A systematic study of the effects of , flow rate, voltage, and composition on the morphology of electrospun PLGA nanofibers is reported. It is shown that changes of voltage and flow rate do not appreciably affect the morphology. However, the of PLGA predominantly determines the formation of bead structures. Uniform electrospun PLGA nanofibers with controllable diameters can be formed through optimization. Further, multi‐walled carbon nanotubes can be incorporated into the PLGA nanofibers, significantly enhancing their tensile strength and elasticity without compromising the uniform morphology. The variable size, porosity, and composition of the nanofibers are essential for their applications in regenerative medicine.
Highly‐aligned luminescent electrospun nanofibers were successfully prepared from two binary blends of PFO/PMMA and PF+/PMMA. The PFO/PMMA aligned electrospun fibers showed a core/shell structure but the PF+/PMMA fibers exhibited periodic aggregate domains in the fibers. The aligned fibers had polarized steady‐state luminescence with a polarized ratio as high as 4, much higher than the non‐woven electrospun fibers or spin‐coated film. Besides, the PF+/PMMA aligned electrospun fibers showed an enhanced sensitivity to plasmid DNA. Such aligned electrospun fibers could have potential applications in optoelectronic or sensory devices.
In this work, polyacrylonitrile (PAN) and carbon nanofibers with controllable nanoporous structures were successfully prepared via electrospinning technique. For the preparation of porous PAN nanofibers, two kinds of polymers of PAN and polyvinylpyrrolidone (PVP) were used as electrospun precursor materials, and then the bicomponent nanofibers of PAN and PVP were extracted with water to remove the PVP in the composite polymer nanofibers. By altering the ratio of PAN/PVP in the precursor, the pore size and pore distribution of porous PAN nanofibers could be easily controlled. By using the porous PAN nanofibers as structures directing template and through heat treatment, carbon nanofibers with nanoporous structures were obtained. The porous nanofibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR), differential thermal analyses (DTA), Brunauer–Emmett–Teller (BET) nitrogen adsorption, X‐ray diffraction (XRD), and Raman spectra.
A novel technique was developed to control the deposition of electrospun polyurethane fibers using a silicone collector substrate patterned with soft lithography. This method can be used to control selective fiber deposition with broad pattern dimensions (50–500 µm) over a large area. The combination of ease of use, low cost, tunability, and generation of relatively large fiber mats available with this technique is expected to advance our ability to mimic the orientation and anisotropic properties of native tissues to generate improved tissue engineering scaffolds.
Continuous and uniform yarns of thermoplastic nanofibers were prepared via direct melt extrusion of immiscible blends of thermoplastic polymers with CAB and subsequent extraction removal of CAB. Ratios of thermoplastic/sacrificial polymers, melt viscosity, and interfacial tensions affect the formation of nanofibers. Dominating sacrificing polymer content in the blends and low interfacial tensions between thermoplastic polymer and CAB are two key factors. This fabrication process possesses features of high productivity, versatility of thermoplastics, controllability, and environment friendliness in manufacturing thermoplastic nanofibers.
Novel silver/polymer composites based on thiol‐ene chemistry are prepared by an in situ bottom‐up approach. The in situ synthesis of silver particles inside the polymer matrix is achieved in one pot by photoreduction reaction in presence of a silver precursor and the concurrent crosslinking reaction. XPS analysis confirms the formation of silver particles; TEM morphological investigation shows a very good dispersion and distribution of the nanometric silver particles within the thiol‐ene network. Antimicrobial properties of the photocured hybrids are also evaluated.
Two novel cationic RAFT agents, PCDBAB and DCTBAB, were anchored onto MMT clay to yield RAFT‐MMT clays. The RAFT‐MMT clays were then dispersed in styrene where thermal self‐initiation polymerization of styrene to give rise to exfoliated PS/clay nanocomposites occurred. The RAFT agents anchored onto the clay layers successfully controlled the polymerization process resulting in controlled molecular masses and narrow polydispersity indices. The nanocomposites prepared showed enhanced thermal stability, which was a function of the clay loading, clay morphology, and slightly on molecular mass.
Lysozyme, an enzyme with bactericidal activity over Gram‐positive bacteria cells, is incorporated into PEDOT to prepare films with high biological and electrochemical activity. Two different strategies are used: (1) PEDOT films are coated with a layer of enzyme, which was adsorbed on the surface; and (2) the lysozyme is added to the polymerization medium used for the preparation of the conducting polymer. The enzyme adsorbed at the surface of the polymer produces a biphasic system that retains the electrochemical properties of the conducting polymer but is not able to protect against bacterial growth. In contrast, the addition of lysozyme to the polymerization medium results in a homogeneous composite with high bactericidal and electrochemical activities.
The electrospinning method was used to fabricate nanostructures of Nafion‐poly(vinyl alcohol) (PVA) and Nafion‐poly(ethylene oxide) (PEO). Depending on the ratio between the two polymers, nanospheres and/or nanofibers could be obtained in a reproducible manner. The Nafion‐PVA mats were found to be more conductive than the Nafion‐PEO ones, possibly because of their better mechanical properties when swollen by water. The fiber morphology was always found to be more conductive than the sphere morphology. However, all electrospun mats presented ionic conductivities slightly lower than extruded Nafion 115 or Nafion‐PVA cast films.
Temperature‐responsive PVCL homopolymers and functional PVCL polymers containing carboxylic acids are prepared in organic and aqueous solutions. PVCL bulk polymers are characterized using 1H NMR, photometry, ATR‐FTIR, and thermal analysis. A finite phase transition at 37–40 °C occurs in aqueous solutions of PVCL and PVCL‐COOH. PVCL and PVCL‐COOH polymers are electrospun into fibers ranging from 100 to 2300 nm in diameter. PVCL/cellulose bi‐component films are obtained by electrospinning of CA and PVCL followed by alkaline hydrolysis. These tunable thermo‐responsive PVCL/cellulose nanofibers have potential applications in developing affinity membranes.
In order to enhance the molecular orientation of electrospun nanofibers, a novel collection technique is proposed and applied to the spinning of polyethylene from high temperature solution. The technique makes use of a parallel‐electrode collector that acts before solidification of the fiber occurs. The resulting multiple‐necking morphology is composed of fine nanofibrils with very small diameter and narrow size distribution. The crystalline orientation of the nanofibrils was analyzed by TED. The formation mechanism of the nanofibrils is discussed. The strong elongational effect of the electric‐field‐induced stretching force in the parallel‐electrode collector is demonstrated by the orientational analysis and by observation of the multiple‐necking morphology.
Thermoresponsive nanofibers by very fast grafting of N,N‐isopropylacrylamide (NIPAAm) from electrospun atom transfer radical polymerization (ATRP) macroinitiator are presented in this work. The heterogenous grafting of NIPAAm onto macroinitiator fibers could be done in few minutes, i.e., in less than 5 min. The procedure involved electrospinning of an ATRP macroinitiator and subsequent PNIPAAm grafting using “grafting from” technique. The ATRP Macroinitiator was based on a copolymer of methyl methacrylate (MMA) and 2‐hydroxyethyl methacrylate (HEMA). The growth of the PNIPAAm layer on electrospun fibers was followed by IR‐spectroscopy and SEM analysis. The temperature‐dependent‐phase transition was proven by contact angle measurements and could be shown on the same surface for many cycles.
Micron‐sized fibers of UHMWPE reinforced with CNT were fabricated by the electrospinning process. Conditions for a metastable mutual solution of UHMWPE and CNTs were found at elevated temperature. These solutions were used for electrospining using a device having controlled temperature and gaseous environment around the electrospun liquid jet. The fabricated micron‐sized fibers exhibited the reinforcing CNTs as self‐organized nano‐ropes embedded within them. A post‐spinning drawing process enhanced the mechanical properties of the composite fibers to the level of 6.6 GPa strength and elongation at break of 6%. The CNT nano‐ropes form spontaneously in the liquid jet during electrospinning, and provide the reinforcement framework which is amenable for post‐drawing of the fibers for subsequent utilization as composite nanofibers. The experimental results exhibit the highest strength value reported to date for electrospun fibers.
PLLA and stereocomplexed polylactide (sc‐PLA) nanofibers were formed by electrospinning solutions of the polymers in HFIP. A highly semi‐crystalline sc‐PLA nanofiber having only sc crystallites was confirmed by WAXD analysis. The diameters of the nanofibers of both polymers decreased slightly when they were annealed at 60 °C, which was near Tg. Enzyme degradation of both as‐spun PLLA and sc‐PLA nanofibers by proteinase K from Tritirachium album was carried out. The rate of degradation of the nanofibers can be controlled by varying annealing conditions, hence the extent of crystallinity.
The thermal conductivity of a rubber compound is studied as a function of its state of curing. The device is presented and the calculations in order to obtain samples with controlled and homogeneous vulcanization rates are performed. The hot disk technique is used to measure the thermal conductivity of the rubber. This transient, plane‐source and non‐destructive method allows rapid and accurate measurement of the thermal conductivity based on the measurement of the electrical resistance of a plane sensor placed between two identical samples. The obtained results show that the thermal conductivity may vary significantly as a function of vulcanization rate. The effect of this variation on the prediction of the reaction progress is discussed.
Low density polyethylene (LDPE) was prepared into micro‐ or submicro‐spheres or nanofibers via melt blending or extrusion of cellulose acetate butyrate (CAB)/LDPE immiscible blends and subsequent removal of the CAB matrix. The sizes of the PE spheres or fibers can be successfully controlled by varying the composition ratio and modifying the interfacial properties of the blends. The surface structures of LDPE micro‐ or submicro‐spheres and nanofibers were analyzed using SEM and FTIR‐ATR spectroscopy. In addition, the crystalline structures of the LDPE nanofibers were characterized.
A novel method to produce uniaxially aligned nanofibers is described, in which a pair of parallel auxiliary electrodes at a positive potential is placed between the needle and the collector electrodes. Charged nanofibers ejecting from the polymer solution are pre‐aligned by the electrostatic repulsion originating from the auxiliary electrodes and deposited on the collector electrodes, forming a narrow mat with the fiber segments strongly curved. By adjusting the conductivity and shape profile of the collector, the curved segments can be straightened longitudinally. A seamless tube composed of longitudinally aligned nanofibers can be obtained. Such seamless tubes may be useful as biomaterials in tissue engineering.
Thermo‐responsive PNIPAAm/PLLA nanofibrous films with tunable surface morphologies and better biocompatibility were prepared by electrospinning technique. The electrospun composite films possessed a “bead‐on‐string” structure. The wettability of nanofibrous films was observed by water CA measurements. The results showed that the electrospinning process and addition of PLLA did not change the thermo‐sensitivity of PNIPAAm. The wettability of electrospun PNIPAAm/PLLA composite films could switch from superhydrophilic to superhydrophobic when the temperature increased from 20 to 50 °C. Electrospinning is a promising way to create stimuli‐responsive surfaces with potential application in the design and tactics of controllable drug delivery system.
A fabrication setup was specially designed so that one stream of sol of polyvinyl pyrrolidone (PVP), electrospun to form a bundle of fibers, acted as an axis between two rotating needles, and a second stream of PVP sol containing copper nitrate was electrospun around the fiber bundle axis to form a coil. This was turned into a coiled ribbon upon treatment in moisture. After calcination and reduction, a helical microcoil of nanocopper ribbon was produced, with controlled diameter and pitch. The width and thickness of the ribbon could be varied by manipulating the diameter of the coiled fiber and its treatment time in moisture.
Ultra‐thin fibers, consisting of blends of a PPE derivative and polystyrene, with average diameters ranging from 430 to 1 200 nm, were produced by electrospinning. The electrospinnability was significantly improved by adding pyridinium formate to the spinning solution. FT‐IR spectroscopy was used to confirm the composition of the electrospun fibers and their morphology was probed by SEM. The optical properties of the as‐prepared solutions, pristine and annealed fibers, and corresponding spin‐coated and solution‐cast films were investigated by UV‐vis spectroscopy. A comparison of the PL emission spectra revealed aggregation of PPE molecules in the electrospun materials but the extent of aggregation can be reduced if the materials are annealed above the glass transition temperature.
