Crystal phase transition dependence of the energy storage performance of poly(vinylidene fluoride) and poly(vinylidene fluoride‐hexafluoropropene) copolymers

Large‐scale mechanical stretching has been performed to modify the crystal phase structures of the pristine poly(vinylidene fluoride) (PVDF) and its copolymer poly(vinylidene fluoride‐hexafluoropropylene) [P(VDF‐HFP)] with various molar contents HFP in an attempt to improve their energy storage performances. It is found that the physical stretched PVDF and P(VDF‐HFP) 95.5/4.5 mol % films have a phase transition from the nopolar α‐phase to highly polar β‐phase, which is different from the P(VDF‐HFP) films with relative high HFP molar contents (α to γ phases). The following results show that the phase transition in these PVDF‐based polymers has a significant effect on their dielectric and energy storage performances. On account of the reformation of the crystalline property and elimination of the impurity defects, an ultra‐high breakdown electric field of ∼900 MV/m has been obtained in all the stretched samples. Consequently, the higher discharged energy densities of 27.1 and 27.7 J/cm³ are calculated from the D–E loops of the β‐PVDF and β‐P(VDF‐HFP) 95.5/4.5 mol % films, respectively. Regarding their excellent discharging energy density of ∼10 J/cm³ under 600 MV/m for thousands of times, the stretched PVDF and its copolymer P(VDF‐HFP)s are promising candidates for high power capacitors applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46306.     

Ferroelectric nanodot formation from spin‐coated poly(vinylidene fluoride‐co‐trifluoroethylene) films and their application to organic solar cells

We demonstrated a facile route to the preparation of self‐assembled poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐TrFE)] nanodots from spin‐coated thin films. We found that the initial film thickness would play an important role in the formation of such P(VDF‐TrFE) nanodots. Interestingly, the electric dipoles of such nanodots were self‐aligned toward the bottom electrode and their ferroelectric properties were determined by using piezoresponse force microscopy. In addition, the self‐polarized ferroelectric nanostructures were introduced to small molecular organic photovoltaic devices and allowed for enhancing the short circuit current density (J_sc) from 9.4 mA/cm² to 10.2 mA/cm² and the power conversion efficiency from 2.37% to 2.65%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41230.     

Lewis acid–base property of P(VDF‐co‐HFP) measured by inverse gas chromatography

Poly (vinylidene fluoride‐co‐hexafluoropropylene) P(VDF‐co‐HFP) is an excellent material for polymer electrolytes of lithium ion battery. To enhance the lithium ion transference number, some metal oxides were often embedded into P(VDF‐co‐HFP). The promising mechanism for the increase in lithium ionic conductivity was Lewis acid‐base theory. In this experiment, the Lewis acid–base properties of P(VDF‐co‐HFP) were measured by inverse gas chromatography (IGC). The Lewis acid constant K_a of P(VDF‐co‐HFP) is 0.254, and the base constant K_b is 1.199. Compared with other polymers characterized by IGC, P(VDF‐co‐HFP) is the strongest Lewis basic polymers. Except aluminum ion, lithium ion is the strongest Lewis acidic ion according to their η value of Lewis acids. Therefore, a strong Lewis acid–base interaction will exist between lithium ion and P(VDF‐co‐HFP). This will restrict the transference of lithium ion in P(VDF‐co‐HFP). To enhance the lithium ion transference by blending other metal ions into P(VDF‐co‐HFP), it is suggested that the preferential ions should be Al³⁺, Mg²⁺, Na⁺, and Ca²⁺ because these metal ions have relative large η values. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and performance study on P(St‐MMA)‐SiO2 doped P(VDF‐HFP) based composite polymer electrolyte

The organic–inorganic hybrid material poly(styrene‐methyl methacrylate)‐silica (P(St‐MMA )‐SiO₂) was successfully prepared by in situ polymerization confirmed by Fourier transform infrared spectroscopy and was employed to fabricate poly(vinylidene fluoride‐hexafluoropropylene) (P(VDF‐HFP )) based composite polymer electrolyte (CPE ) membrane. Desirable CPEs can be obtained by immersing the CPE membranes into 1.0 mol L^?1 LiPF₆‐EC /DMC /EMC (LiPF₆ ethylene carbonate + dimethyl carbonate + ethylmethyl carbonate) liquid electrolyte for about 0.5 h for activation. The corresponding physicochemical properties were characterized by SEM , XRD , electrochemical impedance spectroscopy and charge–discharge cycle testing measurements. The results indicate that the as‐prepared CPEs have excellent properties when the mass ratio of the hybrid P(St‐MMA )‐SiO ₂ particles to polymer matrix P(VDF‐HFP ) reaches 1:10, at which point the SEM analyses show that the as‐prepared P(St‐MMA )‐SiO ₂ particles are uniformly dispersed in the membrane and the CPE membrane presents a homogeneous surface with abundant interconnected micropores. The XRD results show that there may exist interaction forces between the P(St‐MMA )‐SiO ₂ particles and the polymer matrix, which can obviously decrease the crystallinity of the composite membrane. Moreover, the ionic conductivity at room temperature and the electrochemical working window of the CPE membrane can reach 3.146 mS cm^?1 and 4.7 V, respectively. The assembled LiCoO₂/CPE /Li coin cell with the CPE presents excellent charge–discharge and C ‐rate performance, which indicates that P(St‐MMA )‐SiO ₂ hybrid material is a promising additive for the P(VDF‐HFP ) based CPE of the lithium ion battery. © 2016 Society of Chemical Industry     

Facile preparation of ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) thick films by solution casting

We investigated the effects of annealing temperature and vacuum treatment on the crystallinity and ferroelectric properties of solution‐casted poly(vinylidenefluoride‐co‐trifluoroethylene), P(VDF‐TrFE), thick films. We varied the annealing temperature from 70°C to 150°C and achieved high‐quality ferroelectric thick films annealed at 130°C. Ferroelectric domains and their properties were confirmed using X‐ray diffraction, Fourier transform infrared spectroscopy with attenuated total reflection mode and ferroelectric/piezoelectric measurement systems. Drying and/or annealing in the vacuum allowed for the improvement of crystallinity and ferroelectric/piezoelectric properties. Importantly, the piezoelectric coefficient, d₃₃, of our optimal P(VDF‐TrFE) films after sufficient poling treatment was 36 pC/N and our P(VDF‐TrFE) power generator produced an output voltage of ～6 V under periodic bending and unbending motions. POLYM. ENG. SCI., 54:466–471, 2014. © 2013 Society of Plastics Engineers     

Electrical energy discharging performance of poly(vinylidene fluoride‐co‐trifluoroethylene) by tuning its ferroelectric relaxation with polymethyl methacrylate

Poly(methyl methacrylate) (PMMA) was introduced into ferroelectric Poly(vinylidene fluoride‐co‐trifluoroethylene) P(VDF‐co‐TrFE) via a simple solution blending process and a series of P(VDF‐co‐TrFE)/PMMA blends with varied PMMA content was obtained in an effort to investigate the confinement effect of PMMA on the crystalline, dielectric, and electric energy storage properties of P(VDF‐co‐TrFE). PMMA addition could reduce the crystallinity dramatically as well as the crystal size due to its dilution effect and impediment effect on the crystallization of P(VDF‐co‐TrFE). PMMA introduction is also responsible for the phase transition of P(VDF‐co‐TrFE) from α phase into γ phase. As expected, both the dielectric constant and loss of the blends are reduced as PMMA addition increases for the dilute, decoupling, and confinement effect of PMMA on the relaxation behavior of crystal phases of P(VDF‐co‐TrFE) under external electric field. As a result, both the maximum and remnant polarization of the blends are significantly depressed. The irreversible polarization of P(VDF‐co‐TrFE) is effectively restricted by the addition of PMMA due to its impeding effect on the crystallization of P(VDF‐co‐TrFE) and restricting effect on the switch of the polar crystal domains. Therefore, the energy loss induced by the ferroelectric relaxation of P(VDF‐co‐TrFE) is significantly reduced to less than 25% at an electric field of 450 MV/m while the energy storage density is well maintained at about 10 J/cm^?3 in the blend with 30 wt % PMMA. The results may help to understand how the ferroelectric relaxation affects the energy loss of ferroelectrics fundamentally and design more desirable materials for high energy storage capacitors. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40114.     

Dielectric relaxation in vinylidene fluoride–hexafluoropropylene copolymers

The molecular mobility in copolymers of vinylidene fluoride–hexafluoropropylene VDF/HFP of 93/7 and 86/14 ratios has been investigated by means of broadband dielectric relaxation spectroscopy (10^?1–10⁷ Hz), differential scanning calorimetry DSC (?100 to 150°C), and of wide angle X‐ray diffraction WAXS. Four relaxation processes and one ferroelectric‐paraelectric phase transition have been detected. The process of the local mobility β‐ (at temperatures below glass transition point) is not affected by chemical composition of the copolymer and the formed structure. Parameters of segmental mobility in the region of glass transition (α_a‐relaxation) depend on the ratio of comonomer with lower kinetic flexibility. α_c‐relaxation is clearly observed only in VDF/HFP 93/7 copolymer, which is characterized by a higher crystallinity and a higher perfection of crystals of α‐ (α_p‐) phase. Diffuse order–disorder relaxor type ferroelectric transition connected with the destruction of the domains in low‐perfect ferroelectric phase in the amorphous regions has been detected for both copolymers. An intensive relaxation process (α‐process) was observed for both copolymers in high‐temperature region. DSC data shows that it falls on the broad temperature region of α‐phase crystals melting. It is considered to be connected with the space charge relaxation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Grafting of 4‐Hydroxybenzenesulfonic Acid onto Commercially Available Poly(VDF‐co‐HFP) Copolymers for the Preparation of Membranes

The grafting of a phenate bearing sulfonate group in solution onto commercially available poly(VDF‐co‐HFP) copolymers, where VDF and HFP stand for vinylidene fluoride and hexafluoropropene, respectively, is presented. This reaction leads to novel fluoropolymers, bearing aryl sulfonic acid side functions, which are fuel cell membrane precursors. A mechanism similar to the grafting of bisphenol onto VDF‐containing copolymers is discussed. First, the sulfonate phenate is modified to give the didecyldimethylammonium bromide sulfonate phenate salt, in order to promote the substitution onto a fluorine atom in VDF unit adjacent to one HFP unit onto a fluorine atom in the copolymer. The substitution of this salt onto the fluorinated copolymer yields low molar percentages of grafted phenate, ranging from 1.8 to 5.1 mol‐%, whereas it reaches values up to 13 mol‐% grafting when the NH₂‐CH₂‐CH₂‐S‐CH₂‐CH₂‐C₆H₄‐SO₃Na amine is used as the grafting agent. NMR characterization is used to monitor the grafting process. The electrochemical properties of the resulting phenate grafted‐poly(VDF‐co‐HFP) copolymer are studied. The theoretical ion exchange capacities are half that of Nafion®. The proton conductivities are also lower than that of Nafion®, although one conductivity measurement reached a value of 5.1 mS cm^–1, showing a non‐negligible conductivity. The water uptake is lower than these noted for a sulfonated amine‐grafted copolymer, and is of the same order as that for Nafion®. Finally, it is shown that these novel materials start to decompose above 200 °C, showing a similar thermostability as that of an amino‐containing aryl sulfonate‐grafted poly(VDF‐co‐HFP) copolymer.     

Fracture phenomena in micro‐ and nano‐layered polycarbonate/poly(vinylidene fluoride‐co‐hexafluoropropylene) films under electric field for high energy density capacitors

The long‐term dielectric lifetime properties of multilayered polycarbonate/poly(vinylidene fluoride‐co‐hexafluoropropylene) [PC/P(VDF‐HFP)] films were measured as a function of the layer thickness. An optimum layer thickness of 160 nm was determined with the longest dielectric lifetime. The morphology of the damaged sites after dielectric breakdown was examined using scanning electron microscope. Acoustic emission detection system was coupled with the dielectric setup to correlate fracture events and dielectric breakdown to thereby elucidate the mechanisms of the enhancements in dielectric lifetime properties. Two types of acoustic signals were always observed during the breakdown process for multilayered films. The high‐amplitude signals were attributed to the formation of breakdown pinholes caused by the primary discharge from top to bottom electrode. The subsequent low‐amplitude signals were attributed to internal discharges that could further damage the film. The total number of acoustic hits, in particular, low‐amplitude hits, increased with decreasing layer thickness, indicating more internal discharges occurred along the layered interface. It was concluded that the breakdown event initiated at a defect initiated “hotspot” formed because of internal pressure buildup. The film was punctured when the pressure buildup inside the film overcame the mechanical strength of the film. More number of PC layers and layer interfaces were desirable to slow down and divert the damage propagation through the film thickness direction. The crazes in P(VDF‐HFP) can, however, easily propagate across PC layers with less than 160 nm layer thickness. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39877.     

Microstructure and properties of novel fluorescent pyrene functionalized PANI/P(VDF‐HFP) blend

We herein report the preparation and properties of the first polymer blend using pyrene functionalized polyaniline (pf‐PANI). The pf‐PANI has been synthesized and its blend has been prepared with the copolymer of vinylidene fluoride and hexafluoropropylene P(VDF‐HFP). The FTIR results reveal intermolecular interaction between the polar amide group of pf‐PANI and the polarized CH₂ group of P(VDF‐HFP). The crystalline phase of PVDF of the copolymer revealed a transformation from α to β crystalline form after blending with pf‐PANI, as found from FTIR and XRD measurements. The calorimetric measurements together with DMA results revealed the blend is partially miscible. The SEM measurements showed that the pf‐PANI has been dispersed uniformly in the P(VDF‐HFP) matrix. The solution photoluminescence spectrum of the pf‐PANI exhibited emission in the purple–blue region and is slightly red shifted for the blend. The possible applications of this flexible fluorescent pf‐PANI/P(VDF‐HFP) has been suggested. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40162.     

Dielectric property,electric breakdown,and discharged energy density of a poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) copolymer with low temperature processing

Different thermal processing methods were used to fabricate the crystalline properties of poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) [P(VDF‐co‐CTFE)] films. We observed that the crystallinity and crystal grain size of the various samples decreased with the quenching temperature. Compared to that of the annealed P(VDF‐co‐CTFE) sample, a higher dielectric constant of 13.9 at a frequency of 100 Hz was obtained in the film with liquid nitrogen quenching because the increasing small crystalline regions were susceptible to the excitation of external electric field. Meanwhile, the breakdown electric strength of the low‐temperature‐quenched film increased to 530 MV/m when the depth of shallow electronic energy level decreased, as depicted by Fröhlich collective electron approximated electric breakdown theory. Moreover, when we introduced the leakage current density curves, the effect of the space charges on the electric displacement was proven. As a result, the discharged energy density of the liquid‐nitrogen‐quenched P(VDF‐co‐CTFE) film was enhanced to 15.32 J/cm³ at an electric field of 530 MV/m; this provided an effective way in addition to chemical modification to achieve a high energy storage ability in this poly(vinylidene fluoride)‐based fluoropolymer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42794.     

Influence of the processing parameters on the electrocaloric effect of poly(vinylidene fluoride–trifluoroethylene) copolymers

The influence of the processing parameters on the electrocaloric effect of a ferroelectric polymer was investigated. A normal ferroelectric poly(vinylidene fluoride–trifluoroethylene) [P(VDF–TrFE)] (55:45 mol %) copolymer was selected and fabricated. The crystallinity, microstructure, mechanical properties, and refrigeration capability of this copolymer were characterized with X‐ray diffraction, scanning electron microscopy, differential scanning calorimetry, and thermogravimetric analysis, respectively. We found that N,N‐dimethylformamide was the most suitable solvent for enhancing the crystallinity of the copolymer film. In combination with the consideration of the effect of the processing parameters on the microstructure of copolymer, a lower spin‐coating temperature and annealing temperature at 140 °C gave the highest crystallinity and uniform microstructure without defects. The highest temperature change was 12.13 °C when the copolymer film was operated at 110 °C under a higher electric field. The direct measurement of the refrigeration was carried out with an IR thermometer. We found that the P(VDF–TrFE) copolymer film had a considerable refrigeration capability, which increased as the applied electric field strength increased before electric breakdown. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44413.     

Strengthening of electromechanical properties for poly(vinylidene fluoride‐trifluoroethylene) films under tailored electric cycling

Copolymers of polyvinylidene fluoride and trifluorethylene [P(VDF‐TrFE)] have potential applications in wearable and implantable electromechanical devices since they are mechanically flexible, and biocompatible. A tailored electric cyclic process is employed to enhance both electrical and mechanical properties in P(VDF‐TrFE) 65/35 mol % copolymer films. The films are subjected to lower and higher field magnitude electric cycling successively. For electrical properties, enhancement in remnant polarization, dielectric and piezoelectric constants occurs. From mechanical point of view, strengthening in the fracture strength happens. Wide‐angle X‐ray diffraction techniques examine changes of the orientation of the molecular chains, grain size, and crystallinity after electric cycling for the copolymer films. Scanning electron microscopy reveals evolutions of the microstructure, including rod‐like textures and fractography of the films. The results indicate that electric cycling causes the molecular chains to orient gradually along the direction perpendicular to the applied electric field. Consequently, an enhancement of 12.2% and 45% is realized for the remnant polarization and fracture strength, respectively for P(VDF‐TrFE) 65/35 copolymer film. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45926.     

Polarization behavior of sol‐gel‐derived relaxor Ba(Zr,Ti)O3 films

Films of the relaxor ferroelectric BaZr_0.25Ti_0.75O₃ (0.25‐BZT) were synthesized via a sol‐gel route to investigate the effect of film thickness on the dielectric properties and for comparison with normal ferroelectric BaTiO₃ (BT). The as‐prepared films on Nb‐doped SrTiO₃ (Nb–ST) displayed a (100) orientation; thinner films had stronger (100) orientations. Microwave dielectric measurements up to a few GHz quantified the polarizations, that is, the dipole contribution, ε_dipole, the combination of the ionic and electronic polarizations, ε_ionic+el., and the total contribution, ε_total. The ε_dipole in the relaxors at a film thickness of t=630 nm was 360, which was double that for the normal ferroelectric BT (ε_dipole=180) at t=735 nm. The larger apparent permittivity of the BZT therefore originated from the larger ε_dipole of the polar nanoregions (PNRs), while the nanograins of BT with few domain walls led to a comparably smaller ε_dipole. The volume ratio of the surface and film‐substrate interface lacking the dipole interactions increased with the reduction in the film thickness, leading to the significant depression in the permittivity for both specimens. The difference in the thickness dependence of the dielectric properties of the sol‐gel derived relaxor BZT and the normal ferroelectric BT films was attributed to the different origins of their dipole contribution, that is, the PNRs and ferroelectric domains, respectively.     

Preparation and properties of alkaline anion exchange membrane with semi‐interpenetrating polymer networks based on poly(vinylidene fluoride‐co‐hexafluoropropylene)

Alkaline anion exchange membrane with semi‐interpenetrating polymer network (s‐IPN) was constituted based upon quaternized poly(butyl acrylate‐co‐vinylbenzyl chloride) (QPBV) and poly(vinylidene fluoride‐co‐hexafluoropropylene) [P(VDF‐HFP)]. The QPBV was synthesized via the free radical copolymerization, followed by quaternization with N‐methylimidazole. The s‐IPN system was constituted by melting blend of QPBV and P(VDF‐HFP), and then crosslinking of P(VDF‐HFP). Ion exchange capacity, water uptake, mechanical performance, and thermal stability of these membranes were characterized. TEM showed that alkaline anion exchange membrane exhibited s‐IPN morphology with microphase separation. The fabricated s‐IPN membrane exhibited hydroxide ion conductivity up to 15 mS cm^?1 at 25 °C and a maximum DMFC power density of 46.55 mW cm^?2 at a load current density of 98 mA cm^?2 at 30 °C. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45775.     

Mesophase Structure‐Enabled Electrostrictive Property in Nylon‐12‐Based Poly(ether‐block‐amide) Copolymers

To search for alternative electrostrictive polymers and to understand the underlying mechanism, the structure‐ferroelectric/electrostrictive property relationship for nylon‐12‐based poly(ether‐b‐amide) multiblock copolymers (PEBAX) is investigated. Two PEBAX samples are studied, namely, P6333 and P7033 with 37 and 25 mol.% of soft poly(tetramethylene oxide) (PTMO) blocks, respectively. In both samples, poorly hydrogen‐bonded mesophase facilitates electric field‐induced ferroelectric switching. Meanwhile, the longitudinal electrostrictive strain (S₁)–electric field (E) loops are obtained at 2 Hz. Different from conventional poly(vinylidene fluoride‐co‐trifluoroethylene) [P(VDF‐TrFE)]‐based terpolymers, uniaxially stretched nylon‐12‐based PEBAX samples exhibit negative S₁, that is, shrinking rather than elongation in the longitudinal direction. This is attributed to the unique conformation transformation of nylon‐12 crystals during ferroelectric switching. Namely, at a zero electric field, crystalline nylon‐12 chains adopt a more or less antiparallel arrangement of amide groups. Upon high‐field poling, ferroelectric domains are enforced with more twisted chains adopting a parallel arrangement of amide groups. Meanwhile, extensional S₁ is observed for P6333 at electric fields above 150 MV m^?1. This is attributed to the elongation of the amorphous phases (i.e., amorphous nylon‐12 and PTMO). Therefore, competition between shrinking S₁ from mesomorphic nylon‐12 crystals (i.e., nanoactuation) and elongational S₁ from amorphous phases determines the ultimate electrostriction behavior in stretched PEBAX films.     

Preparation and photocurrent generation of an electrostatically self‐assembled film of hemicyanine and poly(4‐styrenesulfonic acid‐co‐maleic acid)

In this article, we report on electrostatically self‐assembled thin films prepared by the alternative immersion of quartz‐coated and indium tin oxide coated glass substrates in aqueous solutions of a copolymer of poly(4‐styrenesulfonic acid‐co‐maleic acid) (PSSMA) and a hemicyanine of (E)?1,1′‐(propane‐1,3‐diyl)bis{4‐[4‐(dimethylamino)styryl]pyridinium} bromide (H³Br₂). The films were studied by means of ultraviolet–visible absorption and X‐ray photoelectron spectroscopies, scanning electron microscopy, and photoelectrochemical measurements. When irradiated with white light, the PSSMA/H³ monolayer film gave a stable cathodic photocurrent. The effects of the applied bias voltages, layer numbers of the (PSSMA/H³)_n films (where n stands for the number of bilayer films on both sides of the substrates), light intensities, pH value, and electron acceptor on the photocurrent generation of the (PSSMA/H³)_n film were examined. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39871.     

Crystallographic Orientation Dependence on Electrical Properties of (Bi,Na)TiO3‐based Thin Films

Orientation‐engineered (La, Ce) cosubstituted 0.94(Bi_0.5Na_0.5)TiO₃–0.06BaTiO₃ thin films were epitaxially deposited on CaRuO₃ buffered (LaAlO₃)_0.3(Sr₂AlTaO₆)_0.35 single‐crystal substrates by pulsed laser deposition. The ferroelectric, piezoelectric, dielectric, and leakage current characteristics of the thin films were significantly affected by the crystallographic orientation. We found that the (001)‐oriented film exhibited the best ferroelectric properties with remnant polarization P_r = 29.5 μC/cm² and coercive field E_c = 7.4 kV/mm, whereas the (111)‐oriented film demonstrated the largest piezoelectric response and dielectric permittivity. The bipolar resistive switching behavior, which is predominantly attributed to a combined effect of ferroelectric switching and formation/rupture of conductive filaments, was observed. The conduction mechanisms were determined to be ohmic conduction and Poole–Frenkel emission at high‐ and low‐resistance states, respectively, in all the films.     

Facile patterning and transfer printing of ferroelectric P (VDF‐TrFE) microstructures by topographic dewetting and Rayleigh‐Plateau instability

Facile microscale patterning of ferroelectric P(VDF‐TrFE) thin films are presented. Simple spin‐coating of the polymer solution on a patterned stamp has led to a variety of features due to the topographic dewetting. The effects of important experimental parameters, such as polymer solution concentration, spin speed, and stamp geometry, are systematically examined and the results are presented as morphological phase diagrams. Further, the dewetted cylindrical lines on the stamp protrusions are found to undergo Rayleigh‐Plateau instability, which leads to the break‐up of lines into dots in a row. The various pattern features formed on structured stamp has then been successfully transfer‐printed onto various substrates such as Si, glass, polymers. The P(VDF‐TrFE) micropatterns have shown more uniform ferroelectric performances than those of unpatterned film, due likely to confinement effect. The proposed simple patterning and transfer‐printing of ferroelectric polymer thin films can be found very useful in various emerging applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45028.     

A study on thermal behavior of a poly(VDF‐CTFE) copolymers binder for high energy materials

This article describes a study on thermal behavior of poly(vinylidene fluoride‐chlorotrifluoroetheylene) [poly(VDF‐CTFE)] copolymers as polymeric binders of specific interest for high energy materials (HEMs) composites by thermal analytical techniques. The non‐isothermal thermogravimetry (TG) for poly (VDF‐CTFE) copolymers was recorded in air and N₂ atmospheres. The results of TG thermograms show that poly(VDF‐CTFE) copolymers get degrade at lower temperature when in air than in N₂ atmosphere. In the derivative curve, there was single maximum degradation peak (T_max) indicating one‐stage degradation of poly(VDF‐CTFE) copolymers for all the samples. The other thermal properties such as glass transition temperature (T_g) and degradation temperature (T_d) for poly(VDF‐CTFE) copolymers were measured by employing differential scanning calorimeter (DSC) technique. The kinetic parameters related to thermal degradation of poly(VDF‐CTFE) copolymers were investigated through non‐isothermal Kissinger kinetic method using DSC method. The activation energies for thermal degradation of poly(VDF‐CTFE) copolymers were found in a range of 218–278 kJ/mol. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013