Electrospun fibers often have beads as byproducts. Bead formation can be substantially minimized by the introduction of additives, such as ionic salts or surfactants, to the electrospinning polymeric solution. Polyetherimide (PEI) fibers were fabricated using electrospinning. Four different additives, Lithium Chloride (LiCl), Sodium Chloride (NaCl), Triton X-100 and Hexadecyltrimethylammonium Bromide (HTAB) were utilized to alter the polymer solution electrical conductivity and surface tensions. The effects of solution conductivity and surface tension on the electrospinning and the thermal, mechanical stability of the polymeric fibers were investigated. Morphology, thermal properties, permeability and mechanical strength of the fiber mats were investigated using Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), Frazier Permeability Test, and Tensile tester respectively. The addition of 1.5wt.% HTAB was found to be the optimum concentration to produce PEI fibers without beads. The addition of HTAB produced fiber mats with higher air permeability, higher thermal stability and higher mechanical strength in comparison to the other additives. Finally, a filtration test was conducted on a simple custom model to compare the performance of beaded and non-beaded PEI fiber mats. The non-beaded PEI fiber mat performed better in terms of both separation efficiency (%E) and differential pressure drop (∆P) separating water droplets from diesel fuel.
In this study, we aimed to improve our understanding of the response mechanisms associated with the formation of CdS thin films. CdS thin film remains the most valuable option for many researchers, since it has shown to be an effective buffer material for film-based polycrystalline solar cells (CdTe, CIGSe, CZTS). We performed experimental and numerical simulations to investigate the effect of different thiourea concentrations on the characteristics of the CdS buffer layer. The experimental results reveal that an increase in thiourea concentrations had a direct effect on the optical results, with bandgap values ranging from (2.32 to 2.43) eV. XRD analysis confirmed that all deposited films were polycrystalline, except for [1/0.75], where there is no CdS formation. Electrical studies indicated that CdS with a molar ratio of [Cd]/[S] of 1 had the maximum carrier concentration (3.21 × 1014 cm−3) and lowest resistivity (1843.9 Ω·cm). Based on the proposed mechanism, three kinds of mechanisms are involved in the formation of CdS layers. Among them, the ion-by-ion mechanism has a significant effect on the formation of CdS films. Besides, modelling studies reveal that the optic-electrical properties of the buffer layer play a crucial role in influencing the performance of a CIGS solar cell.
Cyclohexanone is an important industrial intermediate in the synthesis of materials such as nylons, but preparing it efficiently through one-step hydrogenation of phenol is hindered by over-reduction to cyclohexanol. Using an efficient catalyst can enhance the selectivity of cyclohexanone at high phenol conversion. In this study, catalysts comprised of palladium nanoparticles supported on electrospun PVDF-HFP (polyvinylidene fluoride-co-hexafluoropropylene) nanofibers were prepared using the electrospinning technique. The catalysts were characterized using thermogravimetric analyzer (TGA), scanning electron microscopy (SEM), transmission electron microscope (TEM), and drop shape analyzer (DSA). The prepared catalysts were used to hydrogenate phenol into cyclohexanone in a batch reactor. The Pd/PVDF-HFP catalyst showed a very high product selectivity and high phenol conversion. The conversion of phenol achieved was 98% with 97% cyclohexanone selectivity in 7 h using 15 wt% of palladium (0.0021 moles) relative to phenol (0.0159 moles). The turnover number (TON) and turnover frequency (TOF) values calculated were 7.38 and 1.05 h −1 , respectively. This paper presents original research in heterogeneous catalysis using novel electrospun nanofibers. Multiphase hydrogenation of phenol to cyclohexanone over electrospun Pd/PVDF-HFP catalyst has not been reported by any researcher in the literature. This work will also provide a research window for the application of electrospun polymeric nanofibers in multiphase reactions.Fibers 2019, 7, 28 9 of 11 applications of polymeric nanofibers in multiphase reactions. The polymeric structure provided the advantages of easy separation and high mechanical strength.
A high-quality buffer layer serves as one of the most significant issues that influences the efficiency of solar cells.
Correction for ‘Mechanism and principle of doping: realizing of silver incorporation in CdS thin film via doping concentration effect’ by A. S. Najm et al., RSC Adv., 2022, 12, 29613–29626, https://doi.org/10.1039/D2RA04790J.
Fuel contamination by water is one of the major factors of engine failures. Separation of water from diesel fuel is often achieved by coalescing or depth filter media. The separation performance is strongly related to the motion of drops on the surface and in the depth of a filter medium. The dynamics of the motions of drops on a filter surface are influenced by many factors such as the wetting properties of the media. Direct observations of drop movements on fiber surfaces are not well documented. Of particular interest in this work are the dynamics of drops on surfaces of hydrophobic mats that resist drop movement into the interior of the mat, forcing the drops to move on the surface of the mat. Such materials function as barriers to the dispersed phase and allow the continuous phase to move through the mat. In this paper, the motions of water drops were studied on surfaces of mats woven of polypropylene, nylon and Teflon TM (ie, polytetrafluoroethylene) fibers. Pore sizes of the mats ranged from 100 to 1000 microns and drop sizes ranged from 200 to 6000 microns. The flow of ultra low sulfur diesel fuel parallel to the mat surface provided a drag force that induced the movement of the drops. The effects of surface wettability, flow velocity, drop size, fiber size, fiber mat pore size, fiber mat orientation were considered. A correlation for a drag coefficient to estimate the average velocity of drops moving on the woven mats surfaces was derived from the flow and the material's characteristics. In addition, another correlation was obtained for estimating the minimum velocity, or minimum Reynolds number, required to initiate the drop motion on the woven mat surfaces.
Coalescence of water drops phenomena is important to many industrial applications. One approach for coalescing water droplets is by introducing electrical charges by applying an external voltage potential gradient across the drops. Electro-coalesce occurs when spreading and motion of the drops due to the electrical field brings two drops into contact. In this paper, the phenomena of electro-coalescence is investigated for different electrical and geometric spacing conditions applied to 5 microliter drops of deionized water on electrowettable surfaces. The electrowettable surfaces were prepared with poly(styrene-co-methyl methacrylate) as the coated dielectric film followed by FluoroPel as the hydrophobic film. Coalescence was studied for two methods of applying the electrical field to the drops. The first method was by using a programmable power supply with 10 Volt/millisecond slew rate up to 200 VDC maximum. The second method for applying the field was by using a relay switch to give a sudden step change of 200 VDC. Coalescence events were video recorded in a high-speed frame rate and the coalescence of the drops were observed to coalesce within about 15 ± 5 milliseconds once the drops interfaces came in contact with each other regardless of the method used for applying the field. The rate limiting step for coalescence to take place was the method of applying the field.
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