Thesis (PhD)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The synthesis of structured nanoparticles, in particular core/shells, IS of great
technological and economical importance to modem materials science. One of the
advantages of structured particles is that they can be synthesized with either a solid core
(albeit soft or hard) or a liquid core (of varying viscosity). This adds to the versatility of
structured particles and their relevance to a majority of industrial and commercial endapplications.
The synthesis of core/shell particles with liquid cores was investigated for the
effective impact modification of glassy amorphous polymers. Polybutyl acrylate was
chosen as the shell due to its rubbery nature. Hexadecane functioned as the core oil and
facilitated osmotic stability by being a suitable hydrophobe for the miniemulsion
synthesis. Polymer synthesis was preceded by the prediction of particle morphology by
using thermodynamic prediction models.
Core/shell particles with liquid cores were synthesized via miniemulsion
polymerization. This resulted in the direct introduction of core-oil and monomer into the
miniemulsion droplets. Polymerization was achieved in situ, resulting in the formation of
particles with the desired morphology. For additional strength, stability and matrix
mixing capabilities, methyl methacrylate (MMA) was grafted onto the initial core/shell
particles. The obtained morphology was in contradiction with the predicted morphology,
thus pointing to strong kinetic influences during the polymerization process. These
influences could be attributed to surface anchoring of polymer chains due to the initiator
(KPS) used, the establishment of the polymerization locus as well as the increase in
viscosity at the polymerization locus. To test these influences a surface-inactive
initiating species (AIBN) and an interfacial redox initiating species (cumyl
hydroperoxide/Fe/") were used. Use of the former resulted in the formation of solid
polymer particles due to homogeneous polymerization throughout the droplet, thus
leading to an inverse core/shell morphology as a result of thermodynamic considerations. The redox initiator promoted kinetic influences as a result of fast polymerization kinetics
at the droplet/water interface. This, as well as the increase in viscosity, facilitated the
production of core/shell particles.
To obtain core/shell particles with the desired size, the influence of surfactant
concentration was investigated. Capillary hydrodynamic fractionation (CHDF) was used
to determine the particle size of the initial core/shell particles as well as the size of the
MMA-grafted core/shell particles. The area stabilized per surfactant molecule was
calculated stoichiometrically and compared to "classical" miniemulsion results, i.e. data
generated from the synthesis of polymeric latexes in the presence of a hydrophobe, but at
a much lower hydrophobe:monomer ratio than was used here. The influence of methanol
as well as the possibility of scaling-up the process was also investigated.
The study was further expanded to the investigation of living miniemulsion
polymerization techniques to control the molecular architecture of synthesized core/shell
latexes. The influence of different RAFT agents, initiators and monomers were
investigated on the core/shell formation properties of the investigated systems. The
combined effects of establishing the polymerization locus as well as increased
polymerization kinetics, thus increasing the viscosity at the polymerization locus, lead to
the successful formation of liquid- filled core/shell particles.
To conclude, the ability of the synthesized core/shell particles to induce impact
modification in glassy amorphous polymers was investigated. Results showed that
incorporation of these particles could effectively modify the intrinsic properties of the
investigated polymers, resulting in a brittle-to-ductile transition. Improved impact results
of the investigated glassy matrix were obtained. Keywords: core/shell, liquid-filled, RAFT, miniemulsion, impact modification / AFRIKAANSE OPSOMMING: Die sintese van gestruktureerde nano-partikels, meer spesifiek kern/skil partikels, is
van onskatbare tegnologiese en ekonomiese belang vir moderne materiaalkunde. Een van
die voordele van hierdie tipe partikels is dat sintese kan geskied met 'n soliede kern (hard
of sag) of vloeistofkern (met wisselende viskositeit). Dit dra by tot die veelsydigheid van
gestruktureerde partikels en dus tot grootskaalse aanwending in industriële en
kommersiële toepassings.
Die sintese van kern/skiI partikels met vloeistofkerne is ondersoek met die oog op
effektiewe slagsterkte modifikasie van glasagtige amorfe polimere. Polibutielakrilaat is
gekies as skil-polimeer op grond van sy rubberige voorkoms. Heksadekaan moes
funksioneer as die kern-olie, maar het ook bykomende osmotiese stabiliteit verleen
tydens die miniemulsie-polimerisasie proses. Dit is as gevolg van die gepaste
hidrofobiese eienskappe van heksadekaan. Polimeer sintese is voorafgegaan deur die
voorspelling van partikel morfologie met behulp van termodinamies gebaseerde
voorspellingsmodelle.
Kern/skil partikels is gesintetiseer deur middel van 'n miniemulsie-polimerisasie
reaksie wat die direkte inkorporering van kern-olie en monomeer in die miniemulsiedruppel
teweeg bring. Polimerisasie vind in situ (lat. vir in die oorspronklike plek,
m.a.w. binne-in die druppel) plaas en lei tot die vorming van partikels met die gewenste
morfologie. Metielmetakrilaat is ge-ent op die oorspronklike kern/skil partikels om
addisionele sterkte, stabiliteit en vermenging met die matriks polimeer te bewerkstellig.
Die verkrygde morfologie is teenstrydig met die voorspelde morfologie, wat dus die
teenwoordigheid van sterk kinetiese invloede aandui. Hierdie invloede kan toegeskryf
word aan die oppervlak-aktiewe afsetter (KPS, kaliumpersulfaat) wat gebruik is, die
daarstelling van die polimerisasie lokus asook die toename in viskositeit by die lokus van
polimerisasie. Om hierdie invloede te toets is 'n oppervlak-onaktiewe afsetter (AIBN,
asobisisobutironitriel) en intervlak redoks-afsetter (kumielhidroperoksied/Pe'") gebruik. Gebruik van eersgenoemde het die vorming van soliede partikels teweeg gebring. Dit is
as gevolg van homogene polimerisasie in die druppel en dus die ontstaan van
omgekeerde kern/skiI partikels weens termodinamiese oorwegings. Die redoks-afsetter
het egter die kinetiese oorwegings bevoordeel as gevolg van vinnige polimerisasiekinetika
by die druppel/water intervlak. Dit, tesame met die toename in viskositeit, maak
die produksie van kern/skil partikels moontlik.
Vir die verkryging van kern/skiI partikels met die gewenste partikelgrootte is die
invloed van die seep konsentrasie ondersoek. CHDF (eng. capillary hydrodynamic
fractionation) is gebruik om die partikelgrootte van die oorspronklike kern/skiI partikels,
sowel as dié ge-ent met metielmetakrilaat, te bepaal. Die area gestabiliseer per
seepmolekule is bereken d.m.v. stoichiometrie en vergelyk met "klassieke" miniemuisie
data, d.i. data verkry deur die sintese van latekse in die teenwoordigheid van 'n
hidrofoob, maar teen 'n baie laer hidrofoob:monomeer-verhouding as wat hier gebruik is.
Die invloed van metanol, asook die moontlikheid om die reaksie op te skaal, is
ondersoek.
Die studie is verder uitgebrei om die invloed van lewende miniemulsie-polimerisasie
tegnieke in te sluit, om sodoende beheer uit te oefen oor die molekulêre argitektuur van
die gesintetiseerde latekse. Die invloed van verskeie RAFT (eng. reversible additionfragmentation
chain transfer) agente, afsetters en monomere op die kern/skiI
vormingsmoontlikhede van die bestudeerde stelsels, is ondersoek. Die gesamentlike
effek van die daarstelling van die polimerisasie lokus en dus die verhoging van die
viskositeit by die lokus, lei tot die suksesvolle vorming van vloeistof-gevulde kern/skiI
partikels. Laastens is die invloed van die gesintetiseerde kern/skil partikels op die slagsterkte
van glasagtige amorfe polimere ondersoek. Resultate dui daarop dat die insluiting van
hierdie partikels kan lei tot die effektiewe verandering van die intrinsieke eienskappe van
die bestudeerde polimere, en dus 'n oorgang van bros na rekbaar kan veroorsaak. 'n Verbetering in die slagsterkte resultate van die bestudeerde glasagtigte matriks is ook
waargeneem.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53609 |
| Date | 12 1900 |
| Creators | Van Zyl, A. J. P. (Andries Jakobus Petrus) |
| Contributors | Klumperman, B., Sanderson, R. D., Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 167 p. : ill. |
| Rights | Stellenbosch University |
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