A novel double metal-dithizone functionalized polyurethane electrospun nanofiber and film for colorimetric determination of hexavalent chromium.

This work proposes a highly specific method of Cr6+ determination based on the double reactions of two metals, Co2+ with dithizone to form a (DTZ)-Co2+ complex, and the replacement of Co2+ in the formed complex with Cr6+. The fast degradation of DTZ in solution in wet analysis was overcome by preparing dithizone functionalized polyurethane nanofibers that were electrospun into a membrane (DTZ/PU-NF) and a microwell plate film (DTZ/PU-MPF). For comparison, the performance of diphenylcarbazide (DPC), a currently used complexing agent for Cr6+, was also investigated. Colour changes were detected as red-green-blue values. The DTZ/PU-NF was smooth, with an average diameter of 384.09 nm and no bead appeared. A dense network structure was formed. The best formulation of DTZ, PU and Co2+ was also applied as a microwell plate film. In the presence of Cr6+, the colour of DTZ-Co2+ changed from red to magenta. Among the three studied methods, the colorimetric DTZ-Co2+/PU-NF presented the best results. Its linearity range was 0.001-1.0 mg L-1, with a regression equation of Cr6+ = -0.189 + (0.0056 × red) + (0.0086 × green) - (0.0129 × blue), R 2 of 0.990. The limit of detection was 0.001 mg L-1 and the precision was 1.7%. The applicability of DTZ/PU-NF was validated for Cr6+ in vegetable oils with recoveries of 89.5-116.8%. The sensitivity of DTZ/PU-NF was ten times higher than that of DTZ/PU-MPF. The methods based on DTZ-Co2+/PU-NF and DTZ-Co2+/PU-MPF proved to be highly selective, rapid, user-friendly, simple and reliable.

Lifetime Evaluation of Photovoltaic Polymeric Backsheets under Ultraviolet Radiation: From Chemical Properties to Mechanical Modeling.

Photovoltaic (PV) power generation plays a significant role with the increase of installed capacity of renewable energy. The effects of environmental stress on insulating backsheets have been considered as the main cause of failure in PV systems. However, traditional aging models are difficult to realize the comprehensive evaluation of the lifetime of insulating backsheets. In this paper, the analytical method of complex chemical degradation related to the insulation was replaced by a physics-based method to quantify the elongation at the break as a function of time corresponding to temperature and radiation. In contrast to traditional aging models, this model simply used one parameter, namely drop-off rate (v), to reflect the degradation of polymers under various environmental stresses. The effect of ultraviolet (UV) radiation on the model was considered. Moreover, the electrical degradation, chemical changes, and mechanical properties caused by UV radiation were investigated to provide the reference for the lifetime of evaluation. The research is significant for comprehensively evaluating the lifetime of insulating materials for PV systems and other power equipment.

Electrostrictive and Structural Properties of Poly(Vinylidene Fluoride-Hexafluoropropylene) Composite Nanofibers Filled with Polyaniline (Emeraldine Base).

Previous studies have reported that poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymers can exhibit large electrostrictive strains depending on the filler. This work examines the electrostrictive and structural properties of P(VDF-HFP) nanofibers modified with conductive polymer polyaniline (PANI). The P(VDF-HFP)/PANI composite nanofibers were prepared by an electrospinning method with different PANI concentrations (0, 0.5, 1, 1.5, 3 and 5 wt.%). The average diameter, water contact angle and element were analyzed by SEM, WCA and EDX, respectively. The crystalline, phase structure and mechanical properties were investigated by XRD, FTIR and DMA, respectively. The dielectric properties and electrostrictive behavior were also studied. The results demonstrated that the composite nanofibers exhibited uniform fibers without any bead formation, and the WCA decreased with increasing amount of PANI. However, a high dielectric constant and electromechanical response were obtained. The electrostrictive coefficient, crystalline, phase structure, dielectric properties and interfacial charge distributions increased in relation to the PANI content. Moreover, this study indicates that P(VDF-HFP)/PANI composite nanofibers may represent a promising route for obtaining electrostrictive composite nanofibers for actuation applications, microelectromechanical systems and sensors based on electrostrictive phenomena.

Phase and Structure Behavior vs. Electromechanical Performance of Electrostrictive P(VDF-HFP)/ZnO Composite Nanofibers.

In this work, we improved the electromechanical properties, electrostrictive behavior and energy-harvesting performance of poly(vinylidenefluoridene-hexafluoropropylene) P(VDF-HFP)/zinc oxide (ZnO) composite nanofibers. The main factor in increasing their electromechanical performance and harvesting power based on electrostrictive behavior is an improved coefficient with a modified crystallinity phase and tuning the polarizability of material. These blends were fabricated by using a simple electrospinning method with varied ZnO contents (0, 5, 10, 15 and 20 wt%). The effects of the ZnO nanoparticle size and content on the phase transformation, dielectric permittivity, strain response and vibration energy harvesting were investigated. The characteristics of these structures were evaluated utilizing SEM, EDX, XRD, FT-IR and DMA. The electrical properties of the fabrication samples were examined by LCR meter as a function of the concentration of the ZnO and frequency. The strain response from the electric field was observed by the photonic displacement apparatus and lock-in amplifier along the thickness direction at a low frequency of 1 Hz. Moreover, the energy conversion behavior was determined by an energy-harvesting setup measuring the current induced in the composite nanofibers. The results showed that the ZnO nanoparticles' component effectively achieves a strain response and the energy-harvesting capabilities of these P(VDF-HFP)/ZnO composites nanofibers. The electrostriction coefficient tended to increase with a higher ZnO content and an increasing dielectric constant. The generated current increased with the ZnO content when the external electric field was applied at a vibration of 20 Hz. Consequently, the ZnO nanoparticles dispersed into electrostrictive P(VDF-HFP) nanofibers, which offer a large power density and excellent efficiency of energy harvesting.

Osseointegrated membranes based on electro-spun TiO2/hydroxyapatite/polyurethane for oral maxillofacial surgery.

Membranes which have an osseointegration abilty are often selected as biomaterials in oral and maxillofacial surgery. Although these membranes are often the best option for certain uses, it is a challenge to create functionally attractive membranes. In this research, electro-spun titanium oxide (TiO2)/hydroxyapatite (HA)/polyurethane (PU) membranes were fabricated with different ratios of HA and TiO2: 100: 0, 70:30, 50:50, 30:70 and 0:100 w/w. The morphologies of the different mixtures were assessed with a Scanning Electron Microscope (SEM) and Field Emission Microscope (FESEM). Element analysis was performed with EDX. The physical properties of the water contact angles and mechanical strength were tested and the membranes cultured with osteoblasts to evaluate their biological functions, cell adhesion, viability, proliferation, alkaline phosphatase (ALP) activity, and calcium content. The results showed that the membranes with TiO2 and HA had smaller fibers than those without TiO2 and HA. The TiO2- and HA-including compounds showed the formation of particle aggregation on the surface of the fibers. They also had higher water contact angles, mechanical strength, and stiffness than those without TiO2 and HA, and they had better cell adhesion, viability, proliferation, ALP activity and calcium content. The membrane with a 50:50 TiO2:HA ratio had more unique biological functions than the others. Finally, our research demonstrated that osseointegrated membranes with 50:50 TiO2:HA are promising for oral and maxillofacial surgery.

High Electromechanical Deformation Based on Structural Beta-Phase Content and Electrostrictive Properties of Electrospun Poly(vinylidene fluoride- hexafluoropropylene) Nanofibers.

The poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) polymer based on electrostrictive polymers is essential in smart materials applications such as actuators, transducers, microelectromechanical systems, storage memory devices, energy harvesting, and biomedical sensors. The key factors for increasing the capability of electrostrictive materials are stronger dielectric properties and an increased electroactive ß-phase and crystallinity of the material. In this work, the dielectric properties and microstructural ß-phase in the P(VDF-HFP) polymer were improved by electrospinning conditions and thermal compression. The P(VDF-HFP) fibers from the single-step electrospinning process had a self-induced orientation and electrical poling which increased both the electroactive ß-crystal phase and the spontaneous dipolar orientation simultaneously. Moreover, the P(VDF-HFP) fibers from the combined electrospinning and thermal compression achieved significantly enhanced dielectric properties and microstructural ß-phase. Thermal compression clearly induced interfacial polarization by the accumulation of interfacial surface charges among two ß-phase regions in the P(VDF-HFP) fibers. The grain boundaries of nanofibers frequently have high interfacial polarization, as they can trap charges migrating in an applied field. This work showed that the combination of electrospinning and thermal compression for electrostrictive P(VDF-HFP) polymers can potentially offer improved electrostriction behavior based on the dielectric permittivity and interfacial surface charge distributions for application in actuator devices, textile sensors, and nanogenerators.

Layer-by-layer electrospun membranes of polyurethane/silk fibroin based on mimicking of oral soft tissue for guided bone regeneration.

Guided bone regeneration is an effective method that can enhance bone volume at a defect site of the mandible before material implantation. Layer-by-layer electrospun membranes of polyurethane/silk fibroin (SF) were fabricated to mimic oral soft tissue. The electrospun polyurethane fibers were initially fabricated into a membrane. Next, the polyurethane layer was covered with electrospun SF fibers at different thicknesses. Then, the SF layer was covered with electrospun polyurethane fibers. Afterward, the morphologies of the membranes were observed and analyzed by scanning electron microscopy. The physical properties of the membranes were evaluated from the contact angle and mechanical properties. The biological performances were evaluated by observing cell adhesion, viability and proliferation, alkaline phosphatase activity, and calcium content. The results demonstrated that the membrane with a thin SF core showed better physical properties and mechanical performance than the thicker SF cores. Finally, the results deduced that the membrane with a thin SF core was promising for guided bone regeneration.

Colorimetric determination of sialic acid based on boronic acid-mediated aggregation of gold nanoparticles.

The authors describe a rapid, sensitive and selective colorimetric assay for sialic acid (SA) based on the use of gold nanoparticles (AuNPs) modified with 3-aminophenylboronic acid (3-APBA) which acts as the recognition probe for SA. 3-APBA contains amino groups and boronic acid groups through which it can assemble on citrate stabilized AuNPs. It reacts with the cis-diol groups of SA by reversible formation of a cyclic boronate ester in slightly acidic buffer. Detection involves the sequential addition of AuNPs, phosphate buffer, 3-APBA and SA in a tube, vortex mixing, acquisition of photographic images or absorption spectra, and calculation of the result. The method is simple, rapid, and does not require cumbersome steps such as the preparation of stable boronic acid functionalized AuNPs as used in colorimetric sensing of saccharides. Under the optimum conditions, the ratio of absorbances at 700 and 520 nm increases linearly in the 0.15-1.00 mM SA concentrations range, and the detection limit is 60 µM. This is comparable to the detection limit obtained in other colorimetric assays reported. Acceptable intra- and inter-day precisions of three SA concentrations (0.50, 1.00 and 2.00 mM) ranged from 1.9-4.2% and 4.2-6.4%, respectively. The efficacy of the method was demonstrated by analyzing simulated human saliva which gave recoveries ranging from 98.7-106.0%. Graphical abstract Schematic of a colorimetric method for detection of sialic acid (SA) in simulated saliva. It is based on aggregation of gold nanoparticles with 3-aminophenyl boronic acid (3-APBA) which assembles on AuNPs while the boronic acid group binds to cis-diols of SA to form a boronate ester.

Analysis of ac-dc conversion for energy harvesting using an electrostrictive polymer P(VDF-TrFE-CFE).

Harvesting systems capable of transforming unused environmental energy into useful electrical energy have been extensively studied for the last two decades. The recent development of electrostrictive polymers has generated new opportunities for harvesting energy. The contribution of this study lies in the design and validation of electrostrictive polymer- based harvesters able to deliver dc output voltage to the load terminal, making the practical application of such material for self-powered devices much more realistic. Theoretical analysis supported by experimental investigations showed that an energy harvesting module with ac-to-dc conversion allows scavenging power up to 7 µW using a bias electric field of 10 V/µm and a transverse strain of 0.2%. This represents a power density of 280 µW/cm(3) at 100 Hz, which is much higher than the corresponding values of most piezo-based harvesters.

Modeling and experimentation on an electrostrictive polymer composite for energy harvesting.

The harvesting of energy from ambient environments is an emerging technology with potential for numerous applications, including portable electronic devices for renewable energy. Most of the current research activities refer to classical piezoelectric ceramic materials, but more recently the development of electrostrictive polymers has generated novel opportunities for high-strain actuators. At present, the investigation of using electrostrictive polymers for energy harvesting (a conversion of mechanical to electrical energy) is beginning to show potential for this application. This paper discusses the development of a model that is able to predict the energy harvesting capabilities of an electrostrictive polymer composite (EPC). An equivalent electrical scheme has been developed by using the model of current that was recently developed by our group. After the validation of the model on a macroscopic level, an empirical relationship was established to predict the value of power from the electrostriction coefficient, the dielectric permittivity, and the compliance of the material. Finally, results indicated that the dielectric permittivity was the crucial parameter for energy harvesting.