Electrospun composite nanofibres with magnetic carbon nanotubes

Van Deventer, Nedine (2016-03)

Thesis (MSc)--Stellenbosch University, 2016.

Thesis

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.

AFRIKAANSE OPSOMMING: Suksesvolle sintese van funksionele saamgestelde nanovesels is bereik deur gebruik te maak van die elektrospin-tegniek. Magnetiese koolstof nanobuisies (CNTs) is inkorporeer in die nanovesels – dit is die eerste voorbeeld van die samevoeging van sulke saamgestelde nanovesels. In die studie bestaan die polimeer matriks uit ‘n mat van elektro-gespinde nanovesels. As versterking word verskillende CNTs bygevoeg om polimeer/CNT nanosamestellings (PCNs) te vorm. Poli(metiel metakrilaat) polimeer, wat ‘n hoë molêre massa voldoende vir elektrospin besit, is sintetiseer om as polimeer matriks te dien. Die uitwerking van die verskillende polimeer-oplossings, prosesse en omgewings parameters op die morfologie van die vesels, word bespreek. In ‘n vergelykbare studie, is multi-wand koolstof nanobuisies (MWCNTs) en magnetiese CNTs (waar ‘n beheerde aantal magnetiese nanopartikels ingebed is in die wande) chemies verander om PCNs met eweredig verspreide CNTs te produseer. Chemiese modifikasie, deur middel van oksidasie en daaropeenvolgende polimeer-enting, sorg dat die nanomateriaal wat ter versterking by die polimeer matriks gevoeg word PCNs met ‘n eweredige samestelling produseer. In aansluiting by bogenoemde magnetiese CNTs, is magnetiese CNTs ook sintetiseer deur die oppervlak van geoksideerde MWCNTs met magnetiese nanopartikels te versier. Die teenwoordigheid van karboksielsuur op die geoksideerde MWCNT oppervlak het as ankerpunte gedien waaraan paslike chemiese nanopartikels kon bind. Suksesvolle sintese van MWCNT-Fe3O4 is bereik deur ‘n ex-situ, sowel as eenvoudiger enkel stap in-situ metode. Die orige karboksielsuur, as resultaat van vroeëre oksidasie, sorg vir PCNs met ‘n eweredige samestelling wat waargeneem is deur MWCNT-Fe3O4 wat in verhouding versprei in die polimeer matriks. Verskillende CNTs is as vullers by die elektro-gespinde nanovesels inkorporeer om PCNs te vorm. Toenemende hoeveelhede van die verskillende CNTs is by die elektrospin-polimeer-oplossing gevoeg. Die byvoeging van CNTs het die viskositeit van die elektrospin-oplossing verhoog, en dit het tot ‘n oneffektiewe elektrospin-proses gelei. Gevolglik is die polimeer-oplossing konsentrasie proporsioneel aangepas, afhangende van die hoeveelheid CNTs wat inkorporeer is. Die effek van die toevoeging van die CNTs op die morfologie van die vesels, word bespreek. Vesels van nanometer grootte is verkry as resultaat van die elektrospin-proses. Suksesvolle inkorporasie is bevestig deur STEM beelde wat dui op die interaksie van die CNTs met die elektro-gespinde polimeer matriks. Die beelde toon eweredig verspreide CNTs wat in lyn is met die lengte van die vesels as gevolg van die rekking van die vesels gedurende die elektrospin-proses. Nanovesels met ex-situ en in-situ MWCNT-Fe3O4 as vuller het superparamagnetiese eienskappe getoon. Resultate verwerk in grafieke toon S-vormige kurwes wat die 0-0-as kruis, wat kenmerkend is van superparamagnetisme. In opsomming, waarde is toegevoeg tot die eienskappe van elektro-gespinde polimeer-nanovesels deur die inkorporasie van twee soorte nanomateriale as vullers – CNTs en magnetise nanopartikels. Die magnetiese eienskappe toegevoeg deur die gebruik van magnetiese CNTs as vuller besit groot potensiaal vir gebruik in “SMART” polimeer-materiale. “SMART”-materiale reageer op ‘n voorspelbare en meetbare wyse wanneer dit blootgestel word aan eksterne stimuli. Elektro-gespinde saamgestelde nanovesels met MWCNT-Fe3O4 wat ex-situ produseer is, is die mees magneties van al die samestellings. Die nanovesels kan potensieel gebruik word in “SMART” polimeer toepassings soos magnetiese filters of as raamwerk vir ‘n menslike weefsel-mat.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98333
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