Single Nanofiber Research Articles

Microfiber-nanofiber composite filter for high-efficiency and low pressure drop under nano-aerosol loading

Abstract Nano-aerosols are airborne aerosols in the range of 100 nm. They are present abundantly in both pollutants and viruses, both of which affect human health. Filtering these nano-aerosols leads to high-pressure drop in cabin filters due to their small sizes forming impermeable dust cake, and prior to cake formation the capture efficiency is rather poor with conventional microfiber filters. We have investigated a composite filter with a microfiber layer positioned immediately upstream of a nanofiber layer. Such composite filter provides high efficiency and low-pressure drop during all phases of filtration of nano-aerosols: initial depth filtration, transition, and final cake filtration. The behavior of the composite filter together with various filter benchmarks (single and composite filters of microfiber/nanofiber filters) has been investigated by monitoring the pressure drop, especially during cake filtration. Using the measurements together with Ergun/Kozeny-Carman equation and material balance we come up with a new method to determine the solid volume fraction and permeability of the cake. The grade efficiency for the most penetrating particle is also measured concurrently to define the incipient point to cake formation and provide material balance. Most importantly, for the first time we have confirmed that the cake ultimately forms on the composite filter is due to the cake that originates from the upstream microfiber layer and not from the downstream nanofiber layer. Therefore, the pressure drop for the composite filter can be sustained relatively low throughout the filtration. On the other hand, the aerosol capture efficiency stays very high from start-to-end of filtration, with high initial filtration efficiency courtesy of the nanofiber filter installed downstream of the composite filter. The price to pay is a slightly higher pressure drop for the composite filter in the clean unloaded state, but this is insignificant during aerosol loading as most pressure drop is attributed to that of the cake. For the first time we have introduced, also independently using Buckingham-Pi analysis, a brand new dimensionless parameter, Beta, which measures the equivalent “thickness” of additional cake deposition (in molten form) to the viscous flow resistance “path length” due to the additional cake deposit. A high-capacity filter aimed for heavy aerosol loading should have large Beta that results in low solidosity, high porosity, and high permeability for the cake. In our study, the microfiber-nanofiber composite filter has the highest Beta of nearly 4 and also highest efficiency. Despite high efficiency the single nanofiber filter has much lower Beta of 2, while the single microfiber filter has Beta of 3, yet much lower efficiency, especially at initial filtration. Using the microfiber-nanofiber composite filter design, we can “engineer the cake” deposited on the filter to be more permeable and with least flow resistance during aerosol loading to attain high Beta values. This is an innovative approach to increase the badly needed aerosol storage capacity with low pressure drop for the nanofiber filter while maintaining high efficiency throughout the aerosol loading for extended filtration applications. The highly permeable aerosol cake can also be cleaned by backpulsed-and-backblow readily for filter reuse.

The Cooperative Effect of Both Molecular and Supramolecular Chirality on Cell Adhesion

AbstractAlthough helical nanofibrous structures have great influence on cell adhesion, the role played by chiral molecules in these structures on cells behavior has usually been ignored. The chirality of helical nanofibers is inverted by the odd–even effect of methylene units from homochiral l‐phenylalanine derivative during assembly. An increase in cell adhesion on left‐handed nanofibers and weak influence of cell behaviors on right‐handed nanofibers are observed, even though both were derived from l‐phenylalanine derivatives. Weak and negative influences on cell behavior was also observed for left‐ and right‐handed nanofibers derived from d‐phenylalanine, respectively. The effect on cell adhesion of single chiral molecules and helical nanofibers may be mutually offset.

The Cooperative Effect of Both Molecular and Supramolecular Chirality on Cell Adhesion.

Although helical nanofibrous structures have great influence on cell adhesion, the role played by chiral molecules in these structures on cells behavior has usually been ignored. The chirality of helical nanofibers is inverted by the odd-even effect of methylene units from homochiral l-phenylalanine derivative during assembly. An increase in cell adhesion on left-handed nanofibers and weak influence of cell behaviors on right-handed nanofibers are observed, even though both were derived from l-phenylalanine derivatives. Weak and negative influences on cell behavior was also observed for left- and right-handed nanofibers derived from d-phenylalanine, respectively. The effect on cell adhesion of single chiral molecules and helical nanofibers may be mutually offset.

Electrospun CuO nanofibers for room temperature volatile organic compound sensing applications

Volatile organic compound (VOC) sensing performance and kinetics of adsorption onto electrospun CuO nanofibers have been studied. The effect of the relative humidity (between 5% and 50%) on VOC sensing behavior and adsorption kinetics have also been investigated. The formation of single phase monoclinic CuO nanofibers with preferentional orientation of (002) were confirmed by X-ray diffraction and scanning electron microscopy studies. Three different kinetic models, Elovich model, pseudo first-order equation, and the Ritchie's equation were selected to follow the adsorption process. Sensing studies revealed that electrospun CuO nanofibers have a great potential for room temperature VOC sensing applications with high sensitivity, short response and recovery times. From the analysis of kinetic studies, it was observed that the kinetics of VOC vapors onto the electrospun CuO nanofibers strongly depends on level of the relative humidity and the concentration of VOC vapors.

Single-Crystal Electrospun Plasmonic Perovskite Nanofibers

Hexagonal single-crystal perovskite-like (A3B8O21) nanofibers were synthesized via the electrospinning technique. High-resolution transmission electron microscopy imaging showed that each single nanofiber is composed of several interconnected small crystals. The selected-area electron diffraction analysis reveals a single crystalline nature of the fabricated nanofibers. The fabricated nanofibers showed surface plasmon resonance characteristics. Theoretical and computational calculations using the Mie–Gans theory were performed to investigate the plasmonic and optical properties of the obtained nanofibers, which were also confirmed experimentally and compared to gold nanoparticles. The fabricated nanofibers were tested as novel substrate materials for surface-enhanced Raman spectroscopy, showing exceptional performance.

Piezoelectric and optoelectronic properties of electrospinning hybrid PVDF and ZnO nanofibers

Polyvinylidene fluoride (PVDF) is a unique ferroelectric polymer with significant promise for energy harvesting, data storage, and sensing applications. ZnO is a wide direct band gap semiconductor (3.37 eV), commonly used as ultraviolet photodetectors, nanoelectronics, photonicsand piezoelectric generators. In this study, we produced high output piezoelectric energy harvesting materials using hybrid PVDF/ZnO nanofibers deposited via electrospinning. The strong electric fields and stretching forces during the electrospinning process helps to align dipoles in the nanofiber crystal such that the nonpolar α-phase (random orientation of dipoles) is transformed into polar β-phase in produced nanofibers. The effect of the additional ZnO nanowires on the nanofiber β-phase composition and output voltage are investigated. The maximum output voltage generated by a single hybrid PVDF and ZnO nanofiber (33 wt% ZnO nanowires) is over 300% of the voltage produced by a single nanofiber made of pure PVDF. The ZnO NWs served not only as a piezoelectric material, but also as a semiconducting material. The electrical conductivity of the hybrid PVDF/ZnO nanofibers increased by more than a factor of 4 when exposed under ultraviolet (UV) light.

Humidity induced inhibition and enhancement of spontaneous emission of dye molecules in a single PEG nanofiber

Intrinsic properties of a polyethylene glycol nanofiber are utilized for the first time to dynamically modify the spontaneous emission rate of encapsulated boradiazaindacene dye molecules with fluorescence lifetime imaging. Nanofibers, fabricated by the electrospinning technique, are exposed to relative humidity up to 80%. The spontaneous emission rate of the confined boradiazaindacene is observed to inhibit and enhance the nanofibers’ swelling. The Purcell factor is determined to demonstrate an oscillatory behavior resulting from the distinct characteristics of the mode volume, and the step-like increase of the quality factor of the nanofiber cavity due to the changes in the refractive index and fiber diameter.

Synergistic combination of electronic and electrical properties of SnO2 and TiO2 in a single SnO2-TiO2 composite nanofiber for dye-sensitized solar cells

Tin dioxide (SnO2) and titanium dioxide (TiO2) are popular metal oxide semiconductors; they are explored for many applications because of their unique properties. This paper details that electronic and electrical properties of SnO2 and TiO2 can be synergistically combined in an one-dimensional nanostructure, such as electrospun nanofibers. The resulting composite nanofibers (CNFs) showed beneficial properties when used as a photoanode in dye-sensitized solar cells (DSSCs). In particular, the CNFs showed higher conduction band energy than SnO2 and higher electrical conductivity than TiO2. The SnO2-TiO2 CNFs are synthesized by electrospinning a polymeric solution containing equimolar concentration of tin chloride and titanium alkoxide precursors and subsequent annealing. The composite formation is demonstrated by X-ray diffraction and energy dispersive X-ray measurements and morphology by scanning electron microscopy. Synergy in electronic and electrical properties are demonstrated by cyclic voltammetry, absorption spectroscopy, and electrochemical impedance spectroscopy. Dye-sensitized solar cells fabricated using the CNFs as photoanode showed higher open circuit voltage and short circuit current density than those achieved using pure SnO2 and pure TiO2, respectively.

Effect of localized electric field on the carrier transport properties of NiO nanofibers

Nickel oxide nanofibers were synthesized using an electrospinning technique. X-ray diffraction revealed the formation of single phase polycrystalline NiO nanofibers when calcined at 600 °C. Scanning electron microscopy demonstrated that the average diameter of composite nanofibers dried at 100 °C was ∼400 nm, which decreased to ∼100 nm for samples calcined at 600 °C. The smooth surface of these nanofibers turned highly porous upon burning of the remnant organic constituents (e.g., PVP, acetic acid and other volatile components) and crystallization of the nanofibers upon calcination at 600 °C. At higher voltages, the IV curves followed the bulk limited Poole Frenkel (PF) conduction mechanism. The theoretical field lowering coefficient βTh was in good agreement with the experimental Poole Frenkel field lowering coefficient βPF. The variation in field lowering coefficient may be attributed to the presence of localized electric field due to difference in the work function of NiO nanofibers and electrode material.

Electrospinning water-soluble/insoluble polymer blends

Electrospun nanofiber mats can be used, e.g., as filter materials, in biotechnological and medical applications, as precursors for the preparation of carbon nanofibers, etc. In most cases, the large surface-to-volume ratio and correspondingly large contact area with the environment is utilized. This ratio can even be further increased by introducing nanostructures into the nanofibers. One possibility to modify the morphology of the nanofibers or the whole mats is based on the introduction of water-soluble additions in spinning solutions of insoluble polymers and afterwards washing them out. In this paper, polyacrylonitrile (PAN) nanofiber mats were blended with eight water-soluble polymers to test which blends are spinnable and result in which modifications of the single nanofibers and the nanofiber mats. Optical examination shows a broad range of possible morphologies which can be gained in this way, paving the way to tailoring the desired geometric properties of PAN nanofiber mats.

Pathway driven self-assembly and living supramolecular polymerization in an amyloid-inspired peptide amphiphile.

Peptide 1 with an Aβ42 amyloid nucleating core demonstrates step-wise self-assembly in water. Variation of temperature or solvent composition arrests the self-assembly to give metastable nanoparticles, which undergo self-assembly on gradual increase in temperature and eventually produce kinetically controlled nanofibers and thermodynamically stable twisted helical bundles. Mechanical agitation of the fibers provided access to short seeds with narrow polydispersity index, which by mediation of seeded supramolecular polymerization establishes perfect control over the length of the nanofibers. Such pathway dependence and the length control of the supramolecular peptide nanofibers is exploited to tune the mechanical strength of the resulting hydrogel materials.

Temperature-induced molecular orientation and mechanical properties of single electrospun polyimide nanofiber

Mechanical properties of polyimide (PI) electrospun nanofibers could be improved by increasing imidization temperatures. However, the intrinsic mechanism on this phenomenon is highly required, which is helpful to improve mechanical properties of electrospun nanofibers by external thermal treatment. In this work, single electrospun PI nanofibers (SNF-PI) with different imidization temperatures were prepared. The nanofiber morphology was studied by SEM and AFM and the mechanical properties were measured by single fiber micro-tensile test. Polarized Raman Spectroscopy was applied to determine the PI molecular orientation in SNF-PI. The molecular orientation factor provides directly explanation on the effect of imidization temperatures on the mechanical properties of SNF-PI.

Mathematical Modeling and Experimental Evaluation for the predication of single nanofiber modulus.

Electrospun nanofiber matrices are widely used as scaffolds for the regeneration of different tissues due to similarities with fibrous components of the extracellular matrix. These scaffolds could act as a substrate for inducing mechanical stimuli to cells. The main mechanical stimuli factor in nanofiber scaffolds for determining the cell behaviors is stiffness of single nanofibers. This paper especially highlights the finding that the young's modulus of single nanofibers can be obtained from aligned nanofibers matrix. It is assume that, the modulus of single nanofibers are equal to modulus of completely aligned nanofibers. However, due to difficulty of producing completely aligned nanofibers, the obtained modulus of single nanofiber wouldn't have significant value. Therefore, we propose a new mathematical model to predict the stiffness of single nanofibers from non-perfectly aligned nanofibers matrix.

Analysis of the Comprehensive Tensile Relationship in Electrospun Silk Fibroin/Polycaprolactone Nanofiber Membranes.

The mechanical properties of electrospun nanofiber membranes are critical for their applications. A clear understanding of the mechanical properties that result from the characteristics of the individual fiber and membrane microstructure is vital in the design of fiber composites. In this reported study, silk fibroin (SF)/polycaprolactone (PCL) composite nanofiber membranes were preparedusing an electrostatic spinning technology. The nanofiber orientation distribution (FOD) of the membrane was analyzed using multi-layer image fusion technology, and the results indicated the presence of an approximately uniform distribution of fibers in the electrospun membranes. The relationship between the single nanofiber and the membrane was established by analyzing the geometrical structure of the cell by employing a representative volume element (RVE) analysis method. The mechanical properties of the 272 nm diameter SF/PCL composite fibers were then predicted using the developed model.

Interface Controlled Growth of Single-Crystalline PbTiO3 Nanostructured Arrays

PbTiO3 (PTO) ferroelectric perovskite has appealing electromechanical characteristics such as low aging rate of the dielectric constant, a high pyroelectric coefficient, a high piezoelectric voltage constant (gij), and a high Curie temperature of 490 °C. However, the high tetragonality of PTO ceramics makes them difficult to be synthesized via conventional high-temperature techniques. Here, a novel synthesis methodology is reported that results in epitaxial growth of a vertically aligned array of PTO nanofibers on a Ti metal substrate. High quality single crystal PTO nanofibers oriented along the [001] PTO direction were obtained on a (110) oriented TiO2 seed layer using a low-temperature hydrothermal synthesis technique. Fundamental understanding of the nucleation and growth criterion is provided through a combination of modeling of the geometric matching of crystal surfaces and experiments detailing the role of underlying TiO2 phase and interplanar atomic configuration. Crystal matching revealed good co...

Removal of 4-chlorophenol from water using different carbon nanostructures: A comparison study

In this research, performance of different carbon structures including multiwalled carbon nanotubes (MWNT), single walled carbon nanotubes (SWNT), carbon nanofibers (CNF), nano carbon (NC), nanoporous graphene (G) and mesoporous carbon (CMK) was studied as sorbents for removal of 4-chlorophenol (4-CP) from water. Nanostructures were synthesized and their morphologies studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The structure and surface properties of carbon nanostructures were characterized using XRD, BET and Raman spectrometry. In several batch adsorption experiments, the effect of main factors including pH, temperature, time, and pollutant concentration on the adsorption of 4-chlorophenol as a chlorinated organic compound has been investigated. The results revealed proper consistency of adsorption data with Freundlich and Langmuir adsorption isotherms. For all nanostructures, the pseudo-second-order model was the most suitable model to describe the adsorption kinetics. Furthermore, thermodynamic parameters related to each sorbent were calculated and compared. Finally the sorbents were compared according to results of regeneration-reuse cycles. The optimum pH for 4-CP removal was obtained to be 5.0–7.0. The obtained equilibrium adsorption capacities were in the range of 58.82 to 334.34mgg−1 for various nanostructures due to their different surface properties.The obtained results showed that the adsorption trend was as CMK-3n>porous graphene>MWCNT>Carbon nanofiber>SWCNT, in which the CMK-3 possessed the highest equilibrium adsorption capacity and retained near 90% of its initial adsorption capacity even after 3 regeneration-reuse cycles.

Measuring Interfacial Adhesion of Carbon Nanotube Bundles and Electrospun Polymer Fibers.

Adhesion at the dissimilar interface of single wall carbon nanotube (SWCNT) bundles and electrospun polymer nanofibers (Espun) was directly measured using a nano cheese cutter. A sample fiber suspended at the tip of an atomic force microscope cantilever and another freestanding fiber on a mica substrate were arranged in a cross-cylinder configuration and allowed to adhere. External tensile load led to spontaneous detachment or "pull-off". Adhesion was shown to be dominated by van der Waals attraction, and the detachment process conforms to the classical Maugis parameter in the JKR-DMT transition.

Highly aligned continuous mullite nanofibers: Conjugate electrospinning fabrication, microstructure and mechanical properties

Continuous mullite nanofibers with highly aligned structure were fabricated by conjugate electrospinning technique combined with the sol-gel method. Aluminum acetate stabilized with boric acid and tetraethyl orthosilicate (TEOS) were used as raw materials. Aligned and continuous as-spun nanofibers were prepared first. After calcining at 1000 °C, the obtained mullite nanofibers retained decent alignment and continuous structure despite the decomposition of PVP and other organics. Such fibers were composed of Al4B2O9 phase and amorphous SiO2. The elastic modulus of a single mullite nanofiber was 12.27 ± 1.77 GPa and the tensile strength of the aligned mullite nanofiber bundle was 32.21 ± 3.73 MPa.

Characterization of single polyvinylidene fluoride (PVDF) nanofiber for flow sensing applications

The use of Polyvinylidene Fluoride (PVDF) based piezoelectric nanofibers for sensing and actuation has been reported widely in the past. However, in most cases, PVDF piezoelectric nanofiber mats have been used for sensing applications. This work fundamentally characterizes a single electrospun PVDF nanofiber and demonstrates its application as a sensing element for nanoelectromechanical sensors (NEMS). PVDF nanofiber mats were spun by far field electrospinning (FFES) process and complete material characterization was conducted by means of scanning electron microscope (SEM) imaging, Raman Spectroscopy and FTIR spectroscopy. An optimized recipe was developed for spinning a single suspended nanofiber on a specially designed MEMS substrate which allows the nano-mechanical and electrical characterization of a single PVDF nanofiber. Electrical characterization is conducted using a single suspended nanofiber to determine the piezoelectric coefficient (d33) of the nanofiber to be -58.77 pm/V. Also the mechanical characterization conducted using a nanoindenter revealed a Young’s Modulus and hardness of 2.2 GPa and 0.1 GPa respectively. Finally, an application that utilizes the single PVDF nanofiber as a sensing element to form a NEMS flow sensor is demonstrated. The single nanofiber flow sensor is tested in presence of various oscillatory flow conditions.

Modulus of elasticity of randomly and aligned polymeric scaffolds with fiber size dependency.

The stiffness of a nano-fibrous scaffold is generally enhanced due to the size-dependency of the thin nanofibers contained in the scaffold. We proposed a model that incorporates size-dependency of single nanofibers to predict the scaffold effective modulus, in which the fibers' random or orientation distribution are considered. In the model the fiber segments between rigid fiber-fiber bonds can be stretching, shearing and bending. Using deformation energy equilibrium between sum of individual fibers and the plate of nano-fibrous scaffold, the scaffold effective modulus was derived explicitly. The model was verified via finite element analysis (FEA) and published experimental results. The parametric studies revealed that the fiber diameter is the dominant parameter to stiffen the scaffold beyond the fiber density and fiber aspect ratio when the fiber diameter is reduced below the onset value of size-dependencies. As a result, the scaffold stiffness can maintain its higher value and lower decrease rate because of the size-dependency with a decreasing diameter of the nanofiber as a result of biodegradation. This inspires the idea of selecting nanofibers near the onset value of size-dependency to obtain a controlled tuning of the scaffold stiffness in the design of novel nano-fibrous scaffolds.