Fabrication of cadmium titanate nanofibers via electrospinning technique

Here we present an electrospinning technique for the fabrication of cadmium titanate/polyvinyl-pyrrolidone composite nanofibers. The composite nanofibers are then annealed at 600 °C to obtain ilmenite rhombohedral phase cadmium titanate nanofibers. The structure, composition, thermal stability and optical properties of as synthesized and annealed cadmium titanate nanofibers are characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy. The average diameter and length of the nanofibers are found to be ～150–200 nm and ～100 μm, respectively.     

Preparation and characterization of barium titanate nanofibers by electrospinning

PVP–BaTiO₃ composite nanofibers were successfully prepared by electrospinning and pure BaTiO₃ fibers were produced after calcination at 1000 °C. A homogeneous viscous solution of barium acetate + titanium acetate/titanium isopropoxide in poly vinyl pyrrolidone (PVP) was prepared by varying PVP concentration in the range of 8–12%. The above sols were electrospun at 9 kV DC by maintaining tip to collector distance (TCD) of 7 cm. The electrospun fibers were calcined at 1000 °C for 2 h. Thermo gravimetric analysis (TGA) of the fibers indicates the complete decomposition of organics below 700 °C with 45% weight loss. Scanning electron microscopy (SEM) study shows the fibers cylindrical, smooth with diameters in the range of 50–400 nm and the aspect ratio >1000. The average diameter of the fibers increases with the increase in PVP concentration. The calcined BaTiO₃ nanofibers were found to be coarse, brittle and diameter reduced by 12%. FT-IR study confirms the formation of metal oxide bond at higher temperature.     

Influence of humidity,temperature, and annealing on microstructure and tensile properties of electrospun polyacrylonitrile nanofibers

This study investigates the microstructure and mechanical properties of electrospun nanofibers from polyacrylonitrile (PAN)‐dimethylformamide (DMF) solution at different relative humidity (RH) in the range from 14% to 60% and two different temperatures (20°C and 40°C). Nanofibers produced at low RH (22% or less at 20°C) exhibit relatively smooth surface and solid core, whereas at higher RH (30% or higher at 20°C) rough surface and porous core are observed. The resulting morphology is explained by means of H₂O/DMF/PAN ternary phase diagram. At higher RH, the water diffusion into polymer‐solution jet brings thermodynamic instability into the system leading to separation of polymer‐rich phase and polymer‐lean phase, where the later contributes to porosity. Higher process temperature (40°C) yields larger miscibility area in the ternary phase diagram leading to formation of porous structure at relatively higher RH (40%). Tensile strength of nanofibrous yarns is found to vary from 80 MPa to 130 MPa depending on the processing temperature and RH. The amount of porosity is found to affect the tensile properties of nanofibers most significantly, although diameter and crystallinity play important role. Annealing is found to alleviate surface roughness and porosity and increase crystallinity. Tensile strength of nanofibrous yarns is found to improve by up to 25% after annealing. POLYM. ENG. SCI., 58:998–1009, 2018. © 2017 Society of Plastics Engineers     

Effect of BaTiO3 on the sensing properties of PVDF composite-based capacitive humidity sensors

Capacitive humidity sensors consisting of materials such as polymers, ceramics, and piezoelectrics are widely used to monitor relative humidity levels. The effect of barium titanate (BaTiO₃) nanoparticles on the humidity sensing properties, dielectric response, thermal stability, and hydrophilicity of the polyvinylidene fluoride (PVDF)-BaTiO₃ composite films is investigated. Hydrophilicity and surface morphology of the PVDF-BaTiO₃ composite films are modified for the development of a good humidity sensor. The nanocomposite solutions are prepared by mixing an optimized concentration (2.5 wt%) of PVDF with different concentrations (0.5, 1, and 2 wt%) of BaTiO₃ nanoparticles. X-ray diffraction, thermogravimetric analysis, field emission scanning electron microscopy, and contact angle measurements are used to characterize the structure, morphology, thermal stability, and hydrophilicity of the spin-coated sensing films. The dielectric study of PVDF-BaTiO₃ composite film shows that as the concentration of BaTiO₃ particles increase, the dielectric constant of the composite films increases as well. PVDF-BaTiO₃ (2.5 wt%-1 wt%) based capacitive sensors show stable capacitive response and low hysteresis as compared to the other concentrations of the PVDF-BaTiO₃ composites. The maximum hysteresis of the capacitive PVDF-BaTiO₃ (2.5 wt%- 1 wt%) humidity sensor is found to be ~2.5%. The response and recovery times of the PVDF-BaTiO₃ (2.5 wt%-1 wt%) based capacitive sensors are determined as 40 s and 25 s, respectively, which are significantly lower than those reported for the other PVDF composite based sensors.     

Electrospinning preparation and characterization of cadmium oxide nanofibers

Using a facile synthesis route, cadmium oxide (CdO) nanofibers in the diameter range of 50–60 nm have been prepared employing the electrospinning technique followed by a single-step calcination from the aqueous solution of polyvinyl alcohol (PVA) and cadmium acetate dihydrate. Electron microscopy (EM) and the Brunauer–Emmett–Teller (BET) technique were employed to characterize the as-spun nanofibers as well as the calcined product. The specific surface area of the product was calculated to be 42.6711 m² g⁻¹. Infrared (IR) absorbance spectroscopy and X-ray powder diffractometery were conducted on the samples to study their chemical composition as well as their crystallographic structure. The study on the optical properties based on the photoluminescence (PL) spectrum demonstrated that the emission peaks of CdO nanofibers are centered at 493 and 528 nm. The direct bandgap of the CdO nanofibers was determined to be 2.51 eV.     

Piezoelectric calcium/manganese-doped barium titanate nanofibers with improved osteogenic activity

The piezoelectric nature of natural bone tissue makes the use of piezoelectric biomaterials in promoting bone regeneration to be a feasible and attractive strategy. Barium titanate (BaTiO₃) is well-known for its high piezoelectricity and widely studied as bone repairing bioceramic, but its lacking of bioactive ions may compromise its contribution to osteogenesis. Calcium is the richest metallic element in bone mineral, and manganese is an important doping element for hydroxyapatite, therein, Ca²⁺ and Mn⁴⁺ were individually or co-doped into BaTiO₃ nanofibers via sol-gel/electrospinning/calcination technique in this study. Compared to pure BaTiO₃ nanofibers, though the piezoelectric coefficient (d₃₃) of Ca²⁺ and/or Mn⁴⁺-doped BaTiO₃ nanofibers decreased with increase in ion doping amount, it could maintain approx. 0.9–3.7 pC/N and comparable to that of native bone (0.7–2.3 pC/N) at an optimized content. Under the synergistic effect of the released bioactive ions and the material piezoelectricity, the BaTiO₃ nanofibers co-doped with Mn⁴⁺ (2 mol%) and Ca²⁺ (10 mol%) (i.e., the sample 2Mn10Ca-BT) achieved the strongest capacity in enhancing the osteogenic differentiation of bone marrow mesenchymal stromal cells (BMSCs), while showing no cytotoxicity. In summary, bioactive ions-doped BaTiO₃ nanofibers are promising scaffolds for bone tissue engineering, thanks to their acceptable biocompatibility, appropriate piezoelectricity, and improved osteogenic activity.     

Copper cadmium titanate prepared by different methods: Phase formation,dielectric properties and relaxor behaviors

Giant permittivity was performed in CdCu₃Ti₄O₁₂ ceramics separately fabricated via the sol-gel technique (SG) and the standard solid-state technique (SS). XRD patterns and Raman spectrums revealed that CdCu₃Ti₄O₁₂ ceramics with single perovskite-related crystal phase were obtained irrespective of the preparation processing. TG-DSC, XRD, and FT-IR were carried out to explore the formation temperature of crystal phases as well as reaction mechanisms. The results indicated that the phase formation temperature of CdCTO-SG powders is at least 100?°C lower than that of CdCTO-SS powders and the dielectric properties of the CdCTO-SG ceramics are superior to those of the CdCTO-SS ceramics. In addition, three abnormal dielectric peaks were observed in dielectric temperature spectrum regardless of the two methods. Besides, data acquired from impedance and modulus assessments indicated that Maxwell-Wagner polarization contributed to the dielectric responses of samples. Therefore, giant dielectric properties of CdCu₃Ti₄O₁₂ ceramics conformed to internal barrier layer capacitor (IBLC) effect. Semiconducting grains are closely associated with the presence of mixed valence states of Cu⁺/Cu²⁺ and Ti³⁺/Ti⁴⁺ in samples.     

Zinc modified cadmium titanite nanoparticles: Electrical and room temperature methanol sensing properties

In this work Zn_xCd_1?xTiO₃ (x=0.25, 0.5, 0.75) nanoparticles were synthesized using solid state reaction method. Detailed investigation of electrical properties and room temperature methanol sensing characteristics of synthesized nanoparticles was carried out. X-ray diffraction (XRD) and Scanning Electron Microcopy (SEM) were used to determine the crystal structure and morphology of the prepared material. The transition from positive temperature coefficient of resistivity (PTCR) to negative temperature coefficient of resistivity (NTCR) was observed in Zn_0.75Cd_0.25TiO₃, Zn_0.50Cd_0.50TiO₃ and Zn_0.25Cd_0.75TiO₃ nanoparticles at 268 K, 248 K and 278 K respectively. Prototype sensors of prepared Zn_xCd_1?xTiO₃ (x=0.25, 0.5, 0.75) nanoparticles were tested at 10 ppm, 20 ppm, 30 ppm and 40 ppm of methanol at room temperature. The Zn_0.75Cd_0.25TiO₃ and Zn_0.25Cd_0.75TiO₃ nanoparticles sensors exhibited fast response and recovery times and a linear response with increase in methanol concentration. The Zn_0.5Cd_0.5TiO₃ nanoparticles sensors exhibited nonlinear response and slow response and recovery times. Response of sensors based on all compositions was stable over period of 30 days.     

Filtration properties of electrospinning nanofibers

Electrospinning is a relatively simple method to produce submicron fibers from solutions of different polymers and polymer blends. The extensive application in future of electrospinning nanofibers is filtration. In this article, the filtration properties of electrospinning nanofibers were investigated. During the experiments, nanofibers layers with different area weight were electrospun on the spunbonded or meltblown sublayers. Fiber diameter, pore diameter, filtration efficiency as well as filtration resistance of nanofibers web and sublayers were measured, respectively, through a series of experiments. The results show that the fiber diameter of nanofibers is much smaller than that of sublayers. It is also found that the pore diameter of nanofibers web is much smaller than sublayers and coefficient variation of the pore diameter of nanofibers web is much smaller than sublayers. Moreover, the filtration efficiency and filtration resistance of sublayers are lower than nanofibers webs. The balance between efficiency and press drop is also investigated in the article. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1285–1290, 2006     

Some new observations on the structural and phase evolution of nickel titanate nanofibers

In this study, we report for the first time the synthesis of nickel titanate (NTO) nanofibers containing a mixture of ilmenite and spinel phases of NTO, at an atypical low temperature. Precursor nanofibers produced by sol-gel electrospinning were calcined at three different temperatures to produce the NTO nanofibers. Thermal analysis along with X-ray photoelectron spectroscopy confirmed the formation of non-crystalline stable phases of TiN and Ti-O-N that restrained the formation of ilmenite NTO, and the Ni-rich environment pushed the Ti atoms to tetrahedral sites to form a defective spinel structure. The crystallite size of spinel NTO was observed to increase as a function of the calcination temperature above 700 °C, as the activation energy for coalescence and growth of spinel NTO was favorable. NTO nanofibers obtained above the calcination temperature of 700 °C exhibited new band gap energy around 2.5 eV in Tauc plot. Oxygen vacancies in these ceramic nanofibers decreased as the calcination temperature was increased. A hypsochromic shift of 20 nm in the photoluminescence spectra suggested that the material had a Ni²⁺ rich NTO (spinel).     

Strong tribocatalysis of strontium titanate nanofibers through harvesting friction energy for dye decomposition

Friction is a common clean energy and can be harvested and converted into electricity energy via triboelectricity, which can electrochemically drive dye decomposition in theory. In this work, the tribocatalytic Rhodamine B dye decomposition has been experimentally realized in strontium titanate (SrTiO₃) nanofibers, which are synthesized via a hydrothermal method. In the tribocatalytic dye decomposition process, the friction is exerted in the interface between catalyst surface and a polytetrafluoroethylene (PTFE) Teflon rod setup with the different stirring speed. The RhB dye decomposition ratios of SrTiO₃ nanofibers at these stirring speeds of 200 rpm, 400 rpm, 600 rpm, and 800 rpm are respectively 24.2%, 51.8%, 73.9% and 88.6%, yielding to these reaction rate constants of ～0.0112 h^?1, ～0.0260 h^?1, ～0.0562 h^?1 and ～0.0877 h^?1. The main active species, which play an important role in tribocatalytic process, are the superoxide radicals and holes on basis of the active species quenching experiment results. The excellent tribocatalysis activity makes SrTiO₃ nanofibers potential for application in dye wastewater treatment through utilizing the environmental friction energy.     

Controllable fabrication of cadmium phthalocyanine nanostructures immobilized on electrospun polyacrylonitrile nanofibers with high photocatalytic properties under visible light

A novel photocatalyst of nanostructured cadmium phthalocyanine (CdPc) immobilized on the surface of polyacrylonitrile (PAN) nanofibers had been successfully fabricated by a simple combination of electrospinning technique and the solvent-thermal process. FE-SEM micrographs indicated that the nanostructured CdPc uniformly immobilized on the surface of PAN nanofibers without agglomeration. And the obtained CdPc/PAN composite nanofibers exhibited high visible light photocatalytic activity for the degradation of rhodamine B. Moreover, this photocatalyst could be easily separated for reuse due to the one-dimensional nanostructural property of the CdPc/PAN composite nanofibers.     

Electrorheological properties of thermo-oxidative polypyrrole nanofibers

Using a chemical oxidative polymerization, polypyrrole (PPy) nanofibers were synthesized. After further thermo-oxidative treatment in air, the conductivity of PPy nanofibers was adjusted to a suitable level for use as a non-conventional nanofiber-based electrorheological (ER) suspension. Under electric fields, rheological properties of thermo-oxidative PPy nanofiber suspension were characterized. It showed that the nanofiber suspension possessed notable ER effect and low current density. Especially, the yield stress and shear modulus of nanofiber suspension were stronger than that of conventional granular suspension at the same volume fraction though the off-field viscosity of former was lower than that of latter. The ER effect and current density of thermo-oxidative PPy nanofiber suspension depended on the thermo-oxidative time and the nanofibers obtained after treatment for 3-5 h at 240 °C exhibited the optimal ER performances. It also showed that the thermo-oxidative PPy nanofiber suspension could maintain good ER properties within a wide operating temperature range of 25-115 °C.     

Piezoresistive effect of individual electrospun carbon nanofibers for strain sensing

Piezoresistive behavior of individual electrospun carbon nanofibers (CNF) was studied for the first time via a microelectromechanical systems platform. The gage factor of CNFs was found to vary from 1.96 to 2.55, not correlating with nanofiber diameter. The measured strain sensitivity of electrical resistance of individual CNFs could not be solely explained based on strain induced dimensional changes of CNFs, pointing to piezoresistivity in nanofibers. The microstructure of CNFs was studied via TEM imaging and Raman spectroscopy, suggesting the presence of sp² and sp³ hybridized carbon atoms in CNFs. The piezoresistivity of CNFs was explained in light of their hybrid structure. A one-dimensional model was adopted to relate CNFs piezoresistivity to their microstructure and electron tunneling between sp² hybridized regions through sp³ hybridized regions. The calibrated model revealed tunneling distances of 0.15–0.3 nm between sp² hybridized atoms. Moreover, our study pointed to the degree of graphitization and elastic mismatch between differently hybridized carbon atom regions in CNFs as critical parameters controlling CNFs’ piezoresistivity. This study sets the stage for the utilization of CNFs, not just as load bearing elements, but also as multifunctional nanoscale components with strain sensing capabilities, for instance in Nanoelectro-mechanical systems applications.     

Piezoelectric properties of PVDF-conjugated polymer nanofibers

This study presents the development and characterization of PVDF-conjugated polymer nanofiber-based systems. Five different conducting polymers (CPs) were synthesized successfully and used to create the nanofiber systems. The CPs used are polyaniline (PANI), polypyrrole (PPY), polyindole (PIN), polyanthranilic acid (PANA), and polycarbazole (PCZ). Nanofiber systems were produced utilizing the Forcespinning® technique. The nanofiber systems were developed by mechanical stretching. No electrical field or post-process poling was used in the nanofiber systems. The morphology, structure, electrochemical and piezoelectric performance was characterized. All of the nanofiber PVDF/CP systems displayed higher piezoelectric performance than the fine fiber PVDF systems. The PVDF/PPY nanofiber system displays the highest piezoelectric performance of 15.56 V. The piezoelectric performance of the PVDF/CP nanofiber systems favors potential for an attractive source of energy where highly flexible membranes could be used in power actuators, sensors and portable, and wireless devices to mention some.     

PLA-TiO2 nanocomposites: Thermal,morphological, structural,and humidity sensing properties

In this paper, the effect of TiO₂ ceramic nanoparticles on the thermal stability, morphology, molecular mass, structure and electrical properties of the polylactic acid-Titanium dioxide (PLA-TiO₂) composites, aimed for relative humidity (RH) sensing have been reported. PLA-TiO₂ nanocomposites films were developed through a spin coating process. The developed films were characterized by X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and electrochemical impedance spectroscopy analysis (EIS). To investigate the RH-dependent characteristics, the devices were prepared on pre-patterned ITO substrates. The capacitive and resistive response of the nanocomposite films were studied under RH levels ranging from 20–90%. The PLA-TiO₂ nano-sensing films, having modified surface by acetone etching, exhibited superior morphological and electrical performance when compared to PLA-TiO₂ pristine samples.     

Enhancing dielectric properties of barium titanate macrofibers

The motivation of this work was to improve the dielectric properties of BaTiO₃ (BT) macrofibers by mixing BT nanofibers and commercial BT powder. BT nanofibers were fabricated via electrospinning synthesis. The calcined electrospun nanofibers were chopped and mixed with BT powder and converted in to a thermoplastic feedstock for extrusion of ceramic macrofibers with a diameter of 500 μm. The electromechanical properties of the BaTiO₃ macrofibers were investigated by varying calcination temperature of the nanofibers. For both nano and macro fibers, microstructure and phase composition was investigated by SEM and XRD. It could be observed that an increase in calcination temperature of the nanofibers enhanced the final electromechanical properties of the sintered macrofibers. The relative permittivity increased almost twice, the remanent polarisation increased about 4 times and the strain almost increased 10 times with the addition of calcined nanofibers to macrofibers.     

Gas transport properties of electrospun polymer nanofibers

Although the basic principles of gas flow through unidirectional fibers have been widely studied and well understood since the 1950s, questions arise when these principles are applied to electrospun polymer nanofibers. Classic theories based on orderly packed coarse fibers are inadequate in accounting for the influences of random fiber distribution and slip flow. In this work, a mechanistic model in terms of fiber volume fraction and fiber radius is presented to determine the through-plane permeability of electrospun nanofiber layers. The fibrous system is subdivided into a series of cells of orthogonal fibers with random volumes. A single factor is proposed to quantify the effect of randomness of fiber distribution on flow behaviors. When the fiber radius is comparable with the mean free path of air molecules, the slip flows in the nanoscale fibrous media are particularly explored. The solutions obtained are successfully validated through comparison with experimental and numerical results. It is demonstrated that the through-plane permeability of electrospun nanofibers is enhanced by the slip effect and randomly distributed fibers are more permeable than ordered structures.