Facile method for producing silicon containing porous carbon nanofibres from amphiphilic copolymers and controlling precursor fibre morphology
| dc.contributor.advisor | Mallon, Peter Edward | en_ZA |
| dc.contributor.author | Human, Chantelle | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. | en_ZA |
| dc.date.accessioned | 2015-12-14T07:42:07Z | en_ZA |
| dc.date.available | 2016-07-01T03:00:04Z | en_ZA |
| dc.date.issued | 2015-12 | en_ZA |
| dc.description | Thesis (MSc)--Stellenbosch University, 2015. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: Amphiphilic graft copolymers PAN-g-PDMS were synthesized via a conventional free radical polymerization. The dispersities and molecular weights are typical of that of conventional free radical polymerizations. From the relative integration of NMR peaks it was found that the copolymer composition present could be varied by variation of the PDMS feed ratio. Subsequently, precursor fibres have been produced from the PAN-g-PDMS copolymers series by single needle electrospinning. SEM analysis revealed an increase in fibre diameter and a change in porous structure as the PDMS content increased which could be explained by self-assembly of the amphiphilic molecules. With the addition of MWCNTs, a drastic decrease in fibre diameter was apparent due to the conductive nature of the MWCNTs. TEM images showed that the MWCNTs are distributed and aligned inside the electrospun fibres. Surprisingly, despite the wide use of PAN to produce polymer nanofibres by solution electrospinning, there are no reports on the effect of solution ageing on this process. The investigation revealed an increase in fibre diameter and viscosity for the PAN and grafted copolymers when dissolved in DMF. The effect is more exaggerated for the homo-PAN than the graft copolymers, which is indicative that the effect is caused by PAN rather than PDMS. UV-VIS and XRD results showed the formation of dipole-dipole interaction aggregates in solution accompanied by a decrease in crystallinity in the fibres with an increase in ageing time. Precursor films were also prepared and found to be porous. The precursor fibres and films were subjected to a carbonization process in order to obtain silicon containing porous carbon nanomaterial as stated above. The carbonized samples were analysed with SEM, FE-SEM, EDX, XRD, DSC, BET and TEM to quantify the effect of the thermal treatment. The carbonizations led to major mass loss of the samples and thus a decrease in fibre diameter. FE-SEM and TEM analysis showed that the porous morphology is still present after carbonization. The subsequent carbonized fibres and films consisted largely of carbon, but contained silicon and oxygen from the PDMS. It was found that the carbonization mechanism is similar to that of PAN, but that the PDMS grafts retard the cyclization of the PAN in the stabilization step as shown by DSC. The results also show a comparable difference between the fibres and films. This was attributed to the non-equilibrium morphology present in the electrospun fibres. A possible application of the porous carbon nanofibres was also investigated. The sorption capacity for various oils and organic solvents was found to be higher than that of other carbon-silica nanofibre membranes. PAN-g-PEO and PAN:PEO blends were electrospun and carbonized as an alternative method for porous carbon fibre production. The results showed successful carbonization where porosity of the carbon fibres was strongly dependant on the size of the sacrificial PEO domains. Lastly, an alternative method for more efficient production of precursor fibres was utilized. The ball electrospinning process showed the same trend with regards to the PDMS content and porosity as the single needle technique, but with a throughput rate of 36 times faster. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Amfifiliese entkopolimere van PAN-ent-PDMS is gesintetiseer deur konvensionele vryeradikaalpolimerisasie. Die kettinglengte verspreiding en molekulêre gewigte is tipies van dié van konvensionele vrye radikale polimerisasies. Van die relatiewe integrasie van KMR pieke is daar gevind dat die kopolimeer samestelling beheer kan word deur die PDMS verhouding tydens polimerisasie te varieer. Die PAN-ent-PDMS kopolimeer reeks is daarna ge-elektrospin met die enkel naald tegniek om voorloper vesels te vervaardig. Die SEM analise het 'n toename in veseldeursnit en 'n verandering in poreuse struktuur aangedui soos die PDMS inhoud in die polimere verhoog was. Die verskynsels kan verklaar word deur die outokonstruksie van aggregaatstrukture van die amfifiliese molekules. Met die toevoeging van die multi-omuurde koolstof nanobuisies is 'n drastiese afname in veseldeursnit waargeneem wat toegeskryf kan word aan die geleidende aard van die nanobuisies. TEM beelde het getoon dat die nanobuisies geïnkorpireer is en versprei is binne in die nanovesels. Verbasend, ten spyte van die wye gebruik van PAN om polimeer nanovesels te produseer deur die oplossing elektrospin proses, is daar geen gepubliseerde verslae oor die uitwerking van die oplossing se veroudering op hierdie proses nie. Die ondersoek van die oplossings verouderings proses het 'n toename in veseldeursnit en viskositeit vir die PAN en entkopolimere oplossings tot gevolg gehad. Die effek is meer oordrewe vir die PAN as vir die entkopolimere oplossings, wat aandui is dat die effek eerder veroorsaak word deur die PAN segment as deur die PDMS. UV-VIS en XRD resultate het getoon dat die vorming van dipool-dipool wisselwerking aggregate vergeseling gepaard met 'n afname in kristalliniteit, met 'n toename in die oplossings verouderings tydperk wat verantwoordelik is vir die toename in viskositeit. Voorloper films is ook voorberei. Die voorloper vesels en films was onderworpe aan 'n verkolings proses om ‘n silikoon bevattende poreuse koolstof nanomaterial te bekom. Die verkoolde monsters is ontleed met SEM, FE-SEM, EDX, XRD, DSC, BET en TEM om die effek van die hoë temperatuur behandeling te kwantifiseer. Die verkolings proses het gelei tot ‘n groot massa verlies van die monsters en dus 'n afname in veseldeursnit. FE-SEM en TEM analise het getoon dat die poreuse morfologie nog teenwoordig was na die verkolings proses. Die resultante koolstof nanovesel en films bestaan hoofsaaklik uit koolstof, maar bevat ook silikoon en suurstof afkomstig van die PDMS. Daar is gevind dat die verkolings meganisme soortgelyk is aan dié van PAN, maar dat die PDMS ente die sikliseerings van PAN vertraag in die stabiliserings stap soos getoon deur DSC. Die resultate toon ook 'n soortgelyke onderskeid tussen die vesels en films. Die verskille kan toegeskryf word aan die nie-ewewig morfologie wat teenwoordig is in die geelektrospinde nanovesels. ‘n Moontlike toepassing van die poreuse koolstof nanovesels is ook ondersoek. Daar is gevind dat die sorpsie kapasiteit van die koolstof vesels hoër is as dié van ander koolstof-silika nanovesel membrane vir die soprsie van verskeie olies en organiese oplosmiddels. PAN-ent-PEO en PAN:PEO mengsels is ge-elektrospin en verkool as 'n alternatiewe metode vir poreuse koolstof nanovesel produksie. Die resultate het suksesvolle verkoling getoon waar porositeit van die koolstof nanovesel grootliks afhanklik was van die grootte van die opofferende PEO domeine. Die bal elektrospin proses het dieselfde tendense gewys met betrekking tot die PDMS inhoud en porositeit as die enkel naald tegniek, maar met 'n deurset van 36 keer vinniger as die enkel naald elektrospin tegniek. | af_ZA |
| dc.description.version | Masters | en_ZA |
| dc.embargo.terms | 2016-07-01 | en_ZA |
| dc.format.extent | ix, 117 pages : illustrations | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/97749 | en_ZA |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject.lcsh | Carbon nanofibers | en_ZA |
| dc.subject.lcsh | Carbonization | en_ZA |
| dc.subject.lcsh | Graft copolymers | en_ZA |
| dc.subject.lcsh | Electrospinning | en_ZA |
| dc.subject.lcsh | Porous silicon | en_ZA |
| dc.title | Facile method for producing silicon containing porous carbon nanofibres from amphiphilic copolymers and controlling precursor fibre morphology | en_ZA |
| dc.type | Thesis | en_ZA |