Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Two series of amphiphilic, organic-inorganic graft copolymers of poly(methyl
methacrylate) and poly(dimethylsiloxane) (PMMA-graft-PDMS), as well as
poly(acrylonitrile) and poly(dimethylsiloxane) (PAN-graft-PDMS), were synthesized
via conventional free radical copolymerization using the ―grafting through‖ technique.
In both series the PDMS macromonomer content varied from 5 wt.% - 25 wt.% and
different graft lengths of 1000 g/mol and 5000 g/mol were used. A gradient elution
profile was developed to monitor the removal of the unreacted PDMS
macromonomer using hexane extraction. In the case of the PAN copolymer series,
the gradient profile showed that as the PDMS content in the feed increased, more
PAN-graft-PDMS molecules formed relative to homopolymer PAN. In the case of the
PMMA copolymer series, mostly PMMA-graft-PDMS molecules were formed as the
PDMS content in the feed increased. In the case of the PAN-graft-PDMS series, the
PDMS content affected the crystallization behaviour of the PAN segments and lead
to a decrease in crystallinity across the composition range as the PDMS content
increased. It is shown that the synthesized graft copolymers can be electrospun to
produce continuous nanofibers. The effects of polymer solution concentration,
copolymer composition and tip-to-collector distance on the fiber morphology are
discussed. The rapid stretching of the polymer jet, as well as the rapid solvent
evaporation during the electrospinning process, resulted in highly complex nonequilibrium
morphologies in the case of the electrospun PAN-graft-PDMS
copolymers. The crystallization behaviour of the electrospun fibers of PAN-graft-
PDMS was shown to be different from the unprocessed precursor material. Surface
oxidised MWCNTs were successfully incorporated and well dispersed into the graft
copolymers via the electrospinning process to produce nanocomposite nanofibers. In
the case of the PAN-graft-PDMS copolymer series, the presence of MWCNTs in the
nanocomposite nanofibers enhanced the overall degree of crystallinity when
compared to the unfilled nanofibers. For the first time positron annihilation lifetime
spectroscopy (PALS) analysis was performed on the various complex graft
copolymer compositions and their electrospun fiber analogues, as well as
nanocomposites, to investigate the free volume properties of the various materials. The results revealed that there are two distinct ortho-positronium (o-Ps) lifetime
parameters for these complex multiphased materials. The shorter lived lifetime -3
was attributed to the o-Ps annihilation in the amorphous regions of the crystalline
PAN phase in the PAN-graft-PDMS copolymer series, as well as to the o-Ps
annihilation in the amorphous PMMA phase in the case of the PMMA-graft-PDMS
copolymer series. The longer lived lifetime -4 was attributed to the o-Ps annihilation
in the more amorphous PDMS phase. In the case of the PMMA series the relative
fractional free volume was influenced by the graft lengths, where the 5000 g/mol
series showed a larger increase in fractional free volume relative to the shorter 1000
g/mol series. The effects of the tip-to-collector distance during electrospinning, as
well as the inclusion of MWCNTs, on the free volume properties are also discussed.
It is demonstrated how positron annihilation lifetime spectroscopy can provide
valuable and unique information on the internal structure and morphology of the
electrospun nanofibers. / AFRIKAANSE OPSOMMING: Twee reekse amfifiliese, organies-anorganiese entkopolimere van
poli(metielmetakrilaat) en poli(dimetielsiloksaan) (PMMA-ent-PDMS), asook
poli(akrilonitriel) en poli(dimetielsiloksaan) (PAN-ent-PDMS), is gesintetiseer deur
konvensionele vrye-radikaalkopolimerisasie. Die PDMS makromonomeerinhoud het
gewissel tussen 5 wt.% - 25 wt.% in albei reekse en sykettinglengtes van 1000 g/mol
en 5000 g/mol is gebruik. `n Gradient-eluasieprofiel is opgestel om die verwydering
van ongereageerde PDMS makromonomeer d.m.v. heksaanekstraksie te monitor. In
die PAN kopolimeer reeks het die gradient-eluasieprofiel gewys dat meer PAN-ent-
PDMS molekules vorm relatief tot die PAN homopolimeer sodra meer PDMS
bygevoeg word. In die PMMA kopolimeer reeks het meer PMMA-ent-PDMS
molekules gevorm sodra meer PDMS toegevoeg is. In die geval van die PAN-ent-
PDMS reeks, het die PDMS die kristallisasiegedrag van die PAN segmente
geaffekteer en `n afname in die totale kristalliniteit veroorsaak soos die PDMS
inhoud vermeerder het. Daar word bewys dat die gesintetiseerde entkopolimere geelektrospin
kan word om nanovesels te vorm. Die effek van
polimeeroplossingskonsentrasie, kopolimeersamestelling en punt-tot-versamelaarafstand
op die nanoveselmorfologie word bespreek. Die vinnige strekking van die
polimeerjet sowel as die vinnige verdamping van die oplosmiddel gedurende die
elektrospinproses het gelei tot hoogs komplekse nie-ekwilibrium morfologieë in die
geval van die ge-elektrospinde PAN-ent-PDMS kopolimere. Die kristallisasiegedrag
van die nanovesels van PAN-ent-PDMS het verskil van die onverwerkte voorloper
materiaal. Oppervlakgeoksideerde MWCNTs is suksevol geïnkorporeer en versprei
in die entkopolimere d.m.v. die elektrospinproses om nanosaamgestelde nanovesels
te vorm. Die teenwoordigheid van MWCNTs in die nanosaamgestelde nanovesels in
die PAN-ent-PDMS kopolimeerreeks het gelei tot `n verbetering in die algehele
kristalliniteit in vergelyking met die nanovesels sonder MWCNTs. Positronvernietigingsleeftyd-
spektroskopie (PALS) is vir die eerste keer gebruik om die vrye
volume van verskillende kompleks entkopolimeersamestellings, hul ge-elektrospinde
nanovesels sowel as nanosaamgestelde nanovesels te bestudeer. Die resultate het
getoon dat daar twee verskillende orto-positronium (o-Ps) leeftydparameters vir hierdie komplekse multifase materiale bestaan. Die korter leeftydparameter -3 word
toegeskryf aan die o-Ps vernietiging in die amorfe areas van die kristallyne PAN fase
in die PAN-ent-PDMS kopolimeerreeks, sowel as die o-Ps vernietiging in die amorfe
PMMA fase in die PMMA-ent-PDMS kopolimeerreeks. Die langer leeftydparameter
-4 word toegeskryf aan die o-Ps vernietiging in die amorfe PDMS fase. Die relatief
fraksionele vrye volume van die PMMA reeks is deur die verskillende syketting
lengtes beïnvloed. Die 5000 g/mol syketting het `n groter toename in fraksionele vrye
volume veroorsaak relatief tot die korter 1000 g/mol syketting. Die effek van die punttot-
versamelaar-afstand tydens die elektrospinproses op die vrye volume
eienskappe, sowel as die insluiting van MWCNTs, word bespreek. Daar word
aangedui hoe positron-vernietigingsleeftyd-spektroskopie waardevolle en unieke
inligting kan verskaf oor die interne struktuur en morfologie van die nanovesels.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86676 |
| Date | 04 1900 |
| Creators | Basson, Neil |
| Contributors | Mallon, Peter E., 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, en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xiii, 133 p. : ill. (some col.) |
| Rights | Stellenbosch University |
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