Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: In this study, the use of surfactants, plate-like clays, organophilic molecules and side-chain
crystallinity was investigated for their impact on the transport mechanisms of water vapour
through polymer films. A model polymer latex, poly(styrene-co-butyl acrylate), was prepared using miniemulsion
polymerization. Three different types of surfactants, sodium dodecyl benzene sulfonate (SDBS, an
anionic surfactant), octyl phenol ethoxylate (OPE, a nonionic surfactant) and dodecyl ammonium-
3-butenoate (DA3B, a reactive surfactant) were used to stabilize the latex. Films were prepared
from the resultant latices and their water vapour sorption behaviour determined across a water
vapour partial pressure range of 0.1 to 0.9. Sigmoidal kinetic behaviour was seen for all three
films, with the DA3B stabilized film exhibiting high diffusion coefficients compared to films
stabilized with SDBS and OPE. The thermodynamic behaviour of the films differed and was
dependent on the reactivity of the surfactant. SDBS and OPE stabilized films exhibited Flory-
Huggins behaviour, while the DA3B stabilized film followed Henry’s Law. Despite significant
differences in terms of these properties, the permeability coefficients were similar for the three
films across the water vapour partial pressure range evaluated.
The impact of sodium montmorillonite (Na-MMT) clay and an organophilic modifier, 2-
acrylamido-2-methylpropanesulfonic acid (AMPS), on the water vapour sorption properties of
poly(styrene-co-butyl acrylate) was evaluated. These polymer clay nanocomposites (PCNs) were
synthesized using miniemulsion polymerization. The resultant latex films were characterized and
used for water vapour sorption analyses. It was shown that complete exfoliation of the Na-MMT
was necessary to minimize the equilibrium water vapour uptake. Even when Na-MMT was
completely exfoliated, the amount of water vapour sorbed by the PCN was high and this was
attributed to the hydrophilic nature of the clay. Using a least squares regression fit, good
correlation was obtained between the experimental isotherms and the sorption behaviour
predicted by the Dual Mode Sorption model which was originally developed for polymers in their
glassy state. The impact of side chain crystallinity on the water vapour sorption properties of
poly(methyl methacrylate-co-octadecyl acrylate) was evaluated. These random
copolymers containing increasing amounts of octadecyl acrylate, and therefore increasing
degrees of crystallinity, were synthesized using solvent polymerization. Although it could
be expected that side chain crystallinity would be the main contributing factor resulting in
a reduction in the diffusion coefficient, it was shown that the methyl group on the á-
carbon of the vinyl group in the methacrylate reduced the diffusion to a greater extent
through the increased stiffness of the polymer backbone. This was also reflected in
poly(methyl methacrylate-co-octadecyl acrylate) having a greater activation energy for
diffusion compared to polyoctadecyl acrylate. / AFRIKAANSE OPSOMMING: In hierdie studie is die gebruik van sepe, plaatagtige kleie, organofiliese molekules en sykettingkristalliniteit
ondersoek ten opsigte van die impak op transportmeganismes van
waterdamp deur polimeerfilms.
‘n Model polimeerlateks, polistireen-ko-butielakrilaat, is voorberei deur miniemulsiepolimerisasie.
Drie verskillende tipes sepe, natriumdodekielbenseensulfonaat (NDBS, ‘n anioniese seep),
oktielfenoletoksilaat (OFE, ‘n nie-ioniese seep) en dodekielammonium-3-butenoaat (DA3B, ‘n
reaktiewe seep) is gebruik om die lateks te stabiliseer. Films is van die resultante lateks voorberei
en hul waterdampsorpsie –eienskappe oor die parsiële waterdampdrukreeks van 0.1 tot 0.9
bepaal. Sigmodale kinetiese gedrag is vir al drie films waargeneem, met die DA3B gestabiliseerde
film wat hoër diffusiekoëffisiënte toon in vergelyking met die films wat met NDBS en OFE
gestabiliseer is. Die termodinamiese gedrag van die films het verskil en was afhanklik van die
reaktiwiteit van die seep. NDBS en OFE gestabiliseerde films het Flory-Huggins gedrag getoon,
terwyl die DA3B gestabiliseerde film Henry se Wet gevolg het. Ten spyte van die beduidende
verskille ten opsigte van hierdie eienskappe was die permitiewe koëffisiënte soortgelyk vir die
drie films regoor die parsiële waterdampdrukreeks wat vir die evaluasie gebruik is.
Die impak van natriummontmorilloniet (Na-MMT) klei en ‘n organofiliese modifiseerder, 2-
akrielamido-2-metielpropaansulfoonsuur (AMPS), op die waterdampsorpsie-eienskappe van
polistireen-ko-butielakrilaat is geevalueer. Hierdie polimeer-klei-nanosaamgesteldemateriale
(PKNe) is gesintetiseer deur van miniemulsiepolimerisasie gebruik te maak. Die resultante
lateksfilms is gekarakteriseer en gebruik vir waterdampsorpsie analises. Daar is getoon dat
algehele afskilfering van die Na-MMT nodig was om die ewewigswaterdampopname te
minimaliseer. Selfs wanneer Na-MMT algeheel afgeskilfer was, was die hoeveelheid waterdamp
gesorbeer deur die PKN hoog en kan dit toegeskryf word aan die hidrofiliese karakter van die klei.
Deur ‘n kleinste-kwadrate-regressie passing te doen, is ‘n goeie korrelasie verkry tussen die
eksperimentele isoterme en die sorpsie gedrag voorspel deur die Dubbelmodussorpsiemodel wat
oorspronklik ontwikkel is vir polimere in hul glasagtige toestand. Die impak van sykettingkristalliniteit op die waterdampsorpsie-eienskappe van
poli(metielmetakrilaat-ko-oktadekielakrilaat) is ondersoek. Hierdie ewekansige kopolimere wat
toenemende hoeveelhede oktadekielakrilaat, en dus toenemende grade van kristalliniteit bevat,
is gesintetiseer deur van oplossingspolimerisasie gebruik te maak. Alhoewel dit te wagte was dat
sykettingkristalliniteit die hoofbydraende faktor is in die redusering van die diffusiekoeffisiente, is
daar getoon dat die metielgroep aan die α-koolstof van die vinielgroep in die metakrilaat die
diffusie tot 'n groter mate gereduseer het deur toenemende styfheid van die polimeerrugraat. Dit
is ook gereflekteer deur poli(metielmetakrilaat-ko-oktadekielakrilaat) wat 'n groter
aktiveringsenergie vir diffusie het in vergelyking met polioktadekielakrilaat.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17890 |
| Date | 12 1900 |
| Creators | Cloete, Valeska |
| Contributors | Pasch, H., Hartmann, P. C., 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 | Unknown |
| Type | Thesis |
| Rights | Stellenbosch University |
Page generated in 0.0022 seconds