Needleless eletrospinning of polystyrene fibers with an oriented surface line texture

We have demonstrated that polystyrene (PS) nanofibers having an ordered surface line texture can be produced on a large scale from a PS solution of acetone and N,N′-dimethylformamide (2/1, vol/vol) by a needleless electrospinning technique using a disc as fiber generator. The formation of the unusual surface feature was investigated and attributed to the voids formed on the surface of jets due to the fast evaporation of acetone at the early stage of electrospinning, and subsequent elongation and solidification turning the voids into ordered lines on fiber surface. In comparison with the nanofibers electrospun by a conventional needle electrospinning using the same solution, the disc electrospun fibers were finer with similar diameter distribution. The fiber production rate for the disc electrospinning was 62 times higher than that of the conventional electrospinning. Fourier transform infrared spectroscopy and X-ray diffraction measurements indicated that the PS nanofibers produced from the two electrospinning techniques showed no significant difference in chemical component, albeit slightly higher crystallinity in the disc spun nanofibers.

A novel alcohol detector based on ZrO2-doped SnO2 electrospun nanofibers

To overcome the interference of acetone when detecting alcohol, a novel alcohol detector based on zirconia-doped SnO2 nanofibers were fabricated through electrospinning technique and calcination process. The samples have been characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and their gas sensing properties have also been investigated. When exposed to alcohol vapor, the nanofibers containing 15 mol% zirconia exhibit the best sensing properties. Moreover, the sensor holds the successful discrimination between acetone and alcohol, which makes our product a good candidate in fabricating highly selective sensors in practice.

Bionanocomposites from electrospun PVA/pineapple nanofibers/Stryphnodendron adstringens bark extract for medical applications

Tissue engineering has been defined as an interdisciplinary field that applies the principles of engineering and life sciences for the development of biological substitutes to restore, maintain or improve tissue function. This area is always looking for new classes of degradable biopolymers that are biocompatible and whose activities are controllable and specific, more likely to be used as cell scaffolds, or in vitro tissue reconstruction. In this paper, we developed a novel bionanocomposite with homogeneous porous distribution and prospective natural antimicrobial properties by electrospinning technique using Stryphodedron barbatimao extract (Barbatimão). SEM images showed equally distribution of nanofibres. DSC and TGA showed higher thermal properties and change crystallinity of the developed bionanocomposite mainly because these structural modification. © 2012 Elsevier B.V.

Using an additive to control the electrospinning of fibres of poly(epsilon-caprolactone)

Electrospinning is a route to polymer fibres with diameters considerably smaller than available from most fibre-producing techniques. We explore the use of a low molecular weight compound as an effective control additive during the electrospinning of poly(epsilon-caprolactone). This approach extends the control variables for the electrospinning of nanoscale fibres from the more usual ones such as the polymer molecular weight, solvent and concentration. We show that through the use of dual solvent systems, we can alter the impact of the additive on the electrospinning process so that finer as well as thicker fibres can be prepared under otherwise identical conditions. As well as the size of the fibres and the number of beads, the use of the additive allows us to alter the level of crystallinity as well as the level of preferred orientation of the poly(epsilon-caprolactone) crystals. This approach, involving the use of a dual solvent and a low molar mass compound, offers considerable potential for application to other polymer systems. (C) 2010 Society of Chemical Industry

Development of orientation during electrospinning of fibres of poly(ε-caprolactone)

We explore the influence of a rotating collector on the internal structure of poly(ε-caprolactone) fibres electrospun from a solution in dichloroethane. We find that above a threshold collector speed, the mean fibre diameter reduces as the speed increases and the fibres are further extended. Small-angle and wide-angle X-ray scattering techniques show a preferred orientation of the lamellar crystals normal to the fibre axis which increases with collector speed to a maximum and then reduces. We have separated out the processes of fibre alignment on the collector and the orientation of crystals within the fibres. There are several stages to this behaviour which correspond to the situations (a) where the collector speed is slower than the fibre spinning rate, (b) the fibre is mechanically extended by the rotating collector and (c) where the deformation leads to fibre fracture. The mechanical deformation leads to a development of preferred orientation with extension which is similar to the prediction of the pseudo-affine deformation model and suggests that the deformation takes place during the spinning process after the crystals have formed.

Recent developments in electrospinning of nanofiber yarns

Nanofibers possess high surface area and excellent porosity. Though nanofibers can be produced by a variety of techniques, electrospinning stands distinct because of its simplicity and flexibility in processing different polymer materials, and ability to control fiber diameter, morphology, orientation, and chemical component. Nonetheless, electrospun nanofibers are predominantly produced in the form of randomly oriented fiber webs, which restrict their wide use. Converting nanofibers into twisted continuous bundles, i.e., nanofiber yarns, can improve their strength and facilitate their subsequent processes, but remains challenging to make. Nanofiber yarns also create enormous opportunities to develop well-defined three-dimensional nanofibrous architectures. This review article gives an overview of the state-of-the-art techniques for electrospinning of nanofiber yarns and control of nanofiber alignment. A detailed account on techniques to produce twisted/non-twisted short bundles and continuous yarns are discussed.

Highly-twisted, continuous nanofibre yarns prepared by a hybrid needle-needleless electrospinning technique

Nanofibres prepared by electrospinning have shown enormous potential for various applications. They are obtained predominantly in the form of nonwoven fibre webs. The 2-dimensional nonwoven feature and fragility have considerably confined their further processing into fabrics through knitting or weaving. Nanofibre yarns, which are nanofibre bundles with continuous length and a twist feature, show improved tensile strength, offering opportunities for making 3-dimensional fibrous materials with precisely controlled fibrous architecture, porous features and fabric dimensions. Despite a few techniques having been developed for electrospinning nanofibre yarns, they are chiefly based on the needle electrospinning technique, which often has low nanofibre productivity. In this study, we for the first time report a nanofibre yarn electrospinning technique which combines both needle and needleless electrospinning. A rotating intermediate ring collector was employed to directly collect freshly-electrospun nanofibres into a fibrous cone, which was further drawn and twisted into a nanofibre yarn. This novel system was able to produce high tenacity yarn (tensile strength 128.9 MPa and max strain 222.1%) at a production rate of 240 m h^-1, with a twist level up to 4700 twists per metre. The effects of various parameters, e.g. position of the electrospinning units, operating conditions and polymer concentration, on nanofibre and yarn production were examined.

Analytical Parametric Model Used to Study the Influence of Electrostatic Force on Surface Coverage During Electrospinning of Polymer Fibers

Electrospinning (ES) can readily produce polymer fibers with cross-sectional dimensions ranging from tens of nanometers to tens of microns. Qualitative estimates of surface area coverage are rather intuitive. However, quantitative analytical and numerical methods for predicting surface coverage during ES have not been covered in sufficient depth to be applied in the design of novel materials, surfaces, and devices from ES fibers. This article presents a modeling approach to ES surface coverage where an analytical model is derived for use in quantitative prediction of surface coverage of ES fibers. The analytical model is used to predict the diameter of circular deposition areas of constant field strength and constant electrostatic force. Experimental results of polyvinyl alcohol fibers are reported and compared to numerical models to supplement the analytical model derived. The analytical model provides scientists and engineers a method for estimating surface area coverage. Both applied voltage and capillary-to-collection-plate separation are treated as independent variables for the analysis. The electric field produced by the ES process was modeled using COMSOL Multiphysics software to determine a correlation between the applied field strength and the size of the deposition area of the ES fibers. MATLAB scripts were utilized to combine the numerical COMSOL results with derived analytical equations. Experimental results reinforce the parametric trends produced via modeling and lend credibility to the use of modeling techniques for the qualitative prediction of surface area coverage from ES. (Copyright: 2014 American Vacuum Society.)

Investigating polymer-peptide conjugates and electrospinning for the production of advanced materials

This thesis describes the production of advanced materials comprising a wide array of polymer-based building blocks. These materials include bio-hybrid polymer-peptide conjugates, based on phenylalanine and poly(ethylene oxide), and polymers with intrinsic microporosity (PIMs). Polymer-peptides conjugates were previously synthesised using click chemistry. Due to the inherent disadvantages of the reported synthesis, a new, simpler, inexpensive protocol was sought. Three synthetic methods based on amidation chemistry were investigated for both oligopeptide and polymerpeptide coupling. The resulting conjugates produced were then assessed by various analytical techniques, and the new synthesis was compared with the established protocol. An investigation was also carried out focussing on polymer-peptide coupling via ester chemistry, involving deprotection of the carboxyl terminus of the peptide. Polymer-peptide conjugates were also assessed for their propensity to self-assemble into thixotropic gels in an array of solvent mixtures. Determination of the rules governing this particular self-assembly (gelation) was required. Initial work suggested that at least four phenylalanine peptide units were necessary for self-assembly, due to favourable hydrogen bond interactions. Quantitative analysis was carried out using three analytical techniques (namely rheology, FTIR, and confocal microscopy) to probe the microstructure of the material and provided further information on the conditions for self-assembly. Several polymers were electrospun in order to produce nanofibres. These included novel materials such as PIMs and the aforementioned bio-hybrid conjugates. An investigation of the parameters governing successful fibre production was carried out for PIMs, polymer-peptide conjugates, and for nanoparticle cages coupled to a polymer scaffold. SEM analysis was carried out on all material produced during these electrospinning experiments.