Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Physically crosslinked thermo-responsive hydrogel nanofibres with tunable hydrophobicity based on poly(N-isopropyl acrylamide)-graft-poly(dimethyl siloxane)
Thesis (MSc)--Stellenbosch University, 2019.
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | en_ZA |
| Published: |
2019
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867613958978928640 |
|---|---|
| access_status_str | Open Access |
| author | Kuyler, Gestél Christine |
| author2 | Mallon, Peter |
| author_browse | Kuyler, Gestél Christine Mallon, Peter |
| author_facet | Mallon, Peter Kuyler, Gestél Christine |
| author_sort | Kuyler, Gestél Christine |
| collection | Thesis |
| description | Thesis (MSc)--Stellenbosch University, 2019. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/106982 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:44:25.612Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2019 |
| publishDateRange | 2019 |
| publishDateSort | 2019 |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/106982 Physically crosslinked thermo-responsive hydrogel nanofibres with tunable hydrophobicity based on poly(N-isopropyl acrylamide)-graft-poly(dimethyl siloxane) Kuyler, Gestél Christine Mallon, Peter Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. Nanogels Colloids Electrospinning Crosslinked polymers UCTD Nanofibers Thesis (MSc)--Stellenbosch University, 2019. ENGLISH ABSTRACT: A series of novel physically crosslinked amphiphilic hydrogels based on poly(N-isopropyl acrylamide)-graft-poly(dimethyl siloxane) (PNIPAM-g-PDMS) was synthesized using the simple macromonomer grafting-through technique. The hydrogel materials proved to be both water-insoluble and thermo-responsive. It was shown that the PDMS grafts produce physically crosslinked polymer networks due to intra- and interpolymer hydrophobic interactions of the PDMS side-chains. Structural elucidation and copolymer composition were determined by ATR-FTIR and 1H-NMR spectroscopy. 1H-NMR confirmed the macromonomer incorporation which correlated well with the feed ratios of each reaction. Chromatographic separation by HPLC revealed that the samples consisted of a PNIPAM homopolymer and PNIPAM-g-PDMS copolymer fraction. It was noted that the homopolymer fraction diminished with increased PDMS macromonomer in the feed. Increased PDMS content resulted in longer retention times during analysis which related to the increased hydrophobicity of the copolymers as a function of PDMS content. Molecular weight determination of these amphiphilic copolymers proved to be challenging. After analysis on different SEC solvent systems, AF4 allowed the determination of molecular weights ranging between 53 000 and 280 000 g/mol with dispersities of 1.1 to 1.8. The analytical obstacles confirmed the highly amphiphilic nature of these copolymers. The sufficiently high molecular weights and physical crosslinking of the copolymer systems allowed for solution processing from a common solvent. Hydrogel microfibres were fabricated by the electrospinning technique. An array of analytical techniques was utilized to characterize and analyse the copolymers in both thin film and microfibre form. Varying the amount of PDMS incorporated as well as the length of the PDMS side-chains had an observable effect on the physical properties of the material. This was most notable on the swelling of the hydrogel materials, but the relationship between the PDMS content and the lower critical solution temperature (LCST) of the copolymer hydrogels was more complex. Both the film and fibre form of all copolymers exhibited reversible thermo-responsive behaviour in aqueous solution. All samples underwent a phase transition at a specific LCST value. This LCST value was identified by a change from optically transparent to opaque and deswelling of the hydrogel material. PDMS incorporation resulted in a lowered LCST for all copolymers in film and fibre form compared to PNIPAM homopolymer, yet no definitive trend could be established. Conversely, increased PDMS content resulted in reduced equilibrium swelling. In the form of films, the low PDMS content materials swelled significantly in water reaching 50% saturation within 10 to 15 minutes. Microfibres exhibited rapid dimensional swelling, where the 2.9 mol.% 5 000 g/mol PDMS sample reached 115% swelling within 2 minutes. The stability of the materials in water and high humidity environments increased with increasing PDMS content. The films mostly remained structurally stable after repeated swelling cycles. The fibres, however, lost their individual fibrous structure after deswelling. The effect of PDMS incorporation was investigated by calculating the apparent crosslink density. It was shown that shorter PDMS side-chains resulted in a sharp initial increase in apparent crosslink density, after which more gradual increase occurred as a function of PDMS content. AFRIKAANS OPSOMMING: ‘n Reeks unieke amfifiliese hidrogels gebaseer op poli(N-isopropiel akrilamied)-ent-poli(dimetielsiloksaan) (PNIPAM-ent-PDMS) is gesintetiseer deur middel van die makromonomeer “ent-deur”-tegniek. Die resulterende hidrogel materiaal is beide water-onoplosbaar en temperatuur-responsief. Die insluiting van die PDMS makromonomeer het gelei tot ‘n fisies kruisverbinde netwerk wat ontstaan as gevolg van die hidrofobiese intra- en interpolimeer interaksies tussen die hidrofobiese PDMS sykettings. Strukturele bevestiging en ko-polimeer komposisie is bepaal deur middel van ATR-FTIR en 1H-KMR spektroskopie. 1H-KMR het die makromonomeer inkorporasie, asook die goeie korrelasie tussen die voer verhouding van elke reaksie en die werklik geïnkorporeerde hoeveelheid, bevestig. Kromatografiese skeiding deur middel van HPLC het aangedui dat die monsters uit ‘n PNIPAM homo-polimeer en PNIPAM-ent-PDMS ko-polimeerfraksie bestaan. ‘n Afname in die homo-polimeerfraksie met toename in PDMS makromonomeerinhoud is waargeneem. ‘n Toename in die PDMS inhoud het gelei tot langer retensietye tydens analiese wat ooreenstem met die toenemende hidrofobisiteit van die ko-polimere as ‘n funksie van PDMS inhoud. Die bepaling van die molekulêre massa van hierdie ko-polimere was uitdagend. Na vele analises in verskeie SEC sisteme met verskillende oplosmiddels, kon die molekulêre massa deur middel van AF4 bepaal word en het gewissel tussen 53 000 en 280 000 g/mol met dispersiteite van tussen 1.1 tot 1.8. Die analitiese struikelblokke wat ondervind is, het die hoogs amfifiliese geaardheid van hierdie ko-polimere bevestig. Die hoë molekulêre massa en die fisiese kruisverbinde natuur van die ko-polimeersisteem het toegelaat vir oplossing in ‘n algemene oplosmiddel. Hidrogel mikro-vesels is deur middel van die elekrospintegniek vervaardig. ‘n Verskeidenheid van analitiese tegnieke was onderneem om die ko-polimere in beide film en vesel vorm te analiseer en te karakteriseer. Wisselende hoeveelhede van geïnkorporeerde PDMS, asook die lengte van die PDMS sy-kettings het die fisiese eienskappe van die materiaal waarneembaar beïnvloed. Die effek van die PDMS inhoud was mees oplettend ten opsigte van die materiaal se water-opname eienskappe, alhoewel die effek van PDMS en die laer kritiese oplossings temperatuur (LKOT) van hierdie termo-responsiewe ko-polimeer hidrogels meer kompleks was. Beide die film en die vesel vorm van al die ko-polimere het omkeerbare termo-responsiwiteit vertoon in ‘n waterige oplossing. Al die monsters het by ‘n spesifieke LKOT waarde ‘n fase transisie ondergaan. Die LKOT waarde was geïdentifiseer deur ‘n verandering van opties deursigtig na ondeursigtig, asook deswelling van die hidrogel. PDMS inkorporasie het gelei tot ‘n laer LKOT waardes vir al die ko-polimere in beide film en vesel vorm in vergelyking met die PNIPAM homo-polimeer, alhoewel geen definitiewe tendens bevestig kon word nie. Aan die ander kant het verhoogde PDMS inhoud gelei tot verlaagde ekwilibrium swelling. In die vorm van films, het die lae PDMS inhoud monsters opmerkbare swelling in water vertoon en binne 10 tot 15 min 50% versadigheid bereik. Die mikro-vesels het vinnige dimensionele swelling vertoon, waar die vesels van die 2.9 mol.% 5 000 g/mol PDMS monster 115% swelling bereik het binne 2 min. Die stabiliteit van die vesels in water en hoë humiditeit omgewings, het toe geneem met toenemende PDMS inhoud. Die films het meestal hul strukturele stabiliteit behou na herhaalde swelling siklusse. Die vesels het wel hul individuele veselagtige struktuur verloor na deswelling. Die effek van PDMS inkorporasie was ondersoek deur die oënskynlike kruisverbinde digtheid te bereken. Dit het getoon dat korter PDMS sy-kettings tot ‘n skerp aanvanklike toename in die oënskynlike kruisverbinde digtheid gelei het, waarna ‘n meer geleidelike toename as ‘n funksie van PDMS inhoud plaas gevind het. Langer PDMS sy-kettings het groot inkrementele toename in die oënskynlike kruisverbinde digtheid as a funksie van PDMS inhoud vertoon. Opmerklike verskille in die swelling en die LKOT van dieselfde ko-polimere in die vorm van films en geëlektrospinde vesels het bestaan wanneer hierdie twee vorme van dieselfde materiaal vergelyk word. Hierdie verskille was toegeskryf aan die geïnkorporeerde hoeveelheid PDMS asook die verskille in die soliede-fase morfologie wat deur verskillende voorbereidings metodes geïnduseer word. Dit was bewys dat hierdie slim hidrogels instaat was om op omliggende temperatuur variasies te reageer terwyl dit ook die opsie vir verstelbare hidrofobisiteit bied. Masters 2019-11-26T09:03:35Z 2019-12-11T06:41:37Z 2021-05-31T03:00:10Z 2019-12 Thesis http://hdl.handle.net/10019.1/106982 en_ZA xviii, 107 pages : illustrations application/pdf |
| spellingShingle | Nanogels Colloids Electrospinning Crosslinked polymers UCTD Nanofibers Kuyler, Gestél Christine Physically crosslinked thermo-responsive hydrogel nanofibres with tunable hydrophobicity based on poly(N-isopropyl acrylamide)-graft-poly(dimethyl siloxane) |
| title | Physically crosslinked thermo-responsive hydrogel nanofibres with tunable hydrophobicity based on poly(N-isopropyl acrylamide)-graft-poly(dimethyl siloxane) |
| title_full | Physically crosslinked thermo-responsive hydrogel nanofibres with tunable hydrophobicity based on poly(N-isopropyl acrylamide)-graft-poly(dimethyl siloxane) |
| title_fullStr | Physically crosslinked thermo-responsive hydrogel nanofibres with tunable hydrophobicity based on poly(N-isopropyl acrylamide)-graft-poly(dimethyl siloxane) |
| title_full_unstemmed | Physically crosslinked thermo-responsive hydrogel nanofibres with tunable hydrophobicity based on poly(N-isopropyl acrylamide)-graft-poly(dimethyl siloxane) |
| title_short | Physically crosslinked thermo-responsive hydrogel nanofibres with tunable hydrophobicity based on poly(N-isopropyl acrylamide)-graft-poly(dimethyl siloxane) |
| title_sort | physically crosslinked thermo responsive hydrogel nanofibres with tunable hydrophobicity based on poly n isopropyl acrylamide graft poly dimethyl siloxane |
| topic | Nanogels Colloids Electrospinning Crosslinked polymers UCTD Nanofibers |
| url | http://hdl.handle.net/10019.1/106982 |
| work_keys_str_mv | AT kuylergestelchristine physicallycrosslinkedthermoresponsivehydrogelnanofibreswithtunablehydrophobicitybasedonpolynisopropylacrylamidegraftpolydimethylsiloxane |