Crystallization Of PVDF Research Articles

PVDF/NiFe2O4 multiferroic composite membranes for dual mechanical and magnetic energy harvesting devices

A multiferroic composite membrane, combining PVDF piezoelectric polymer and nickel ferrite (NFO) nanofibers, was successfully fabricated and studied as an active material layer in multifunctional devices designed to harvest both mechanical and magnetic energy. Optimization of the manufacturing process ensured an even distribution of NFO fibers within the PVDF matrix, enhancing the crystallization of PVDF in the electroactive β phase. The resulting PVDF/NFO multiferroic films exhibited both piezoelectric and magnetic properties, along with a pronounced magnetoelectric (ME) effect. In a structure comprising Al/PVDF-NFO/PDMS/Al, the device operated as a piezoelectric generator (PEG) under a pressing force of 0.5 MPa, achieving a maximum output power density of 14.7 μW cm−12 with a peak-to-peak voltage of 12.2 V. When subjected to an AC magnetic field of 20 Oe at 50 Hz, the device functioned as a magneto-mechano-electrical (MME) generator, producing a sinusoidal waveform voltage of 486 mV. The cost-effective and easily integrable PVDF/NFO composite membrane presents promising opportunities for developing flexible, self-powered smart sensors for human health monitoring systems and implantable biomedical devices.

Nanoscale study on the initial stages of the interdiffusion across the amorphous/crystalline interface of poly(methyl methacrylate)/poly(vinylidene fluoride) (PMMA/PVDF) via STEM plus EDX/EELS

Interdiffusion across the interface of poly(methyl methacrylate)/poly(vinylidene fluoride) (PMMA/PVDF) was investigated thoroughly by scanning transmission electron microscopy (STEM) plus electron energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectrometry (EDX) and further with the assistance of laser-Raman spectroscopy. The factors of the annealing temperature and the time on the interfacial widths and the concentration profiles of PMMA and PVDF across the interface of PMMA/PVDF have been considered in detail. It was found that the concentration profiles of PMMA and PVDF were determined by the crystallization of PVDF, especially at the high annealing temperature (220 °C) in the PMMA part of the interface. Under the influence of the PVDF crystallization, the concentration profiles of F (from PVDF) and O (from PMMA) monitored by STEM-EDX/EELS changed gradually from parabola-shape to linear-shape in the PMMA part. The activation energy for the interdiffusion across the interface of PMMA/PVDF was calculated to be 51.0 kJ/mol, lower than the other reported pairs like poly(vinyl chloride)/poly(ε-caprolactone) (PVC/PCL) (69.8 kJ/mol) and poly(styrene-ran-acrylonitrile)/poly(methyl methacrylate) (SAN-29/PMMA) (175 ± 15 kJ/mol).

Ion-conductive crystals of poly(vinylidene fluoride) enable the fabrication of fast-charging solid-state lithium metal batteries

Dipolar defects enable an easy flipping and vibrating of PVDF dipoles, which triggers a concomitant migration of Li+ through ion–dipole interactions and transforms the ion-insulated crystals of PVDF into fast ion conductors.

Dual PVP roles for preparing PVDF hollow fiber membranes with bicontinuous structures via the complex thermally induced phase separation (c-TIPS)

Polyvinylpyrrolidone (PVP) is a widely used water-soluble polymer that can act as a pore-forming additive in ultrafiltration membrane preparation. Here, the PVDF hollow fiber membranes were prepared via the c-TIPS method by introducing PVP to the casting solution. The dual PVP roles in the membrane fabrication process enabled the production of PVDF hollow fiber membranes composed of bicontinuous structures. The PVP inhibited PVDF crystallization and then reduced the gelation temperature of the casting solution. They grew faster at coarsening, allowing greater growth of pores, and the formation of gap-connected pores and interlinked pores, which formed the bicontinuous structure. The PVP also acted as an effective pore-forming agent, giving porous outer surface. PVP can be removed almost completely from the membrane and did not lead to the wetting of PVDF membranes. Therefore, the synthesized PVDF membrane under optimal conditions could be used in the DCMD process with a maximum vapor flux of 18 ± 3 kg m−2 h−1, the pure water flux in ultrafiltration process reached 335.91 L m−2 h−1 bar−1, and the tensile stress was 5.8 MPa. This work presents a new route for preparing PVDF hollow fiber membranes using conventional spinning equipment with simple operation and moderately elevated temperature that is scalable to industry level.

Influence of poly(methyl methacrylate) on the structure and phase transition behavior of poly(vinylidene fluoride)

The structure and organization of poly(vinylidene fluoride) (PVDF) spherulites in blends with poly(methyl methacrylate) of high (PMMA-H) and low (PMMA-L) molecular weights, respectively, have been studied in details. It is confirmed that the addition of PMMA-H and PMMA-L have different influence on the morphologies of PVDF spherulites in several aspects, such as the spacing of ring-band α-PVDF spherulites, the kinetics of both α-PVDF crystallization and α−γ′ solid phase transition, as well as the formation of Wagon-Wheel spherulites. First, incorporation of PMMA-L enlarges the band spacing, which is associated to the increased chain mobility of crystallizable PVDF that helps to release the surface stresses of lamellae. In contrast, the low mobility of PMMA-H chains enhances the congestion at fold surfaces, which results in a vigorous twisting and thus the formation of tightened ring-band α-PVDF structure. Second, the PMMA-H reduces the crystallization rate of PVDF more severely than the PMMA-L, resulting in an extremely slow growth rate of α-PVDF spherulites in PVDF/PMMA-H sample at 160 °C, only about one-twenty-third compared to the neat PVDF. Third, the remarkably reduced α-PVDF spherulite growth rate and enhanced α−γ′ transition rate at 160 °C lead to the formation of Wagon-Wheel PVDF spherulites with inner γ′-PVDF crystals and outer γ crystals. It originates from the synchronization of slow α-PVDF growth and accelerated α−γ′ transition rate through homoepitaxy. That is, when the α−γ′ transition with exceeded rate reaches the growth front of the original α-PVDF spherulite, the transformed γ′-PVDF crystals trigger the growth of γ-PVDF crystals directly from melt with non-band feature. These results help to unravel the formation mechanism of Wagon-Wheel PVDF spherulites to be the competition of α-γ′ crystal transformation and α-spherulite radial growth rates.

Surface Nucleation-Induced Raspberry-like PVDF@P(St-co-MPS-co-AA) Core–Shell Latex Particles via Seeded Emulsion Polymerization and Their High Efficiency for Confined Crystallization of PVDF in Nanospheres

Surface Nucleation-Induced Raspberry-like PVDF@P(St-<i>co</i>-MPS-<i>co</i>-AA) Core–Shell Latex Particles via Seeded Emulsion Polymerization and Their High Efficiency for Confined Crystallization of PVDF in Nanospheres

Molecular Mechanism of the Piezoelectric Response in the β-Phase PVDF Crystals Interpreted by Periodic Boundary Conditions DFT Calculations.

A theoretical approach based on Periodic Boundary Conditions (PBC) and a Linear Combination of Atomic Orbitals (LCAO) in the framework of the density functional theory (DFT) is used to investigate the molecular mechanism that rules the piezoelectric behavior of poly(vinylidene fluoride) (PVDF) polymer in the crystalline β-phase. We present several computational tests highlighting the peculiar electrostatic potential energy landscape the polymer chains feel when they change their orientation by a rigid rotation in the lattice cell. We demonstrate that a rotation of the permanent dipole through chain rotation has a rather low energy cost and leads to a lattice relaxation. This justifies the macroscopic strain observed when the material is subjected to an electric field. Moreover, we investigate the effect on the molecular geometry of the expansion of the lattice parameters in the (a, b) plane, proving that the rotation of the dipole can take place spontaneously under mechanical deformation. By band deconvolution of the IR and Raman spectra of a PVDF film with a high content of β-phase, we provide the experimental phonon wavenumbers and relative band intensities, which we compare against the predictions from DFT calculations. This analysis shows the reliability of the LCAO approach, as implemented in the CRYSTAL software, for calculating the vibrational spectra. Finally, we investigate how the IR/Raman spectra evolve as a function of inter-chain distance, moving towards the isolated chain limit and to the limit of a single crystal slab. The results show the relevance of the inter-molecular interactions on the vibrational dynamics and on the electro-optical features ruling the intensity pattern of the vibrational spectra.

Nanocomposite Solid Polymer Electrolytes with Polymer Blend (PVDF‐HFP/Pluronic) as Matrix and GO as Nanofiller: Preparation, Structural Characterization, and Lithium‐Ion Conductivity Analysis

AbstractNanocomposite solid polymer electrolytes (NSPEs) with PVDF‐HFP/Pluronic as blend polymer matrix, graphene oxide (GO) as nanofiller, and LiClO4 are reported. FTIR spectroscopy reveals the crystal phase transformation of PVDF‐HFP from nonpolar α phase to electroactive γ phase upon salt addition that suggests the ion‐dipole interaction between the salt and the matrix. Further, Pluronic not only hinders the PVDF crystallization that increases the amorphous character of the matrix but also interacts with the salt and hence assists in salt dissociation in the blend matrix. The dc conductivity of PVDF‐HFP/Pluronic/LiClO4 blend SPE improves with increasing the Pluronic content reaching 0.73 × 10−6 Scm−1 at room temperature with 60 wt.% Pluronic. The dispersion of GO in the same blend SPE leads to a significant jump in room temperature ion conductivity (≈1.2 × 10−6 Scm−1) with 0.4% GO. Temperature‐dependent ion conductivity of the NSPEs reveals an Arrhenius type thermally activated process. The dc polarization data indicates that the conductivity is predominantly due to ions. Impedance plots exhibit a distorted semicircle at higher frequency and a tilted spike at lower frequency. The spike is an indication of ion diffusion and electrode polarization effect. Further, GO also has enhanced the mechanical properties of the fabricated NSPEs.

Flexible ZnO:PVDF based free standing piezoelectric nanogenerator for vibrational energy harvesting and wearable shoe insole pedometer sensor

The increasing demand of energy harvesting and wearable electronics applications requires the development of flexible and highly durable piezoelectric nanogenerators (PENG). In this work, We have fabricated flexible ZnO:PVDF based PENGs for vibrational energy harvesting and shoe insole pedometer applications. ZnO nanorods were grown by hydrothermal method and incorporated into PVDF matrixes in the concentration range of 5–15 wt%. These homogeneous ZnO:PVDF composite films were sandwiched between Al electrodes to realize flexible free standing PENGs. The open circuit voltage (Voc), short circuit current (Isc) and instantaneous power density of PENGs increased from ∼ 4 V, 0.4 µA and 1.6 µW/cm2 to ∼ 14.6 V, 0.6 µA and 21.3 µW/cm2 respectively when ZnO nanorods concentration in PVDF increased from 0 to 10 wt% and decreased with further increase in ZnO nanorods concentration. The enhancement in output characteristics of ZnO:PVDF PENG with increasing ZnO concentration was attributed to β-phase crystallization of PVDF, which was confirmed by XRD and FTIR measurements. The deterioration in output characteristics beyond 10 wt% of ZnO nanorods concentration was explained considering the variation of dielectric constant and remnant polarization. The rectified output of the PENGs was effectively stored in various commercially available capacitors and used to power LEDs and stopwatch displays. The PENG with 10 wt% ZnO concentration was used to develop shoe insole pedometer which was interfaced with android based mobile application via Bluetooth. The shoe insole pedometer was successfully tested for 5000 steps at different walking frequencies ranging from 0.5 Hz to 2 Hz in the speed range of ∼ 1.4 km/h to 5.5 km/h. This study not only gives an insight into the mechanism of ZnO:PVDF based PENGs but also opens up their potential in vibration energy harvesting and shoe insole pedometer applications.

Rationalizing the Dependence of Poly (Vinylidene Difluoride) (PVDF) Rheological Performance on the Nano-Silica

Research on the rheological performance and mechanism of polymer nanocomposites (PNCs), mainly focuses on non-polar polymer matrices, but rarely on strongly polar ones. To fill this gap, this paper explores the influence of nanofillers on the rheological properties of poly (vinylidene difluoride) (PVDF). The effects of particle diameter and content on the microstructure, rheology, crystallization, and mechanical properties of PVDF/SiO2 were analyzed, by TEM, DLS, DMA, and DSC. The results show that nanoparticles can greatly reduce the entanglement degree and viscosity of PVDF (up to 76%), without affecting the hydrogen bonds of the matrix, which can be explained by selective adsorption theory. Moreover, uniformly dispersed nanoparticles can promote the crystallization and mechanical properties of PVDF. In summary, the viscosity regulation mechanism of nanoparticles for non-polar polymers, is also applicable to PVDF, with strong polarity, which is of great value for exploring the rheological behavior of PNCs and guiding the process of polymers.

The β Form in PVDF Nanocomposites with Carbon Nanotubes: Structural Features and Properties

Different amounts of carbon nanotubes (CNT) have been incorporated in materials based on poly(vinylidene fluoride) (PVDF) by solvent blending followed by their further precipitation. Final processing was performed by compression molding. The morphological aspects and crystalline characteristics have been examined, additionally exploring in these nanocomposites the common routes described in the pristine PVDF to induce the β polymorph. This polar β phase has been found to be promoted by the simple inclusion of CNT. Therefore, coexistence of the α and β lattices occurs for the analyzed materials. The real-time variable-temperature X-ray diffraction measurements with synchrotron radiation at a wide angle have undoubtedly allowed us to observe the presence of the two polymorphs and determine the melting temperature of both crystalline modifications. Furthermore, the CNT plays a nucleating role in the PVDF crystallization, and also acts as reinforcement, increasing the stiffness of the nanocomposites. Moreover, the mobility within the amorphous and crystalline PVDF regions is found to change with the CNT content. Finally, the presence of CNT leads to a very remarkable increase in the conductivity parameter, in such a way that the transition from insulator to electrical conductor is reached in these nanocomposites at a percolation threshold ranging from 1 to 2 wt.%, leading to the excellent value of conductivity of 0.05 S/cm in the material with the highest content in CNT (8 wt.%).

Crystallization-templated high-performance PVDF separator used in lithium-ion batteries

In this work, high-performance PVDF separators have been successfully fabricated for lithium-ion batteries (LIBs) based on crystallization template in PVDF/PBSU blends. The crystallization of PVDF produces co-continuous structures of crystalline phase and amorphous phase. On one hand, the continuous state of PBSU enables its removal via selective solvent extraction, yielding 3D interpenetrated nanochannels which have been confirmed with the help of X-ray imaging technology. On the other hand, the continuous PVDF crystal framework contributes to superior mechanical performance and heat resistance of resultant separator, playing crucial roles in the inhibition of Li dendrite growth and improvement of LIBs safety. The optimal specimen of PVDF-30 (from PVDF/PBSU 30/70) exhibits higher discharge capacity (135.5 mA h g−1), higher coulombic efficiency (∼99.9% after 200 cycles) and enhanced cycle stability relative to the reference (commercial polypropylene separator). Such a significant improvement can be attributed to the combination of excellent connectivity of diffusion channels, outstanding mechanical performance and higher electrolyte uptake resulting from stronger polarity of PVDF. Our results provide a novel strategy for fabricating PVDF separators with superior performances used in lithium-ion batteries.

Effect of cation and anion sizes of additive ionic liquid on the crystal structure of poly(vinylidene fluoride) nanofiber

We investigated the additive ionic liquid (IL) type dependence on the crystal structure of poly(vinylidene fluoride) (PVDF) nanofibers. As additive ILs, we used imidazolium based ILs with different cation and anion sizes. From differential scanning calorimetry (DSC) measurements, we found that there is a proper amount for the additive IL to promote PVDF crystallization, and the proper amount is influenced by the cation size, not by the anion size. In addition, it was found that IL itself inhibited the crystallization, but IL can promote crystallization under the presence of DMF.

Enhanced Separation Performance of Hierarchically Porous Membranes Fabricated via the Combination of Crystallization Template and Foaming.

In this work, poly (vinylidene fluoride) (PVDF) hierarchically porous membranes (HPMs) with isolated large pores and continuous narrow nano-pores have been fabricated from its blend with poly (methyl methacrylate) (PMMA) based on the combination of crystallization template with chemical or supercritical CO2 foaming. On the one hand, the decomposition of azodicarbonamide (ADC, chemical foaming agent) or the release of CO2 can produce isolated large pores. On the other hand, PMMA is expelled during the isothermal crystallization of PVDF in their miscible blend, yielding narrow nano-pores upon etching with a selective solvent. In the case of supercritical CO2, the attained PVDF HPMs fail to improve separation performance because of the compact wall of isolated-large-pore and consequent poor connectivity of hierarchical pores. In the case of ADC, the optimal HPM exhibits much higher flux (up to 20 times) without any loss of selectivity compared with the reference only with nano-pores. The enhanced permeability can be attributed to the shorter diffusion length and lower diffusion barrier from isolated large pores, while the comparable selectivity is determined by narrow nano-pores in THE matrix.

Exploiting Partial Solubility in Partially Fluorinated Thermoplastic Blends to Improve Adhesion during Fused Deposition Modeling.

This work studies the effect of interlayer adhesion on mechanical performance of fluorinated thermoplastics produced by fused deposition modeling (FDM). Here, we study the anisotropic mechanical response of 3D-printed binary blends of poly (vinylidene fluoride) (PVDF) and poly (methyl methacrylate) (PMMA) with the isotropic mechanical response of these blends fabricated via injection molding. Various PVDF/PMMA filament compositions were produced by twin-screw extrusion and, subsequently, injection-molded or 3D printed into dog-bone shapes. Specimen mechanical and thermal properties were evaluated by mode I tensile testing and differential scanning calorimetry, respectively. Results show that higher PMMA concentration not only improved the tensile strength and decreased ductility but reduced PVDF crystallization. As expected, injection-molded samples revealed better mechanical properties compared to 3D printed specimens. Interestingly, 3D printed blends with lower PMMA content demonstrated better diffusion (adhesion) across interfaces than those with a higher amount of PMMA. The present study provides new findings that may be used to tune mechanical response in 3D printed fluorinated thermoplastics, particularly for energy applications.

Evident improvement in burning anti-dripping performance, ductility and electrical conductivity of PLA/PVDF/PMMA ternary blend-based nanocomposites with additions of carbon nanotubes and organoclay

In this study, carbon nanotubes (CNTs) and organoclay (30B) were introduced into poly(lactic acid) (PLA)/poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) (70/30/30) ternary blend, with PMMA acting as a compatibilizer for the PLA and PVDF phases. Morphological results indicated that PMMA tended to entangle more with PVDF than with PLA, and thus formed a pseudo co-continuous PLA(rich)-PVDF(rich) phase morphology in the blend. The added CNTs and 30B clay were mainly distributed in the PVDF(rich) phase and PLA(rich) phase, respectively, to achieve nanocomposites. The co-continuous bi-phasic morphology was more evident in the composites than in the parent blend. Thermal property results revealed the nucleation effect of CNTs and 30B on the crystallization of PLA and PVDF; the presence of PMMA obviously retarded the crystal growth of PVDF due to their miscibility. Adding CNTs or hybrid CNT/30B evidently improved the anti-dripping performance of the ternary blend in burning tests. The ductility (elongation at break) of PLA/PVDF blend drastically improved with PMMA inclusion, and the composites also showed excellent ductility. The ductility of PLA and PLA/PVDF blend increased by up to 18.9 and 14.4 times, respectively, after forming the 3-phr hybrid CNT/30B-loaded composite. Rigidity of the ternary blend increased after forming the composites; flexural modulus increased by 16% with 3 phr CNT inclusion. Rheological properties revealed the (pseudo)network structure development in the composites. The electrical resistivity of the ternary blend reduced by 11 orders at 2 phr CNT loading (double percolation achieved), and the percolation threshold was at 0.5 phr CNT loading.

PMMA-driven morphology modification and dramatic improvement in ductility for PVDF/PLA blends

Poly(methyl methacrylate) (PMMA) was incorporated as compatibilizer in immiscible poly(vinylidene fluoride) (PVDF)/poly(lactic acid) (PLA) blends at different ratios. Scanning electron microscopy results revealed that, after adding PMMA, the phase morphology of PVDF/PLA blends evidently changed and the boundary became diffused, indicating improved interaction between PVDF and PLA. The sea-island biphasic morphology of PVDF/PLA (1:1) blend transferred to pseudo co-continuous morphology with the incorporation of PMMA. Differential scanning calorimetry and polarized light microscopy results showed that the presence of pre-crystallized PVDF facilitated the crystallization of PLA on cooling from the melt, but the molten PLA slightly retarded the crystallization of PVDF. With the inclusion of PMMA in the blends, PVDF crystal growth was further inhibited due to its miscibility with PMMA, and its crystallinity was also decreased. The elongation at break (ductility) of PLA and PVDF/PLA blends increased drastically by up to 27.8 and 11.1 times respectively, after formation of ternary PVDF/PLA/PMMA blends. Dynamic mechanical analysis results showed that the individual glass transition temperatures of PVDF and PLA in the blends shifted to higher temperatures after adding PMMA. PMMA showed more affinity to PVDF than to PLA. Rheological property measurements confirmed the increase in complex viscosity and storage modulus of the blends with increasing PMMA loading.

Lightweight, strong, flame-retardant PVDF/PMMA microcellular foams for thermal insulation fabricated by supercritical CO2 foaming

An innovative method of improving PVDF foaming behavior and foam performance by blending with polymethyl methacrylate (PMMA) was devised, and lightweight, strong, flame-retardant foams with wider foaming window and excellent thermal insulation performance were successfully achieved. PMMA not only improves CO2 uptake and melt viscoelasticity, but also decreases PVDF crystallinity and increases melting range of PVDF crystals. Compared to PVDF foams, expansion ratio of the blend foams increased from 21.9 to 31.2, and effective foaming window was expanded from 3.6 °C to 17.4 °C. Thanks to the blend foams' high expansion and PMMA's strong infrared absorption ability and high rigidity, thermal conductivity and compression modulus of the foams are 33.85 mW m−1 K−1 and 3.51 MPa, respectively. Moreover, the blend foams also show a lower heat release rate and favorable flame retardancy.

Exploration of the Nucleation-Growth Effect of Cetyltrimethylammonium Bromide for High β-Poly(Vinylidene Fluoride) Crystallization

Poly(vinylidene fluoride) (PVDF, β-phase) exhibits excellent electrical properties because of its all-trans conformation in the crystalline phase, which has attracted much attention in electronic device applications. This paper describes our studies of the cetyltrimethylammonium bromide (CTAB)-induced PVDF crystallization in PVDF thin films via solution crystallization and melt crystallization by compression molding. In the solution crystallization process the relative crystal content of the polar crystals phase of PVDF reached 90% due to the solvent effect and low crystallization temperature. During the melt crystallization process the polar crystal nucleation effect of CTAB (powders) was pronounced. The strong "ion-dipole" interaction between the positive charges on the surface of CTAB and the -CF2 of PVDF promoted the formation of polar crystals. The incorporation of 1 wt% CTAB in PVDF led to the nucleation of polar crystallites up to 97.6%. Additionally, the tensile strength and elongation at break reached 39.8 MPa and 172.5%. The crystallinity of the PVDF increased with an increase in the content of CTAB. The electrostatic interaction between CTAB and the PVDF molecular chains induced and stabilized the all-trans conformation of the PVDF crystals, resulting in PVDF films with high polar phase content, which are expected to be applicable to industrially produced piezoelectric films.

Anti-fouling and easy-cleaning PVDF membranes blended with hydrophilic thermo-responsive nanofibers for efficient biological wastewater treatment

Membrane technology can minimize spread of viruses in the environment during pandemics, however, its efficiency is highly limited by biofouling. In the current study, a composite membrane composed of commercial membrane material, poly(vinylidene fluoride) (PVDF), and thermo-responsive attapulgite (t-ATP) was developed. The t-ATP was synthesized by surface modification of attapulgite (ATP) nanofiber with poly(N-isopropylacrylamide) (PNIPAM). t-ATP acted as a nucleating seed to expedite crystallization of PVDF and as a hydrophilic modifier to enhance the wetting performance of membrane. The tensile strength, elongation, and permeance of membrane increased with increase in t-ATP content without compromising pore structure. PNIPAM chains in t-ATP were swollen or shrunken with the change in temperature, thus releasing adhesion between membrane and biofoulants. The modified membrane exhibited superior biofouling resistance performance compared with the pristine PVDF membrane owing to the hydrophilic property of t-ATP and the stretchable chains on its surface. Notably, 89% of biofouling on membrane surface was easily removed through a simple temperature-change coupling ultrasonic cleaning process. High performance of the PVDF/t-ATP membrane indicates its potential application for high-efficient biological wastewater treatment.