Phase Of PVDF Research Articles

Enhancement of polar phases in PVDF by forming PVDF/SiC nanowire composite

Different contents of silicon carbide (SiC) nanowires were mixed with Poly(vinylidene fluoride) (PVDF) to facilitate the polar phase crystallization. It was shown that the annealing temperature and SiC content affected on the phase and crystalline structures of PVDF/SiC samples. Furthermore, the addition of SiC nanowire enhanced the transformation of non-polar α phase to polar phases and increased the relative fraction of β phase in PVDF. Due to the nucleating agent mechanism of SiC nanowires, the ion-dipole interaction between the negatively charged surface of SiC nanowires and the positive CH 2 groups in PVDF facilitated the formation of polar phases in PVDF.

Enhancement of polar crystalline phase formation in transparent PVDF-CaF2 composite films

We consider the influence of calcium fluoride (CaF2) nanoparticles on the crystalline phase formation of poly(vinylidene fluoride) (PVDF) for the first time. The transparent PVDF-CaF2 composite films were prepared by casting on PET substrates using N,N-dimethylacetamide (DMAc) as a solvent. It was found that CaF2 promoted the formation of polar crystalline phase of PVDF in composites, whereas nonpolar α-phase was dominant in the neat PVDF film prepared at the same condition. The portion of polar crystalline phase increased in proportional to the weight fraction of CaF2 in the composite films up to 10wt%. Further addition of CaF2 suppressed completely the α-phase formation. Polar crystalline phase observed in as-cast composite films was a mixture of β- and γ-polymorph structures. It was also shown that much ordered γ-phase could be obtained through thermal treatment of as-cast PVDF-CaF2 composite film at the temperatures above the melting temperature of the composite films, but below that of γ-phase.

Polymorphic Crystallization and Crystalline Reorganization of Poly(l-lactic acid)/Poly(d-lactic acid) Racemic Mixture Influenced by Blending with Poly(vinylidene fluoride).

The effects of poly(vinylidene fluoride) (PVDF) on the crystallization kinetics, competing formations of homocrystallites (HCs) and stereocomplexes (SCs), polymorphic crystalline structure, and HC-to-SC crystalline reorganization of the poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) racemic mixture were investigated. Even though the PLLA/PDLA/PVDF blends are immiscible, blending with PVDF enhances the crystallization rate and SC formation of PLLA/PDLA components at different temperatures that are higher or lower than the melting temperature of the PVDF component; it also facilitates the HC-to-SC melt reorganization upon heating. The crystallization rate and degree of SC crystallinity (Xc,SC) of PLLA/PDLA components in nonisothermal crystallization increase after immiscible blending with PVDF. At different isothermal crystallization temperatures, the crystallization half-time of PLLA/PDLA components decreases; its spherulitic growth rate and Xc,SC increase as the mass fraction of PVDF increases from 0 to 0.5 in the presence of either a solidified or a molten PVDF phase. The HCs formed in primary crystallization of PLLA/PDLA components melt and recrystallize into SCs upon heating; the HC-to-SC melt reorganization is promoted after blending with PVDF. We proposed that the PVDF-promoted crystallization, SC formation, and HC-to-SC melt reorganization of PLLA/PDLA components in PLLA/PDLA/PVDF blends stem from the enhanced diffusion ability of PLLA and PDLA chains.

Tuning the microwave absorption through engineered nanostructures in co-continuous polymer blends

Herein, we report tailor-made properties by dispersing nanostructured materials in a co-continuous polymer blend (PVDF/ABS) that is capable of shielding electromagnetic (EM) radiation. To accomplish this, lossy materials were employed like multi-walled carbon nanotubes (MWNTs), and barium titanate (BT), (which exhibit relaxation losses in the microwave frequency domain) and ferrites (like Fe3O4). To improve the state of dispersion, the MWNTs were non-covalently modified using 3,4,9,10-perylenetetracarboxylic dianhydride (PTCD) via π–π stacking, and for effective shielding the MWNTs were conjugated with either BT or Fe3O4 nanoparticles through suitable modifications. The hybrid nanoparticles were selectively localized in the PVDF phase, governed by its polarity, and exhibited excellent microwave attenuation. In order to gain insight into the dielectric and magnetic attributes, the microwave parameters were assessed systematically. Taken together, our results uncover polymer blend as a promising candidate for designing lightweight, thermally stable microwave absorber materials.

Composites of Carbon Nanotubes with the Blend of Poly(vinylidene fluoride)/Poly(vinyl acetate)

Poly(vinylidene fluoride)/poly(vinyl acetate)/carbon nanotubes, PVDF/PVAc/CNT, composite films were prepared at various compositions via a solution casting method. The amorphous PVAc formed a miscible blend with PVDF and drastically improved dispersion of CNT in PVDF/CNT composites. Combination of ductile PVAc and rigid CNT had favorable effects on mechanical properties of PVDF. The elongation of PVDF increased from 8% to 300% with addition of 40 wt% PVAc and 0.5 wt% CNT and the modulus at 1.5 wt% CNT was almost 2.3 fold of that of the neat PVDF while retaining high ductility and tensile strength. XRD and FTIR results showed that CNT favored formation of β-crystalline phase in PVDF. Also DSC results showed that the addition of CNT resulted in higher melting temperatures, TSUBm/SUB, and higher crystallinity. Electrical conductivity of the composite films increased sharply by addition of only 1 wt% CNT that attributed to development of CNT network morphology in PVDF/PVAc matrix.

Formation mechanisms of low-biofouling PVDF/F127 membranes prepared by VIPS process

Research on the preparation by in-situ modification of antifouling membranes has grown exponentially. Yet, little is known on their formation mechanisms and dedicated studies could help at improving the fine control of their structure. Our purpose here was to investigate the formation of PVDF/F127 membranes (PEG-type PVDF membranes). F127 was blended with PVDF and vapor-induced phase separation process applied to form the membranes. Like for virgin PVDF membranes, morphology of PVDF/F127 membranes is dependent on the dissolution temperature of the casting solution. The thermodynamic and kinetic effects of copolymer were investigated through the establishment of phase diagram and diffusion kinetics of non-solvent during phase separation. In the conditions tested, solutions containing PVDF and F127 are less viscous than those only containing PVDF. Also, as F127 enhances the chemical affinity of the blend with water, it eventually promotes non-solvent diffusion. Additionally, it reduces the stability of the system. However, despite a major role of copolymer on thermodynamic and kinetic of phase separation, crystallization (size of nodules, nature of polymorphs) is unaffected by F127. The morphology and arising bulk properties of low-biofouling PVDF/F127 membranes is only dependent on the initial nucleation density of crystals prior to phase separation, controlled by the dissolving temperature.

Bacterial Nanocellulose Aerogel Membranes: Novel High-Porosity Materials for Membrane Distillation

We fabricated, characterized, and tested novel fibrous aerogel membranes in direct contact membrane distillation (MD) to elucidate the effects of a model high-porosity membrane material on MD performance. Unsupported bacterial nanocellulose aerogels exhibit higher porosity, thinner fibers, and lower bulk thermal conductivity than any previously reported MD materials. Modeling and experiments demonstrate that these material properties confer significantly higher intrinsic membrane permeability and thermal efficiency than symmetric PVDF phase inversion membranes with lower porosity. Development of macroporous fibrous membranes with aerogel-like porosity and thermal conductivity (>98% and <0.03 W m–1 K–1, respectively) in thinner-film formats may further improve MD flux.

Enhanced dielectric and piezoelectric properties of 0–3 PZT/PVDF composites

Flexible piezoelectric composite films of ([PZT/]x/[PVDF]1-x (x = 0, 0.1, 0.2, 0.3) with 0–3 connectivity were synthesized from 0.2 wt% Li2CO3 added PZT ceramic powders in the morphotropic phase boundary (MPB) and PVDF polymer by solution cast technique under optimized thermal processing conditions. It is seen that crystallinity and β phase are enhanced with the addition of Li in the composite films and as well as with the volume content of PZT ceramics in PVDF matrix, thereby resulting in superior dielectric and piezoelectric properties. It is also seen that reasonably high dielectric and piezoelectric properties are obtained for 30 % of the volume content of PZT ceramics as compared to 50 % of the volume content of ceramic in the polymer matrix as reported in literature and hence, the flexibility is better in these films.

Mechanical and electro-mechanical properties of three-dimensional nanoporous graphene-poly(vinylidene fluoride) composites

Three-dimensional nanoporous graphene monoliths are utilized to prepare graphene-poly(vinylidene fluoride) nanocomposites with enhanced mechanical and electro-mechanical properties. Pre-treatment of the polymer (poly(vinylidene fluoride), PVDF) with graphene oxides (GOs) facilitates the formation of uniform and thin PVDF films with a typical thickness below 100 nm well coated at the graphene nano-sheets. Besides their excellent compressibility, ductility and mechanical strength, the nanoporous graphene-PVDF nanocomposites are found to possess high sensitivity in strain-dependent electrical conductivity. The improved mechanical and electro-mechanical properties are ascribed to the enhanced crystalline β phase in PVDF which possesses piezoelectricity. The mechanical relaxation analyses on the interfaces between graphene and PVDF reveal that the improved mechanical and electro-mechanical properties could result from the interaction between the –C=O groups in the nanoporous graphene and the –CF2 groups in PVDF, which also explains the important role of GOs in the preparation of the graphene-polymer nanocomposites with superior combined mechanical and electro-mechanical properties.

Isothermal and Non-Isothermal Crystallization Kinetics of Conductive Polyvinylidene Fluoride/Poly(Ethylene Terephthalate) Based Composites

This work deals with isothermal and non-isothermal crystallization kinetics of electrically conductive polyvinylidene fluoride/poly(ethylene terephthalate) (PVDF/PET) based composites. It completes our previous work in which we related the crystallinity of these conductive PVDF/PET based composites to their through-plane resistivity [1]. Isothermal crystallization was described using the logarithmic form of the Avrami equation and it was observed that the crystallization rate of the PVDF phase inside the composite became slower compared to that of neat PVDF. In non-isothermal crystallization, the Avrami exponent of PVDF phase did not show any noticeable variation; however, that of PET phase, which contains the major part of the conductive carbon black (CB) and graphite (GR) additives, showed an evident decrease compared with neat PET. It was also observed that, at the same cooling rate, the crystallization rate of PVDF and PET phases inside the composite was slower than that of neat PVDF and PET.

Dielectric, enhanced magnetic and magnetodielectric properties of hot pressed (BNBT-BFO)/PVDF composite films

The thick composites film 0.8(0.65BaTiO3-0.35Bi0.5Na0.5TiO3)-0.2BiFeO3 /Poly(vinylidene fluoride) (BNBT-BFO/PVDF) with 20 %, 30 %, 40 % and 50 % concentration of PVDF were synthesized by hot polymer press. The structural analysis was carried out by X-ray diffraction (XRD), which reveals the crystalline phases corresponding to ferroelectric, ferrites and PVDF phases. The grain sizes and roughness of composites films were observed by using AFM analysis. Dielectric study of thick composites films were done with frequency and temperature and found that the effective dielectric permittivity of composites films decreases with increase in the volume fraction of PVDF at all the frequencies under investigation. The magnetic and magnetodielectric properties of composites films have been also systematically investigated and found to be enhanced as compare to BNBT-BFO with increase in PVDF.

Tailor-Made Distribution of Nanoparticles in Blend Structure toward Outstanding Electromagnetic Interference Shielding.

Engineering blend structure with tailor-made distribution of nanoparticles is the prime requisite to obtain materials with extraordinary properties. Herein, a unique strategy of distributing nanoparticles in different phases of a blend structure has resulted in >99% blocking of incoming electromagnetic (EM) radiation. This is accomplished by designing a ternary polymer blend structure using polycarbonate (PC), poly(vinylidene fluoride) (PVDF), and poly(methyl methacrylate) (PMMA) to simultaneously improve the structural, electrical, and electromagnetic interference shielding (EMI). The blend structure was made conducting by preferentially localizing the multi-wall nanotubes (MWNTs) in the PVDF phase. By taking advantage of "π-π stacking" MWNTs was noncovalently modified with an imidazolium based ionic liquid (IL). Interestingly, the enhanced dispersion of IL-MWNTs in PVDF improved the electrical conductivity of the blends significantly. While one key requisite to attenuate EM radiation (i.e., electrical conductivity) was achieved using MWNTs, the magnetic properties of the blend structure was tuned by introducing barium ferrite (BaFe) nanoparticles, which can interact with the incoming EM radiation. By suitably modifying the surface of BaFe nanoparticles, we can tailor their localization under the macroscopic processing condition. The precise localization of BaFe nanoparticles in the PC phase, due to nucleophilic substitution reaction, and the MWNTs in the PVDF phase not only improved the conductivity but also facilitated in absorption of the incoming microwave radiation due to synergetic effect from MWNT and BaFe. The shielding effectiveness (SE) was measured in X and Ku band, and an enhanced SE of -37 dB was noted at 18 GHz frequency. PMMA, which acted as an interfacial modifier in PC/PVDF blends further, resulting in a significant enhancement in the mechanical properties besides retaining high SE. This study opens a new avenue in designing mechanically strong microwave absorbers with a suitable combination of materials.

Thermoplastic vulcanizate based on poly(vinylidene fluoride) and methyl vinyl silicone rubber by using fluorosilicone rubber as interfacial compatibilizer

To successfully fabricate a thermoplastic vulcanizate (TPV) based on poly (vinylidene fluoride) (PVDF) and high loading level of methylvinyl silicone rubber (MVSR), stabilizing the phase structure during blending is a challenge due to the distinct interface properties of the two materials. Herein, we report a feasible method to fabricate a desired PVDF/MVSR TPV by using fluorosilicone rubber (FSR) as an interfacial compatibilizer. We found that the FSR was self-assembly migrated from MVSR phase toward PVDF phase and finally located at the interface between PVDF and MVSR, forming core–shell-like spherical particles with a rough surface, and surprisingly, the crosslinked rubber particles were connected by fiber-like elastomeric materials which bonded onto the surfaces of the particles. The excellent property of repeat processing of the PVDF/MVSR/FSR TPV with such novel phase morphology makes it a potential alternative of fluorosilicone rubber in future.

Fabrication of form-stable poly(ethylene glycol)-loaded poly(vinylidene fluoride) nanofibers via single and coaxial electrospinning

Two types of form-stable phase change material based on poly(ethylene glycol)-loaded poly(vinylidene fluoride) (PVDF) nanofibers were fabricated via single and coaxial electrospinning. Blends of two different kinds of poly(ethylene glycol) (PEG600 and PEG1000) were used as the phase change material (PCM) and PVDF was used as supporting polymers in the PCM-loaded electrospun PVDF nanofibers. By single electrospinning, SiO2 was added into the PEGs-loaded PVDF to prevent PEGs leakage and to maintain the shape of the nanofibers during the melting and solidifying processes. The addition of SiO2 also increased the mechanical strength of the nanofibers. By coaxial electrospinning, the core/shell structured nanofibers, in which the PEGs and PVDF were the active core and protective shell layers, respectively, were fabricated. The microstructure of the e-spun nanofibers was investigated by FE-SEM. TEM images show that PEGs were encapsulated by PVDF shell. The ATR-FTIR analysis and water contact angle measurements confirm that good core/shell-structured nanofibers were obtained when the core feed rate was lower than 4.0 µL/min. During the water immersion test, the PEGs on the surface of the PVDF/SiO2 composite nanofibers were dissolved, while no leakage of PEGs from the core/shell-structured nanofibers was observed. A hot oven and a DSC cycling tests were conducted to evaluate the thermal stability. These results show that the PEGs-loaded core/shell nanofibers had better thermal stability than the PEGs-loaded PVDF/SiO2 composite nanofibers. Therefore, the non-woven mats of the core/shell-structured nanofibers could have extensive applications in thermal energy storage and fabrication of smart textile.

Compatibilization effect of MMA-co-GMA copolymers on the properties of polyamide 6/Poly(vinylidene fluoride) blends

Methyl methacrylate-co-glycidyl methacrylate copolymers (MMA-co-GMA) with different GMA contents were prepared to compatibilize the polyamide 6 (PA6) and poly(vinylidene fluoride) (PVDF) blend. The chemical reactions between the carboxyl/amino end groups of PA6 and the epoxy groups, and the good miscibility between PVDF and MMA-co-GMA were responsible for the excellent compatibilization effect. DMA results showed that the glass transition peaks of PVDF phase almost disappeared in the PA6/PVDF/MMA-co-GMA blends; this proved the suppressed thermal transition due to the restricted movement of PVDF chains. MMA-co-GMA copolymers significantly decreased the phase domain size of the PA6/PVDF blends. PVDF dispersed in the PA6 matrix uniformly and the interface between the two phases was obscure due to the compatibilization. The addition of MMA-co-GMA into the PA6/PVDF blend decreased the crystallization temperature of the PVDF phase, which proved that the compatibilizer enhanced the interaction between PVDF and PA6 and retarded the crystallization. Mechanical tests indicated that the impact strength and elongation at break of the PA6/PVDF blends increased with the addition of MMA-co-GMA. The increase of the fracture toughness was due to the compatibilization effect of MMA-co-GMA copolymers, which induced a delay of the debonding of PA6 and PVDF phases at the interface and inhibited the initiation and propagation of cracks.

New tools for elucidating the environmental origins of single molecule photoluminescence intermittency

New experimental and analysis methods for investigating the role local environment has on photoluminescence intermittency (PI) exhibited by single luminophores are presented. Quasi-single molecule (SM) microscopy provides spatial resolution of dielectric environments within poly(vinylidene fluoride) (PVDF) films, and reveals annealing's effect on the structural phase of PVDF. New analysis methods establish that the PI exhibited by nile red (NR) SMs in PVDF are consistent with photoinduced electron transfer between NR and PVDF, where transfer rates depend on local dielectric environment. These methods should prove useful for SM studies of guest–host materials where elucidating PI contribution from the host is required.

Joint experimental and computational investigation of the structural and spectroscopic properties of poly(vinylidene fluoride) polymorphs.

State-of-the-art density functional theory calculations are here adopted for the investigation of the crystal structure and of the vibrational properties of α, β, γ, and δ phases of poly(vinylidene fluoride) (PVDF), in comparison with IR and Raman measurements. DFT calculations allowed a detailed interpretation of the IR and Raman spectra of α and β phases, giving vibrational assignments useful for qualitative and quantitative characterization of these systems. From a molecular perspective, the computational investigation of the crystal structure and the spectra of PVDF polymorphs helped in clarifying the role of supramolecular dipole-dipole interactions, which indeed modulate the vibrational properties of these systems, indicating also that intermolecular interaction could play a significant role in the modulation of ferroelectric properties. Furthermore, the combined experimental and computational approach allowed us to identify and characterize the thermally and mechanically induced γ phase, shedding light on the far-IR marker bands of this elusive phase of PVDF.

Ion Exchange Dependent Electroactive Phase Content and Electrical Properties of Poly(vinylidene fluoride)/Na(M)Y Composites

Different metal ion exchanged NaY zeolite, Na(M)Y, were used to prepare poly(vinylidene fluoride) based composites by solvent casting and melting crystallization. The effect of different metal ion exchanged zeolites on polymer crystallization and electrical properties was reported. Cation–framework interactions and hydration energy of the cations determined that K+ is the most efficient exchanged ion in NaY zeolite, followed by Cs+ and Li+. The electroactive phase crystallization strongly depends on the ions present in the zeolite, leading to variations of the surface energy characteristics of the Na(M)Y zeolites and the polymer chain ability of penetration in the zeolite. Thus, Na(Li)Y and NaY induce the complete electroactive γ-phase crystallization of the crystalline phase of PVDF, while Na(K)Y only induces it partly and Na(Cs)Y is not able to promote the crystallization of the electroactive phase. Furthermore, different ion size/weight and different interaction with the zeolite framework result in significant variations in the electrical response of the composite. In this way, iinterfacial polarization effects in the zeolite cavities and zeolite–polymer interface lead to strong increases of the dielectric constant on the composites with lightest ions weakly bound to the zeolite framework. Polymer composites with Na(Li)Y show the highest dielectric response, followed by NaY and Na(K)Y. Zeolite Na(Cs)Y contributes to a decrease of the dielectric constant of the composite. The results show the relevance of the materials for sensor development.

Imaging the effects of annealing on the polymorphic phases of poly(vinylidene fluoride).

The effect of annealing on the phase transformation and the dielectric properties of poly(vinylidene fluoride) (PVDF) is explored using quasi-single molecule (quasi-SM) microscopy. The solvatochromic properties of nile red (NR) are employed to measure the spatial distribution of the local dielectric constant (ε) in ∼30 μm thick PVDF films before and after annealing at 90 °C. The results presented here demonstrate that nonannealed films exhibit much larger ε distributions, both in terms of magnitude and distribution, when compared to annealed films. The polymorphic phase of PVDF before and after annealing is also confirmed using X-ray diffraction. Nonannealed films are found to be in the γ-phase with annealing promoting the transition to primarily β-phase. Combining these results, we conclude that the decrease in ε with annealing time is due to the phase transformation from γ- to β-phase. Using quasi-SM imaging techniques one can readily visualize the ε environments present within different polymorphic phases of PVDF.

Self-poled transparent and flexible UV light-emitting cerium complex-PVDF composite: a high-performance nanogenerator.

Cerium(III)-N,N-dimethylformamide-bisulfate [Ce(DMF)(HSO4)3] complex is doped into poly(vinylidene fluoride) (PVDF) to induce a higher yield (99%) of the electroactive phases (β- and γ-phases) of PVDF. A remarkable enhancement of the output voltage (∼32 V) of a nanogenerator (NG) based on a nonelectrically poled cerium(III) complex containing PVDF composite film is achieved by simple repeated human finger imparting, whereas neat PVDF does not show this kind of behavior. This high electrical output resembles the generation of self-poled electroactive β-phase in PVDF due to the electrostatic interactions between the fluoride of PVDF and the surface-active positive charge cloud of the cerium complex via H-bonding and/or bipolar interaction among the opposite poles of cerium complex and PVDF, respectively. The capacitor charging capability of the flexible NG promises its applicability as piezoelectric-based energy harvester. The cerium(III) complex doped PVDF composite film exhibit an intense photoluminescence in the UV region, which might be due to a participation of electron cloud from negative pole of bipolarized PVDF. This fact may open a new area for prospective development of high-performance energy-saving flexible solid-state UV light emitters.