Electrospinning of polystyrene/poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylene vinylene) blends

Ultrafine polystyrene (PS)/poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylene vinylene) (MEH‐PPV) fibers were successfully prepared by electrospinning of PS/MEH‐PPV solutions in chloroform, 1,2‐dichloroethane, and tetrahydrofuran (THF). Three concentrations of the solutions were prepared: 8.5, 16, and 23.5% (w/v), with the compositional weight ratios between PS and MEH‐PPV being 7.5:1, 15:1, and 22.5:1, respectively. Smooth fibers only observed from 23.5% (w/v) PS/MEH‐PPV solution in chloroform. Improvement in the electrospinnability of 8.5% (w/v) PS/MEH‐PPV solution in chloroform was achieved by addition of an organic salt, pyridinium formate (PF), or by addition of a minor solvent with a high dielectric constant value. The average diameters of the as‐spun PS/MEH‐PPV fibers were between 0.30 and 5.11 μm. Last, photoluminescence of 8.5% (w/v) solutions of PS/MEH‐PPV in a mixed solvent system of chloroform and 1,2‐dichloroethane of various volumetric compositions and the resulting as‐spun fibers was investigated and compared. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1881–1891, 2005     

Multifunctional Hybrid Materials From Poly(3‐Hydroxybutyrate), TiO2 Nanoparticles,and Chitosan Oligomers by Combining Electrospinning/Electrospraying and Impregnation

Several types of fibrous material containing poly(3‐hydroxybutyrate) (PHB), nanosized TiO₂‐anatase (nanoTiO₂), and chitosan oligomers are prepared by combining the electrospinning, electrospraying, and impregnation techniques. Simultaneous electrospinning/electrospraying provides uniform distribution of electrosprayed nanoTiO₂ along the PHB fibers and throughout the mat. Hybrid materials of different design manifest excellent photocatalytic activity, even after repeated use. They exhibit high bactericidal activity against Escherichia coli. In addition, the fibrous scaffolds are compatible with human mesenchymal stem cells and provide a favorable environment for their development.

     

Fabrication of Light‐Guiding Core/Sheath Fibers by Coaxial Electrospinning

Light‐guiding core/sheath fibers are fabricated from two different refractive index (RI) polymers by coaxial electrospinning. The morphology and fiber diameter are analyzed with scanning electron and fluorescence microscopies. It is found that the diameter of the core and the thickness of the sheath could be varied from 100 to 400 nm by changing the concentration of the outer solution. The incorporation of a chromophore into the inner material confirmed the uniformity of the core/sheath structure in long segments of the fibers. The boundary is clearly seen: the core diameter and the thickness of the sheath are constant along the fiber axis in fluorescence images. The ejected beam is circular and light‐guided along the fiber axis as in an optical fiber.

     

Colloid‐Electrospinning: Fabrication of Multicompartment Nanofibers by the Electrospinning of Organic or/and Inorganic Dispersions and Emulsions

Solution‐, melt‐, and co‐axial electrospinning are well‐known methods for producing nano‐ and microfibers. The electrospinning of colloids (or colloid‐electrospinning) is a new field that offers the possibility to elaborate multicompartment nanomaterials. However, the presence of colloids in the electrospinning feed further complicates theoretical predictions in a system that is dependent on chemical, physical, and process parameters. Herein, we give a summary of recent important results and discuss the perspectives of electrospinning of colloids for the synthesis and characterization of multicompartment fibers.     

Synthesis and characterization of new blue‐light‐emitting polymers based on PPP and PPV having fluorene pendant at vinyl bridge

The new poly(arylene vinylene) derivatives, which are composed of biphenylene vinylene phenylene vinylene, biphenylene vinylene m‐phenylene vinylene, terphenylene vinylene phenylene vinylene, and terphenylene vinylene m‐phenylene vinylene as backbone and bulky fluorene pendants at each vinyl bridge, were designed, synthesized, and characterized. The obtained polymers showed weight‐average molecular weights of 11,100–39,800 with polydispersity indexes ranging from 1.5 to 2.1. The resulting polymers were amorphous with high thermal stability and readily soluble in common organic solvents. The obtained polymers showed blue emission (λ_max = 456–475 nm) in PL spectra, and polymer 4 containing terphenylene vinylene m‐phenylene vinylene showed the most blue shifted blue emission (λ_max = 456 nm). The double layer light‐emitting diode devices fabricated by using obtained polymers as emitter emitted bright blue light. The device showed turn on voltage around 6.5 V and brightness of 70–250 cd/m². © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4923–4931, 2006     

Fabrication of CdS Nanorods in PVP Fiber Matrices by Electrospinning

Summary: A controlled fabrication of rod‐like nanostructures of cadmium sulfide (CdS) incorporated into polymer fiber matrices has been developed by an electrospinning method. Here, poly(vinyl pyrrolidone) (PVP) was used as a polymer capping reagent, utilizing the interactions of cadmium ions with the carbonyl groups in the PVP molecules. The formation of CdS nanorods inside the PVP was carried out via the reaction of Cd²⁺ with H₂S. SEM images showed that the electrospun films of PVP/CdS are composed of fibers with a diameter between 100 and 900 nm. TEM proved that most of the CdS nanorods are incorporated in the PVP fibrous film. The diameter of the rod is about 50 nm and the length is from 100 to 300 nm.

TEM image of the CdS nanorods formed in the PVP fibrous film.     

Poly(dicyclopentadiene) Submicron Fibers Produced by Electrospinning

Summary: We have used the process of electrospinning to produce fibers of poly(dicyclopentadiene) with diameters on the submicron scale. The material, formed from a monomer‐catalyst solution, polymerized in flight during the electrospinning process. Fibers were collected over trenches etched in silicon and the Young's moduli were measured using an atomic force microscope to measure force‐displacement curves. The resulting values of Young's moduli are larger than typical values for bulk polymer material.

SEM image of suspended PDCPD fiber.     

Photo‐Induced Solid‐State Crosslinking of Electrospun Poly(vinyl alcohol) Fibers

Summary: Poly(vinyl alcohol) (PVA) was derivatized by polymer analogous reaction with thienyl acryloyl chloride and processed to submicrometer fibers by electrospinning from aqueous solution. Water solubility of otherwise water‐soluble PVA fibers was reduced considerably by UV crosslinking of thienyl acrylate modified PVA fibers in the solid state. Water stability of these crosslinked fibers was proven by water steam test at 95 °C.

UV/Vis spectrum of PVA‐Thio fibers irradiated for different periods at 300 nm.     

Poly(amino acid)‐Based Gel Fibers with pH Responsivity by Coaxial Reactive Electrospinning

Electrospinning is a well‐known technique for the preparation of scaffolds for biomedical applications. In this work, a continuous electrospinning method for gel fiber preparation is presented without a spinning window. As proof of concept, the preparation of poly(aspartic acid)‐based hydrogel fibers and their properties are described by using poly(succinimide) as shell polymer and 2,2,4(2,4,4)‐trimethyl‐1,6‐hexanediamine as cross‐linker in the core of the nozzle. Cross‐linking takes place as the two solutions get in contact at the tip of the nozzle. The impact of solution concentrations and feeding rates on fiber morphology, proof of the presence of cross‐links as well as pH sensitivity after the transformation of the poly(succinimide)‐based material to poly(aspartic acid) is presented.

     

Water‐soluble poly(ethylene oxide)‐block‐poly(p‐phenylene vinylene) copolymer: Synthesis and characterization

Water‐soluble and photoluminescent block copolymers [poly(ethylene oxide)‐block‐poly(p‐phenylene vinylene) (PEO‐b‐PPV)] were synthesized, in two steps, by the addition of α‐halo‐α′‐alkylsulfinyl‐p‐xylene from activated poly(ethylene oxide) (PEO) chains in tetrahydrofuran at 25 °C. This copolymerization, which was derived from the Vanderzande poly(p‐phenylene vinylene) (PPV) synthesis, led to partly converted PEO‐b‐PPV block copolymers mixed with unreacted PEO chains. The yield, length, and composition of these added sequences depended on the experimental conditions, namely, the order of reagent addition, the nature of the monomers, and the addition of an extra base. The addition of lithium tert‐butoxide increased the length of the PPV precursor sequence and reduced spontaneous conversion. The conversion into PPV could be achieved in a second step by a thermal treatment. A spectral analysis of the reactive medium and the composition of the resulting polymers revealed new evidence for an anionic mechanism of the copolymerization process under our experimental conditions. Moreover, the photoluminescence yields were strongly dependant on the conjugation length and on the solvent, with a maximum (70%) in tetrahydrofuran and a minimum (<1%) in water. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4337–4350, 2005     

Fabrication of Electrospun Polymer Fibers with Nonspherical Cross‐Sections Using a Nanopressing Technique

The fabrication of electrospun polymer fibers is demonstrated with anisotropic cross‐sections by applying a simple pressing method. Electrospun polystyrene or poly(methyl methacrylate) fibers are pressed by flat or patterned substrates while the samples are annealed at elevated temperatures. The shapes and morphologies of the pressed polymer fibers are controlled by the experimental conditions such as the pressing force, the pressing temperature, the pressing time, and the surface pattern of the substrate. At the same pressing force, the shape changes of the polymer fibers can be controlled by the pressing time. For shorter pressing times, the deformation process is dominated by the effect of pressing and fibers with barrel‐shaped cross‐sections can be generated. For longer pressing times, the effect of wetting becomes more important and fibers with dumbbell‐shaped cross‐sections can be obtained. Hierarchical polymer fibers with nanorods are fabricated by pressing the fibers with porous anodic aluminum oxide templates.

     

Synthesis,characterization, and electroluminescence of new conjugated PPV derivatives bearing triphenylamine side‐chain through a vinylene bridge

Three new conjugated poly(p‐phenylene vinylene) (PPV) derivatives bearing triphenylamine side‐chain through a vinylene bridge, poly(2‐(4′‐(diphenylamino)phenylenevinyl)‐1,4‐phenylene‐vinylene) (DP‐PPV), poly(2‐(3′‐(3″,7″‐dimethyloctyloxy)phenyl)‐1,4‐phenylenevinylene‐alt‐2‐(4′‐ (diphenylamino)phenylenevinyl)‐1,4‐phenylenevinylene) (DODP‐PPV), and poly(2‐(4′‐(diphenylamino)phenylenevinyl)‐1,4‐phenylenevinylene‐co‐2‐(3′,5′‐bis(3″,7″‐dimethyloctyloxy)‐1,4‐phenylenevinylene) (DP‐co‐BD‐PPV), were synthesized according to the Gilch or Wittig method. Among the three polymers, the copolymer DP‐co‐BD‐PPV is soluble in common solvents with good thermal stability with 5% weight loss at temperatures higher than 386°C. The weight‐average molecular weight (M_w) and polydispersity index (PDI) of DP‐co‐BD‐PPV were 1.83 × 10⁵ and 2.33, respectively. The single‐layer polymer light‐emitting diodes (PLEDs) with the configuration of Indium tin oxide (ITO)/poly (3,4‐ethylenedioxythiophene): poly(4‐styrene sulfonate)(PEDOT:PSS)/DP‐co‐BD‐PPV/Ca/Al were fabricated. The PLED emitted yellow‐green light with the turn‐on voltage of ca. 4.9 V, the maximum luminance of ca. 990 cd/m² at 15.8 V, and the maximum electroluminescence (EL) efficiency of 0.22 cd/A. Copyright © 2007 John Wiley & Sons, Ltd.     

The Enhanced Encapsulation Capacity of Polyhedral Oligomeric Silsesquioxane‐based Copolymers for the Fabrication of Electrospun Core/Shell Fibers

This paper reports the use of polyhedral oligomeric silsesquioxane (POSS)‐based copolymers to stabilize the core/shell interface for the facile fabrication of electrospun core/shell fibers. For the poly[(propylmethacryl‐heptaisobutyl‐polyhedral oligomeric silsesquioxane)‐co‐(methyl methacrylate)] (POSS‐MMA)/poly(ε‐caprolactone) (PCL) system, the bicontinuity of hybrid core/shell fibers can be tuned by controlling the phase separation of POSS‐MMA/PCL in electrospinning solutions and therefore the size of PCL‐in‐POSS‐MMA emulsion droplets. Our results demonstrate the enhanced encapsulation capacity of POSS‐MMA copolymers as shell materials. Taking advantage of the rapid advancement of POSS‐based copolymer synthesis, this study can potentially be generalized to guide the fabrication of various other POSS‐based core/shell nano‐/microstructures by using single‐nozzle electrospinning or coaxial electrospinning.

     

Highly Extensible Bio‐Nanocomposite Fibers

Here, we show that a poly(ethylene oxide) polymer can be physically cross‐linked with silicate nanoparticles (Laponite) to yield highly extensible, bio‐nanocomposite fibers that, upon pulling, stretch to extreme lengths and crystallize polymer chains. We find that both, nanometer structures and mechanical properties of the fibers respond to mechanical deformation by exhibiting strain‐induced crystallization and high elongation. We explore the structural characteristics using X‐ray scattering and the mechanical properties of the dried fibers made from hydrogels in order to determine feasibility for eventual biomedical use and to map out directions for further materials development.

     

Electrospinning of Chitosan

Summary: An electrospun nonwoven fabric of a cationic polysaccharide, chitosan, was successfully prepared. The present study focuses on the effect of the electrospinning solvent and the chitosan concentration on the morphology of the resulting nonwoven fabrics. The solvents tested were dilute hydrochloric acid, acetic acid, neat formic acid and trifluoroacetic acid. As the chitosan concentration was increased, the morphology of the deposition on the collector changed from spherical beads to interconnected fibrous networks. The addition of dichloromethane to the chitosan‐TFA solution improved the homogeneity of the electrospun chitosan fiber. Under optimized conditions, homogenous (not interconnected) chitosan fibers with a mean diameter of 330 nm were prepared.

Effects of the coexisting dichloromethane (MC) in the prespun chitosan‐TFA solution on the morphology of the electrospun chitosan fibers. The volume ratio of TFA:MC was 70:30 (×5 000).     

Propolis Integration Methods into Solutions for Highly Loaded Propolis Fibers by Needleless Electrospinning

A load-bearing matrix filled with biologically active compounds is an efficient method for transporting them to the target location. Bee-made propolis has long been known as a natural product with antibacterial and antiviral, anti-inflammatory, antifungal properties, and anti-oxidative activity. The aim of the research is to obtain stable propolis/PVA solutions and produce fibers by electrospinning. To increase propolis content in fibers as much as possible, various types of propolis extracts were used. As a result of the research, micro- and nano-fiber webs were obtained, the possible use of which have biomedical and bioprotective applications. All used materials are edible and safe for humans, and fiber webs were prepared without using any toxic agent. This strategy overcomes propolis processing problems due to limitations to its solubility. The integration of different combinations of extracts allows more than 73 wt% of propolis to be incorporated into the fibers. The spinning solution preparation method was adapted to each type of propolis, and by combining the methods, solutions with different propolis extracts were obtained. Firstly, the total content of flavonoids in the propolis extracts was determined for the assessment and prediction of bioactivity. The properties of the extracts relevant for the preparation of electrospinning solutions were also evaluated. Secondly, the most appropriate choice of PVA molecular weight was made in order not to subject the propolis to too high temperatures (to save resources and not reduce the bioactivity of propolis) during the solution preparation process and to obtain fibers with the smallest possible diameter (for larger surface-to-volume ratios of nanofibers and high porosity). Third, electrospinning solutions were evaluated (viscosity, pH, conductivity and density, shelf life) before and after the addition of propolis to predict the maximum propolis content in the fibers and spinning stability. Each solution combination was spun using a cylindrical type electrode (suitable for industrial production) and tested for a stable electrospinning process. Using adapted solution-mixing sequences, all the obtained solutions were spun stably, and homogeneous fibers were obtained without major defects.     

Living Polymerization via Anionic Initiation for the Synthesis of Well‐Defined PPV Materials

The anionic polymerization of PPV via the sulfinyl precursor route is further investigated. When LHMDS is employed as the base to form the actively propagating quinodimethane system and THF as the solvent, anionic polymerizations can be observed. With the use of tert‐ butyl‐substituted anionic initiators, specific functional groups can be built in the polymer chain and the chain length can be efficiently controlled, which is demonstrated here for the first time. With introduction of branched side chains on the aromatic core, soluble conjugated PPV material can be obtained with molecular weights in the range of 5000–16 000 g mol⁻¹.     

Preparation and study of PPV/PVA nanofibers via electrospinning PPV precursor alcohol solution

We have found a simple method to prepare poly(phenylene vinylene) (PPV) nanofibers via electrospinning PPV precursor alcohol solution under annealed at 180 °C in a N₂ atmosphere. The nanofibers are uniform in diameter and long in decimeter magnitudes with resistance in decay, which makes them have potential applications in optical and electronic devices. The morphology can be better controlled by blend PPV precursor solution with poly(vinylalcohol) (PVA) aqueous solution. The fluorescence spectrum of PPV/PVA nanofibers exhibited appreciable blue shift, which made it possible to fabricate nanofibers with fluorescence from yellow-green to blue.     

Controllable Fabrication of TiO2 1D‐Nano/Micro Structures: Solid,Hollow, and Tube‐in‐Tube Fibers by Electrospinning and the Photocatalytic Performance

The solid, hollow, and tube‐in‐tube porous nanofiber structures of TiO₂ are synthesized successfully by a simple non‐coaxial electrospinning method without using a complicated coaxial jet head, combined with adjusting the concentration of the TiO₂ precursor and the pinhole diameter of the jet head and by final calcination. The formation mechanisms of different structured TiO₂ fibers are discussed in detail. This method is facile and effective, and easy to scale up. Furthermore, it is a versatile method for constructing tube‐in‐tube fibers of other metal oxides such as ZrO₂, SiO₂, SnO₂, and In₂O₃. The photocatalytic activity of tubular TiO₂ nanofibers for the degradation of 2‐chlorophenol and 2,4‐dichlorophenol under UV or visible‐light irradiation is better than the one of commercial available TiO₂ powder, rutile, and anatase TiO₂ fibers.     

Polymorphism Control of Poly(vinylidene fluoride) through Electrospinning

Polymorphism control of PVDF has been realized through electrospinning. PVDF fibrous membranes with fiber diameter in the range of 100 nm to several micrometers were produced by electrospinning and the crystal phase of electrospun PVDF fibers can be adjusted at the same time. Through the control of electrospinning parameters such as the solvent, electrospinning temperature, feeding rate, and tip‐to‐collector distance, PVDF fibrous membranes containing mainly α‐ or β‐ or γ‐phase could be fabricated successfully.