Browsing by Author "Van Deventer, Nedine"
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- ItemElectrospun composite nanofibres with magnetic carbon nanotubes(Stellenbosch : Stellenbosch University, 2016-03) Van Deventer, Nedine; Mallon, Peter E.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: Functional composite nanofibres incorporated with magnetic carbon nanotubes (CNTs) were successfully synthesized using the electrospinning technique. This is the first example of the preparation of such composite nanofibres. In this study, a nanofibrous mat of electrospun nanofibres constitutes the polymer matrix, with the addition of various CNTs as reinforcing nanomaterials in order to form polymer/CNT nanocomposites (PCNs). Poly(methyl methacrylate) homopolymer, possessing a sufficiently high molar mass for electrospinning, was synthesized for use as polymer matrix. The effect that the polymer solution parameters, processing parameters and ambient parameters have on the fibre morphology are discussed. In a parallel study, multi-wall carbon nanotubes (MWCNTs) and magnetic CNTs (with controlled amounts of magnetic nanoparticles embedded in the walls) were chemically modified by means of oxidation and subsequent polymer grafting. Chemical modification was carried out in order to compatibilize the reinforcing nanomaterials with the polymer matrix for production of PCNs with a well dispersed and exfoliated structure. As a comparison to the magnetic CNTs mentioned above, magnetic CNTs were synthesized by decorating the surface of oxidized MWCNTs with magnetic nanoparticles. Decoration was made possible by carboxylic acid moieties present on the oxidized MWCNT backbone, which acted as anchoring sites through which chemical functionalities could be attached. Successful synthesis of MWCNT-Fe3O4 was achieved using an ex-situ and simpler single-step in-situ approach. Compatibilization with the polymer matrix for production of PCNs is achieved via the remaining carboxylic acid functionalities present as a result of initial oxidation. The various CNTs were incorporated into electrospun nanofibres as reinforcing nanomaterials and PCNs were thus formed. Increasing amounts of the various CNTs were added to the electrospinning polymer solution. By the addition of CNTs, the viscosity of the electrospinning solution increased, which prevented efficient electrospinning. The polymer concentration was, therefore, varied in specific ratios depending on the amount of CNTs incorporated. The effect the addition of CNTs has on the fibre morphology is discussed. After electrospinning, fibres in the nanometer range were obtained. Successful incorporation, and thus interaction of the CNTs with the electrospun polymer matrix, was confirmed by scanning transmission electron microscopy (STEM) images which verified the presence of well distributed CNTs which align along the electrospun polymer nanofibres due to the stretching of the fibres during electrospinning. The magnetic response of nanofibres reinforced with ex-situ and in-situ MWCNT-Fe3O4 exhibited superparamagnetic behaviour; as was proved with superconducting quantum interference device magnetometry where curves with the characteristic sigmoidal shape showing zero coercivity, zero remanence and no hysteresis loops were obtained. In summation, property enhancement of electrospun polymer nanofibres was achieved by the incorporation of two different types of reinforcing nanomaterials – CNTs and magnetic nanoparticles. The magnetic properties induced by the reinforcing materials can potentially be used for SMART polymer applications; where SMART polymer materials (also referred to as stimuli-responsive polymer materials) are materials which behave in predictable and measurable ways when exposed to various external stresses. Electrospun composite nanofibres containing ex-situ synthesized MWCNT-Fe3O4 possessed the highest magnetization value of all the composites; and is proposed for use in SMART polymer applications such as magnetic filters or tissue scaffolds.