Electrospinning induced ferroelectricity in poly(vinylidene fluoride) fibers

Poly(vinylidene fluoride) (PVDF) fibers with diameters ranging from 70 to 400 nm are produced by electrospinning and the effect of fiber size on the ferroelectric β-crystalline phase is determined. Domain switching and associated ferro-/piezo-electric properties of the electrospun PVDF fibers were also determined. The fibers showed well-defined ferroelectric and piezoelectric properties.     

Antibacterial electrospun chitosan/poly(vinyl alcohol) nanofibers containing silver nitrate and titanium dioxide

Chitosan/poly(vinyl alcohol) (PVA) nanofibers with antibacterial activity were prepared by the electrospinning of a chitosan/PVA solution with a small amount of silver nitrate (AgNO₃) and titanium dioxide (TiO₂). Nanofibers with diameters of 270–360 nm were obtained. The yield of low‐viscosity chitosan (LCS)/PVA nanofibers was higher than that of high‐viscosity chitosan (HCS)/PVA, and the water content of the HCS/PVA nanofibers and the LCS/PVA nanofibers were 430 and 390%, respectively. The nanofibers developed in this study exhibited antibacterial activities of 99 and 98% against Staphylococcus aureus and Escherichia coli, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Durable adhesives based on electrospun poly(vinylidene fluoride) fibers

Herein, the fabrication of poly(vinylidene fluoride) (PVDF) fibrous membrane using electrospinning is reported and its use for dry‐adhesive applications is demonstrated. The shear and normal adhesion performance of the samples was investigated using an Instron tensile tester and an atomic force microscope (AFM) respectively. For shear adhesion measurements, the electrospun membrane was finger pressed on to a glass slide and pulled in shear mode using a tensile tester. The thickness of the electrospun membrane was varied and the effect of thickness on shear adhesion was investigated. The shear adhesion strength increased when the thickness of the samples was reduced. Shear adhesion strength of a 200 µm thick sample was determined to be approximately 0.165 N/cm. For normal adhesion measurements, a flat tipless cantilever was used to indent the sample and then retract back to measure the pull‐off force. High shear adhesion strength and normal pull‐off force recorded are attributed to the fine size of the fibers that conform to the asperities present on the surfaces of the glass slide and the AFM cantilever. The durability of the adhesive was also verified by repeating the AFM adhesion measurements over 1000 consecutive attachment–detachment cycles. The pull‐off force was seen to be constant over 1000 attachment–detachment cycles. Our results indicate that these electrospun fibrous membranes can potentially be used as reusable dry‐adhesives. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44393.     

Comparative performance analysis of electrospun TiO2 embedded poly(vinylidene fluoride) nanocomposite membrane for supercapacitors

For an efficient energy storage system, effective material is to be used. In the present work, novel poly(vinylidene fluoride)/titanium oxide (PVdF/TiO₂) composite membranes were developed using electrospinning technique, as separator for supercapacitors. Different weight percentages of TiO₂ nanoparticle (0, 5, 10, 15, and 20 wt%) were mixed with 20 wt% of PVdF in a 50:50 wt% of tetrahydrofuran and dimethylacetamide solvent. Various physical and electrochemical properties including fiber diameter, thermal stability, crystallinity, porosity, and electrolytic uptake were studied to identify the best membrane with optimum TiO₂ wt% exhibiting superior characteristics. SEM and TGA studies revealed that the developed PVdF/TiO₂ composite membrane with 10 wt% showed improved properties with a lower average diameter of about 66 ± 8 nm, enhanced thermal stability up to 513.15°C and higher porosity of 89%, respectively compared to other membranes. The crystallinity, ionic conductivity, and specific capacitance of the nonwoven separator membranes were determined using X-ray diffraction technique, electrolytic uptake, and charge–discharge studies, respectively. The present study revealed that the addition of TiO₂ nanoparticles improved the physical and thermochemical properties of the separator membrane substantially and PVdF/TiO₂ composite membrane with 10 wt% displayed superior performance compared to other membranes.     

Study of crystallization behavior of neat poly(vinylidene fluoride) and transcrystallization in carbon fiber/poly(vinylidene fluoride) composite under a temperature gradient

The crystallization behavior of poly(vinylidene fluoride) (PVDF) and transcrystallization in carbon fiber (CF)/PVDF composite were investigated under a temperature gradient. The crystallization temperature (T_c) was controlled in the range of 110–180 °C. For neat PVDF, the results showed that exclusive γ phase formed at T_c above 164 °C, but coexisted with α phase at T_c ranging from 137 to 160 °C. The promotion of γ phase to nucleation of α phase at low T_c was observed for the first time. For CF/PVDF composite, a cylindrical transcrystalline (TC) layer formed on the surface of CF when T_c was between 137 and 172 °C. The TC layer was exclusively composed of γ phase at T_c above 164 °C. The hybrid nucleation was dominated by γ phase though some α phase nuclei emerged on the surface of CF when T_c was in the range of 144–160 °C. As T_c decreased, competition between the hybrid nucleation of α and γ phase became more intense. The γ phase nuclei was soon circumscribed by the rapidly developed α phase when T_c was below 144 °C. Furthermore, some α phase nuclei were induced at the surface of the γ phase TC layer, and developed into α phase TC layer when T_c was in the range of 146–156 °C, which resulted in a doubled TC layer of α and γ phase at the interface of the composite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43605.     

Improvement of the thermal transport performance of a poly(vinylidene fluoride) composite film including silver nanowire

The miniaturization trend of electronic devices requires that components have a high heat dissipation in industrial applications and in daily life. In this context, a highly thermally conductive film was fabricated with silver nanowire (AgNW) and poly(vinylidene fluoride) (PVDF) with a bar‐coating method. The thermal transport performance and mechanism of the AgNW/PVDF composite film were investigated. The through‐plane and in‐plane thermal conductivity of the AgNW/PVDF composite film reached 0.31 and 1.61 W m^?1 K^?1, respectively; these values far exceeded those of the pristine PVDF film. The experiment illustrated that the thermally conductive pathways formed successfully in the PVDF substrate with the addition of AgNW, and the heat tended to transfer along the thermally conductive pathway rather than along the PVDF substrate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43554.     

Silver-incorporated poly vinylidene fluoride nanofibers for bacterial filtration

An anti-bacterial filter was developed using poly vinylidene fluoride (PVDF) nanofibers using electrospinning method blended with silver nanoparticles (AgNO₃) of varying weight percentages of filler. Polypropylene (PP) non-woven substrate was used as base material for collecting the nanofibers. It also acted as a barrier to protect the fibers. UV-visible spectroscopy and fourier transform infra red spectroscopy confirmed the uniform dispersion of silver nanoparticles throughout the nanofibers. The experiment was designed using Box–Behnken statistical tool through three different variables namely, PP non-woven sheets (GSM), electrospinning time (hours), concentration of silver (wt%) in 15 runs. Surface morphology was analyzed using scanning electron microscopy and atomic force microscopy. Thermogravimetric analysis was performed for the analyses of mass decomposition of the material. Bacterial filtration efficiency and anti-bacterial activity studies were tested against Staphylococcus aureus and Escherichia coli for both PVDF + 0?wt% Ag fibers and PVDF-Ag nanofibers. This research shows the bacterial filtration efficiency for the prepared PVDF-Ag nanofibers as 99.86%. The prepared nanofilter was shown providing greater possibilities towards the application for clean air management.

© Copyright 2019 American Association for Aerosol Research     

In situ synthesis of iron oxide nanoparticles on poly(ethylene oxide) nanofibers through an electrospinning process

Iron oxide nanoparticle coated poly(ethylene oxide) nanofibers as organic–inorganic hybrids with 200–400‐nm diameters were prepared by the in situ synthesis of iron oxide nanoparticles on poly(ethylene oxide) nanofibers through the electrospinning of a poly(ethylene oxide) solution having Fe²⁺ and Fe³⁺ ions in a gaseous ammonia atmosphere. Transmission electron microscopy analysis proved the presence of iron oxide nanoparticles on the polymer nanofibers. The thermal properties of the nanofiber mat were also studied with differential scanning calorimetry and thermogravimetric analysis techniques. X‐ray diffraction showed that the formed iron oxide nanoparticles were maghemite nanoparticles. The results were compared with those of the electrospinning of a poly(ethylene oxide) solution having Fe²⁺ and Fe³⁺ ions and a pure poly(ethylene oxide) solution in an air atmosphere. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Chlorinated poly(vinylidene fluoride)

Chlorinated poly(vinylidene fluoride) (PVF₂) was prepared by introducing chlorine gas into a CCI₄ suspension of PVF₂ at reflux temperature. Polymer crystallinity and softening point decrease, while solubility and adhesion increase with the degree of chlorination. In contrast to PVF₂, the chlorinated polymer is soluble in low-boiling common organic solvents, such as acetone, methyl ethyl ketone, and 1,2-dimethoxyethane. Chlorinated PVF₂ is resistant to dehydrochlorination and is thermally more stable than PVF, chlorinated PVF, PVC, or chlorinated PVC. Chlorinated PVF₂ coatings on wood, prepared by solution casting at room temperature, show outstanding weathering resistance.     

Crystal polymorphism in electrospun composite nanofibers of poly(vinylidene fluoride) with nanoclay

We investigated for the first time the morphology and crystal polymorphism of electrospun composite nanofibers of poly(vinylidene fluoride) (PVDF) with two nanoclays: Lucentite™ STN and SWN. Both nanoclays are based on the hectorite structure, but STN has organic modifier in between the layers of hectorite while SWN does not. PVDF/nanoclay was dissolved in N,N-dimethylformamide/acetone and electrospun into composite nanofiber mats with fiber diameters ranging from 50-800 nm. Scanning electron microscopy shows that addition of STN and SWN can greatly decrease the number of beads and make the diameter of the nanofibers more uniform due to the increase of electrospinning solution conductivity brought by the nanoclay. Infrared spectroscopy and X-ray diffraction confirm that both STN and SWN can induce more extended PVDF chain conformers, found in beta and gamma phase, while reducing the alpha phase conformers in electrospun PVDF/Nanoclay composite nanofibers. With the attached organic modifier, even a small amount of STN can totally eliminate the non-polar alpha crystal conformers while SWN cannot. The ionic organic modifier makes STN much more effective than SWN in causing crystallization of the polar beta and gamma phases of PVDF. An ion-dipole interaction mechanism, suggested by Ramasundaram, et al. is utilized to explain the crystal polymorphism behavior in electrospun PVDF/nanoclay composite nanofibers.     

Crystallization behavior of poly(vinylidene fluoride) composites containing zinc phenylphosphonate

Poly(vinylidene fluoride) (PVDF) composites with different ratios of zinc phenylphosphonate (ZPP) were prepared by mixing in a kneader. The crystallization behavior of the composites from the melt was investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WAXD). The POM observations directly showed that nucleation of the PVDF crystal was promoted by adding ZPP. The data obtained from DSC measurements also indicated that the crystallization temperature of the composites became higher than that of pure PVDF. These results suggested that ZPP acted as a good nucleating agent for PVDF. Nonisothermal crystallization behavior was analyzed by Avrami equation adopted by Jeziorny. The results of the analysis were found to be consistent with the POM observations for the composites. WAXD analysis suggested that the PVDF crystal structure was influenced by ZPP addition. These results proved that as a nucleating agent, ZPP increased the crystallization rate and temperature of PVDF. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Properties of poly(vinylidene fluoride)

The properties of fluorocarbon plastics have made them desirable for numerous new applications. Poly(vinylidene fluoride) (PVF₂) can be easily extruded into films or fibers or injection molded into a variety of shapes. It was found that crystallinity, molecular weight distribution and polymer structure are important in establishing resin properties. Highly crystalline PVF₂ with a narrow Gaussian molecular weight distribution gives specimens with optimum physical and chemical properties.     

Electrospinning of polyacrylonitrile nanofibers

Polyacrylonitrile (PAN) was electrospun in dimethylformamide as a function of electric field, solution flow rate, and polymer concentration (C). The fiber diameter increased with C and ranged from 30 nm to 3.0 μm. The fiber diameter increased with the flow rate and decreased when the electric field was increased by a change in the working distance; however, it did not change significantly when the electric field was varied by a change in the voltage at a given working distance. The fibers below about 350 nm diameter contained beads, whereas above this diameter, bead‐free fibers were obtained. For PAN with a molecular weight of 100,000 g/mol, the fiber diameter scaled as C^1.2 and C^7.5 at low (5.1–16.1 wt %) and high (17.5–22.1 wt %) C values, respectively. Both concentrations were in the semidilute entangled regime, where the specific viscosity scaled as C^4.4, consistent with De Gennes's scaling concepts. In the semidilute unentangled regime (0.5–3.1 wt %), where the viscosity scaled as C^1.3, microscopic or nanoscopic particles rather than fibers were obtained. Concentration‐ dependent electrospinning studies were also carried out for higher molecular weight PAN (250,000 and 700,00 g/mol). The results of these studies are also presented and discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1023–1029, 2006     

A new approach for conductive network formation in electrospun poly(vinylidene fluoride) nanofibers

Conductive nanofibers of poly(vinylidene fluoride) (PVDF) filled with polyaniline (PANi)‐coated multi‐wall carbon nanotubes (MWCNTs) were fabricated using the electrospinning technique. PANi is an intrinsically conductive polymer. The addition of PANi‐coated MWCNTs to PVDF created short conductive strands on the surface of the nanofibers, facilitating the formation of a conductive network in the transverse direction of the nanofibers. Piezoelectricity along with electric conductivity makes these PVDF nanofibers promising for applications such as sensors and actuators. Electrospun PVDF nanofiber mats had higher piezoelectricity than melt‐processed samples produced using traditional polymer processing techniques, such as compression molding. Spectroscopic imaging techniques were employed to study the effects of the filler and processing conditions on the nanofiber structure. X‐ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry results indicated a large increase in the β‐phase crystals of the PVDF nanofibers. This higher content of β‐phase crystals enhanced the piezoelectricity of the nanofibers. © 2015 Society of Chemical Industry     

Graphite nanofibers prepared from catalytic graphitization of electrospun poly(vinylidene fluoride) nanofibers and their hydrogen storage capacity

Electrospun poly(vinylidene fluoride) nanofibers were carbonized with iron(III) acetylacetonate to induce catalytic graphitization within the temperature range 800–1800 °C. Carbonization in the presence of the catalyst produced graphite nanofibers (GNFs). Their structural properties and morphology were investigated. GNFs with a high surface area of 377–473 m²/g showed the typical Type II containing mesopore in nitrogen adsorption–desorption isotherms. The hydrogen storage capacity of these GNFs was evaluated by the gravimetric method using a magnetic suspension balance (MSB) at room temperature and about 80 bar. The hydrogen storage capacity was 0.11–0.18 wt.%. The effective pore size for hydrogen storage compared to the diameter of the hydrogen molecule is discussed.     

Crystallization kinetics of poly(vinylidene fluoride)

Specimens of poly(vinylidene fluoride) were crystallized isothermally at a series of temperatures in the vicinity of the melting point. The -form was the only crystalline polymorph present in the crystallized samples. Crystallization rates have been measured by differential scanning calorimetry. The results were analysed in terms of the Avrami equation. The rates of crystallization depend upon the undercooling and the data agree with a process of growth of spherulites controlled by a secondary surface coherent nucleation mechanism. The equilibrium melting temperature, the Avrami exponent, the free energy of formation of a nucleus of critical dimensions and the surfaces free energy of the lamellar crystallites were determined.     

Antibacterial poly(vinyl alcohol) film containing silver nanoparticles: Preparation and characterization

The importance of antibacterial materials for biomedical applications is growing nowadays. The presented article deals with the characterization of structural, mechanical and thermal properties and of antibacterial polymeric films based on polyvinyl alcohol (PVA) and silver nitrate, which can find their applicability in wound dressing components and protective coating. The methods of transmission electron microscopy, UV–vis and XRD spectroscopy, optical microscopy, differential scanning calorimetry, stress–strain analysis, and agar diffusion test were used to characterize the polymer films prepared. The results showed strong antibacterial activity against Escherichia coli and Staphylococcus aureus already at the lowest addition level of silver nitrate. An improvement of mechanical properties (Young's modulus) was also noticed due to a modification of PVA with silver nitrate up to 1 wt. % of silver content. Furthermore, the results show a strong effect of the thermal history of the sample preparation on the degree of silver‐ion reduction and formation of nanoparticles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Wound-dressing materials with antibacterial activity from electrospun gelatin fiber mats containing silver nanoparticles

Ultrafine gelatin fiber mats with antibacterial activity against some common bacteria found on burn wounds were prepared from a gelatin solution (22%w/v in 70 vol% acetic acid) containing 2.5 wt% AgNO₃. Silver nanoparticles (nAg), a potent antibacterial agent, first appeared in the AgNO₃-containing gelatin solution after it had been aged for at least 12 h, with the amount of nAg increasing with increasing aging time. The average diameters of the as-formed nAg ranged between 11 and 20 nm. Electrospinning of both the base and the 12 h-aged AgNO₃-containing gelatin solutions resulted in the formation of smooth fibers, with average diameters of ∼230 and ∼280 nm, respectively. The average diameter of the as-formed nAg in the electrospun fibers from the 12 h-aged AgNO₃-containing gelatin solution was ∼13 nm. The nAg-containing gelatin fiber mats were further cross-linked with moist glutaraldehyde vapor to improve their stability in an aqueous medium. Both the weight loss and the water retention of the nAg-containing gelatin fiber mats in acetate buffer (pH 5.5), distilled water (pH 6.9) or simulated body fluid (SBF; pH 7.4) decreased with increasing cross-linking time. The release of Ag⁺ ions from both the 1- and 3 h-cross-linked nAg-containing gelatin fiber mats - by the total immersion method in acetate buffer and distilled water (both at a skin temperature of 32 °C) - occurred rapidly during the first 60 min, and increased gradually afterwards; while that in SBF (at the physiological temperature of 37 °C) occurred more gradually over the testing period. Lastly, the antibacterial activity of these materials, regardless of the sample types, was greatest against Pseudomonas aeroginosa, followed by Staphylococcus aureus, Escherichia coli, and methicillin-resistant S. aureus, respectively.     

Preparation and characterization of poly(vinylidene fluoride) nanocomposites containing multiwalled carbon nanotubes

Poly(vinylidene fluoride) (PVDF) nanocomposites with different loadings of multiwalled carbon nanotubes (MWNT) were prepared by melt‐compounding technique. A homogeneous dispersion of MWNT throughout PVDF matrix was observed on the cryo‐fractured surfaces by scanning electron microscopy. Thermogravimetric analysis results indicated that the thermal stability of neat PVDF was improved with the incorporation of MWNT. Dynamic mechanical analysis showed a significant improvement in the storage modulus over a temperature range from ?125 to 75°C with the addition of MWNT. The melt‐rheological studies illustrated that incorporating MWNT into PVDF matrix resulted in higher complex viscosities (|η*|), storage modulus (G′), loss modulus (G″), and lower loss factor (tan δ) than those of neat PVDF. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of superhydrophobic nanocomposite fiber membranes by electrospinning poly(vinylidene fluoride)/silane coupling agent modified SiO2 nanoparticles

Superhydrophobic nanocomposite fiber membranes were prepared by blend electrospinning of poly(vinylidene fluoride) (PVDF) mixed with silane coupling agent modified SiO₂ nanoparticles. The nanoparticles were prepared by the sol–gel method, and the average particle diameter was measured by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The effects of the type of silane coupling agent, such as n‐octyltriethoxysilane, vinyltrimethoxysilane (A‐171), and vinyltriethoxysilane (A‐151), and the mass ratio of the modified silica particles and PVDF on the surface wettability of the composite fiber membrane were investigated. The results indicated that the incorporation of silane coupling agent modified silica particles into the PVDF membrane increased the roughness of the surface and formed micro/nano dual‐scale structure compared to the pristine PVDF membrane, which was responsible for the superhydrophobicity and self‐cleaning property of the nanocomposite fiber membranes. The value of water contact angle (CA) increased with the increase of the content of modified SiO₂ nanoparticles in the nanocomposite membrane, ranging from 149.8° to 160.1° as the mass ratio of modified 170 nm SiO₂ with PVDF matrix increased from 0.5:1 to 5:1, indicating the membrane possesses a superhydrophobic surface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44501.