Saeed D. Mohan

Carbon nanotubes in electrospun polyethylene oxide nanofibres: A potential route to conducting nanofibres

Polyethylene oxide solution containing multi-walled carbon nanotubes have been electrospun onto a rotating collector to produce highly aligned arrays of electrospun nanofibers ranging in diameters from (200 – 360) nanometres. The addition of a surfactant (Triton X-100) is highly effective in dispersing carbon nanotube within an aqueous solution of polyethylene oxide and the resulting mixture can be electrospun without excessive clumping to produce nanofibers containing high loadings of nanotubes; in this case up to 5% wt thereby providing an effective route to electrically conductive nanofibres.

Chapter 8:Structure Development in Electrospun Fibres

Electrospinning is a process which transforms polymer solutions in to solid fibres in ∼25 ms. In the case of an amorphous polymer, the resultant molecular organisation may not be so different from that of the solution. However, polymers are rich in different types of ordering processes and these may be encountered during electrospinning. In many areas of polymer processing, the processing procedures can have a significant impact on the structure and hence properties of the final product as the selection of the chemical configuration

Modelling Small Angle Neutron Scattering Data from Electrospun Fibres

Electrospinning is a technique employed to produce nanoscale to microscale sized fibres by the application of a high voltage to a spinneret containing a polymer solution. Here we examine how small angle neutron scattering data can be modelled to analyse the polymer chain conformation. We prepared 1:1 blends of deuterated and hydrogenated atactic-polystyrene fibres from solutions in N, N-Dimethylformamide and Methyl Ethyl Ketone. The fibres themselves often contain pores or voiding within the internal structure on the length scales that can interfere with scattering experiments. A model to fit the scattering data in order to obtain values for the radius of gyration of the polymer molecules within the fibres has been developed, that includes in the scattering from the voids. Using this model we find that the radius of gyration is 20% larger than in the bulk state and the chains are slightly extended parallel to the fibre axis.

Electrospinning of food-grade nanofibres from whey protein

In this study, electrospinning has been employed to produce micro to nano scale fibres of whey protein in order to investigate their potential for use in the food industry. Initially, spinning of pure whey protein proved challenging; so in order to facilitate the spinning of freshly prepared aqueous solutions, small amounts of polyethylene oxide (as low as 1% w/w in solution) were incorporated in the spinning solutions. The electrospun composite polyethylene-oxide/whey fibres exhibited diameters in the region of 100 to 400 nm, showing the potential to build fibre bundles from this size up. Time-dependent examinations of pure whey protein aqueous solutions were conducted using rheometery and small angle neutron scattering techniques, with the results showing a substantial change in the solution properties with time and stirring; and allowing the production of fibres, albeit with large diameters, without the need for an additive. The spinability is related to the potential of the whey protein composites to form aggregate structures, either through hydration and interaction with neighbouring proteins, or through interaction with the polyethylene oxide.

Electrospinning atactic polystyrene: A neutron scattering study

Electrospinning is a method used to produce nanoscale to microscale sized polymer fibres. In this study we electrospin 1:1 blends of deuterated and hydrogenated atactic-Polystyrene from N,N-Dimethylformamide for small angle neutron scattering experiments in order to analyse the chain conformation in the electrospun fibres. Small angle neutron scattering was carried out on randomly orientated fibre mats obtained using applied voltages of 10kV-15kV and needle tip to collector distances of 20cm and 30cm. Fibre diameters varied from 3μm - 20μm. Neutron scattering data from fibre samples were compared with bulk samples of the same polymer blend. The scattering data indicates that there are pores and nanovoiding present in the fibres; this was confirmed by scanning electron microscopy. A model that combines the scattering from the pores and the labelled polymer chains was used to extract values for the radius of gyration. The radius of gyration in the fibres is found to vary little with the applied voltage, but varies with the initial solution concentration and fibre diameter. The values for the radius of gyration in the fibres are broadly equivalent to that of the bulk state.

Defining Structure in Electrospun Polymer Fibres

We use a combination of microscopy, x-ray scattering and neutron scattering to show how structure develops in micro and nano-size polymer fibres prepared by electrospinning. The technique has been applied to a range of different polymers, an amorphous system (polystyrene), a crystallisable polymer (poly-ε-caprolactone), a composite systems (polyethylene oxide or poly vinyl alcohol containing polypyrrole) and consider the possibility of self assembly (gelatin).

Evaluating Scales of Structures

The study of polymeric materials at several scales of structure will almost certainly require the use of a number of complementary techniques. This chapter provides an overview of the experimental techniques available for visualizing and evaluating polymer morphology. The chapter sets out to provide sufficient information to enable the reader to appreciate the research work described in the following chapters. Imaging techniques can provide invaluable information of many different scales. For the nanoscale, transmission electron microscopy is the technique of choice but at the expense of a much reduced sampling volume and more involved sample preparation. Recent developments in scanning electron microscopes, particularly in terms of field emission sources mean that nanometre resolution is readily available with the attendant advantages of the ease of screening large areas. However as a surface topology technique we need to develop a contrast, which can be readily achieved using, for example, the etching techniques described in this chapter or through examination of a fractured surface. Scattering techniques probe a volume and in some cases information can be obtained in a time-resolving manner, so that the development of structure can be followed in real time. Neutron scattering provides a different contrast to X-ray scattering which can be useful with halogenated polymers or with metal fillers. Recent developments in pulsed neutron sources have resulted in instruments which can provide data in a single calibrated file over length scales from 0.1 to 10 nm. We also show how indirect methods such as thermal analysis can be used to obtain morphological data.