl ) of the α-phase of PVF 2 do not change with the H—H defect concentration, but for the β-phase d 200 increases with the defect concentration. The reason for this difference in behaviour has been attributed to the more compact nature of the β-polymorph unit cell, when compared to that of the α-polymorph. The limiting value of the Δ defect for cocrystallization in the α-phase has been attributed to the larger difference in the intramolecular potential energy, whereas that of the β-phase has been attributed to the compact nature of the unit cell.

ＰＶＤＦ／ＩｎＳｅおよびＰ（ＶＤＦ・ＴＦＥ）／ＩｎＳｅ接合系の電気特性

Indium monoselenide (InSe) is a layer structure semiconductor, with interlayer bonding by van der Waals' force, and because of the small number of dangling bonds at layer cleavage planes. InSe is well suited to forming junction systems with different substances. Polyvinylidene-fluoride (PVDF) and vinylidene fluoride-tetrafluoroethylene copolymer [P(VDF·TFE)=β PVDF type], on the other hand, readily form ferroelectric thin films. The PVDF polarized in to flying clusters in the vacuum vapor deposition atmosphere, so that the probability of sticking differs depending on the kind of substrate. InSe single crystals prepared by the synthesis solute diffusion (SSD) method had n-type electric conduction, electric conductivity σ of 3.1×10-1S/cm, Hall mobillity μ of 200cm2/v·s, and a band gap of 1.1eV at room temperature. Thin films of PVDF were formed by vacuum vapor deposition on the InSe cleavage layer planes. The equivalent circuit of the PVDF/InSe junction system obtained was a parallel circuit consisting of a resistance and a condenser, and differences were observed in the capacity-voltage curve for the junction system due to polarization, according to whether the PVDF was α or β. The change in this curve becomes greater as the dielectric constant of the PVDF increases. In the PVDF/InSe junction system, a variation of the space-charge density were dependent on polarization voltage and molecule structure of the PVDF.

Structural changes in ferroelectric phase transitions of vinylidene fluoride-tetrafluoroethylene copolymers: 2. Normal-modes analysis of the infra-red and Raman spectra at room temperature

Normal-modes calculation was made for a series of model polymer chains of vinylidene fluoride-tetrafluoroethylene (VDF-TFE) copolymers so as to interpret the systematic variation in the i.r. and Raman spectra. The model chains are alternating copolymers of [-(VDF) m (TFE) n -] with m n = ∞ 0 , 8 2 , 5 5 , 2 ∞ and 0 ∞ . Utilizing the normal-modes frequencies and the corresponding eigenvectors calculated for these model chains, the frequency-phase difference dispersion curves and the density of state (or the frequency distribution function) were constructed. Based on these results, the assignments of the intrinsic bands of the VDF sequence, TFE sequence and VDF-TFE boundary were made and the changes in the i.r. and Raman spectra observed at room temperature were interpreted.

Structural changes in ferroelectric phase transitions of vinylidene fluoride-tetrafluoroethylene copolymers: 1. Vinylidene fluoride content dependence of the transition behaviour

Structural changes occurring in the ferroelectric phase transitions of vinylidene fluoride-tetrafluoroethylene (VDF-TFE) copolymers with VDF contents of 81-0 mol% have been investigated by X-ray diffraction and i.r. and Raman spectroscopies. In a VDF 81%-TFE sample, the conformational change between the trans (low temperature) and gauche (high temperature) phases occurs in the temperature region close to the melting point with thermal hysteresis. The VDF 75%-TFE sample shows a similar transition between the low and high temperature phases but via the disordered cooled phase: the behaviour is close to that observed for vinylidene fluoride-trifluoroethylene (VDF-TrFE) copolymer with VDF 65 mol%. As the VDF content decreases, the transition becomes more diffuse: for the VDF 64%-TFE sample the trans-gauche conformational change occurs gradually over a wide temperature region with almost no detectable hysteresis. The X-ray fibre diagram taken at room temperature is of the cooled phase, which reversibly transfers into the low temperature phase by the application of tensile force. The same phenomenon is observed for VDF-TrFE copolymer with VDF 37%. In this way the transition behaviour of VDF-TFE copolymers with VDF contents of 60–80% corresponds to that of VDF-TrFE copolymers with lower VDF content. As the VDF content decreases, the low temperature phase is stabilized more due to the effect of the TFE monomeric units. The as-drawn VDF 41%-TFE sample shows an X-ray fibre pattern characteristic of the low temperature phase, which transforms irreversibly to the cooled phase by heating above 110°C. Tensile force causes the transition to the original low temperature phase irreversibly. VDF 23%-TFE sample exists in the stable ‘untilted’ all- trans chain conformation above room temperature. Below −40°C, the X-ray fibre diagram changes into an overlap of the patterns of the poly (vinylidene fluoride) planar zigzag structure and of the poly(tetrafluoroethylene) helical structure. The transitional behaviour has been discussed in comparison with that of VDF-TrFE copolymers and the factors governing these structural phase transitions have been investigated.