Polymer magnetic composite (PMC) nanoparticles have gained a large attention due to their potential use in several biomedical applications from biomedical to engineering field. Among the different heterogeneous polymerization techniques that are generally used to prepare hybrid polymer particles, miniemulsion polymerization is proved to be an efficient one. The occurrence of preferential droplet nucleation in case of miniemulsion polymerization results in a 1:1 copy of monomer droplets to the polymer particles and such a mechanistic pathway offers a suitable environment for the preparation of hybrid polymer nanoparticles in the range between 50 to 500 nm. The surfactant in miniemulsoin plays a significant role to stabilize the droplets/particles and also in the encapsulation of nanoparticles. In the present study, a new class of surfactant, called amphiphilic ionic liquid, has been employed in the field of miniemulsion. The amphiphilic ionic liquid has amazing ability to impart surface tunable characteristics to the polymer particles when present on the surface of the particles. Thus the aim of the present work is to synthesize polymer magnetic composite nanoparticles with good colloidal stability, high content of magnetic nanoparticles as well as the chance for further surface functionality. Such magnetic nanoparticles may find applications in various fields. At first, the aim of the work was to establish a suitable recipe with ionic liquid as surfactant for the execution of miniemulsion polymerization. Monodisperse polystyrene nanoparticles were possible to be synthesized reproducibly. The established recipe was utilized to carry out the synthesis of PMC nanoparticles. Iron oxide (Fe3O4) was taken as magnetic nanoparticles (MNP) and it was hydrophobized with oleic acid to disperse in styrene. The concentration of feed MNP was varied to observe its influence on the characteristics of PMC nanoparticles. Stable dispersion of magnetic polystyrene particles was possible to be synthesized up to 8 wt% feed MNP. But feeding 12 wt% MNP resulted in the development of large amount of coagulum associated with instability in the dispersion. TGA investigation confirmed a significantly lower MNP content (8.2 wt%) of the composite compared to the feed amount. TEM investigation showed inhomogeneous distribution of MNP among polystyrene particles and agglomeration of MNP was observed on the surface of polystyrene particles. Considering the inability of the single step miniemulsion polymerization for the preparation of high MNP content polymer particles, it was aimed to find a new strategy which can produce such material. Inspired from the affinity of carboxylic acid group towards the surface of MNP, it was aimed to synthesize carboxyl functionalized polystyrene which was expected to improve the interaction between polymer and magnetic nanoparticles. For this purpose, RAFT mediated miniemulsion polymerization was performed in presence of a carboxyl functionalized chain transfer agent (CTA). The colloidal stability was much better compared to the previous case of non-RAFT experiments. From a feed MNP of 8 wt%, a high final MNP content up to ~27 wt% could be achieved and all the dispersions were highly stable. The higher MNP content in the final composites compared to the feed ratio was a result of the low monomer conversion and could be adjusted by a proper tuning of AIBN to CTA mole ratio. Another significant influence of the carboxyl functionalized CTA was observed on the morphology of the composite nanoparticles. The MNP were distributed homogeneously among the PS particles. Regarding the dispersion of MNP in the individual polystyrene particles, it was observed that higher amount of CTA resulted in a homogeneous dispersion of MNP whereas higher amount of initiator ended up producing asymmetric Janus like morphology. Apart from that, due to the involvement of CTA in the polymerization, much lower molecular weight of the polystyrene chains was developed compared to the free radical process and the molecular weight distribution of PS in the composite nanoparticles became much narrower through the RAFT polymerization. Thus a relatively good control over the polymerization process was achieved through RAFT polymerization which was confirmed by a nearly linear increase of molecular weight (Mn) with time of polymerization and thus, monomer conversion. In the recipe of miniemulsion, costabilizer plays an important role to retard monomer diffusion from smaller to larger droplets. Hexadecane, being the most frequently used costabilizer for miniemulsion, has been employed in this study so far. But its volatile nature restricts its utilization in several applications. For the replacement of hexadecane, a carboxyl functionalized polystyrene is employed as a costabilizer as well as a macro CTA in miniemulsoin polymerization of styrene. For this purpose, low molecular weight carboxyl bi-functionalized polystyrene (9000 g/mole) was synthesized by thermal bulk RAFT polymerization. The carboxylated polystyrene worked successfully as a costabilizer in miniemulsion and molecular weight investigation confirmed the integration of the carboxyl functionalized macro CTA into the developing polystyrene chain via RAFT polymerization. This strategy was employed successfully to synthesize stable dispersion of PMC nanoparticles with a reasonable content of MNP in the system. A homogeneous morphology was observed regarding the distribution of MNP among the polystyrene particles. The strategy of using macro CTA as costabilizer can be utilized to synthesize various functional copolymers with control architecture without any added monomer and CTA in the system. Moreover, presence of functionality within the monomer droplets can be effective to encapsulate several nanomaterials using miniemulsion polymerization.

Polymerverkapselte magnetische Nanopartikel versprechen, in der Zukunft sehr erfolgreich bei Anwendungen in der Biologie und der Medizin eingesetzt werden zu können z. B. in der Krebstherapie und als Kontrastmittel bei der magnetischen Kernspinresonanztomographie. Diese Arbeit zeigt, dass durch die interdisziplinäre Kombination verschiedener Techniken Herstellungsverfahren und Eigenschaften solcher Partikel verbessert werden können. <br /> <br /> Unter Miniemulsionen versteht man wässrige Dispersionen relativ stabiler Öltröpfchen, zwischen 30 und 50 nm Größe. Ein Nanometer (nm) ist der 1.000.000.000ste Teil eines Meters. Ein Haar ist ungefähr 60.000 Nanometer breit.<br /> <br /> Hergestellt werden Miniemulsionen durch Scherung eines Systems bestehend aus Öl, Wasser, Tensid (Seife) und einer weiteren Komponente, dem Hydrophob, das die Tröpfchen stabilisieren soll. Die Polymerisation von Miniemulsionen ermöglicht die Verkapselung anorganischer Materialen z. B. magnetischer Teilchen oder Gadolinium-haltiger Komponenten. Zu Optimierung des Verkapselung, ist es notwendig, die richtige Menge eines geeigneten Tensids zu finden. <br /> <br /> Die magnetischen polymerverkapselten Nanopartikel, die in einer wässrigen Trägerflüssigkeit dispergiert sind, zeigen in Abhängigkeit von Partikelgröße, Zusammensetzung, elektronischer Beschaffenheit, etc. ein sogenanntes superpara- oder paramagnetisches Verhalten. Superpara- oder paramagnetisches Verhalten bedeutet, dass die Flüssigkeiten in Anwesenheit äußerer Magnetfeldern ihre Fließfähigkeit beibehalten. Wenn das Magnetfeld entfernt wird, haben sie keine Erinnerung mehr daran, unter dem Einfluss eines Magnetfeldes gestanden zu haben, d. h., dass sie nach Abschalten des Magnetfeldes selbst nicht mehr magnetisch sind. <br /> <br /> Die Vorteile des Miniemulsionsverfahrens sind der hohe Gehalt und die homogene Verteilung magnetischer Teilchen in den einzelnen Nanopartikeln. Außerdem ermöglicht dieses Verfahren nanostrukturierte Kompositpartikel herzustellen, wie z. B polymerverkapselte Nanopartikel mit Nanoschichten bestehend aus magnetischen Molekülen. / Combining the magnetic properties of a given material with the tremendous advantages of colloids can exponentially increase the advantages of both systems. This thesis deals with the field of magnetic nanotechnology. Thus, the design and characterization of new magnetic colloids with fascinating properties compared with the bulk materials is presented. <br /> <br /> Ferrofluids are referred to either as water or organic stable dispersions of superparamagnetic nanoparticles which respond to the application of an external magnetic field but lose their magnetization in the absence of a magnetic field. <br /> <br /> In the first part of this thesis, a three-step synthesis for the fabrication of a novel water-based ferrofluid is presented. The encapsulation of high amounts of magnetite into polystyrene particles can efficiently be achieved by a new process including two miniemulsion processes. The ferrofluids consist of novel magnetite polystyrene nanoparticles dispersed in water which are obtained by three-step process including coprecipitation of magnetite, its hydrophobization and further surfactant coating to enable the redispersion in water and the posterior encapsulation into polystyrene by miniemulsion polymerization. It is a desire to take advantage of a potential thermodynamic control for the design of nanoparticles, and the concept of &quot;nanoreactors&quot; where the essential ingredients for the formation of the nanoparticles are already in the beginning. The formulation and application of polymer particles and hybrid particles composed of polymeric and magnetic material is of high interest for biomedical applications. Ferrofluids can for instance be used in medicine for cancer therapy and magnetic resonance imaging.<br /> <br /> Superparamagnetic or paramagnetic colloids containing iron or gadolinium are also used as magnetic resonance imaging contrast agent, for example as a important tool in the diagnosis of cancer, since they enhance the relaxation of the water of the neighbouring zones. New nanostructured composites by the thermal decomposition of iron pentacarbonyl in the monomer phase and thereafter the formation of paramagnetic nanocomposites by miniemulsion polymerization are discussed in the second part of this thesis. In order to obtain the confined paramagnetic nanocomposites a two-step process was used. In the first step, the thermal decomposition of the iron pentacarbonyl was obtained in the monomer phase using oleic acid as stabilizer. In the second step, this iron-containing monomer dispersion was used for making a miniemulsion polymerization thereof. <br /> <br /> The addition of lanthanide complexes to ester-containing monomers such as butyl acrylate and subsequent polymerization leading to the spontaneous formation of highly organized layered nanocomposites is presented in the final part of this thesis. By an one-step miniemulsion process, the formation of a lamellar structure within the polymer nanoparticles is achieved. The magnetization and the NMR relaxation measurements have shown these new layered nanocomposites to be very apt for application as contrast agent in magnetic resonance imaging.

Miniemulsionen bestehen aus zwei miteinander nicht mischbaren Flüssigkeiten, von der die eine in Form kleiner Tröpfchen fein in der anderen verteilt (dispergiert) ist. Miniemulsionströpfchen sind mit Durchmessern von ungefähr 0,1 Mikrometer kleiner als herkömmliche Emulsionen und können u. a. als voneinander unabhängige Nanoreaktoren für chemische Reaktionen verwendet werden. Man unterteilt sie in direkte Miniemulsionen, in denen ein Öl in Wasser dispergiert ist, und inverse Miniemulsionen, in denen Wasser in Öl dispergiert wird. In dieser Arbeit wird das besondere chemische und physikalische Verhalten solcher Miniemulsionen unter dem Einfluß von Mikrowellenstrahlung untersucht. Dabei werden sowohl für Öl-in-Wasser als auch für Wasser-in-Öl-Miniemulsionen grundlagenwissenschaftliche Entdeckungen beschrieben und durch neue Modelle erklärt. Der praktische Nutzen dieser bislang unbeschriebenen Effekte wird durch ingenieurwissenschaftliche Anwendungsbeispiele im Bereich der Polymerchemie verdeutlicht. <br><br> 1. Polymerisation mit "überlebenden Radikalen" (Surviving Radical Polymerization)<br> Für die Herstellung von sog. Polymerlatizes (Kunststoffdispersionen, wie sie u. a. für Farben verwendet werden) aus direkten Styrol-in-Wasser Miniemulsionen werden die Styroltröpfchen als Nanoreaktoren verwendet: Sie werden mit Hilfe von Radikalen durch eine Kettenreaktion zu winzigen Polymerpartikeln umgesetzt, die im Wasser dispergiert sind. Ihre Materialeigenschaften hängen stark von der Kettenlänge der Polymermoleküle ab. In dieser Arbeit konnten durch den Einsatz von Mikrowellenstrahlung erstmals große Mengen an Radikalen erzeugt werden, die jeweils einzeln in Tröpfchen (Nanoreaktoren) auch noch lange Zeit nach dem Verlassen der Mikrowelle überleben und eine Polymerisationskettenreaktion ausführen können. Diese Methode ermöglicht nicht nur die Herstellung von Polymeren in technisch zuvor unerreichbaren Kettenlängen, mit ihr sind auch enorm hohe Umsätze nach sehr kurzen Verweilzeiten in der Mikrowelle möglich – denn die eigentliche Reaktion findet außerhalb statt. Es konnte gezeigt werden, dass durch Einsatz von Zusatzstoffen bei unvermindert hohem Umsatz die Polymerkettenlänge variiert werden kann. Die technischen Vorzüge dieses Verfahrens konnten in einer kontinuierlich betriebenen Pilotanlage nachgewiesen werden. <br><br> 2. Aufheizverhalten inverser Miniemulsionen in Mikrowellenöfen<br> Das Aufheizverhalen von Wasser-in-Öl Miniemulsionen mit kleinen Durchmessern durch Mikrowellen ist überaus träge, da sich nur das wenige Wasser in den Tröpfchen mit Mikrowellen aufheizen lässt, das Öl jedoch kaum. Solche Systeme verhalten sich gemäß der "Theorie des effektiven Mediums". Werden aber etwas größere Tröpfchen im Mikrometerbereich Mikrowellen ausgesetzt, so konnte eine wesentlich schnellere Aufheizung beobachtet werden, die auf eine Maxwell-Wagner-Grenzflächenpolarisation zurückgeführt werden kann. Die Größenabhängigkeit dieses Effekts wurde mit Hilfe der dielektrischen Spektroskopie quantifiziert und ist bislang in der Literatur nie beschrieben worden. Zur genauen Messung dieses Effekts und zu seiner technischen Nutzung wurde ein neuartiges Membranverfahren für die Herstellung von großen Miniemulsionströpfchen im Mikrometerbereich entwickelt. <br><br> 3. Herstellung von Kompositpolymeren für Mikrowellenanwendungen<br> Um die untersuchte Maxwell-Wagner-Grenzflächenpolarisation technisch nutzen zu können, wurden als dafür geeignete Materialien Kompositpolymere hergestellt. Das sind Kunststoffe, in denen winzige Wassertropfen oder Keramikpartikel eingeschlossen sind. Dazu wurden neuartige Synthesewege auf der Grundlage der Miniemulsionstechnik entwickelt. Ihr gemeinsames Ziel ist die Einschränkung der üblicherweise bei Polymerisation auftretenden Entmischung: In einem Verfahren wurde durch Gelierung die Beweglichkeit der emulgierten Wassertröpfchen eingeschränkt, in einem anderen wurde durch das Einschließen von Keramikpartikeln in Miniemulsionströpfchen die Entmischung auf deren Größe beschränkt. Anwendungen solcher Kompositpolymere könnten künstliche Muskeln, die Absorption von Radarstrahlung, z. B. für Tarnkappenflugzeuge, oder kratzfeste Lacke sein.<br><br>Bei diesen Experimenten wurde beobachtet, daß sich u. U. in der Miniemulsion große Tröpfchen bilden. Ihr Ursprung wird mit einer neuen Modellvorstellung erklärt, die die Einflüsse auf die Stabilität von Miniemulsionen beschreibt. / Miniemulsions are composed of two immiscible fluids. One of which is distributed as small droplets (dispersed) in the other one. Having diameters of down to 0.05 micrometers, droplets of miniemulsions are smaller than those of conventional emulsions. Among other applications, they can be employed as independent nano-reactors for chemical reactions. They are subdivided in direct miniemulsions, for which an oil is dispersed in an aqueous phase, and inverse miniemulsions, for which water is dispersed in an oil phase. In this work, the specific chemical and physical behaviour of miniemulsions under the influence of microwave-radiation was investigated. For water-in-oil as well as for oil-in-water miniemulsions fundamental discoveries are described and explained by new models. The practical importance of these new effects is exemplified by applications in the field of polymer-chemistry. <br><br> 1. Polymerization with "surviving radicals"<br> For the production of so-called polymer-latices (dispersions of plastics, as they are used in paints and coatings) from direct styrene-in-water miniemulsions, the styrene-droplets can be considered as separate nano-reactors. Upon radical polymerization, they may be transformed to polymer particles dispersed in water in a 1:1 conversion. Their material properties strongly depend on the chain-length of the polymer molecules. In this work, using microwave radiation, for the first time great quantities of radicals could be generated that survive within the individual droplets (nano-reactors) even for a long time after leaving the microwave oven, carrying out polymerization. This method is suited for the production of polymers with great chain-lengths that cannot be obtained with other technically relevant methods. Moreover, it yields great conversion after very short residence-times in the microwave-oven: the actual reaction takes place outside of the oven. Employing additives allows the variation of chain-length at the same great net rates of conversion. The technical promises of this method could be demonstrated in a continuously operated pilot plant. <br><br> 2. Heating behaviour of inverse miniemulsions with microwave-radiation<br> The heating of water-in-oil miniemulsions with small droplets using microwaves is very slow, as only the water absorbs microwave-radiation and not the oil. The system behaves according to the "effective medium theory". If slightly larger droplets with diameters of about a micron are subjected to microwaves, they are being heated much more readily, which can be attributed to a Maxwell-Wagner-effect. The size-dependence of this effect has never been described in the literature. It could be quantified with dielectric spectroscopy. For the controlled production of big miniemulsion droples on the micron-scale and for the technical application of the size-dependence, a continuously operated membrane-emulsification device was developed. <br><br> 3. Production of composite polymers for microwave-applications<br> Suitable composite polymers were produced in order to technically exploit the size-dependence of the Maxwell-Wagner-effect. They may contain sub-micron sized water droplets or ceramic nanoparticles. For their synthesis, new strategies on the basis of miniemulsion-systems were developped, which avoid the usual phase-separation upon polymerization. In one approach, the mobility of the dispersed water droplets was limited through the gelation of the oil phase, in another approach phase separation of ceramic nanoparticles entrapped within miniemulsion droplets was restricted to the dimensions of the droplets. Applications of such composite polymers could be the development of artificial muscles, the absorption of radar radiation (e.g. for stealth applications) or scratch-resistant coatings.<br><br> In these experiments the existence of stable big droplets in miniemulsions was discovered. Their origin can be explained by a new model that describes the influences on miniemulsion stability.

La limitation de solvants toxiques halogénés dans les procédés de préparation de matériaux photoactifs est primordiale pour l’industrialisation des cellules solaires organiques. L’objectif de ce travail de thèse a été de préparer des nanoparticules composées de polymère π-conjugué (PCDTBT) et d’accepteur d’électron (PC71BM) dans l’eau ou en milieu alcool. Des particules composites (PCDTBT+ PC71BM) ontété synthétisées avec deux types de stabilisants : un tensio-actif anionique (SDS) et un copolymère à blocs P3HT-b-PEO, ainsi que sans stabilisant. L’intégration de ces nanoparticules dispersées en phase aqueuse dans la couche active de cellules solaires organiques a par exemple permis d’obtenir des rendements de l’ordre de1%. / The replacement of halogenated toxic solvents is fundamental in photoactive material processes to make the organic photovoltaic sector viable. Herein the use of nanoparticles made of π-conjugated polymer (PCDTBT) and electron-acceptor(PC71BM) was targeted in order to allow for instance the control of the phase separation between the two materials. Thus composite particles of PCDTBT and PC71BM have been synthesized using two kinds of stabilizers: an anionic surfactant (SDS) and a block copolymer P3HT-b-PEO, as well as without stabilizer. As an example such nanoparticles were integrated as active layer into photovoltaic device enabling a power conversion efficiency of 0.94% from aqueous based inks.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / Polymerization using the reversible addition-fragmentation chain transfer (RAFT) process affords a researcher control over the molecular weight and polydispersity of the final polymer. Research is being carried out globally, using heterogeneous RAFT systems, as these systems offer superior industrial possibilities. Many emulsion systems fail when incorporating RAFT agents due to phase separation and colloidal instability. Exchanging conventional emulsion polymerizations with predispersed polymerization systems (i.e. miniemulsions) has shown many improvements. Evidence of uncontrolled aqueous phase polymerization (i.e. not mediated by the RAFT process) has however been found. This behaviour is similar to polymerization in a conventional emulsion polymerization system, but is not expected in miniemulsion polymerization.

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.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: A new class of nanocolorants is described for the use as a colorant in hot-melt ink application for ink-jet printing technology. An inverse miniemulsion polymerization process was utilized successfully as a one-step encapsulation process to encapsulate the highly hydrophilic water-soluble fluorescent Rhodamine B dye (RhB) by the hydrophilic water-soluble poly(acrylamide) (PAAm). Three types of Rhodamine B-based nanocolorants, PAAm/RhB, crosslinked-PAAm/RhB and poly(AAm-co-Sty)/RhB, were synthesized using inverse miniemulsion polymerization. The PAAm/RhB nanocolorants exhibited solid dark nanoparticles morphology, while crosslinked-PAAm/RhB and poly(AAm-co-Sty)/RhB showed a core-shell type of morphology. The nanocolorants showed improved light and dye migration fastness as well as high thermal stability, especially, nanocolorants with core-shell morphology. The synthesis of polymerizable RhB-based nanocolorants is described. Poly(AAm-co-RhB) nanocolorants were successfully synthesized for the first time via inverse miniemulsion polymerization. RhB dye was first functionalized by esterification reaction to introduce an acrylate polymerizable group. The RhB-acrylate dye was copolymerized with AAm monomer in an inverse miniemulsion polymerization to produce nanocolorants with superior light and migration fastness. Crosslinked-poly(AAm-co-RhB) nanocolorants could be obtained based on the incorporation of a crosslinking agent. Poly(AAm-co-RhB) and crosslinked-poly(AAm-co-RhB) nanocolorants exhibited a morphology of dark solid and core-shell particles, respectively. In both nanocolorants, the RhB-acrylate dye was completely integrated by copolymerization into the polymer matrix, and by that, the dye migration was completely supressed. Both poly(AAm-co-RhB) and crosslinked-poly(AAm-co-RhB) nanocolorants showed high thermal stability as well as high Tg values. The syntheses of PAAm/RhB nanocolorants-based solid inks were carried out successfully via inverse miniemulsion polymerization. An in situ inverse miniemulsion polymerization, with the paraffin wax as the organic phase, was utilized in making a crosslinked-PAAm/RhB nanocolorants-based solid ink. A crosslinked-poly(AAm-co-RhB) nanocolorants-based solid ink was prepared by the direct mixing of the readymade crosslinked-PAAm/RhB nanocolorants (suspended in cyclohexane) with paraffin wax at temperature above the melting temperature of the wax until all the cyclohexane evaporated. The obtained solid inks appeared as a solid homogenous waxy material with a deep bright colour reflecting that the nanocolorants were well dispersed in the wax. DSC thermograms showed that the solid inks have one sharp melting transition indicating the applicability of our nanocolorants for hot-melt ink applications. / AFRIKAANSE OPSOMMING: ‘n Nuwe reeks nonokleursels word beskryf vir die gebruik in ink-smelt drukker tegnologie. Inverse minie-emulsie polymerisasie was suksesvol gebruik om die kleurstof Rhodamine B (RhB) in die water oplosbare poly(akrielamied) (PAAm) te enkapsuleer. Die roete is gebruik om drie tipes kleurstof te produseer. Elk van die kleurstowwe was gebaseer op Rhodamine B en ‘n PAAm, naamlik PAAm/RhB, kruisgebonde PAAm/RhB en poli(akrielamied-ko-stireen)/RhB. PAAm/RhB nanokleursel was in die vorm van soliede donker nanopartikels. Die kruisgebonde PAAm/RhB en poli(akrielamied-ko-stireen) het bestaan uit nanoparikels met ‘n kern en skil morfologie. Die nanokleursels het ‘n verbetering in terme van lig en hitte stabiliteit getoon. Die migrasie van kleursel uit die nanopartikels, veral die met kern en skil morfologie, was baie minder. Die sintese van ‘n polimeeriseerbare nanokleursel gebaseer op RhB word beskryf. Poly(AAm-ko-RhB) nanokleursels was vir die eerste keer suksesvol gesintetiseer met behulp van ‘n inverse minie-emulsie polimerisasie. RhB kleursel was eers gefunksionaliseer deur middel van ‘n esterifikasie reaksie om ‘n polimeeriseerbare akrilaat groep te verkry. Die RhB-akrilaat kleursel was gekopolimeeriseer met AAm monomeer in ‘n inverse minie-emulsie polimerisasie om nanokleursels met verbeterde lig en migrasie stabiliteit te verkry. Kruisgebonde poli(AAm-ko-RhB) nanokleursels was verkry deur ‘n geskikte verbinding in die reaksie mengsel by te voeg. Beide poli(AAm-ko-RhB) and kruisgebonde poly(AAm-ko-RhB) nanokleursels was verkry as donker partikels met ‘n kern en skil morfologie. In beide gevalle was die RhB-akrilaat kleursel deeglik geintegreer in die matriks en sodoende was die migrasie van die kleursel heeltemal onderdruk. In albei gevalle het poli(AAm-ko-RhB) en kruisgebonde poli(AAm-ko-RhB) nanokleursels hoë hitte stabiliteit en hoë Tg waardes getoon. Die sintese van nanokleursels gebaseer op PAAm/RhB was sukselvol uit gevoer via inverse minie-emulsie polimerisasie. ‘n In situ inverse minie-emulsie polimerisasie met paraffin waks as die organiese fase was gebruik om soliede ink te produseer wat opgemaak is uit kruisgebonde PAAm/RhB nanokleursel. Die kruisgebonde poli(AAm-ko-RhB) soliede ink was voorberei deur die kruisgebonde PAAm/RhB nanokleursels (in suspensie met sikloheksaan) direk met die paraffin waks te meng by ‘n temperatuur hoër as die smeltpunt van die waks todat al die sikloheksaan verdamp het. Die soliede ink was verkry as ‘n homogene waksagtige materiaal met ‘n diep en helder kleur wat ‘n aanduiding was dat die nanokleursels goed versprei was in die waks. DSC termogramme het bewys dat die ink slegs een skerp smelt punt oorgang het wat beteken dat die materiaal geskik is om te gebruik in ink-smelt drukkers.

Les problématiques et potentialités de la photopolymérisation radicalaire en miniémulsion ont été discutées, en partant de l’étude des propriétés optiques des miniémulsions de monomère jusqu’à la synthèse de nouvelles nanoparticules polysulfures semi-cristallines par réaction thiol-ène. En premier lieu, l'interaction entre les propriétés optiques de miniémulsion de monomère et l'efficacité de photopolymérisation a été clarifiée. Nous avons établi le rôle majeur de la diffusion optique sur les cinétiques de photopolymérisation de nanogouttelettes acrylates, tandis que l'absorption s’est révélé de moindre importance. Que ce soit en milieu dilué ou concentré (modèle de Kubelka-Munk), la diffusion de la lumière est atténuée lorsque la taille de gouttelettes diminue. La conséquence immédiate est une amélioration significative de la pénétration de la lumière induisant une accélération des cinétiques de polymérisation. Néanmoins, cette conclusion doit être pondérée car l’effet de compartimentage de la polymérisation radicalaire n’a pu être dissocié des effets optiques. On notera qu’en milieu concentré (contenu en solide de 30 % massique), au-delà de 150 nm pour le diamètre de gouttelette, le coefficient de diffusion atteint un palier et devient indépendant de la taille des gouttelettes. La chute d’absorbance, observée par spectroscopie UV-visible, tout au long de l’irradiation pour des miniémulsions acrylates de faible taille (40 nm) a mis en évidence un mécanisme de polymérisation par diffusion de monomère des gouttelettes non nucléées vers les particules en croissance. Cette analyse non invasive (aucune dilution n’a été nécessaire) présente un intérêt évident pour l’étude du mécanisme de nucléation. Nous avons ensuite démontré que la photopolymérisation pouvait être réalisée en utilisant le caractère auto-amorçant des acrylates sous irradiation UV court ( < 300 nm). Ce type d’amorçage photochimique a permis d’éviter l’emploi de photoamorceur, limitant ainsi les risques liés à leur présence résiduelle dans le matériau final. Les photopolymérisations ont été réalisées dans un microréacteur modèle (cuve spectroscopique d’épaisseur 0,1 à 1 mm). La variation de plusieurs paramètres expérimentaux a permis d’identifier un ensemble de paramètres clés influençant les cinétiques de polymérisation tels que la taille des gouttelettes, corroborant ainsi les résultats de l’étude optique. Les longueurs d’onde d’irradiation et le chemin optique ont joué un rôle tout aussi déterminant ; le décalage vers des longueurs d’onde courtes et la diminution de l’épaisseur de l’échantillon accélèrent à la fois la création de radicaux amorceurs et le nombre d’entités nucléées. La versatilité du procédé a été démontrée en polymérisant rapidement (conversion totale en moins de 20 min) une large gamme de monomères acrylate, méthacrylate ou à base d’acétate de vinyle. En ce qui concerne le mécanisme d’auto-amorçage, nous avons prouvé que les espèces amorçantes provenaient vraisemblablement d’un biradical photoinduit, pouvant arracher ou transférer un hydrogène sur des molécules de monomère pour former des monoradicaux amorceurs. Par le biais de ce mécanisme original, la génération de radicaux est constante tout au long de la polymérisation ce qui pour effet d’impacter les caractéristiques des copolymères formés : l’indice de polymolécularité tend à augmenter et les masses molaires à diminuer par rapport à un processus photoamorcé conventionnel. Ces photopolymérisations ont été réalisées dans un photoréacteur annulaire à immersion et ont montré les mêmes évolutions en fonction de la taille de gouttelettes que lors d’expériences en cuve spectroscopique non agitées. A titre d’exemple, une conversion totale est atteinte en 1 h pour des tailles de gouttelettes de 60 nm et un contenu en solide de 30 %. L’auto-amorçage photoinduit a permis de générer rapidement une grande quantité de chaînes en croissance au sein des gouttelettes. [...] / Issues and potentials of miniemulsion radical photopolymerization were discussed, starting from monomer miniemulsions’ optical properties to the synthesis of new semi-crystalline polysulfide nanoparticles by thiol-ene reaction. First, the relationship between the optical properties of miniemulsion and the polymerization efficiency was clarified. We established the major role of optical scattering on the acrylate nanodroplets’ photopolymerization kinetic, while the absorption was found to play a minor role. Whether diluted or concentrated medium (Kubelka-Munk model), light scattering is attenuated when droplet size decreased. The corollary is a significant improvement of UV light penetration within the reactor vessel leading to an acceleration of the polymerization kinetics. However, this conclusion was mitigated by the fact that compartmentalization effect could not be easily dissociated from optical effects. Note that in concentrated medium (solids content of 30 wt %), beyond 150 nm droplet diameter, the scattering coefficient leveled off regardless of droplet size. An absorbance drop was observed using UV-visible spectroscopy throughout the irradiation of the smallest acrylate miniemulsions (40 nm). This result suggested a polymerization mechanism occurring by monomer diffusion from non-nucleated droplets to growing particles. This non-invasive analysis (no dilution was required) is of high interest to study the nucleation mechanism.In a second part, we demonstrated that acrylate miniemulsion photopolymerization could be performed through a monomer self-initiation mechanism induced by short-wavelength UV irradiation ( < 300 nm). Such original photochemical initiation avoided the use of photoinitiator, thus limiting the risks associated with their residual presence in the final material. The self-initiated photopolymerizations were carried out in a model microreactor (spectroscopic cell of 0.1 to 1 mm thick). The variation of several parameters allowed us to identify key parameters influencing polymerization kinetics such as droplet size, thus corroborating the results of the optical study. The irradiation wavelength and the optical path played a crucial role; the shift towards shorter wavelengths and the sample thickness reduction accelerated both the generation of initiating radicals and the number of nucleated entities. The versatility of the method was demonstrated by fast polymerization (complete conversion achieved within 20 minutes) employing a wide range of acrylate, methacrylate and vinyl acetate monomers. Regarding the self-initiating mechanism, one proved that the initiating species likely originated from a biradical able to abstract or transfer hydrogen from monomer molecules, thereby forming initiating monoradicals. Through this original mechanism, the generation of radicals was constant throughout the polymerization, which impacted the characteristics of the copolymer chains: the polydispersity index tended to increase and the molar masses decreases when compared with a conventional photoinduced process. These photopolymerizations were also carried out in an annular immersion photoreactor and showed the same trends regarding the effect of droplet size as the experiments conducted in unstirred spectroscopic tank. For example, a complete conversion was reached after 1 h for a 60 nm acrylate miniemulsion with a solids content of 30 wt %. As a result, a self-initiated polymerization can generate rapidly a large amount of insoluble growing polymer chains within the droplets. This unique feature was exploited to overcome Ostwald ripening without the addition of a specific costabilizer. Photochemical self-initiation could also be used to form surfactant-free nanolatex via Pickering-stabilized miniemulsion photopolymerization. Indeed, Laponite clay adsorbed at the surface of the droplets showed an excellent UV transparency up to 200 nm. [...]

Au cours de ce travail de thèse, nous avons étudié la synthèse de particules de latex par polymérisation en miniémulsion, un procédé de polymérisation en milieu aqueux dispersé. Nous avons synthétisé avec succès et de manière contrôlée des particules de latex de polystyrène de masse molaire élevée (Mn > 30 000 g.mol-1) par polymérisation radicalaire contrôlée par les nitroxydes (NMP) en miniémulsion, en présence et en absence de tensio-actif moléculaire. Des latex stables présentant des diamètres de l’ordre de 150 – 200 nm ont été synthétisés. Une seconde partie de ce travail de thèse est dédié à la transposition de la polymérisation radicalaire contrôlée par les nitroxydes amorcée depuis la surface (« surface-initiated NMP ») d’un procédé en masse vers un procédé en milieu aqueux dispersé (miniémulsion) en vue de synthétiser des nanoparticules cœur@écorce de type silica@polystyrène. La dernière partie du travail de thèse est consacrée à la synthèse de stabilisants polymères et plus précisément à la synthèse de copolymères amphiphiles à base de dextrane ou de poly(acide acrylique) modifiés de manière hydrophobes par des terpènes. L’efficacité de stabilisation de tels copolymères synthétisés à partir de bio-resources a été étudiée au travers leur capacité à stabiliser la polymérisation en miniémulsion du styrène. Tout au long de ce travail, les caractéristiques macromoléculaires des polymères ainsi que la taille et la morphologie des particules ont été caractérisées respectivement par chromatographie d’exclusion stérique, diffusion dynamique de la lumière et microscopie (SEM, TEM, AFM). / During the work of this PhD, we investigated the synthesis of latex particles by miniemulsion, an aqueous dispersed medium process. We managed to synthesize in a controlled manner high molar mass (Mn > 30 000 g.mol-1) polystyrene latex particles via nitroxide mediated radical polymerization (NMP) in miniemulsion in both the presence and absence of molecular surfactant. Stable latex with final diameters within the range of 150-200 nm were synthesized. A second part of the PhD work was devoted to the transposition of surface-initiated NMP from bulk polymerization to polymerization in aqueous dispersed media (miniemulsion) in order to synthesize silica@polystyrene core@shell hybrid nanoparticles. The last part of the PhD work was dedicated to the synthesis of polymeric stabilizers, more precisely to the synthesis of amphiphilic copolymers based on dextran or poly(acrylic acid) polymers hydrophobically modified by terpenes. The stabilization efficiency of such copolymers synthesized from renewable resources to stabilize styrene miniemulsion polymerization was investigated. During this work, we characterized the macromolecular features of polymers along with the size and the morphology of the final particles by respectively size exclusion chromatography (SEC), dynamic light scattering (DLS) and microscopy (SEM, TEM, AFM).

A stable aqueous nanocomposite dispersion containing cellulose whiskers and a polymer matrix was prepared via miniemulsion polymerization. We were able to prepare a stable dispersion with a 250 wt % solid content and a cellulose whiskers content ranging from 1 up to 5 wt % based on polymer content. Cellulose nanocrytals suspension was mixed with monomers phase in presence of anionic or cationic surfactant and a stabilizing additive acting as a hydrophobe. After sonication for a short time to obtain a stable emulsion of small droplet polymerisation reaction was trigged by the addition of the initiator. The nanocomposite dispersion was characterized using dynamic light scattering, ζ-potential measurement, transmission electron microscopy (TEM), atomic force microscopy (AFM) and FE-SEM. It was found that the particle size of the prepared suspensions is in the range of 90-600 nm, and the final nanocrystals composite is stable for months.Films obtained by casting followed by water evaporation and particle coalescence were analyzed by differential scanning calorimetry, dynamic mechanical analysis, and tensile testing. The nanocomposite maintained high transparency, and their storage elastic modulus increased tediously with the increasing nanowhiskers content.