Crystalline Structure Of PVDF Research Articles

High-sensitivity humidity sensor based on Poly(vinylidene fluoride)/Deep eutectic solvent composites

This study explores the incorporation of deep eutectic solvent (DES) into a poly (vinylidene fluoride) (PVDF) matrix to fabricate PVDF/DES composite thin films. Subsequently, electrodes were screen-printed onto the thin films to create PVDF/DES humidity sensors. The investigation delved into the crystalline structure of PVDF, the cross-sectional morphology and electrochemical property of PVDF/DES composite films, and the humidity sensing response of PVDF/DES humidity sensors. The study revealed that adding DES leads to the formation of porous composite films with electrical active phases and high electrical conductivity. The sensitivity of the PVDF/DES humidity sensor increases with the content of DES. This work provides a novel method for the fabrication of humidity sensors, holding significant potential in various applications such as respiratory monitoring.

Investigation of the optimum vibration energy harvesting performance of electrospun PVDF/BaTiO3 nanogenerator

The piezoelectric vibration energy harvesting performance of an electrospun poly(vinylidene fluoride) (PVDF)/Barium Titanate (BaTiO3) nanocomposite piezo polymer nanogenerator was investigated in this study. To obtain the highest piezoelectric output value, electrospinning was performed using four distinct solvent volume ratios of Acetone/Dimethylformamide (DMF) of 0:10, 2:8, 4:6, and 6:4 and three different PVDF weight percent polymer concentrations of 10, 15, and 20. Additionally, three distinct BaTiO3 addition weight percents of 5, 10, and 15 were investigated. The optimal concentration of PVDF (15 wt.%) was combined with a 6:4 volume ratio of Acetone/DMF to form a nanocomposite piezo polymer nanogenerator. The morphology and crystalline structure of PVDF and PVDF/BaTiO3 were analyzed using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) techniques. Nanocomposite piezo polymer nanogenerator was manufactured to harvest energy from vibration. A cantilever beam was developed without a tip mass type system for piezoelectric energy harvesting tests. The highest piezoelectric power output was obtained as 0.243 μW (15 wt.% PVDF and 5 wt.% BaTiO₃), Acetone/DMF (6:4 vol./vol.)) under 10 MΩ at the 15.7 Hz resonance frequency. The morphology of electrospun nanofibers has a significant impact on the piezoelectric performance of a nanocomposite piezo polymer nanogenerator at high-amplitude vibration.

Analysis of electrospinning and additive effect on β phase content of electrospun PVDF nanofiber mats for piezoelectric energy harvester nanogenerators

Harvesting energy with piezoelectric nanoparticles enables the development of self-powered devices. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF) has been widely used in a variety of fields due to its superior piezoelectric properties. PVDF’s piezoelectric performance is affected by the presence of polar phase in the crystalline structure. The electrospinning process was used in this study to achieve high β phase ratios in the PVDF crystalline structure using various additives (graphene, boron nitride, and quartz (SiO2)). The Taguchi experimental design method was used to determine the most significant parameters affecting β phase content from seven factors, as well as the optimal levels of the significant factors. The Fourier transform infrared, x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray and differential scanning calorimetry analyses were used to characterize the composite PVDF nanofiber mats produced under optimal conditions, and the output voltage was measured using an oscilloscope. The composite PVDF nanofiber mat with the highest β phase concentration demonstrated a maximum output voltage of 8.68 V under optimal conditions, indicating that it outperformed than pure PVDF under equal electrospinning conditions.

Studies on electrospun polyvinylidene fluoride/aromatic hyperbranched polyester (gen-1) blend nanoweb for energy harvesting applications

In this work, we studied the piezoelectric characteristics of electrospun neat poly(vinylidene fluoride) (PVDF) and PVDF blended with aromatic hyperbranched polyester of Gen-1 (Ar-HBP-G1, 90/10) blend. Since, the piezoelectric output of PVDF is related to its chain (C–C) and dipole (C-F) orientations, FTIR and XRD were employed to confirm the changes in PVDF crystalline structure as a function of 10 wt-% Ar-HBP-G1 content. FTIR quantitative analysis showed an increase in β-crystalline phase in PVDF/HBP blend in comparison to unmodified PVDF. Further, fabrication of piezoelectric sensors was carried out using electrospun nanoweb samples, and their output voltage signals measured using dynamic pressure custom-made setup under an applied pressure of 1 kgf and frequency of 1.0 Hz. With increasing load i.e. 1 kgf → 3 kgf (under constant frequency of 1 Hz) and decreasing frequency from 1 Hz → 0.1 Hz (under constant load of 1 kgf), Vp-p showed increasing trend for both the samples. Compared to neat PVDF peak-to-peak output voltage (Vp-p) of 0.95 V, PVDF/Ar-HBP-G1 (90/10) showed significant enhancement in Vp-p at 6.42 V, which could play a vital role in preparing a piezoelectric sensor for energy harvesting applications.

Pre‐thermal treatment in binary solvent systems promoting β crystalline phase of electrospun poly(vinylidene fluoride) nanofibers

AbstractPoly(vinylidene fluoride) (PVDF) nanofibers were fabricated via electrospinning with an investigation of various ratios of binary solvents at different temperatures. The amount of acetone influenced the morphology. Scanning electron microscopy showed a PVDF membrane composed of smooth and unblemished fibers without beads and dark spots with small diameters of 201 ± 54 nm at a dimethylformamide‐to‐acetone ratio of 4:6. The temperature of pre‐thermal treatment from room temperature to 120 °C was investigated to promote the β crystalline phase in electrospun PVDF nanofibers. The result was characterized using Fourier transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD). PVDF solution prepared at 80 °C was used to increase the β crystalline phase of the electrospun PVDF nanofibers due to the transformation of α to β phase occurring during the spinning process and also bead‐free PVDF nanofibers were obtained. Differential scanning calorimetry revealed crystallization behavior corresponding with that determined using FTIR spectroscopy and XRD. Therefore, the solvent proportion and pretreatment temperature were observed to affect ultrafine nanofiber and crystalline structure of PVDF, respectively. © 2020 Society of Chemical Industry

PVDF based nanocomposites produced by solution blow spinning, structure and morphology induced by the presence of MWCNT and their consequences on some properties

Nanocomposites based on poly(vinylidene fluoride), PVDF, filled with multiwalled carbon nanotubes, MWCNT, were prepared by solution blow spinning, SBS. PVDF was modified with MWCNT with the aim of changing final properties inducing structural and morphological variations in the polymer by the simple presence of conductive particles. Different compositions were considered (0%, 1%, 2%, 3%, and 5% by weight of MWCNT) to understand the influence of the presence of MWCNT on the polymer structure, morphology, and consequently other properties. Morphology was inspected by optical and electron (SEM and TEM) microscopies, while structure was studied by Fourier transformed infrared spectroscopy, FTIR. Thermal behavior was monitored by differential scanning calorimetry, DSC, while the surface and electrical properties were studied by contact angle and capacitance measurements, respectively. SBS allowed obtaining mats of nanocomposites constituted by submicrometric fibers where the MWCNT are uniformly dispersed and well aligned along the PVDF fibers. In this study, several aspects about structure and thermal behavior of PVDF were clarified in relation to other researches carried out up to the moment. Although MWCNT concentration did not seem to affect much the fibrous morphology of the SBS materials, the PVDF crystalline structure and surface properties of the materials were slightly modified. Dielectric behavior of PVDF was highly affected by the presence of MWCNT leading to a particular change in the permittivity and being possible to obtain a value of 0.023 for the percolation fraction.

Investigation of the Effect of Nanosilica on Rheological, Thermal, Mechanical, Structural, and Piezoelectric Properties of Poly(vinylidene fluoride) Nanofibers Fabricated Using an Electrospinning Technique

The effects of different nano-SiO2 contents on the rheological properties of poly(vinylidene fluoride) (PVDF) solution and mechanical, thermal, structural, and piezoelectric properties of composite nanofibers were investigated. Results showed an increase in fiber diameter (∼125 to 350 nm) and ∼450% increase in tensile strength as the content of nano-SiO2 particles increased. The degree of crystallinity decreased by 19% as the nano-SiO2 content increased by 2% (w/w). Further investigation demonstrated that silica could significantly improve the piezoelectric properties of PVDF nanofibers as the output voltage showed an increase in the presence of silica attributed to change in the crystalline structure of PVDF.

Piezoelectric sensor based on electrospun PVDF-MWCNT-Cloisite 30B hybrid nanocomposites

Piezoelectric materials have attracted substantial interest in applications such as sensors and actuators. Ferroelectric and piezoelectric polymeric fibers doped with nanoparticles are made for use in nanoscale electronic devices. In this paper, we report on poly (vinylidene fluoride) (PVDF) nanocomposites doped with different ratios of multi-walled carbon nanotube (MWCNT) and Cloisite 30B (OMMT) nanoclay prepared by electrospinning technique. The effect of different ratios of OMMT and MWCNT nanofillers and potential synergistic effect of these fillers on the crystalline structure of PVDF and the performance of resulting piezo-device were studied. Results showed that OMMT increases beta phase crystals and piezoelectric properties of PVDF as compared with MWCNT. Meanwhile, MWCNT decreases impedance and increases dielectric constant of PVDF as compared with OMMT. The acoustic absorption behavior of PVDF/MWCNT/OMMT hybrid nanocomposite was also investigated. It was found that the sound absorption efficiency of PVDF/MWCNT/OMMT hybrid nanocomposites was increased compared with that of pure PVDF fibers and film. No synergistic effect of OMMT and MWCNT on the properties of PVDF was observed.

Film Fabrication Using Poly(Vinylidene Fluoride) Solution Droplet

This study was conducted to investigate poly(vinylidene fluoride) (PVDF) film characteristics when fabricated using a proposed method. First, a PVDF film is fabricated by dropping and drying a PVDF solution droplet. In this film fabrication, some PVDF solution droplets are prepared by changing the combination of the PVDF solution drop quantity and PVDF concentration in solution. Second, their PVDF crystalline structure is analyzed using an x-ray diffraction device. Then, the PVDF film profile is measured using a 3D shape measurement machine. In addition, the degree of PVDF crystallinity is measured using differential scanning calorimetry. Third, the crystalline structure formation is investigated using Raman spectroscopy for a PVDF solution droplet under a drying process. Finally, we discuss the PVDF film crystalline structure and profile with the present experimentally obtained results toward point drawing of PVDF, leading to the creation of free-form sensor and actuators.

DSC studies on gamma irradiated poly(vinylidene fluoride) applied to high gamma dose dosimetry

Poly(vinylidene fluoride) homopolymer (PVDF) was investigated for use on high gamma dose dosimetry. Samples were irradiated with gamma doses ranging from 100 kGy to 3000 kGy. Differential scanning calorimetry (DSC) was used to construct an unambiguous relationship between the melting transition latent heat (LM) and the absorbed dose (D). DSC thermograms were taken immediately, 1, 2 and 8 months after the irradiation process revealing that the LMx D relationship presented no change for doses ranging from 100 to 2750 kGy. FTIR and UV–Vis spectroscopy data revealed the radio-induction of C˭O and C˭C bonds. These radio-induced bonds were responsible by the chain stiffening and chain oxidation, respectively. SEM microscopy demonstrates that the spherulitic large crystalline structures present in pristine PVDF are destroyed with doses as low as 100 kGy. The DRX analysis revealed that the main effect of high gamma doses in the crystalline structure of PVDF is to provoke a change from the pristine PVDF α-phase to the γ-phase. Both the ability to detect gamma doses in a large dose range and the low fading features make PVDF homopolymers good candidates to be investigated as high gamma dose dosimeters.

Effect of solvents on the crystal formation of poly(vinylidene fluoride) film prepared by a spin-coating process

The effect of the solvent evaporation rate and solvent type on the crystal formation of poly(vinylidene fluoride) (PVDF) prepared by spin-coating was evaluated over time. In the much-solvent-remaining state, the crystalline phase of PVDF changed in the order of α, γ and β with the increasing dipole moment of the solvent. In the almost-all-solvent-evaporated state, the crystalline structure of PVDF/hexamethylphosphoramide with a higher dipole moment was dominantly dependent on the evaporation rate and varied in the order of β, γ and α with the increasing solvent evaporation rate. However, PVDF/triethyl phosphate, having a lower dipole moment, always formed the α phase, regardless of the evaporation rate. The PVDF α phase in the concentrated solution state is difficult to transform into the β and γ phases because the potential energy of each PVDF crystalline phase increases in the order of α, γ and β. The PVDF crystalline phase in the spin-coating method is strongly affected by both the polymer–solvent electrostatic interactions and the evaporation conditions. From the results of the crystal transition behavior, it was experimentally supported that the potential energy of the PVDF crystalline structure increases in the order of α, γ and β. The crystalline phase of PVDF film prepared by spin-coating changes both of the polymer–solvent interaction and the evaporation rate. In the much solvent remained state, the crystalline phase changes in the order of α, γ and β phase with increasing the dipole moment of solvent. In the solvent-evaporated state, the crystalline phase of PVDF and solvent with higher dipole moment system changes in the order of β, γ and α phase with increasing the solvent evaporation rate, whereas the PVDF and solvent with lower dipole moment system forms into α phase regardless of the evaporation rate.

Electrospun PVDF graphene oxide composite fibre mats with tunable physical properties

This article is aimed at a basic physical characterization of electrospun PVDF/graphene oxide (GO) composite non-woven fibre mats. The morphological characterization of the prepared fabrics was performed via SEM investigations. Introduction of the GO during the electrospinning process caused significant changes in the crystalline structure of PVDF, and a transformation from α- to β-crystalline phases was achieved. Addition of the GO particles into PVDF did not only improve the thermal stability of the polymer, but also acted as a reinforcing filler, giving rise to improved dynamic moduli and tensile strength. The dielectric properties were evaluated over a broad frequency range, and it was confirmed that the presence of small amounts of GO had little effect on the dielectric properties of the PVDF, since the GO has a dielectric character similar to that of the PVDF.

Understanding of intermolecular interaction in PVDF/PTW blends: Crystallization behavior, thermal, and dynamic mechanical properties

ABSTRACTPoly(vinylidene fluoride) (PVDF)/ poly(ethylene–butylacrylate–glycidyl methacrylate) (PTW) blends were directly prepared by melt blending and the interaction and properties of PVDF/PTW blends were explored systematically. The crystallization behavior, thermal stability, dynamic mechanical property, and morphological features of PVDF/PTW blends with different ratios have been studied by XRD, attenuated total reflection Fourier transform infrared spectroscopy, differential scanning calorimeter analysis (DSC), thermal gravimetric analysis (TGA), dynamic mechanical analysis, and polarized optical microscopy (POM). The results showed that the crystalline structure of neat PVDF was dominantly α‐phase crystalline and the incorporation of PTW had no effect on the crystalline structure of PVDF in the PVDF/PTW blends. And Tg of PVDF in PVDF/PTW blends shifted to higher temperature compared with that of neat PVDF, indicating the weak interaction between PVDF and PTW, which was corresponding to DSC and TGA results. An increase in the coarseness and ring‐band spacing observed from POM further substantiated the weak interaction between PVDF and PTW. This work provided a way for preparing improved properties of PVDF/PTW blends for the coating material. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43908.

Structure and dielectric performance of poly(vinylidene fluoride)/organically modified montmorillonites nanocomposites

Poly(vinylidene fluoride)/organically modified montmorillonites (PVDF/OMMT) nanocomposites with different clay contents were prepared by melt intercalation and compression moulding. The dielectric properties were studied, and the effects of montmorillonites on the crystalline structure of PVDF were characterized, compared and discussed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The results show that the dielectric constant of the PVDF/OMMT nanocomposites is improved. XRD and FTIR results indicate that montmorillonites suppress the formation of α-phase crystals and promote the formation of β-phase crystals. DSC studies suggest that the degree of crystallinity is decreased and the melting and crystallization temperature of nanocomposite are increased compared with those of the pristine PVDF.

OS1506-336 プリンタブル圧電ポリマーの開発

We found an original PVDF film fabrication technique which enable us to turn crystalline structure to beta-phase structure only by solution drop and dry. This method can be applied to printing technology, and we will be able to fabricate printable sensor and actuator in near future. The aim of the present study is to investigate the PVDF crystalline structure change due to a kind of solvent in PVDF solution drop. First, three kinds of solvents (Acetone, DMF and HMPA) are prepared. Second, PVDF powder is mixed with a kind of solvent for 24 h using a magnetic stirrer. Third, the mixed solution is dropped on a glass plate using a micro syringe and is dried in a controllable desiccator. Then, we can obtain three kinds of PVDF films. Finally, the PVDF film crystalline structures are investigated by using X-ray diffraction and Raman spectroscopy.

Influence of BaTiO3 submicrometric particles on the structure, morphology, and crystallization behavior of poly(vinylidene fluoride)

ABSTRACTReal uniform dispersion of barium titanate, BaTiO3, submicrometric particles within Poly(vinylidene fluoride), PVDF, was achieved to understand induced structure, morphology, and crystallization process of the polymer. Composites with uniform dispersions of BaTiO3 particles within PVDF were accomplished for the first time, blending the polymer with particles by high energy ball milling, HEBM. Different compositions in PVDF/BaTiO3 composite were considered (0, 1, 5, and 10 weight percent of particles). Morphology and structure were studied by scanning electron microscopy, SEM, and X‐ray diffraction, XRD, respectively. From dynamic experiments by differential scanning calorimetry, DSC, thermal transitions were determined and melting and crystallization processes were studied. To understand the main mechanism by which specific morphologies can be obtained a deep kinetic analysis of the PVDF crystallization process was carried out. Cooling rate and BaTiO3 content did not provide important variations in the PVDF crystalline structure and morphology; however, the presence of BaTiO3 particles seemed to favor an athermal nucleation, leading to higher fraction of crystals in shorter times. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41497.

Effects of B2 O3 addition on structural and dielectric properties of PVDF

α-Crystalline form of PVDF doped with Boron oxide (B2O3) composite films were produced between 0.2 and 1% weight ratio via the casting procedure. This low-level doping rate did not change the crystalline structure of PVDF; however, they increased the lower and upper glass transition temperatures, which are associated with the amorphous ratio of polymer. This increment was found to be the highest for the sample 0.8% B2O3-doped PVDF as 25 and 9.7%, respectively. Because of the low specific volume occurred in the 0.8% doped sample, B2O3 molecules are closer to the side groups of PVDF and, therefore, the coordination bonds also occurred according to the interaction between them and as a result of this interaction a geometric deformation occurred on the morphology of B2O3. In consequence of this deformation, morphology of B2O3 gained net dipole moment and provided a contribution to the dipole moment density of the structure. Hence, higher dielectric constant values obtained than that of pure PVDF. At 1 kHz and 300 K, the real dielectric constant increased by 236% compared to that of pure PVDF. It was shown experimentally by the 0.8% doping level of B2O3 that decreasing porous and gap structure resulted a high dielectric constant. POLYM. ENG. SCI., 54:2536–2543, 2014. © 2013 Society of Plastics Engineers

Quantification of the solvent evaporation rate during the production of three PVDF crystalline structure types by solvent casting

In this study, we quantified the solvent evaporation rate in the production of three poly(vinylidene fluoride) (PVDF) crystalline structures using the solvent casting method, the first known report on such quantification. The evaporation conditions of drying temperature and pressure for the solvent species during solvent casting were varied. The results indicated that the crystalline structures of forms I, II and III of PVDF were obtained when the solvent evaporation rates were <0.0001, >0.2 and between 0.03 and 0.00058 g min−1, respectively. From the above quantitative analysis, it was established that the crystalline structure of PVDF from solvent casting is predominantly determined by the solvent evaporation rate. The solvent evaporation rate in the production of three types of poly(vinylidene fluoride) (PVDF) crystalline structures by using the solvent casting method was quantified. The PVDF crystalline structures were predominantly determined by solvent evaporation rate. PVDF (form I) was obtained when the solvent evaporation rate was <0.0001 g min−1, PVDF (form II) was obtained when the solvent evaporation rate >0.2 g min−1 and PVDF (form III) was obtained when the solvent evaporation rate was from 0.03 to 0.00058 g min−1.

Effect of heat-treatment temperature after polymer melt and blending ratio on the crystalline structure of PVDF in a PVDF/PMMA blend

We analyzed control of the crystalline structure of poly(vinilydene fluoride) (PVDF) in a PVDF/poly(methylmethacrylate) (PMMA) blend by varying the polymer blend ratio (PVDF/PMMA=60/40, 70/30 and 80/20 wt%) and the heat-treatment temperature (160–210 °C) just after the polymer melt. We obtained PVDF (form I) limitedly by heat treatment at 185 and 190 °C after blending PVDF/PMMA 70/30 wt%. The samples produced under other conditions indicated PVDF (form II). Results of differential scanning calorimetry (DSC), polarized light micrography and light transmittance indicated that samples of PVDF/PMMA 70/30 wt% heat-treated at 185 and 190 °C exhibited high compatibility between PVDF and PMMA, respectively. In contrast, PVDF (form II) samples obtained in other conditions indicated lower compatibility. We assumed that PVDF crystalline structure became the structure of the PVDF (form I) according to decrease of the crystallization rate by the highest compatibility between PVDF and PMMA. Pure PVDF crystallized very fast, so PVDF (form I) cannot be developed from pure PVDF by simply controlling the heat-treatment temperature. Control of the crystalline structure of poly(vinilydene fluoride) (PVDF) in a PVDF/poly(methylmethacrylate) (PMMA) blend were analyzed by varying the polymer blend ratio (PVDF/PMMA=60/40, 70/30 and 80/20 wt%) and the heat-treatment temperature (160–210 °C) just after the polymer melt. PVDF (form I) was limitedly obtained by heat treatment at 185 and 190 °C after blending PVDF/PMMA 70/30 wt%. The samples produced under other conditions indicated PVDF (form II). We assumed that PVDF crystalline structure became PVDF (form I) according to decrease of the crystallization rate by the highest compatibility between PVDF and PMMA.

Unusual process-induced curl and shrinkage of electrospun PVDF membranes

A significant shrinkage of about 17% of poly(vinyliedene fluoride) (PVDF) fibrous membranes processed by electrospinning is reported and analyzed for the first time in this article. Such shrinkage leads to a time dependent curl of the membrane, probed by image analysis and tensile test measurements. Crystalline structure of PVDF is analyzed through X-ray diffraction and FTIR analyses while solvent evaporation is monitored by weight lost measurements. The electrospinning process induces a crystal structure change of PVDF from non-polar α phase to polar β phase exhibiting piezoelectric properties. The curl was modeled taking into account the bimorph structure of the polymer membrane deposited onto the aluminum substrate with the electric field acting on the PVDF through the piezoelectric effect. Besides, just after the processing, the membranes exhibited a nearly 15% weight loss ascribed to the evaporation of the solvents entrapped within the solid fibrous membranes. The piezoelectricity of the β-phase together with solvent evaporation may be responsible for the observed contraction inducing the curl, the second mechanism of evaporation being predominant.