Modification of the structure and properties of poly(vinylidene fluoride–trifluoroethylene) 56/44 mol % copolymer by a proton‐irradiation treatment

The effects of high‐energy proton irradiation on the structure and properties of 56/44 mol % poly(vinylidene fluoride–trifluoroethylene) copolymer were studied with differential scanning calorimetry (DSC), X‐ray diffraction (XRD), relative permittivity, and polarization hysteresis measurements. Copolymer films prepared by hot compression molding were irradiated with a broad range of proton dosages (10–107 Mrad) at room temperature. The DSC results showed that the ferroelectric transition was strongly affected by the proton dosages. The XRD data indicated the reduction of polar ordering in the copolymer by the proton‐irradiation treatment. From the relative permittivity and polarization behavior, the copolymer film was found to be converted from a normal ferroelectric material to a relaxor ferroelectric material as the proton dosage was increased to 50 Mrad. The electrostrictive coefficient of the 56/44 mol % copolymer was enhanced after irradiation, and the optimized proton dosage for attaining the highest electrostrictive strain response was determined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2334–2339, 2005     

Experimental characterization of the volume strain of poly(vinylidene fluoride) in the region of homogeneous plastic deformation

Damage to poly(vinylidene fluoride) was studied under uniaxial tension testing at different temperatures and strain rates. A satisfactory accuracy was reached with an original procedure for the assessment of the principal strains and volume strain. The semicrystalline polymer exhibited an increase in the volume strain with the true axial strain caused by material damage. This damage depended on the temperature and strain rate and was related to the whitening phenomenon generally observed. The use of the general ideas of Bucknall's model, based on the decomposition of the whole volume strain into three components, allowed the extraction of the component of the volume strain corresponding to microstructural mechanisms of plastic deformation other than shearing. Therefore, nucleation and growth stages of cavitation were revealed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2516–2522, 2002     

聚偏氟乙烯的辐射交联及其交联度的XPS表征

本文首次用XPS研究了聚偏氟乙烯的辐射交联机理,交联度的XPS表征。计算出聚偏氟乙烯的β值为0.7,发现聚偏氟乙烯的辐射交联的溶胶分数与辐照剂量的关系符合我们提出的通式^[1]。用XPS方法求得聚偏氟乙烯的凝胶化剂量为1.59mrad。     

Enhanced electrostriction based on plasticized relaxor ferroelectric P(VDF‐TrFE‐CFE/CTFE) blends

The purpose of this work aims at enhancing the electrostrictive strain response and the mechanical energy density under moderate electric field, which is essential for actuator applications. For achieving this, plasticized effects as well as the influence of chlorofluoroethylene and chlorotrifluoroethylene defects on the electromechanical behavior of the copolymer matrix poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) are investigated. Experimental results showed that the plasticized terpolymer‐based CFE presented better electrical and mechanical performances than the CTFE one. Furthermore, such interesting properties exhibited superior advantages when CFE was combined with (DEHP) plasticizer, resulting in excellent electrostrictive strain response as well as mechanical energy density. Another aspect of this work reports on the influence of the composition, especially the CTFE content, on the electromechanical properties of the neat and plasticized P(VDF‐TrFE‐CTFE). This enables the determination of the desired terpolymer compositions for given applications, which are based on different criteria, such as crystallinity, elastic modulus, dielectric permittivity, and so forth. All the results demonstrated a possibility to realize high performance electroactive polymer actuators while achieving significant improved strain response and energy density under relatively low electric field. Such an investigation allows overcoming the current technological barrier of conventional electroactive polymers that suffer from the high applied electric field usually required to reach sufficient strain. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1368–1379     

High field electrostrictive response of polymers

It is well known that electrostrictive strains are proportional to the square of the applied electric field. It therefore appeared reasonable to assume that for some polymeric materials, a large acoustic thickness response, d_T, \[ \left( {d_T = \frac{{dS}}{{dE}}} \right) \] might be obtained by application of high dc bias fields, ～ 20 MV/m, to a film while driving the film with an ac signal to access the high slope region of the electrostrictive strain vs. applied field curve. Previous studies of crystallizing poly(vinylidene fluoride) (PVF₂) from solution under high electric fields have demonstrated that gel-like samples of PVF₂ with high content of the plasticizer tricresyl phosphate (TCP) could be subjected to electric fields as high as ～ 100 MV/m. Using this type of heavily plasticized PVF₂ d_T values ～ 4 Å/V were obtained. Values of 9 Å/V were obtained for a certain class of thermoplastic elastomer (i.e., a polyurethane). These d_T values are considerably greater than those obtained from conventional piezoelectric ceramic materials. In addition, large elastic strains (> 3%) were observed as a function of applied dc field. © 1994 John Wiley & Sons, Inc.     

Effect of X-ray radiation on the structure of P (VDF/TrFE) copolymers

Structural changes in poly(vinylidene fluoride)-trifluoroethylene [P(VDF-TrFE)] copolymers caused by X-ray irradiation were investigated by molecular weight determination, EPR analysis, FTIR spectroscopy, gel content, DSC thermal analysis, X-ray diffraction, and piezoelectricity measurements. Samples exhibit radiation-induced conductivity (RIC) due to the formation of radical ions. These radicals are generated by bond cleavage, which could react, leading to structural changes such as oxidation, double bond formation, chain scission, and crosslinking. The increasing gel content with radiation dose indicated that crosslinkings of the polymer chains predominate. Irradiation on P(VDF-TrFE) caused the melting temperature, heat of fusion, and Curie temperature to decrease. These results are consistent with the partial destruction of crystalline domains. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1201–1205, 1997     

Effect of the initial matrix material on the structure of radiation‐grafted ion‐exchange membranes: Wide‐angle and small‐angle X‐ray scattering studies

Seven different fluoropolymer films were used as matrix materials for radiation‐grafted ion‐exchange membranes. The crystallinity and preferred orientation of these membranes were studied with wide‐angle X‐ray scattering, and the lamellar structure of the membranes was examined with small‐angle X‐ray scattering. The crystallinity of poly(vinylidene fluoride) (PVDF)‐based matrix materials varied between 57 and 40%, and the crystallinity of the sulfonated samples varied between 34 and 23%. The lamellar periods of PVDF‐based matrix materials were about 115 Å, and the lamellar periods of poly(ethylene‐alt‐tetrafluoroethylene) and poly(tetrafluoroethylene‐co‐hexafluoropropylene) were 250 and 212 Å, respectively. When the samples were grafted, the lamellar periods increased. Correlation function analysis showed very clearly that the long‐range order decreased because of grafting and sulfonation processes. For those samples that showed good proton conductivity, the lamellar period also increased because of sulfonation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1539–1555, 2002     

Poly(vinylidene fluoride)/clay nanocomposites prepared by melt intercalation: Crystallization and dynamic mechanical behavior studies

The preparation and properties of poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported for the first time. PVDF/clay nanocomposites were prepared by melt intercalation with organophilic clay. The composites were characterized with X‐ray diffraction, differential scanning calorimetry, and dynamic mechanical analysis. X‐ray diffraction results indicated intercalation of the polymer into the interlayer spacing. PVDF in the nanocomposites crystallized in the β form. Differential scanning calorimetry nonisothermal curves showed an increase in the melting and crystallization temperatures along with a decrease in crystallinity, as evidenced by the melting and crystallization peaks. Isothermal crystallization studies showed an enhanced rate of crystallization with the addition of clay, as evidenced by a reduction in the crystallization time. Dynamic mechanical analysis indicated significant improvements in the storage modulus over a temperature range of ?100 to 150 °C. The tan δ peak signifying the glass‐transition temperature of PVDF shifted to higher temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1682–1689, 2002     

Synthesis and characterization of grafted/crosslinked proton conducting membranes based on amphiphilic PVDF copolymer

A novel graft copolymer consisting of a poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) backbone and poly(glycidyl methacrylate) side chains, that is, P(VDF‐co‐CTFE)‐g‐PGMA, was synthesized through atom transfer radical polymerization (ATRP) using CTFE units as a macroinitiator. Successful synthesis and microphase‐separated structure of the polymer were confirmed by ¹H NMR, FTIR spectroscopy, and TEM. As‐synthesized P(VDF‐co‐CTFE)‐g‐PGMA copolymer was sulfonated by sodium bisulfite, followed by thermal crosslinking with sulfosuccinic acid (SA) via the esterification to produce grafted/crosslinked polymer electrolyte membranes. The IEC values continuously increased with increasing SA content but water uptake increased with SA content up to 10 wt %, above which it decreased again as a result of competitive effect between crosslinking and hydrophilicity of membranes. At 20 wt % of SA content, the proton conductivity reached 0.057 and 0.11 S/cm at 20 and 80 °C, respectively. The grafted/crosslinked P(VDF‐co‐CTFE)‐g‐PGMA/SA membranes exhibited good mechanical properties (>400 MPa of Young's modulus) and high thermal stability (up to 300 °C), as determined by a universal testing machine (UTM) and TGA, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1110–1117, 2010     

Intercalated poly(vinylidene fluoride)/clay nanocomposites: Structure and properties

The preparation and characterization of melt‐intercalated poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported. Organophilic clay (clay treated with dimethyl dihydrogenated tallow quaternary ammonium chloride) was used for the nanocomposite preparation. The composites were characterized with X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). XRD results indicated the intercalation of the polymer in the interlayer spacing. The incorporation of clay in PVDF resulted in the β form of PVDF. DSC nonisothermal curves showed an increase in the melting and crystallization temperatures along with a decrease in crystallinity. Isothermal crystallization studies show an enhanced rate of crystallization with the addition of clay. DMA indicated significant improvements in the storage modulus over a temperature range of ?100 to 150 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 31–38, 2003     

Effects of organophilic clay on the solvent‐maintaining capability,dimensional stability,and electrochemical properties of gel poly(vinylidene fluoride) nanocomposite electrolytes

Four quaternary alkyl ammonium salts were used in an organophilic procedure, performed on montmorillonite clay, and resulted in intercalation in dimethylformamide (DMF) or ethylene carbonate (EC)/propylene carbonate (PC) as a cosolvent between poly(vinylidene fluoride) (PVdF) and the organophilic clay. An examination using X‐ray diffraction revealed that PVdF entered galleries of montmorillonite clay, and it exhibited exfoliation and intercalation phenomena when it was analyzed with transmission electron microscopy. Gel PVdF nanocomposite electrolyte materials were successfully prepared by the addition of the appropriate percentages of DMF or PC/EC as a cosolvent, organophilic clay, and lithium perchlorate to PVdF. The maximum ionic conductivity was 1.03 × 10^?2 S/cm, and the materials exhibited better film formation, solvent‐maintaining capability, and dimensional stability than electrolyte films without added organophilic clays. The results of cyclic voltammetry testing showed that the addition of the organophilic clays significantly enhanced the electrochemical stability of the polymer electrolyte system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3873–3882, 2002     

Time‐resolved wide‐angle X‐ray scattering measurements during the isothermal crystallization and ferroelectric phase‐transition processes of a vinylidene fluoride/trifluoroethylene copolymer

The time‐resolved measurement of wide‐angle X‐ray scattering was performed with a synchrotron radiation source during the processes of the isothermal crystallization and ferroelectric phase transition of a vinylidene fluoride/trifluoroethylene copolymer with 73 mol % vinylidene fluoride. When the sample was cooled rapidly from the melt to the temperature region of the paraelectric high‐temperature phase, the peak position of the 200/110 reflection shifted toward the higher angle side and the half‐width became narrower. This indicated an increase in the crystallite size with a more compact chain‐packing mode. Even when the temperature jump was made from the melt into the region of the ferroelectric or low‐temperature phase, the crystallization of the high‐temperature phase was first observed before the appearance of the low‐temperature phase. This was consistent with a prediction based on the so‐called Ostwald state rule: the thermodynamically unstable but kinetically preferable high‐temperature phase can appear first even when the thermodynamically more stable low‐temperature phase should be created. The time‐dependent intensity changes were analyzed with the Avrami kinetic equation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4175–4181, 2004     

Original crosslinking of poly(vinylidene fluoride) via trialkoxysilane‐containing cure‐site monomers

The synthesis of fluorinated monomers bearing an ω‐trialkoxysilane function (4,5,5‐trifluoropent‐4‐ene‐1‐trimethoxysilane and 4,5,5‐trifluoropent‐4‐ene‐1‐triethoxysilane), their radical copolymerization with vinylidene fluoride (VDF), and the crosslinking of resulting copolymers are presented. The silicon‐containing fluoromonomers were prepared from a three step‐reaction from ClCF₂CFClI, last step being the hydrosilylation of 1,1,2‐trifluoro‐1,4‐pentadiene with trialkoxysilane. The copolymerizations of these silicon‐containing fluoromonomers with VDF led to original PVDF bearing pendant trialkoxysilane functions. Their microstructures, characterized by NMR showed that VDF was the more incorporated. These latter ones were crosslinked in the presence of moisture at 200 °C leading to insoluble materials stable in solvents, oils, water, and to acids. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3896–3910, 2006     

Well‐defined copolymers based on poly(vinylidene fluoride): From preparation and phase separation to application

Poly(vinylidene fluoride) (PVDF) has reached the second largest production volume of fluoropolymers in recent years, and its popularity can be ascribed to high thermal stability and chemical inertness combined with its ferroelectric behavior. Copolymerization of vinylidene fluoride with other monomers leads to a wide variety of products with modified or improved properties. Besides commercially available fluorinated random copolymers, well‐defined block‐, graft, and alternating copolymers based on PVDF received more attention in recent years. PVDF‐containing block copolymers that may self‐assemble into well‐ordered morphologies are of particular interest, being potential precursors for functional nanostructured materials applicable in membranes and electronics. This Highlight provides an overview of the routes developed towards these materials via conventional and controlled polymerization techniques. In addition, it discusses their nanoscopic phase behavior and current and potential applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2861–2877     

Crosslinked P(VDF‐CTFE)/PS‐COOH nanocomposites for high‐energy‐density capacitor application

High‐capacity or high‐power‐density capacitors are being actively investigated for portable electronics, electric vehicles, and electric power systems. The dielectric nanocomposite with a small loading of carboxylic polystyrene (PS‐COOH) nanoparticles in poly(vinylidene fluoride‐chlorotrifluoroethylene) [P(VDF‐CTFE)] matrix, followed by chemical crosslinking has been described. Combination of these two methods significantly improved the capacity of electric energy storage at low electric field. Specially, the nanocomposite with 2 wt % nanoparticles and 15 wt % crosslinking agent achieved a dielectric constant of 17.2 and a discharged energy density of 17.5 J/cm³ (4.9 Wh/L) at an electric field as high as 324 MV/m, while corresponding values for pristine P(VDF‐CTFE) are 9.6 and 13.3 J/cm³ (3.7 Wh/L), respectively. Fundamental physics underlying the enhancement in the performance of the nanocomposites with respect to P(VDF‐CTFE) is illustrated by solid‐state ¹⁹F nuclear magnetic resonance of direct excitation or ¹⁹F{¹H} cross polarization. It revealed different dynamics behavior between crystalline/amorphous regions, and PS‐COOH nanoparticles favored the formation of polar γ‐form crystals. Small‐angle X‐ray scattering studies revealed the contribution of the interface to the extraordinary storage of electric energies in the nanocomposites. This approach provided a facile and straightforward way to design or understand PVDF‐based polymers for their practical applications in high‐energy‐density capacitors. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1160–1169     

Characterization of the network properties of poly(ethylene glycol)–acrylate hydrogels prepared by variations in the ethanol–water solvent composition during crosslinking copolymerization

The characteristics of poly(ethylene glycol) (PEG)–acrylate hydrogel networks were investigated as a function of the ethanol–water solvent composition during free‐radical crosslinking copolymerization. Macromonomer (88% ω‐methoxy‐PEG–acrylate and 10% ω‐phenoxy‐PEG–acrylate) and crosslinker (2% PEG–diacrylate) concentrations were kept constant. As the copolymerization progressed, the polymer solution in 100% ethanol became increasingly turbid, indicating the development of a heterogeneous network structure. In 100% water, however, the initially turbid polymer solution became increasingly transparent as the crosslinking copolymerization progressed. All the gels were optically clear upon equilibration in water. Kinetic studies, with attenuated total reflectance‐infrared, showed a long induction period, along with a lowered reaction rate, in 100% ethanol, and a decrease in conversion with an increase in ethanol content. These results agree with the UV analysis of the sol fractions, which indicated an increase in the amounts of unreacted PEG–acrylates with an increase in the ethanol content. The gels which were formed with a high ethanol concentration exhibited lower Young's modulus and higher swelling ability, suggesting that the network structure was significantly affected by the solvent composition during free‐radical crosslinking copolymerization. From the stress–strain and swelling experiments, the Flory–Huggins interaction parameter was evaluated. The creep characteristics of the hydrogels were modeled with two Kelvin elements. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2677–2684, 2002     

ESR studies in γ‐irradiated and PS‐radiation‐grafted poly(vinylidene fluoride)

The fluoropolymer poly(vinylidene fluoride) was irradiated with γ rays to induce a polystyrene (PS) radiation grafting via an indirect method. Electron spin resonance and Fourier transform infrared studies were performed to identify the species that initiated the PS grafting. Specific experiments were performed to prove separately the importance of each kind of radical. A localization of the radicals in this irradiated polymer is proposed, and a kinetic model of the grafting is given. © 2001 John Wiley & Sons, Inc. J Polym Sci B Part B: Polym Phys 39: 1437–1448, 2001     

Fluorinated block copolymers containing poly(vinylidene fluoride) or poly(vinylidene fluoride‐co‐hexafluoropropylene) blocks from perfluoropolyethers: Synthesis and thermal properties

PFPE‐b‐PVDF and PFPE‐b‐poly(VDF‐co‐HFP) block copolymers [where PFPE, PVDF, VDF, and HFP represent perfluoropolyether, poly(vinylidene fluoride), vinylidene fluoride (or 1,1‐difluoroethylene), and hexafluoropropylene] were synthesized by radical (co)telomerizations of VDF (or VDF and HFP) with an iodine‐terminated perfluoropolyether (PFPE‐I). Di‐tert‐butyl peroxide (DTBP) was used and was shown to act as an efficient thermal initiator. The numbers of VDF and VDF/HFP base units in the block copolymers were assessed with ¹⁹F NMR spectroscopy. According to the initial [PFPE‐I]₀/[fluoroalkenes]₀ and [DTBP]₀/[fluoroalkenes]₀ molar ratios, fluorinated block copolymers of various molecular weights (1500–30,300) were obtained. The states and thermal properties of these fluorocopolymers were investigated. The compounds containing PVDF blocks with more than 30 VDF units were crystalline, whereas all those containing poly(VDF‐co‐HFP) blocks exhibited amorphous states, whatever the numbers were of the fluorinated base units. All the samples showed negative glass‐transition temperatures higher than that of the starting PFPE. Interestingly, these PFPE‐b‐PVDF and PFPE‐b‐poly(VDF‐co‐HFP) block copolymers exhibited good thermostability. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 160–171, 2003     

Electrospinning of poly(vinylidene fluoride)/dimethylformamide solutions with carbon nanotubes

For conductive carbon nanotube (CN)/polymer composite fibers to be obtained, CNs were incorporated into poly(vinylidene fluoride) (PVDF) in dimethylformamide (DMF) solutions and electrospun to form CN/PVDF fiber mats. The thinnest fiber was 70 nm thick. The percolation threshold for the insulator‐to‐conductor transition was 0.003 wt % CN for CN/PVDF/DMF solutions, 0.015 wt % CN for CN/PVDF spin‐coated films, and 0.04 wt % CN for CN/PVDF electrospun fiber mats. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1572–1577, 2003     

Preparation and characterization of a nanoscale poly(vinyl alcohol) fiber aggregate produced by an electrospinning method

Nanoscale poly(vinyl alcohol) (PVA) fiber (100–500 nm) aggregates were prepared with an electrospinning technique. Additionally, a chemical crosslinking method was used to crosslink the nanoscale PVA fiber aggregates. Differential scanning calorimetry, wide‐angle X‐ray diffraction, and scanning electron microscopy techniques were employed to characterize the PVA fiber aggregates. The different crosslinking densities of the PVA fiber aggregates were obtained through the control of the weight percentage of glyoxal to PVA. The crosslinking densities due to heat treatment and chemical crosslinking were studied. The influence of heat treatment could be neglected in contrast to chemical crosslinking when the curing temperature was 120 °C. The primary factor that affected the crosslinking density was the volume of the chemical crosslinking agent. The results showed that the properly crosslinked PVA fiber aggregates had better antiwater solubility and mechanical properties than the noncrosslinked PVA fiber aggregates. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1261–1268, 2002