Β-phase Formation Research Articles

Polymer-assisted dispersion of reduced graphene oxide in electrospun polyvinylidene fluoride nanofibers for enhanced piezoelectric monitoring of human body movement

Electrospun graphene oxide (GO)/polyvinylidene difluoride (PVDF) and reduced graphene oxide (rGO)/PVDF piezoelectric hybrid nanofibers were prepared via electrospinning to enhance the β-phase content of the PVDF crystal structure. The addition of rGO increased the number of nucleation sites in the PVDF matrix, leading to an improved β-phase content in the nanofibers. Although the inclusion of GO also increased the β-phase content, rGO addition resulted in higher output voltages due to its greater conductivity compared to GO. rGO/PVDF produced higher output voltages than GO/PVDF because rGO has few oxygen-containing groups on its carbon atoms. The 1 wt% GO/PVDF nanofibers exhibited an 86.24 % β-phase content and an average output voltage of 3.2 V under a 15 N load. The 0.5 wt% rGO/PVDF nanofibers demonstrated an 84.09 % β-phase content and an average output voltage of 3.66 V under the same load. The nonionic surfactant Triton X-100 improved rGO dispersal, enhancing its effectiveness in inducing β-phase formation, and increasing the number of stress concentration points in the nanofibers. A piezoelectric device composed of TX-100/rGO/PVDF nanofibers exhibited stable performance even after 1,500 load cycles, generating an average output voltage of 7.13 V under a 15 N load. This device serves as both an energy harvester and a footwear sensor, offering potential applications in new sports monitoring technologies and self-powered wearables.

In-situ WAXS and SAXS microstructural investigation of Poly(vinylidene fluoride)- Fe3O4 coaxial-electrospun nanocomposites under thermal and mechanical loading: Nanoparticles size effects on fibers molecular orientation, mechanical properties and crystalline polymorphs

In this study, 15 % w/w polyvinylidene fluoride (PVDF)–Fe3O4 nanoparticle (NP) nanocomposite scaffolds were prepared using coaxial electrospinning with a high-speed conductive rotating collector to obtain aligned fibers. The effects of varying the Fe3O4 NP size (6, 9, and 14 nm in diameter) on the fiber morphology, mechanical response, and piezoelectric phase content were investigated. In situ X-ray diffraction measurements during heating-cooling and tensile tests were carried out using synchrotron radiation to study the charge in the β-phase content and polymer chain orientation under different conditions. At zero strain, the presence of smaller NPs seems to impede the β-phase crystallization in PVDF. However, heating-cooling cycles revealed that the NPs acted as nucleation agents, promoting a higher β-phase content after cooling compared to pure PVDF. The mechanical response showed that nanocomposites with smaller NPs exhibited higher stiffness. While the initial degree of polymer chain orientation was higher in the nanocomposites, the presence of NPs hindered the α-to-β phase transformation and chain alignment under tensile deformation compared to pure PVDF. This study highlights the complex interplay among NP size, β-phase formation, mechanical properties, and chain orientation in PVDF-Fe3O4 nanocomposites, providing insights into tailoring their piezoelectric performance for various applications.

Ytterbium-doping effect on the electrochemical and piezoelectric properties of poly(vinylidene fluoride) films

The optimal molar ratio of poly(vinylidene fluoride) (PVDF): dimethyl sulfoxide (DMSO) was investigated that promoted the β-phase formation, used during the PVDF film synthesis. The solution cast method was used for doping the PVDF films with ytterbium (III) nitrate salt hexahydrate. In general, Yb-doping in PVDF films improves thermal resistance, promotes β-phase formation, modifies the monomer conformation, reduces reversibility to electrochemical processes, and increases the d33 coefficient of piezoelectricity. The β-phase formation caused by Yb-doping alters the internal structures of the trans-gauche-trans-gauche’ (TGTG’) and all-trans (TTTT) chains inside the polymeric network. The coexistence between the trans-gauche and all-trans structures provides in both films the α-phase and β-phase coexistence. The presence of self-polarized CH2-CF2 dipoles, where the concentration of fluorine remains the same and the CH2 drastically increases after Yb3+ incorporation. The quasi-reversible shape shown in both voltammetry cyclic curves is related to irreversible oxidation and reduction reactions. Yb-PVDF exhibits specific pseudocapacitance values that are 30% higher than those of the PVDF films. Finally, the piezoelectric properties were improved with ytterbium incorporation.

β-phase formation of poly(vinylidene fluoride) foam based on the porous morphology control via supercritical carbon dioxide

The increase of electroactive β phase of poly(vinylidene fluoride) (PVDF) is important in energy harvesting applications. In this work, a green method of supercritical CO2 physical foaming was applied to obtain the PVDF foams with high content of β-crystal by utilizing the biaxial stretching when the cells grew, which were applied in the field of piezoelectric sensors. By changing the foaming condition, the PVDF foams with various structures were obtained, and a comprehensive study on the crystal transformation of them was carried out. The PVDF foam with increased β crystals content was more accessible to obtain at a high saturation pressure, corresponding to the large expansion ratio and small cell size. The acquisition of β crystals mainly came from the α-β solid-solid phase transformation during decompression, rather than the annealing process. Due to the introduction of cell structure, the piezoelectric output performance of the sample was effectively amplified. The produced PVDF foam with the β-crystal content of 30%, exhibited the low density of 0.11 g/cm3 and the highest piezoelectric output of 4.1 V (corresponding to a specific voltage of 35 V‧cm3/g). This foaming strategy provides guidance for lightweight design and high-performance fabrication of piezoelectric materials.

Tailoring α/β-Brass coating on steel via one-bath co-deposition: Influence of current density and electrolyte composition in pyrophosphate system

Brass electroplating on steel wire is widely employed in the radial tire industry. However, controlling the formation of α/β-brass coating during the co-deposition of Cu-Zn remains challenging. This study investigates the influence of current density, Cu2+/Zn2+ ratio, and pyrophosphate concentration on phase formation using a cyanide-free process. Quantifications of Cu/Zn content and α/β phase ratio in brass coatings were accomplished using EDS and XRD techniques. α-rich brass was favored at moderate current density (5 A/dm2) and an optimal Cu2+/Zn2+ ratio of 1.5:1, while higher currents favored the β-phase regardless of the Cu2+/Zn2+ ratio. An optimal pyrophosphate concentration of 1.0 M yielded α-rich brass, with higher concentrations promoting unalloyed deposits and β-phase formation. α-rich brass coatings exhibited 13–17 % greater adhesion strength to rubber compared to β-rich coatings.

Hybrid carbonaceous filler as promising additives for EMI SE of PVDF-based composites: Comparison between monolayered and multilayered structures

Flexible conducting polymeric composites (CPC) for applications as electromagnetic interference (EMI) shielding materials were successfully prepared by melt-mixing approach using poly (vinylidene fluoride) (PVDF) as the matrix, loaded with hybrid carbonaceous fillers, carbon nanotube (CNT) and graphene nanoplatelets (GNP). Composites with as low as 3 wt% of filler with conductivity values in between 10−3 S/m (PVDF/GNP) and 10−1 S/m (PVDF/CNT) were successfully prepared by using hybrid with different proportions. Multi-layered structure composites displayed significantly higher EMI SE values than the bulk composites, mainly those constituted by CNT and the CNT/GNP (1.5:1.5 wt%) hybrid. By stacking PVDF/CNT, PVDF/CNT/GNP and PVDF/GNP with different arrangements, on can achieve EMI SE around 22 dB (in X-band) and 27 dB (in Ku-band) with absorption contribution of 65–70 % in the X-band and 77–81 % in the Ku-band frequency ranges. The effect of the hybrid composites on the morphological, rheological and thermal properties and on the ability of the β-phase formation on PVDF composites was also investigated. By combining appropriate CNT/GNP ratio, a good compromise between flexibility, conductivity, processability and EM attenuation with absorption characteristics was achieved, thus favoring promising application in stealth technology and also in communication devices.

Self-poled PVDF/recycled cellulose composite fibers utilizing cellulose nanocrystals to induce PVDF β-phase formation through wet-spinning as a flexible fabric piezoelectric sensor

In general, PVDF (Polyvinylidene fluoride) needs polarization treatment to exhibit its piezoelectric properties. Introducing nanofillers or applying stretching during the processing can promote the β-phase transformation in PVDF, achieving self-polarization. Herein, by incorporation of cellulose nanocrystals (CNCs), continuous β-phase enriched PVDF/cellulose composite fibers are prepared via wet spinning and drawing, in which the cellulose is recycled from waste cotton textiles to improve the wet spinnability of PVDF and reduce the cost. The obtained composite fibers are woven into fabrics and subsequently assembled into a flexible sensor, exhibiting excellent piezoelectric performance (d33 = 26.2 pC/N) without requiring additional polarization treatment. It generates an open-circuit voltage of 12 V and a short-circuit current of 100nA, much higher than those of the previously reported piezoelectric PVDF sensors with high-voltage polarization. This fabric-based flexible sensor also exhibits notable characteristics, including stable output signals and heightened sensitivity, thereby fulfilling the demands for monitoring both minute and extensive human movements. Furthermore, it shows great potential for widespread use in sound sensing for human-machine interfaces. The self-poled PVDF composite fibers offer the advantage of being easily woven together with other fiber materials, which contributes towards the development of self-powered flexible piezoelectric fabric sensors.

Enhancing the Piezoelectric Properties of 3D Printed PVDF Using Concurrent Torsional Shear Strain.

Extrusion-based polymer 3D printing induces shear strains within the material, influencing its rheological and mechanical properties. In materials like polyvinylidene difluoride (PVDF), these strains stretch polymer chains, leading to increased crystallinity and improved piezoelectric properties. This study demonstrates a 400% enhancement in the piezoelectric property of extrusion-printed PVDF by introducing additional shear strains during the printing process. The continuous torsional shear strains, imposed via a rotating extrusion nozzle, results in additional crystalline β-phases, directly impacting the piezoelectric behavior of the printed parts. The effect of the nozzle's rotational speed on the amount of β-phase formation is characterized using FTIR. This research introduces a new direction in the development of polymer and composite 3D printing, where in-process shear strains are used to control the alignment of polymer chains and/or in-fill phases and the overall properties of printed parts.

Effects of stretching on phase transformation of PVDF and its copolymers: A review

Abstract Poly(vinylidene fluoride) (PVDF) and its copolymers are promising candidates for energy-harvesting devices because of their flexibility, environmental friendliness, lightweight, and high halogen and acid resistance. However, the relatively low piezoelectricity limits their applications. The piezoelectricity of PVDF and its copolymers highly depends on the polar β-phase, while the non-polar α-phase is the most common one. As a result, the β-phase formation and α- to β-phase transformation have attracted much attention in recent years. Stretching is a widely used method to induce the α- to β-phase transformation for the improvement of piezoelectricity. In this work, the influences of the parameters during stretching on phase evolution and piezoelectricity are discussed and summarized. Besides, nontraditional stretching methods are also introduced and discussed. This work will provide important information for preparing high-performance piezoelectric polymer films.

Investigation on microstructure evolution of Mg-Gd-Zn-Zr alloys during friction stir processing by liquid CO2 cooling assisted stop action

The microstructure evolution of Mg-14Gd-2.5Zn-0.5Zr (wt.%) alloys during friction stir processing (FSP) were investigated through liquid CO2 cooling assisting stop action technology. In particular, solutionizing at 480 °C (LT4) and 520 °C (HT4) was carried out to clarify the evolution of different second phases. The results showed that grain size decreased from ∼20 μm to ∼1–3 μm in the stir zone, and a weak texture intensity could be found after FSP. Although the type of the second phases in as-cast, LT4 and HT4 samples did not change during FSP, different evolution sequences about the second phase and grain refinement could be found. Bulk X phase was broken into finer one later than recrystallization and refinement of α-Mg grain in LT4 alloy, while β-phase fragmentation and formation of recrystallized grains occurred simultaneously in HT4 alloy. In addition, the intragranular 14H-LPSO structure retained in three samples after FSP. Due to the different types and volume fractions of the second phases, the as-cast and LT4 alloy were mainly refined by continuous dynamic recrystallization (CDRX), while both CDRX and geometric dynamic recrystallization (GDRX) occurred in HT4 alloy. After FSP, the yield strength increased by 74%, 110% and 90% for as-cast, LT4, and HT4 alloy, respectively.

ZnO@Carbon Dot Nanoparticles Stimulating the Antibacterial Activity of Polyvinylidene Fluoride-Hexafluoropropylene with a Higher Electroactive Phase for Multifunctional Devices.

To further advance the application of flexible piezoelectric materials in wearable/implantable devices and robot electronic skin, it is necessary to endow them with a new function of antibacterial properties and with higher piezoelectric performance. Introducing a specially designated nanomaterial based on the nanocomposite effect is a feasible strategy to improve material properties and achieve multifunctionalization of composites. In this paper, carbon dots (CDs) were sensitized onto the surface of ZnO to form ZnO@CDs nanoparticles, which were then incorporated into polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) to obtain a multifunctional composite. On the one hand, the antibacterial property of ZnO was improved because CDs had good optical absorption of visible light and their surface functional groups were favorable for electrostatic adsorption with bacteria. Therefore, ZnO@CDs endowed the composite with an outstanding antibacterial rate of 69.1% for Staphylococcus aureus. On the other hand, CDs played a bridging role between ZnO and PVDF-HFP, reducing the negative effect of ZnO aggregation and interface incompatibility with PVDF-HFP. As a result, ZnO@CDs induced β-phase formation of 80.4% in PVDF-HFP with a d33 value of 33.8 pC N-1. The multifunctional device exhibited excellent piezoelectric and antibacterial performance in the application of energy harvesters and self-powered pressure sensors.

Natural sepiolite modified PVDF electrospun films for mechanically robust and high-performance triboelectric nanogenerators

In this work, natural sepiolite and polyvinylidene fluoride (PVDF) electrospun composite films with improved mechanical strength were prepared successfully, in which the natural sepiolite not only decreased fiber slippage, but also promoted the polar β-phase formation to reduce surface potential. It was found that the 25 wt% natural sepiolite modified PVDF film (PVDF-25) achieved a 3.2-fold enhancement in tensile strength. The surface potential decreased to −1.439 V in the 15 wt% natural sepiolite modified PVDF film (PVDF-15). Furthermore, through utilizing this mechanically robust film as triboelectric material, the triboelectric nanogenerator (TENG) held superior output performances, including the open-circuit voltage of 740 V, short-circuit current density of 60 mA/m2, maximum power density of 94.08 W/m2 and the long-term stability over 1000 cycles. This work may provide new insights in developing mechanically and electrically robust triboelectric materials by combining natural clay materials.

Interfacial Engineering of PVDF‐TrFE toward Higher Piezoelectric, Ferroelectric, and Dielectric Performance for Sensing and Energy Harvesting Applications

The electrical properties of pristine fluoropolymers are inferior due to their low polar crystalline phase content and rigid dipoles that tend to retain their fixed moment and orientation. Several strategies, such as electrospinning, electrohydrodynamic pulling, and template-assisted growing, have been proven to enhance the electrical properties of fluoropolymers; however, these techniques are mostly very hard to scale-up and expensive. Here, a facile interfacial engineering approach based on amine-functionalized graphene oxide (AGO) is proposed to manipulate the intermolecular interactions in poly(vinylidenefluoride-trifluoroethylene) (PVDF-TrFE) to induce β-phase formation, enlarge the lamellae dimensions, and align the micro-dipoles. The coexistence of primary amine and hydroxyl groups on AGO nanosheets offers strong hydrogen bonding with fluorine atoms, which facilitates domain alignment, resulting in an exceptional remnant polarization of 11.3µCcm-2 . PVDF-TrFE films with 0.1wt.% AGO demonstrate voltage coefficient, energy density, and energy-harvesting figure of merit values of 0.30VmN-1 , 4.75Jcm-3 , and 14pm3 J-1 , respectively, making it outstanding compared with state-of-the-art ceramic-free ferroelectric films. It is believed that this work can open-up new insights toward structural and morphological tailoring of fluoropolymers to enhance their electrical and electromechanical performance and pave the way for their industrial deployment in next-generation wearables and human-machine interfaces.

Brief Review of PVDF Properties and Applications Potential.

Currently, there is an ever-growing interest in carbon materials with increased deformation-strength, thermophysical parameters. Due to their unique physical and chemical properties, such materials have a wide range of applications in various industries. Many prospects for the use of polymer composite materials based on polyvinylidene fluoride (PVDF) for scientific and technical purposes explain the plethora of studies on their characteristics "structure-property", processing, application and ecology which keep appearing. Building a broader conceptual picture of new generation polymeric materials is feasible with the use of innovative technologies; thus, achieving a high level of multidisciplinarity and integration of polymer science; its fundamental problems are formed, the solution of which determines a significant contribution to the natural-scientific picture of the modern world. This review provides explanation of PVDF advanced properties and potential applications of this polymer material in its various forms. More specifically, this paper will go over PVDF trademarks presently available on the market, provide thorough overview of the current and potential applications. Last but not least, this article will also delve into the processing and chemical properties of PVDF such as radiation carbonization, β-phase formation, etc.

Amplified piezoelectric response with β-phase formation in PVDF blended 3D cotton type nanofibers for osteogenic differentiation

PVDF (Polyvinylidene Fluoride) is a representative piezoelectric polymer, and many studies are being conducted to increase the β-phase, a polar chain structure that exhibits piezoelectricity. Electrospinning is known as an effective method to increase the β-phase of PVDF, and electrospun PVDF fibers are attractive materials that can be widely used in various fields due to their flexibility and high biocompatibility. However, since electrospun fibers are generally manufactured as 2D mats, it is difficult to use them as actual tissue scaffolds. In this study, PVDF was fabricated in 3D form by controlling the relative humidity (RH) during the electrospinning process. When the RH was set high during the electrospinning process, the fibers were manufactured in a cotton-like form. In addition, various post-treatment processes were performed to increase the β-phase, and the analysis showed that the post-treatment was effective in improving the β-phase of PVDF. The 3D cotton-type fibers performed in vitro cell culture experiments using MC3T3-E1 cells, confirming the possibility that they could be applied to tissue regeneration fields such as bone regeneration as scaffolds in the future. The manufactured 3D cotton-type PVDF fiber is expected to be applied not only to bio-scaffold but also to various fields requiring piezoelectricity.

The Effect of Solvents on the Preparation of Poly(9,9-Dioctylfluorene) Thin Films

The optoelectronic properties of Poly(9,9-dioctylfluorene) (PFO) are highly influenced by the existence of a well-defined chain extended “β-phase” conformational isomer. This study aims to evaluate the produced PFO films optical properties. Pristine PFO films and aggregated PFO films were fabricated by the solvent casting method. PFO was first dissolved in chloroform and toluene separately. Meanwhile, for aggregated film, different percentage of methanol (poor solvent) was added to the PFO solution to induce β-phase formation. UV-vis measurement and scanning electron microscopy were used to characterize the films. The results reveal that PFO was fully soluble in chloroform while moderately soluble in toluene. This result was further confirmed by micrograph; the PFO film prepared from chloroform exhibited glassy conformation. While for the aggregation system, the absorption spectra of β-phase becoming more intense as methanol content increase.

(PVDF)2(PEO)2 miktoarm star copolymers: Synthesis and isothermal crystallization leading to exclusive β-phase formation

In this work, we study how chain topology can induce different polymorphic behaviors in poly(vinylidene fluoride) (PVDF)-based materials. A linear PVDF precursor with two azido groups at the junction point, (PVDFx-N3)2 and three 4-miktoarm star copolymers (PVDFx)2-b-(PEOy)2 with two poly(ethylene oxide) (PEO) and two PVDF arms were synthesized and employed in this study. The amphiphilic miktoarm copolymers were prepared by a combination of anionic ring-opening polymerization, iodine transfer radical polymerization (ITP), and copper-catalyzed azide-alkyne cycloaddition (CuAAC). They have practically similar overall molar mass but different compositions, ideal for performing bulk morphology and crystallization investigations. The isothermal overall crystallization kinetics of the PVDF and PEO arms of the 4-miktoarm star copolymers and representative PEO and PVDF precursors was determined by Differential Scanning Calorimetry (DSC). The results indicate that the star arms crystallized faster than the equivalent precursors as the kinetics are dominated by nucleation effects. The phases formed by the PVDF components in the materials examined were analyzed by studying their melting behavior by DSC, their superstructural morphology by Polarized Light Optical Microscopy (PLOM), and the phase structure by Fourier Transform Infrared Spectroscopy (FTIR). The linear PVDF and (PVDF29-N3)2, exhibited α, β and γ-phases (with a majority of β-phase formation) during melting after isothermal crystallization. The ratio of the different phases depends on the crystallization temperature. An analysis of the multiple melting behavior indicated that the sample forms both α and β-phases initially, and the α-phase partially transforms into the γ-phase during isothermal crystallization when the temperature of crystallization increases. We found a remarkable behavior for the 4-miktoarm star copolymers, as the PVDF arms only form the ferroelectric β-phase when all three materials were isothermally crystallized regardless of the crystallization temperature employed. The presence of the polymorphism in the PVDF was detected by DSC, PLOM, and FTIR. Hence, we have shown that tailoring chain topology in PVDF copolymers can lead to exclusive β-phase formation, a path that can be exploited for future piezoelectric applications.

A study of degradation mechanisms in PVDF-based photovoltaic backsheets

Commercial backsheets based on polyvinylidene fluoride (PVDF) can experience premature field failures in the form of outer layer cracking. This work seeks to provide a better understanding of the changes in material properties that lead to crack formation and find appropriate accelerated tests to replicate them. The PVDF-based backsheet outer layer can have a different structure and composition, and is often blended with a poly(methyl methacrylate) (PMMA) polymer. We observed depletion of PMMA upon aging with sequential (MAST) and combined (C-AST) accelerated stress testing. In field-aged samples from Arizona and India, where PVDF crystallizes in its predominant α-phase, the degree of crystallinity greatly increased. MAST and C-AST protocols were, to some extent, able to replicate the increase in crystallinity seen in PVDF after ~ 7 years in the field, but no single-stress test condition (UV, damp heat, thermal cycling) resulted in significant changes in the material properties. The MAST regimen used here was too extreme to produce realistic degradation, but the test was useful in discovering weaknesses of the particular PVDF-based outer layer structure studied. No excessive β-phase formation was observed after aging with any test condition; however, the presence of β-phase was identified locally by Fourier transform infrared spectroscopy (FTIR). We conclude that both MAST and C-AST are relevant tests for screening outdoor failure mechanisms in PVDF backsheets, as they were successful in producing material degradation that led to cracking.

In-situ investigation on hydrogenation-dehydrogenation of Pd–Ag alloy films

The present work reports on synthesis of Pd–Ag nano-composite films by magnetron co-sputtering and the structural changes in the alloy film during hydrogenation and dehydrogenation. Synchrotron X-ray diffraction is employed in-situ to reveal subtle structural changes occurring during hydrogenation and dehydrogenation processes, an aspect not investigated so far. It is revealed that the nanocomposite film having 88 at% Pd shows the formation of α-phase as an intermediate phase, however, completion of the hydrogenation process yields only β-phase. No β-phase formation is observed in nanocomposite thin film containing 54 at% of Pd, suggesting the suppression of formation of β-phase with increase in Ag concentration. On dehydrogenation, the peak returns to its original position i.e. the value before hydrogenation. The data also demonstrated that the addition of Ag in Pd results in complete removal of dissolved hydrogen thereby eliminates the problem of hysteresis. The study shows that the lower concentrations of Ag in Pd are better in terms of extent of peak-shift on hydrogenation/dehydrogenation and faster response/recovery kinetics.

Nanoparticle-Enhanced β-Phase Formation in Electroactive PVDF Composites: A Review of Systems for Applications in Energy Harvesting, EMI Shielding, and Membrane Technology

Nanoparticle-Enhanced β-Phase Formation in Electroactive PVDF Composites: A Review of Systems for Applications in Energy Harvesting, EMI Shielding, and Membrane Technology