Thin poly(ionic liquid) and poly(vinylidene fluoride) blend films with ferro‐ and piezo‐electric polar γ‐crystals

Ferro‐ and piezo‐electric poly(vinylidene fluoride) (PVDF) thin film is reported to be obtained by using a poly(ionic liquid) (PIL) [poly(2‐(dimethylamino)ethyl methacrylate) methyl chloride quaternary salt] through solution route. The short range interactions between localized cationic ions of PIL and polar >CF₂ of PVDF are responsible for modified polar γ‐PVDF (T₃GT₃Ḡ) formation. Modification in chain conformation of PVDF is confirmed by FTIR, XRD, and DSC studies suggesting the miscible PVDF–PIL (PPIL) blend. Up to 40 wt % loading of PIL in PVDF matrix enhances relative intensity of γ‐phase up to 50% in the entire crystalline phase. The P‐E hysteresis loop of PVDF‐PIL blends at 25 wt % PIL loading (PPIL‐25) thin film at sweep voltage of ±50 V shows excellent ferroelectric property with nearly saturated high remnant polarization ∼6.0 µC cm⁻² owing to large proportion of γ‐PVDF. However, non‐polar pure PVDF thin film shows unsaturated hysteresis loop with 1.4 µC cm⁻² remnant polarization. The operation voltage decreases effectively because of the polar γ‐phase formation in PPIL blended film. High‐sensitivity piezo‐response force microscopy shows electromechanical switching property at low voltages in PPIL‐25 thin films through local switching measurements, making them potentially suitable as ferroelectric tunnel barriers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 795–802     

Thin and surface adhesive ferroelectric poly(vinylidene fluoride) films with β phase‐inducing amino modified porous silica nanofillers

We report an efficient route for ferroelectric polar β phase generation in poly(vinylidene fluoride) (PVDF) through incorporation of amine functionalized, porous silica (MCM‐41 and fumed silica) based nanofillers. These porous highly functionalized surfaces exhibit the efficient secondary interaction with polymer chain via hydrogen bonding. Structural analysis through FTIR, XRD, and TEM confirm high degree of ferroelectric polar β phase generation of PVDF through incorporation of amino modified porous silica nanofillers. Optimized loading (5 wt %) of amine functionalized, porous silica in PVDF matrix enhances relative intensity of β phase up to 75%. Disappearance of spherulite structure of PVDF with amino modified porous silica nanofillers, as confirmed through POM, TEM, SEM and AFM studies also supports the above conclusion. The P‐E hysteresis loop at sweep voltage of ±50 V of a thin PVDF‐amino modified porous nanofiller film shows excellent ferroelectric property with nearly saturated high remnant polarization 2.8 µC.cm^?2 owing to its large proportion of β PVDF, whereas, a nonpolar pure PVDF thin film shows unsaturated hysteresis loop with 0.6 µC.cm^?2 remnant polarization. PVDF films with the nanofillers exhibit strong adhesive strength over different metallic substrates making them have edge over PVDF in various thin film applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2401–2411     

Crystal forms and ferroelectric properties of poly(vinylidene fluoride)/polyamide 11 blends prepared by high‐shear processing

Nanostructured poly(vinylidene fluoride) (PVDF)/polyamide 11 (PA11) blends have been melt‐processed using a high‐shear extruder. Uniaxially oriented blended films were fabricated by hot rolling to prepare ferroelectic films. The effects of rolling temperature and draw ratio on the crystal forms of both PVDF and PA 11 were investigated by means of Fourier transform infrared spectra (FTIR) and wide‐angle X‐ray diffraction (WAXD). It was shown that hot rolling in the range of 25–110 °C results in the crystal form transformation from the nonpolar α‐form into the polar β‐form for PVDF. The content and orientation function of β‐crystallites are strongly dependent upon the rolling temperature and the draw ratio. The highest content of well‐oriented β‐crystallites was achieved with a draw ratio of 4.0 upon rolling at 80 °C. At the same time, the content of the α‐form of PA11 in the blend was also found to decrease by hot rolling. The ferroelectric properties (D‐E hysteresis) of the oriented blended films were measured. The remanent polarization of the PVDF/PA11 = 90/10 blend is as high as 91 mC/m², which is about 1.2 times higher than that of pure PVDF. The D‐E hysteresis curves and the temperature dependence of the piezoelectric stress coefficients of the high‐shear‐processed sample suggested that the formation of nano‐dispersed structures resulted in the improvement of the remanent polarization and thermal characteristics at a temperature higher than 80 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2707–2714, 2007     

Synthesis of PVDF/BiFeO3 nanocomposite and observation of enhanced electrical conductivity and low‐loss dielectric permittivity at percolation threshold

A novel two‐phase polymer nanocomposite film comprising of polyvinylidene fluoride (PVDF) and nanocrystalline (～90 nm) semiconducting multiferroic BiFeO₃ (BFO) have been fabricated by hot‐molding technique. Such flexible thick nanocomposite films, semicrystalline in nature, exhibited extraordinarily high effective dielectric permittivity ε_eff ～ 10³ (compared with that of pure PVDF) near the low percolation threshold (f_c = 0.12) at room temperature (RT) and the films also possessed low dielectric loss (～0.18). The polarization‐electric field (P‐E) hysteresis loops are displayed at RT, which indicate ferroelectric like behavior of PVDF still persists in the percolative nanocomposite. There is also large increase of remanent polarization of BFO in the composite indicating improvement of the multiferroic behavior of BFO embedded in the PVDF polymer. The sample also indicates good fatigue endurance. Formation of microcapacitors and percolative behavior are correlated to explain the obtained results based on the special geometry of the BFO nanofillers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Ferroelectric poly(vinylidene fluoride) PVDF films derived from the solutions with retainable water and controlled water loss

To obtain β‐phase dominant ferroelectric poly(vinylidene fluoride) (PVDF) homopolymer thin films on aluminum‐coated silicon substrates, the retaining and loss of water were manipulated by introducing several hydrated and hygroscopic chemicals in the precursor solutions, including aluminum nitrate nonahydrate, aluminum chloride hexahydrate, chromium nitrate nonahydrate, tetra‐n‐butylammonium chloride, and one hygroscopic but nonhydrated chemical, ammonium acetate. Their ability of retaining water during the thermal annealing of the films and the relationship between water retaining and the effects on promoting the β phase were investigated. The results showed an ideal scenario was that the added hydrated salts should be able to retain substantial amount of water during the PVDF crystallization to effectively promote the β phase but completely dehydrate or decompose at the further elevated annealing temperature in order to obtain β‐phase dominant PVDF film without substantially incorporating water and deteriorating the electrical properties. As one of the hydrated chemicals well satisfying the above requirements, Al(NO₃)₃·9H₂O, of different amounts was introduced to the PVDF precursor solutions and the optimal resulting β‐phase dominant ferroelectric PVDF thin films exhibited smooth morphology, low dielectric loss, high remnant polarization of 89 mC/m², and large effective piezoelectric coefficient d₃₃ of ?14.5 pm/V (under the clamping of the substrate). © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2410–2418, 2009     

Enhanced electrical properties of highly oriented poly(vinylidene fluoride) films prepared by solid‐state coextrusion

Oriented poly(vinylidene fluoride) (PVDF) films with β‐form crystals have been commonly prepared by cold drawing of a melt‐quenched film consisting of α‐form crystals. In this study, we have successfully produced highly oriented PVDF thin films (20 µm thick) with β‐crystals and a high crystallinity (55–76%), by solid‐state coextrusion of a gel film to eight times the original length at an established optimum extrusion temperature of 160°C, some 10°C below the melting temperature. The resultant drawn films had a highly oriented (orientation function f_c = 0.993) fibrous structure, showing high mechanical properties of an extensional elastic modulus of 8.3 GPa and tensile strength of 0.84 GPa, along the draw direction. Such highly oriented and crystalline films exhibited excellent ferroelectric and piezoelectric properties. The square hysteresis loop was significantly sharper than that of a conventional sample. The sharp switching transient yielded the remnant polarization P_r of 90 mC/m², and the electromechanical coupling factor k_t was 0.24 at room temperature. These values are about 1.5 times greater than those of a conventional β‐PVDF film. Thus, solid‐state coextrusion near the melting point was found to be a useful technique for the preparation of highly oriented and highly crystalline β‐PVDF films with superior mechanical and electrical properties. The morphology of the extrudate relevant to such properties is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2549–2556, 1999     

Conformational changes and phase transformation mechanisms in PVDF solution‐cast films

The supramolecular crystal structure in poly(vinylidene fluoride) (PVDF) solution‐cast films is studied through changing crystallization conditions in two solvents of different structures and polarities. The crystalline‐state chain conformations of isothermally solution‐crystallized PVDF in N, N‐dimethylacetamide (DMAc), and cyclohexanone are studied through the specific FTIR absorption bands of α, β, and γ phase crystals. There are no changes in the FTIR spectra of cyclohexanone solution‐crystallized films in the temperature range of 50–120 °C. In the case of DMAc solution‐crystallized films, low temperature crystallization mainly results in formation of trans states (β and γ phases), whereas at higher temperatures gauche states become more populated (α phase). This is due to the variations in solvent polarity and ability to induce a specific conformation in PVDF chains, through the changes in chain coil dimensions. This indicates that in spite of cyclohexanone solutions, the intermolecular interactions between PVDF and DMAc are temperature‐sensitive and more important in stabilizing conformations of PVDF in crystalline phase than temperature dependence of PVDF chain end‐to‐end distance <r²>. The high‐resolution ¹⁹F NMR spectroscopy also showed little displacement in PVDF characteristic chemical shifts probably due to changes in PVDF chain conformation resulting from temperature variations. Upon uniaxial stretching of the prepared films under certain conditions, contribution of trans state becomes more prominent, especially for the originally higher α phase‐containing films. Due to formation of some kink bands during film stretching and phase transformation, α phase absorption bands are still present in infrared spectra. Besides, uniaxial stretching greatly enhances piezoelectric properties of the films, maybe due to formation of oriented β phase crystals, which are of more uniform distribution of dipole moments. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3487–3495, 2004     

Thermal properties and structure of electrospun blends of PVDF with a fluorinated copolymer

We report the structure and thermal properties of blends comprising poly(vinylidene fluoride) (PVDF) and a random fluorinated copolymer (FCP) of poly(methyl methacrylate)‐random‐1H,1H,2H,2H‐perfluorodecyl methacrylate, promising membrane materials for oil–water separation. The roles of processing method and copolymer content on structure and properties were studied for fibrous membranes and films with varying compositions. Bead‐free, nonwoven fibrous membranes were obtained by electrospinning. Fiber diameters ranged from 0.4 to 1.9 μm, and thinner fibers were obtained for PVDF content >80%. As copolymer content increased, degree of crystallinity and onset of degradation for each blend decreased. Processing conditions have a greater impact on the crystallographic phase of PVDF than copolymer content. Fibers have polar beta phase; solution‐cast films contain gamma and beta phase; and melt crystallized films form alpha phase. Kwei's model was used to model the glass transition temperatures of the blends. Addition of FCP increases hydrophobicity of the electrospun membranes. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 312–322     

Doping of polyvinylidene difluoride with cobalt nitrate: Structural,electrical, and magnetic properties

Polyvinylidene difluoride (PVDF) doped with a few percentage of cobalt nitrate hexahydrate induces transition into the ferroelectric β‐phase. Infrared spectra show peaks indicative of β‐phase PVDF at 1277 cm^?1 and loss of the α‐phase peak at 790 cm^?1 while polarization measurements show loops consistent with relaxor ferroelectric behavior. Electronic spectroscopy shows that the Co²⁺ ion is in a six‐coordinate environment, and this is confirmed by magnetic susceptibility. Thermal measurements show that the PVDF melts near 155 °C, depending on the Co²⁺ content, and that there are several other thermal features that are associated with the hydrated cobalt nitrate. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Enhanced dielectric properties of polymer composite films induced by encapsulated MWCNTs with a one core‐two shell structure

Multiwalled carbon nanotubes (MWCNTs) can endow high dielectric constant to polymer‐based composites. However, the accompanying poor dispersion of MWCNTs and high dielectric loss for composites severely limit their application in dielectric field. Herein, a modified acid‐treated MWCNTs encapsulated by the polyaniline/poly(sodium 4‐styrenesulfonate) layers (aMWCNTs@PANI‐PSS) with a one core‐two shell structure was fabricated by in situ polymerization followed by electrostatic self‐assembly technique. Furthermore, the composite films based on aMWCNTs@PANI‐PSS/poly(vinylidenefluoride‐hexaflouropropylene) (PVDF‐HFP) were fabricated by a solution‐casting method. An ultrathin insulating PSS shell is wrapped onto aMWCNTs@PANI, resulting in the improvement of dispersibility for aMWCNTs@PANI and the decrease of dielectric loss for composite films. When the content of aMWCNTs@PANI‐PSS is 5.0 wt %, the dielectric constant of aMWCNTs@PANI‐PSS/PVDF‐HFP reaches 430 (100 Hz), which is about 55 times of pure PVDF‐HFP and 1.7 times of aMWCNTs@PANI/PVDF‐HFP (247). Besides, the responding dielectric loss of aMWCNTs@PANI‐PSS/PVDF‐HFP composite film is only 0.67, much lower than that of aMWCNTs@PANI/PVDF‐HFP (25) and aMWCNTs/PVDF‐HFP (3185). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 948–956     

Metal Salt‐Induced Ferroelectric Crystalline Phase in Poly(vinylidene fluoride) Films

In this Communication, the effect of varying mass fractions (0–20 wt.‐%) of calcium chloride (CaCl₂) salt on the α‐ and β‐phase content of poly(vinylidene fluoride) (PVDF) as‐cast films were investigated. Spectral and X‐ray studies revealed the maximum ferroelectric β‐phase for the addition of 15 wt.‐% of CaCl₂ in PVDF compared to neat PVDF samples. The dense β‐phase dominant PVDF–CaCl₂ (15 wt.‐%) thick film used as a ferroelectric insulator in one‐capacitor (1C) type random access memory device exhibited a remnant polarization of 3.1 µC · cm², and is a good indication that the unoriented PVDF–CaCl₂ films can be used in electronic applications without further stretching process.

     

Polymer electrolyte membranes by in situ polymerization of poly(ethylene carbonate‐co‐ethylene oxide) macromonomers in blends with poly(vinylidene fluoride‐co‐hexafluoropropylene)

Salt‐containing membranes based on polymethacrylates having poly(ethylene carbonate‐co‐ethylene oxide) side chains, as well as their blends with poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP), have been studied. Self‐supportive ion conductive membranes were prepared by casting films of methacrylate functional poly(ethylene carbonate‐co‐ethylene oxide) macromonomers containing lithium bis(trifluorosulfonyl)imide (LiTFSI) salt, followed by irradiation with UV‐light to polymerize the methacrylate units in situ. Homogenous electrolyte membranes based on the polymerized macromonomers showed a conductivity of 6.3 × 10^?6 S cm^?1 at 20 °C. The preparation of polymer blends, by the addition of PVDF‐HFP to the electrolytes, was found to greatly improve the mechanical properties. However, the addition led to an increase of the glass transition temperature (T_g) of the ion conductive phase by ～5 °C. The conductivity of the blend membranes was thus lower in relation to the corresponding homogeneous polymer electrolytes, and 2.5 × 10^?6 S cm^?1 was recorded for a membrane containing 10 wt % PVDF‐HFP at 20 °C. Increasing the salt concentration in the blend membranes was found to increase the T_g of the ion conductive component and decrease the propensity for the crystallization of the PVDF‐HFP component. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 79–90, 2007     

ASAXS study of styrene‐grafted sulfonated poly(vinylidene fluoride) membranes

Small‐angle and wide‐angle X‐ray scattering and anomalous small‐angle X‐ray scattering were used to investigate proton‐conducting membranes prepared by radiation‐induced styrene grafting and sulfonation of commercial poly(vinylidene fluoride) (PVDF‐g‐PS) films. The membranes retain the lamellar and highly oriented structure of the original PVDF films even through excessive grafting and sulfonation. The sulfonate groups aggregate in the central part of the amorphous layers, where they form a weakly ordered structure that does not show any preferred orientation. This structure is suggested to be lamellar with alternate metal‐sulfonated hydrate and PVDF‐g‐PS layers. The lamellar period is 15.1 Å. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1734–1748, 2000     

Enhanced dielectric performance and energy storage of PVDF‐HFP‐based composites induced by surface charged Al2O3

In order to enhance dielectric properties and energy storage density of poly(vinylidene fluoride‐hexafluoro propylene) (PVDF‐HFP), surface charged gas‐phase Al₂O₃ nanoparticles (GP‐Al₂O₃, with positive surface charges, ε’ ≈ 10) are selected as fillers to fabricate PVDF‐HFP‐based composites via simple physical blending and hot‐molding techniques. The results show that GP‐Al₂O₃ are dispersed homogeneously in the PVDF‐HFP matrix and the existence of nanoscale interface layer (matrix‐filler) is investigated by SAXS. The dielectric constant of the composites filled with 10 wt % GP‐Al₂O₃ is 100.5 at 1 Hz, which is 5.6 times higher than that of pure PVDF‐HFP. The maximum energy storage density of the composite is 4.06 J cm^?3 at an electrical field of 900 kV mm^?1 with GP‐Al₂O₃ content of 1 wt %. Experimental results show that GP‐Al₂O₃ could induce uniform fillers’ distribution and increase the concentration of electroactive β‐phase as well as enhance interfacial polarization in the matrix, which resulted in enhancements of dielectric constant and energy storage density of the PVDF‐HFP composites. This work demonstrates that surface charged inorganic‐oxide nanoparticles exhibit promising potential in fabricating ferroelectric polymer composites with relatively high dielectric constant and energy storage. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 574–583     

Atom transfer radical polymerization directly from poly(vinylidene fluoride): Surface and antifouling properties

The direct preparation of grafting polymer brushes from commercial poly (vinylidene fluoride) (PVDF) films with surface‐initiated atom transfer radical polymerization (ATRP) is demonstrated. The direct initiation of the secondary fluorinated site of PVDF facilitated grafting of the hydrophilic monomers from the PVDF surface. Homopolymer brushes of 2‐(N,N‐dimethylamino)ethyl methacrylate (DMAEMA) and poly (ethylene glycol) monomethacrylate (PEGMA) were prepared by ATRP from the PVDF surface. The chemical composition and surface topography of the graft‐functionalized PVDF surfaces were characterized by X‐ray photoelectron spectroscopy, attenuated total reflectance/Fourier transform infrared spectroscopy, and atomic force microscopy. A kinetic study revealed a linear increase in the graft concentration of poly[2‐(N,N‐dimethylamino)ethyl methacrylate] (PDMAEMA) and poly[poly(ethylene glycol) monomethacrylate] (PPEGMA) with the reaction time, indicating that the chain growth from the surface was consistent with a controlled or living process. The living chain ends were used as macroinitiators for the synthesis of diblock copolymer brushes. The water contact angles on PVDF films were reduced by the surface grafting of DMAEMA and PEGMA. Protein adsorption experiments revealed a substantial antifouling property of PPEGMA‐grafted PVDF films and PDMAEMA‐grafted PVDF films in comparison with the pristine PVDF surface. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3434–3443, 2006     

PVDF/PMMA brushes membrane for lithium‐ion rechargeable batteries prepared via preirradiation grafting technique

Poly(methyl methacrylate) (PMMA) was anchored to multiporous poly(vinylidine fluoride) (PVDF) surface via electron beam preirradiation grafting technique to prepare PVDF/PMMA brushes. The conformation of the PVDF/PMMA brushes was verified through Attenuated total reflection‐Fourier transform infra red spectroscopy (ATR‐FTIR), energy dispersive X‐ray spectroscopy (EDX), and scanning electron microscopy (SEM). Thermal stability of PVDF/PMMA brushes was characterized by thermo gravimetric analysis (TGA). The degradation of PVDF/PMMA brushes showed a two‐step pattern. PVDF/PMMA brushes membrane could be used as polymer electrolyte in lithium‐ion rechargeable batteries after it was activated by uptaking 1 M LiPF₆/EC‐DMC (ethylene carbonate/dimethyl carbonate; EC:DMC = 1:1 by volume) electrolyte solution. The activated membrane showed high ionic conductivity, 6.1 × 10^?3 S cm^?1 at room temperature, and a good electrochemical stability up to 5.0 V. The excellent performances of multiporous PVDF‐g‐PMMA membranes suggest that they are suitable for application in high‐performance lithium‐ion batteries. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 751–758, 2008     

Fabrication and characterization of SiO2/PVDF composite nanofiber‐coated PP nonwoven separators for lithium‐ion batteries

SiO₂/polyvinylidene fluoride (PVDF) composite nanofiber‐coated polypropylene (PP) nonwoven membranes were prepared by electrospinning of SiO₂/PVDF dispersions onto both sides of PP nonwovens. The goal of this study was to combine the good mechanical strength of PP nonwoven with the excellent electrochemical properties of SiO₂/PVDF composite nanofibers to obtain a new high‐performance separator. It was found that the addition of SiO₂ nanoparticles played an important role in improving the overall performance of these nanofiber‐coated nonwoven membranes. Among the membranes with various SiO₂ contents, 15% SiO₂/PVDF composite nanofiber‐coated PP nonwoven membranes provided the highest ionic conductivity of 2.6 × 10^?3 S cm^?1 after being immersed in a liquid electrolyte, 1 mol L^?1 lithium hexafluorophosphate in ethylene carbonate, dimethyl carbonate and diethyl carbonate. Compared with pure PVDF nanofiber‐coated PP nonwoven membranes, SiO₂/PVDF composite fiber‐coated PP nonwoven membranes had greater liquid electrolyte uptake, higher electrochemical oxidation limit, and lower interfacial resistance with lithium. SiO₂/PVDF composite fiber‐coated PP nonwoven membrane separators were assembled into lithium/lithium iron phosphate cells and demonstrated high cell capacities and good cycling performance at room temperature. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1719–1726     

Crystal‐structure dependence of electroactive properties in differently prepared poly(vinylidene fluoride/hexafluoropropylene) copolymer films

The electroactive properties of two random copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) were studied. The compositions were 95/5 and 85/15 mol % P(VDF/HFP). For each composition, three different film‐preparation methods were used—solvent casting, melt‐pressed quenched, and melt‐pressed slow‐cooled. The ferroelectric properties observed were strongly dependent on the preparation methods of the films as well as the HFP molar content of the samples. The highest remanent polarizations (P_r) obtained from electric displacement versus electric field (D‐E) hysteresis data are 80 and 50 mC/m² for the 5 and 15% HFP solvent‐cast samples, respectively. The slow‐cooled samples do not exhibit any ferroelectric behavior for either the 5 or 15% HFP copolymers. It was also observed that both the 5 and 15% HFP slow‐cooled samples have a smaller electrostrictive response relative to the other two types of samples. Wide‐angle X‐ray diffraction and DSC results suggest that the 5% HFP sample has a higher crystallinity relative to the 15% HFP sample for each preparation method. In addition, different crystal phases form in the samples resulting from the different preparation methods. Fourier transform infrared results suggest that the slow‐cooled samples are in the nonpolar α phase, whereas the quenched and solvent‐cast samples are more likely in the polar β phase. The slow‐cooled samples do not show a switching peak in their nonpolar α‐phase crystalline state. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2793–2799, 2001     

Modeling effect of ferroelectric nanofiller size on bipolar charge transport in nanocomposite film

Bipolar charge injection and field‐dependent mobility transport through nanocomposite film comprised of ferroelectric ceramic nanofillers in an amorphous polymer matrix is simulated using a 3D particle‐in‐cell model which extends the classical electrical double layer by substitution of a dipolar core for the nanofiller. The stability criterion of the explicit algorithm conforms to the Courant–Friedrichs–Levy limit. Simulation results for BaTiO₃ nanofiller in amorphous polymer matrix indicate that antiparallel polarization results in the highest leakage conduction and lowest level of charge trapping in the interaction zone. Theoretical considerations validated simulation prediction in identifying a size range of 80 to 100 nm to minimize attachment and maximize conduction. The largest difference is in attached charge in the antiparallel case where fractions go from 2.2 to 97% as nanofiller size is decreased from 150 to 60 nm. Computed conductivity of 0.4 × 10^?14 S/cm is in agreement with published data for PVDF. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1380–1390     

Enhanced β‐phase in PVDF polymer nanocomposite and its application for nanogenerator

Harvesting energy from the ambient mechanical energy by using flexible piezoelectric nanogenerator is a revolutionary step toward achieving reliable and green energy source. Polyvinylidene fluoride (PVDF), a flexible polymer, can be a potential candidate for the nanogenerator if its piezoelectric property can be enhanced. In the present work, we have shown that the polar crystalline β‐phase of PVDF, which is responsible for the piezoelectric property, can be enhanced from 48.2% to 76.1% just by adding ZnO nanorods into the PVDF matrix without any mechanical or electrical treatment. A systematic investigation of PVDF‐ZnO nanocomposite films by using X‐ray diffractometer, Fourier transform infrared spectroscopy, and polarization‐electric field loop measurements supports the enhancement of β‐phase in the flexible nanocomposite polymer films. The piezoelectric constant (d₃₃) of the PVDF‐ZnO (15 wt%) film is found to be maximum of approximately −1.17 pC/N. Nanogenerators have been fabricated by using these nanocomposite films, and the piezoresponse of PVDF is found to enhance after ZnO loading. A maximum open‐circuit voltage ~1.81 V and short‐circuit current of 0.57 μA are obtained for 15 wt% ZnO‐loaded PVDF nanocomposite film. The maximum instantaneous output power density is obtained as 0.21 μW/cm² with the load resistance of 7 MΩ, which makes it feasible for the use of energy harvesting that can be integrated to use for driving small‐scale electronic devices. This enhanced piezoresponse of the PVDF‐ZnO nanocomposite film‐based nanogenerators attributed to the enhancement of electroactive β‐phase and enhanced d₃₃ value in PVDF with the addition of ZnO nanorods.