Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Thesis presented in partial fulfilment of the requirements for the degree of
Master of Science (polymer science)
at the
University of Stellenbosch / Embargo date 2010-03-31 plt 2010 / ENGLISH ABSTRACT: A novel method, herein referred to as ‘solvent facilitated coaxial electrospinning’, was used
to produce reversibly thermochromic core-shell fibres with poly(methyl methacrylate)
(PMMA) as shell and a thermochromic dye composite as core. The thermochromic dye
composite consisted of combinations of 1-dodecanol, bisphenol A (BPA) and crystal violet
lactone (CVL). In the ‘solvent facilitated coaxial electrospinning’ method, the thermochromic
dye composite was dissolved in a suitable ‘facilitating solvent’ prior to spinning, instead of
being spun into the fibres from the melt as previously described in literature. A low
interfacial tension between the core and shell liquids, which is beneficial to effective core
entrainment, was achieved by using a correctly chosen core ‘facilitating solvent’. The PMMA
was dissolved to form the shell spinning liquid and by selecting the correct core and shell
solvents, spinneret blockage and precipitation due to core and shell liquid interactions were
eliminated. High molar mass PMMA was used to produce fibres with diameters in the range
of 3–10 μm (larger than typical electrospun fibres) in order to minimize light scattering and
subsequently allow visual observation of the thermochromic transitions, unlike the fibres
that were produced in literature. The fibres were analyzed using SEM, TEM, TGA and DSC to
investigate fibre morphology, dye composite thermal transition and fibre composition.
Physical and chemical interactions between the thermochromic dye composite and the
PMMA shell were identified as possible causes of differences between the thermochromic
transition temperatures of the core-shell fibres and the bulk dyes, as well as of the instability
of the colour developed state of certain thermochromic fibres. The spatial confinement of
the dye composite inside the fibres and the extensive volume reduction (from bulk dye to
small volume inside the fibres) affected the thermochromic behaviour of the thermochromic
composite once it was entrained in the fibres. An excess BPA was used in the dye
composition to allow the production of reversibly thermochromic fibres with a stable colour
developed state. / AFRIKAANSE OPSOMMING: A nuwe metode, hierin beskryf as ‘oplosmiddel gefasiliteerde koaksiale elektrospinnery’, is
gebruik om omkeerbare termochromiese kern-skil vesels met polie(metiel metakrilaat)
(PMMA) as skil en ‘n saamgestelde termochromiese kleurmiddel as kern te vervaardig. Die
saamgestelde termochromiese kleurmiddel het bestaan uit kombinasies van 1-dodekanol,
bisfenol A (BPA) en kristal violet laktoon (CVL). Vir die ‘oplosmiddel gefasiliteerde koaksiale
elektrospin’-metode, is die saamgestelde termochromiese kleurmiddel opgelos in ‘n gepaste
‘fasiliterende oplosmiddel’ voordat dit geëlektrospin is, eerder as om dit te smelt om dit
sodoende in vesels te kan inspin soos beskryf in die literatuur. ‘n Lae raakvlakspanning
tussen die kern- en skilspinvloeistowwe, wat voordelig is vir doeltreffende kern insluiting, is
bereik deur gebruik te maak van sorgvuldig verkose ‘fasiliterende oplosmiddels’ vir die kern.
Die PMMA is opgelos om die skilspinoplossing te vorm en, deur die keuse van die korrekte
kern- en skiloplosmiddels, kon spinneret blokkasie en neerslag van die polimeer as gevolg
van kern- en skilvloeistofinteraksies elimineer word. Hoë molekulêre massa PMMA is gebruik
om vesels te vervaardig met deursnee in die omtrek van 3–10 μm (groter as tipiese
elektrogespinde vesels) om sodoende lig-verstrooiing te verminder en daardeur visuele
waarneming van die termochromiese oorgange moontlik te maak, in teenstelling met die
vesels wat in die literatuur gevorm is. Die vesels is ge-analiseer met SEM, TEM, TGA en DSC
om veselmorfologie, termiese omskakelinge van saamgestelde kleurmiddels en
veselsamestelling te bestudeer. Fisiese en chemiese interaksies tussen die saamgestelde
termochromiese kleurmiddel kern en die PMMA skil is geïdentifiseer as moontlike oorsake
van verskille tussen die termochromiese oorgangstemperature van die kern-skil vesels en die
kleurmiddels in grootmaat, asook van die onstabiliteit van die gekleurde toestand van
sommige termochromiese vesels. Die ruimtelike inperking van die saamgestelde kleurmiddel
binne in die vesels asook die beduidende volume verkleining (van grootmaat kleurmiddel tot
klein volume binne in die vesels) het die termochromiese gedrag van die saamgestelde
kleurmiddel binne die vesels beïnvloed. ‘n Oormaat BPA is in die saamgestelde
termochromiese kleurmiddel gebruik om die produksie van omkeerbaar termochromiese
vesels met ‘n stabiele gekleurde toestand toe te laat.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4606 |
| Date | 12 1900 |
| Creators | Malherbe, Ilana |
| Contributors | Sanderson, R. D., Smit, A. E., University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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