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Full-Text Articles in Engineering
Capillary Thinning And Break-Up Of Hydrogel-Elastomer Composites, Darrell Reneker
Capillary Thinning And Break-Up Of Hydrogel-Elastomer Composites, Darrell Reneker
Darrell Hyson Reneker
The development of a filament stretching rheometer with a high magnification and high speed digital imaging system enabled real-time video observation of the extensional behavior of the hydrogel-elastomer complex fluids. Under a motor-controlled process of tip-plate separation, ethanol solutions of polyurethane with superabsorbent particles, which can be electrospun into nanocomposite nanofibers, evolved in profile. The rapidly shrinking jet diameter was measured from video images. As in extensional rheology of homogeneous polymer solutions, the elongational viscosity and the relaxation time calculated from the time dependence of midpoint diameters define a two-dimensional operating diagram for capillary self-thinning and capillary break-up. ootnotetextRodd, L.E.; …
Dynamic Characterization Of Jets Of Polymer Solutions, Darrell Reneker
Dynamic Characterization Of Jets Of Polymer Solutions, Darrell Reneker
Darrell Hyson Reneker
Polymer jets that are accessible for detailed observation are created by electrospinning and by mechanical extension of a polymer solution. Laser Doppler experiments measure the velocity in the axial direction of the jet, and at the same time, the diameter of the jet. The tensile stress along a jet is measured by observation of the widening of a short lateral displacement pulse as the pulse moves along the jet. Observation of the colors produced by subtractive interference of particular wavelengths from a beam of white light provide a dynamic measurement of jet diameter in the range from around 1 micron …
From Electrospinning Model, Darrell Reneker
From Electrospinning Model, Darrell Reneker
Darrell Hyson Reneker
No abstract provided.
Garland Formation Process In Electrospinning, Yu Xin, Darrell Reneker
Garland Formation Process In Electrospinning, Yu Xin, Darrell Reneker
Darrell Hyson Reneker
The electrospinning technique has become a widely used method to produce nanofibers. Much experimental and theoretical work has been done to investigate the electrospinning process. A typical path of a single jet of polymer solution begins with a straight segment, and then a bending instability generates coils inside a cone shaped envelope. The jet elongates and becomes thinner, and dries into a nanofiber. Polystyrene solutions with different salt concentrations were electrospun to investigate the effect of changing the electrical conductivity on the fibers that were formed. Salt increased the conductivity of the solution and smooth fibers formed. Electrospinning a polystyrene …
Fabrication, Characterization, And Electrical Properties Of Ceramic Nanofiber Yarns By Electrospinning, Darrell Reneker
Fabrication, Characterization, And Electrical Properties Of Ceramic Nanofiber Yarns By Electrospinning, Darrell Reneker
Darrell Hyson Reneker
It is more convenient to handle a bundle of nanofibers or nanofiber yarn instead of a single nanofiber. Nanofiber yarns are robust enough to be handled without the requirement of very precise, sophisticated equipment. They can be deposited or transferred onto a substrate as orderly structures. Yarns (twisted and aligned) of several semiconducting ceramic nanofibers (ZnO, NiO, CuO, SnO2) were synthesized using electrospinning method. These yarns had average diameter ~10-30 um and their constituent fibers had the average diameter ~60-100 nm. Fabrication, characterization, and electrical properties of these semiconducting nanofiber yarns will be presented.
Production Of Superabsorbent Electrospun Nanofibers, Darrell Reneker
Production Of Superabsorbent Electrospun Nanofibers, Darrell Reneker
Darrell Hyson Reneker
The process of electrospinning utilizes a high voltage to charge a polymer solution creating an electrically charged jet, which travels to a grounded target. As the jet travels, the solution evaporates, and a dry electrically charged nanofiber remains. Many polymers can be used to produce these nanofibers, and depending upon the desired application, it may be beneficial to use molecular additives in combination with the polymer. In this study, a superabsorbent, Waterlock®, was added to a polymer solution at varying concentrations from 0% to 85% producing structured hydrogels. The superabsorbent nanofibers were tested for absorbency in water and synthetic urine. …
Synthesis And Characterization Of Erbium (Iii)-Doped Polyimide Nanofibers For Low Temperature Thermophotovoltaic Applications, Darrell Reneker
Synthesis And Characterization Of Erbium (Iii)-Doped Polyimide Nanofibers For Low Temperature Thermophotovoltaic Applications, Darrell Reneker
Darrell Hyson Reneker
Thermophotovoltaic conversion technology is a promising way to convert waste heat to electricity via photons. In this research, erbium (III)-doped polyimide nanofibers mats were prepared as selective emitters to explore the selective thermal emission efficiency in a low operating temperature range (< 500 ∘C). The selective emission at 6500 cm−1 of erbium (III)-doped polyimide nanofiber mats was measured on mats characterized with scanning electron microscopy, transmission electron microscopy, FT-IR spectroscopy, and thermogravimetric analysis. A small but potentially useful amount of power was obtained from a 2 mg mat.
Hierarchical Polystyrene Patterns Produced By Electrospinning, Yu Xin, Darrell Reneker
Hierarchical Polystyrene Patterns Produced By Electrospinning, Yu Xin, Darrell Reneker
Darrell Hyson Reneker
When a 25 wt% polystyrene solution was electrospun at relatively low applied voltage, the bending instability initiated, grew and disappeared, repeatedly. Upon further lowering of the applied voltage, the bending instability died immediately after it started and only a straight electrified jet was observed. By manipulating the bending instability of the jet, uniform polystyrene hierarchical patterns were produced by a buckling process. The observed buckling patterns are similar to those of a gravity-driven jet. The conditions for producing buckled polystyrene patterns are reproducible. These small scale buckled polymer patterns can be made very long and uniform. The size of the …
Glints Of Light Reveal Properties Of Coiled Electrospinning Jets In Flight, Darrell Reneker
Glints Of Light Reveal Properties Of Coiled Electrospinning Jets In Flight, Darrell Reneker
Darrell Hyson Reneker
Optical observations of jets provide information needed to control features of polymer nanofibers produced by electrospinning. Quantitative information about the location, vector velocity, and rotation of selected segments of the multiply coiled path of an electrospinning jet of polymer solution was provided by a combination of videography, stereography, and stop motion flash photography. Visual observations of a jet depend largely on glints of incident light that are specularly reflected from particular places on the multiply coiled jet path. The traces of moving glints bifurcate when a new turn is added to a coil, at an observed rate of 600 turns …
Collection Of An Electrospinning Jet, Darrell Reneker
Collection Of An Electrospinning Jet, Darrell Reneker
Darrell Hyson Reneker
No abstract provided.
Single Clay Sheets Inside Electrospun Polymer Nanofibers, Darrell Reneker
Single Clay Sheets Inside Electrospun Polymer Nanofibers, Darrell Reneker
Darrell Hyson Reneker
Nanofibers were prepared from polymer solution with clay sheets by electrospinning. Plasma etching, as a well controlled process, was used to supply electrically excited gas molecules from a glow discharge. To reveal the structure and arrangement of clay layers in the polymer matrix, plasma etching was used to remove the polymer by controlled gasification to expose the clay sheets due to the difference in reactivity. The shape, flexibility, and orientation of clay sheets were studied by transmission and scanning electron microscopy. Additional quantitative information on size distribution and degree of exfoliation of clay sheets were obtained by analyzing electron micrograph …
Characterization Of An Electrospinning Jet From Videographic Observations Of Glints, Darrell Reneker
Characterization Of An Electrospinning Jet From Videographic Observations Of Glints, Darrell Reneker
Darrell Hyson Reneker
Detailed relationships between glints of light reflected from the electrical bending coils of an electrospinning jet and the path of the jet were established. The path of the jet was observed by illuminating the jet with a short, intense flash of light. Glints were formed simultaneously by a continuous, intense beam of light from a chosen set of directions. As the jet path moved through the continuous beam of light, some segments of the path were oriented so that intense specular reflection (a glint) was recorded by a camera. The motion of the jet path caused a glint to create …
Ceramic Electrospun Nanofibers As Selective Emitters For Thermophotovoltaic Energy Conversion, Darrell Reneker
Ceramic Electrospun Nanofibers As Selective Emitters For Thermophotovoltaic Energy Conversion, Darrell Reneker
Darrell Hyson Reneker
Ceramic nanofibers were produced by electrospinning and characterized with electron microscopy, X-ray diffraction, FTIR, and X-ray photoelectron spectroscopy. Rare earth compounds were incorporated in the ceramic nanofibers in order to selectively modify the optical properties of the ceramic electrospun nanofibers. Titania electrospun fibers were studied. X-ray diffraction showed the titania nanofiber annealed at 773 K had the anatase crystal structure, and annealing at 1173 K produced the rutile crystal structure. In order to modify the optical properties, erbia was incorporated into Titania nanofibers. Temperature-dependent emission spectra showed that the erbia-containing nanofibers emit selectively in the near-infrared when convectively heated by …
Nanobiocatalysis For Bio-Based Energy And Products, Darrell Reneker
Nanobiocatalysis For Bio-Based Energy And Products, Darrell Reneker
Darrell Hyson Reneker
No abstract provided.
Polymeric Nanofibers, Darrell Reneker
Nanofibers And Related Structures Formed By Polymerization, Darrell Reneker
Nanofibers And Related Structures Formed By Polymerization, Darrell Reneker
Darrell Hyson Reneker
Nanofibers of cyanoacrylate were obtained by polymerization from the monomer vapor at a temperature near room temperature. The nanofibers had diameters ranging from 20 nm to 100 nm and lengths of up to several millimeters. Water molecules present on the substrate initiated the living anionic polymerization. As growth continued, the living ends were carried on the tip of each growing nanofiber. These nanofibers formed on glass, metal, plastic, electrospun nanofibers of other polymers, and other surfaces. Some fibers were tapered, some were branched, and some were bent. The number of fibers was varied by controlling the exposure of the substrate …
The Path And Motion Of An Electrospinning Jet Observed With Videography And Stereography, Darrell Reneker
The Path And Motion Of An Electrospinning Jet Observed With Videography And Stereography, Darrell Reneker
Darrell Hyson Reneker
An electrospinning jet illuminated with both a steady intense light and a short flash was stereoscopically recorded through a pair of prisms in a video, producing images of both traces of moving glints reflected from the surface of a jet and the instantaneous positions of the path of the jet. The relationship between the visual observation and the jet path described in the Reneker-Yarin model1,2 was explained by analyzing the stereographic images. Computer modeling was used to elucidate the relationship between the onset of the bending instability and the bifurcation of a glint trace. The velocities and positions, in 3-dimensional …
Properties Of Electrospinning Jets, Darrell Reneker
Properties Of Electrospinning Jets, Darrell Reneker
Darrell Hyson Reneker
No abstract provided.
Liquid Drop Growth On A Fiber In Fibrous Filters, Darrell Reneker
Liquid Drop Growth On A Fiber In Fibrous Filters, Darrell Reneker
Darrell Hyson Reneker
This paper describes and verifies a quantitative model to predict the growth by coalescence of oil droplets on a single fiber. The model considered a stream of fluid carrying many tiny droplets of a different fluid. Different capture mechanisms by which the tiny droplets are captured by a drop growing on a fiber were examined, including: interception, Brownian motion of droplets and vapor deposition by diffusion. Number average distribution and volume average distribution of particle diameters were used to characterize the tiny droplets. The comparison, of the predictions for different droplet capture mechanisms, with the experimental data showed that both …
Polymorphism Behaviors Of Electrospun Poly (Vinylidene Fluoride) Nanofibers, Darrell Reneker
Polymorphism Behaviors Of Electrospun Poly (Vinylidene Fluoride) Nanofibers, Darrell Reneker
Darrell Hyson Reneker
Poly(vinylidene fluoride) (PVDF) and its copolymers have drawn great attention in recent years due to their attractive electrical properties such as ferro-, piezo- and pyro-electricity. Depending on its processing, PVDF can exhibit five different polymorphs. Among them, the beta phase has the highest piezo-, pyro- and ferroelectric activities. Electrospinning was used to produce thin polymer fibers. The polymorphic behavior of electrospun PVDF fibers was observed. Long cylindrical PVDF specimens with cross-sections in the range of 10 nm to 1 micron was obtained by varying the electrospinning conditions. Almost pure beta phase was obtained in electrospun PVDF nanofibers. The morphology and …
Electrospun Nanofiber Yarn, Darrell Reneker
Electrospun Nanofiber Yarn, Darrell Reneker
Darrell Hyson Reneker
No abstract provided.
Erbia-Containing Electrospun Titania Nanofibers As Selective Emitters For Low Temperature Thermophotovoltaic Energy Conversion, Darrell Reneker
Erbia-Containing Electrospun Titania Nanofibers As Selective Emitters For Low Temperature Thermophotovoltaic Energy Conversion, Darrell Reneker
Darrell Hyson Reneker
Tetraisopropyl titanate (TPT) has been mixed with a soluion of polyvinylpyrrolidone (PVP) and electrospun into nanofibers. The PVP is pyrolyzed, leaving nanofibers of rutile phase titania as shown by scanning electron microscopy and X-ray diffraction analysis. In order to obtain erbia containing titania nanofibers, erbium(III) oxide particles are added to the solution before electrospinning. After pyrolysis the titania nanofibers encapsulate the smaller erbia particles. Temperature-dependent emission spectra show that the erbia containing nanofibers emit selectively in the near-infrared when convectionally heated. The electrical power generated by a GaSb photodetector placed in line-of-sight geometry with respect to the heated nanofibers is …
Oscillatory Jet Flow In Electrospinning Of Polymer Nanofibers, Darrell Reneker
Oscillatory Jet Flow In Electrospinning Of Polymer Nanofibers, Darrell Reneker
Darrell Hyson Reneker
The development of a filament stretching rheometer with a high magnification and high speed digital imaging system enabled real-time video observation of the extensional behavior of the hydrogel-elastomer complex fluids. Under a motor-controlled process of tip-plate separation, ethanol solutions of polyurethane with superabsorbent particles, which can be electrospun into nanocomposite nanofibers, evolved in profile. The rapidly shrinking jet diameter was measured from video images. As in extensional rheology of homogeneous polymer solutions, the elongational viscosity and the relaxation time calculated from the time dependence of midpoint diameters define a two-dimensional operating diagram for capillary self-thinning and capillary break-up. ootnotetextRodd, L.E.; …
Mechanical Behavior And Toughness Of Electrospun Polycaprolactone Nanofibers, Darrell Reneker
Mechanical Behavior And Toughness Of Electrospun Polycaprolactone Nanofibers, Darrell Reneker
Darrell Hyson Reneker
This study examines the toughness and mechanical properties of biodegradable poly(ε-caprolactone) (PCL) with varying hydroxyapatite (HAP) content (0 – 30 wt%). Fracture toughness of HAP-filled PCL was also examined for the electrospun fibers using the essential work of fracture (EWF) concept. The electrospun fibers exhibited a diameter ranging from 200–500 nm and a combination of HAP particle sizes ranging from (50–100 nm) under the SEM. The tensile stress-strain behavior and fracture toughness of electrospun nanofibers were assessed using a nanoforce tensile tester. The electrospun system showed a substantial increase in plane-stress essential work of fracture in comparison to bulk specimens …
Polymer Based Nanocomposites With Nanofibers And Exfoliated Clay, Michael Meador, Darrell Reneker
Polymer Based Nanocomposites With Nanofibers And Exfoliated Clay, Michael Meador, Darrell Reneker
Darrell Hyson Reneker
Polymer solutions, containing clay sheets, were electrospun into nanofibers and microfibers that contained clay sheets inside. Controllable removal of polymer by plasma etching from the surface of fibers revealed the arrangement of clay. The shape, flexibility, size distribution and arrangement of clay sheets were observed by transmission and scanning electron microscopy. The clay sheets were partially aligned in big fibers with normal direction of clay sheets perpendicular to fiber axis. Crumpling of clay sheets inside fibers was observed when the fiber diameter was comparable to the lateral size of clay sheets. Single sheets of clay were observed both by catching …
Controlling Solidification And Fiber Diameter Of Polyethylene Oxide Nanofibers Electrospun From Aqueous Solution By Controlling The Partial Pressure Of Water Vapor, Darrell Reneker
Darrell Hyson Reneker
Electrospinning is widely in research attention due to its cost effectiveness and straightforwardness for making nanofibers. During the electrospinning process, a charged jet is elongated by repulsive force between electrical charges carried by the jet. The charged jet develops spiral path due to the electrically driven bending instability, which make it possible for the jet to elongate and produce nanofibers in a small space. Solidification has been identified as an important factor that determines the diameter of electrospun nanofibers. The elongation and thinning of a charged jet stops as the charged jet is solidified. Controlling solidification of the charged jet …
Electrospun Liquid Silk From The Gland Of Bombyx Mori Silk/Green Fluorescent Proteins (Gfp)/Poly (Ethylene Oxide), Darrell Reneker
Electrospun Liquid Silk From The Gland Of Bombyx Mori Silk/Green Fluorescent Proteins (Gfp)/Poly (Ethylene Oxide), Darrell Reneker
Darrell Hyson Reneker
We have previously demonstrated that Green Fluorescent Protein (GFP) molecules can be incorporated into silk films and maintain their nonlinear optical properties as well as resist to damage at fluence of 0.1-0.2 J/cm2 [1]. In the present study we report the incorporation of GFP into electrsopun fibers of liquid silk from the gland of B. mori. PEO was added to the silk/GFP solution to improve the processability. The silk/GFP/PEO solutions were successfully elctrospun and the morphology of fibers was characterized using optical microscopy, and scanning electron microscopy. The resulting fibers exhibit fluorescent under the UV microscope in the reflection mode …
Electrical Bending And Mechanical Buckling Instabilities In Electrospinning Jets, Darrell Reneker
Electrical Bending And Mechanical Buckling Instabilities In Electrospinning Jets, Darrell Reneker
Darrell Hyson Reneker
The determination of the behavior of the jet path in the vicinity of the onset of the primary electrical bending instability is important for the orderly collection of the nanofibers produced by electrospinning. A stable jet was observed with a high frame rate, short exposure time video camera. The collection process was complicated but predictable within limits, so the design and creation of some two or three dimensional structures of nanofibers is feasible, if the considerations described below are incorporated into the design and production processes. The fluid jet in the straight segment of the path, and the more solid …
Hierarchical Fiber Structures Made By Electrospinning Polymers, Darrell Reneker
Hierarchical Fiber Structures Made By Electrospinning Polymers, Darrell Reneker
Darrell Hyson Reneker
No abstract provided.
Electrospun Buckling Coils, Darrell Reneker
Electrospun Buckling Coils, Darrell Reneker
Darrell Hyson Reneker
Electrospinning offers a useful way to produce fibers with micron and nanometer scale diameter. The present work deals with the buckling phenomenon characteristic of a jet impinging upon the surface of collector. A viscous jet may have either tensile or compressive forces along its axis. The periodic buckling that is often observed is attributed to the occurrence of compressive forces as the jet decelerates at the collector. With the increase of axial compressive stresses along the jet, a jet with circular cross sections first buckles by formation of sharp folds, and then by formation of coils. The resulting buckling patterns …