Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Since the discovery of carbon nanotubes (CNTs), a large interest has developed around the
incorporation of these into polymeric matrices in order to introduce the excellent mechanical,
thermal and electrical properties of CNTs into the resultant composites. Nanocomposites of
polymer/CNT composition allow for the favourable combination of the physical properties of
the polymeric matrix and of the CNT filler.
The biggest existing challenge of producing such nanocomposites is presented by the
tendency of CNTs to occur in bundles or aggregates which are difficult to break up and to
disperse in solution which leads to non-uniform distributions within the polymeric matrix.
This problem has been combated through the use of CNT surface functionalization. However,
a disadvantage exists with this solution. Since covalent functionalization of the CNT surface
disrupts the electronic π-electron cloud which is responsible for the excellent electronic
properties which CNTs are often desired for, an alternative method of functionalization must
be employed in order to maintain the excellent intrinsic properties of CNTs yet create
uniform dispersion of the nanotubes upon compatibilization with the polymeric matrix.
Two alternative methods for the production of noncovalent compatibilization of multi-walled
carbon nanotubes (MWNTs) with polystyrene were investigated and compared. These two
methods involved the synthesis of a pyrene-functional macroinitiators for reversible addition
fragmentation chain transfer (RAFT) and atom transfer radical polymerization (ATRP). Both
of these methods allow for the controlled polymerisation of pyrene functional polystyrene
chains. For comparison, the direct covalently functional MWNTs were also synthesised first
by oxidation of the MWNT surface and conversion of the MWNT into the multifunctional
RAFT and ATRP macroinitiator in which the styrene chains were controllably directly
grafted from the surface of the MWNTs. The interaction of the pyrene chains with MWCNTs
was monitored by using NMR, TGA and fluorescence spectroscopy. The NMR results showed the broadening and weakening of the pyrene protons as well as the
polystyrene (PS) protons. TGA showed the loss of the pyrene-functional PS portion
throughout the heating process. Fluorescence provided the conclusive result that the
noncovalent compatibilization had occurred through the quenching of the emission and excitation signals as a result of electron transfer being facilitated by the π-stacking
interactions. Finally, the MWNT nanocomposite polymer nanofibres are produced via the electrospinning
technique with the various covalent and non-covalent compatibilized MWNT. The fibre
morphology for the different compatibilization methodologies is compared as a function of
the MWNT content. Distinct differences are observed for the different composites. / AFRIKAANSE OPSOMMING: Sedert die ontdekking van koolstof-nanobuisies (KNBs), het ʼn groot belangstelling ontwikkel
rondom die betrekking van KNBs in polimeriese matrikse om samestellings met uitstekende
meganiese, termiese en elektriese eienskappe te vervaardig. Nanosamestellings van
polimeer/KNB komposisie laat toe dat gunstige kombinasies van fisiese eienskappe van die
polimeer en die KNB vuller gerealiseer kan word.
Die grootste uitdaging van die vervaardiging van sulke nanosamestellings is die neiging van
KNBs om gebondelde formasie te vorm wat baie moeilik is om op te breek. Dit maak hulle
verspreiding in oplossings en in polimeer matrikse oneweredig. Hierdie probleem word deur
funksionalisering opgelos. Nogtans, ʼn nadeel van hierdie oplossing is dat kovalente
funksionalisering verander die elektroniese struktuur van die KNB oppervlakte deur die
ontwrigting van die π-elektron wolk wat vir die uitstekende elektroniese eienskappe
verantwoordelik is. Dus moet ʼn alternatiewe funksionalisering metode gebruik word om die
inherente eienskappe van die KNBs te behou en terselfde tyd ʼn uniforme verspreiding te
bewerkstellig gedurende die vermenging met die polimeer matriks.
Twee alternatiewe metodes vir die vervaardiging van nie-kovalente gefunksionaliserde multiommuurde
koolstof-nanobuisies (Eng: MWNTs) met polistireen (PS) was ondersoek en
vergelyk. Hierdie twee metodes was uitgevoer deur die sintese van ʼn pyreen-funksionele
omkeerbare addisie-fragmentasie-kettingoordrag (OAFO) en atoomorrdragradikaaladdisie
(AORA) makromiddel. Al twee van hierdie metodes lei tot ʼn gekontrollerde polimerisasie
van pyreen-gefunksionaliserde stireen. Vir vergelyking was ʼn kovalente- gefunksionaliserde
MWNT vervaardig deur die oksidasie van die MWNT oppervlakte en die daaropvolgende
immobilisasie van dieselfde AORA en OAFO middel aan hierde aktiewe punte. Daarvan af
was stireen gekontroleerd gepolimeriseer deur middel van die AORA en OAFO middel. Die
interaksie was gekarakteriseer deur TGO, KMR en fluoressensie spektroskopie. Die KMR resultate het seine gewys van die verspreiding en verswakking van die pyreen en
PS protone. TGO het die verlies van die pyreen-funksionele PS deel van die nie-kovalente
produk gewys. Fluoressensie het beslissende bewyse gelewer dat die nie-kovalente funksionalisiering plaas gevind het deur die onderdrukking van die stralende en opwekkings
seine as ʼn gevolg van die elektron oordrag wat deur die π-stapel interaksies gefasiliteer word.
Uiteindelik was die nanosamestellings vermeng met PS en geelektrospin. Die vesel
morfologie vir die verskillende gefunksionaliserde MWNT nanosamestellings metodes was
vergelyk as ʼn funksie van MWNT inhoud. Duidelike verskille is waargeneem vir die
verskillende samestellings.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86354 |
| Date | 04 1900 |
| Creators | Scharlach, Kerstin |
| Contributors | Mallon, Peter, Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xvii, 145 p. : ill. |
| Rights | Stellenbosch University |
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