Membrane technology is one of the most promising technologies for addressing the global water crisis as well as in many other applications. One of the drawbacks of current ultra- and nanofiltration membranes is the relatively broad pore size distribution. Block copolymer membranes with ultrahigh permeability and very regular pore sizes have been recently demonstrated with pores being formed by the supramolecular assembly of core/shell micelles. Our study aimed at developing an innovative and economically efficient alternative method to fabricate isoporous membrane by self-assembly of magnetic nanoparticle with a polystyrene shell, mimicking the behavior of block copolymer micelle. Fe3O4 nanoparticles of ~13 nm diameter were prepared by co-precipitation as cores. The initiator for ATRP was covalently bonded onto the surface of magnetic nanoparticles with two strategies. Then the surface initiated ATRP of styrene was carried out to functionalize nanoparticles with polystyrene through a “grafting from” method. Finally, the nanocomposite membrane was cast from 50 wt % Fe3O4@PS brush polymer solution in DMF via non solvent phase inversion. Microscopies reveal an asymmetric membrane with a dense thin layer on top of a porous sponge-like layer. This novel class of asymmetric membrane, based on the pure assembly of functionalized nanoparticles was prepared for the first time. The nanoparticles are well distributed however with no preferential order yet in the as-cast film.I would like to thank my committee chair and advisor, Prof. Suzana Nunes, and other committee members, Prof. Klaus-Viktor Peinemann and Prof. Gary Amy, for their guidance and support throughout the course of this research. My appreciation also goes to my colleagues in our group for useful discussions and suggestions. I also want to extend my gratitude to the staff from the KAUST Core Lab for Advanced Nanofabrication, Imaging and Characterization, especially Dr. Ali Reza Behzad, Dr. Rachid Sougrat, and Dr. Long Chen, for their assistance for various microscopy measurements. Finally, my heartfelt gratitude is extended to my parents and all my friends. I cannot finish this thesis without their encouragement and support.

In this study, surface modification of both organic and inorganic substrates (in terms of cellulose and silica nanoparticles, respectively) has been explored using surface-initiated atom transfer radical polymerisation (ATRP). The desire to modify bio-based materials to fit into new application areas and the need for bio-based materials with improved material properties is steadily increasing due to environmental concern. Superhydrophobic and self-cleaning cellulose surfaces were fabricated by combining ATRP with post-functionalisation. Glycidyl methacrylate was grafted from filter paper, and the epoxide groups were used as reactive handles to create a branched “graft-on-graft” architecture. Post-functionalisation of this architecture with perfluorinated chains or alkyl chains resulted in the formation of superhydrophobic surfaces. Grafting of N-isopropylacrylamide (NIPAAm) from filter paper yielded cellulose surfaces capable of switching the wettability, from hydrophilic to hydrophobic, in response to changes in temperature. The wettability of cellulose surfaces grafted with poly(4-vinylpyridine) (P4VP) could be adjusted from hydrophilic to hydrophobic by changing pH. Furthermore, cellulose surfaces responding to changes in both pH and temperature were obtained via grafting of block copolymers of PNIPAAm and P4VP. The use of inorganic nano-particles in composites has attracted considerable academic and industrial interest due to their excellent mechanical and thermal properties. Styrene was grafted from the surface of silica nanoparticles using ATRP. The resulting organic-inorganic hybrid materials did not aggregate to the same extent as the un-modified silica particles. The polystyrene-modified silica particles were used for the fabrication of honeycomb membranes. It was evident that the pore sizes and the number of porous layers could be tuned by varying the conditions used for film casting. To broaden the range of polymers available for film casting into honeycomb membranes, a block copolymer of polystyrene and poly(methyl methacrylate) was grafted from silica nanoparticles. Polymer-blends of polystyrene-modified particles and poly(9,9´-dihexylfluorene) (PDHF) were also used as an alternative to incorporate functionality into honeycomb membranes. / QC 20100901

The primary aim of this work is to explore the potential applications of isoporous block copolymer membranes. Block copolymers (BCPs) have demonstrated their versatility in the formation of isoporous membranes. However, application spectrum of these isoporous membranes can be further broadened by exploring the technical aspects, such as desired surface chemistry, well-defined pore size, appropriate pore density, stimuli responsive behavior, and by imparting desired functionalities through chemical modifications. We believe, by exploring these possibilities, isoporous membranes hold tremendous potential as high performance next generation separation membranes. Motivated by these attractive prospects we systematically investigated novel routes for modification of isoporous membranes and their implications on properties and performance of the membranes for various applications. In this work, polystyrene-block-poly(4-vinyl pyridine) (PS-b-P4VP) has been selected to fabricate isoporous membranes using non-solvent induced phase separation (NIPS). We selected PS-b-P4VP since its well-defined isoporous morphology is studied in detail and it is extensively characterized. In order to further widen the application bandwidth of BCP membranes, it is desirable to integrate different functionalities in the BCP architecture through a straightforward approach like post-membrane-modification or fabrication of composite membranes to impart anticipated functionalities. The most critical challenge in this approach is to retain the well-defined nanoporous morphology of BCP membranes. We focused on exploring new routes for chemical functionalization of isoporous PS-b-P4VP membranes via various in-situ and post-membrane fabrication approaches. To date, most of the work reported in the literature on PS-b-P4VP presented different routes to fabricate isoporous membranes and their conventional performance in liquid separations. Few efforts have been dedicated to alter the chemistry of PS-b-P4VP membranes by tuning the reactivity of the chemically active P4VP block or the surface chemistry to enhance the membrane performance for desired applications. During the Ph.D. study, we primarily focused on: (i) post modification approach, (ii) surface modification and (iii) in-situ membrane modification approach for fabrication of the mixed-matrix nanoporous membranes without altering the isoporous morphology of the membrane. The membranes fabricated using the mentioned above routes were tested for different applications like stimuli-responsive separations, self-cleaning membranes, protein separations and high-performance humidity sensors.

Polymeric isoporous membranes have many interesting properties leading to various specific applications in different fields. However, such structures also have one main drawback, namely their poor solvent stability, which should be improved to extend the range of their possible applications. Therefore, this project will focus on the enhancement of solvent stability of polymeric isoporous membranes by UV cross-linking. Stable isoporous films were obtained by creating honeycomb membranes from star polystyrene (PS) and its derivatives. The star PS was synthesized by Atom Transfer Radical Polymerization (ATRP) method and was then functionalized with methacrylate groups. The isoporous films made from these materials maintained the honeycomb structures after curing by UV light and immersion in chloroform. The crosslinking of PS under UV light exposure rather than the cross-linking of the methacrylates groups was responsible for the solvent stability of these membranes. To further investigate the effect of specific end-groups on the film stability, PEG2k-G3-PCL30 linear-dendritic-linear hybrid polymers and its derivatives with allyl, acrylate, methacrylate end-groups were employed to cast films. Functionalized PEG2k-G3-PCL30 linear-dendritic-linear hybrid isoporous films were cross-linked by UV-induced thiol-ene reactions and allyl reactions. However, no significant increase in the solvent stability of these kinds of films was observed. When mixing PEG2k-G3-PCL30 linear-dendritic-linear hybrids with star PS, stable isoporous films could be obtained. The pores became smaller but the isoporous structures were still kept.

Förfrågan efter nya och mer avancerade applikationer är en pågående process vilket leder till en konstant utveckling av nya material. För att förstå relationen mellan en applikations egenskaper och dess sammansättning krävs full förståelse och kontroll över materialets uppbyggnad. En sådan kontroll över uppbyggnaden hos material hittas i en undergrupp till dendritiska polymerer som kallas dendrimerer. I den här doktorsavhandlingen belyses nya metoder för att framställa dendrimer med hjälp av selektiva kemiska reaktioner. Sådana selektiva reaktioner kan hittas inom konceptet klickkemi och har i detta arbete kombinerats med traditionell anhydrid- och karbodiimidmedierad kemi. Denna avhandling diskuterar en accelererad tillväxtmetod, dendrimerer med inre och yttre reaktiva grupper, simultana reaktioner och applikationer baserade på dessa dendritiska material. En accelererad tillväxtmetod har utvecklats baserad på AB2- och CD2-monomerer. Dessa monomerer tillåter tillväxt av dendrimerer utan att använda sig av skyddsgruppkemi eller aktivering av ändgrupper. Detta gjordes genom att kombinera kemoselektiviteten hos klickkemi tillsammans med traditionell syraklorid kopplingar. Dendrimerer med inre alkyn- eller azidfunktionalitet syntetiserades genom att använda AB2C-monomerer. Den dendritiska tillväxten skedde med hjälp av karbodiimidmedierad kemi. Monomererna som användes bär på en C-funktionalitet, alkyn eller azid, och på så sätt byggs får interiören i de syntetiserade dendrimeren en inneburen aktiv funktionell grupp. Ortogonaliteten hos klickkemi användes för att sammanfoga monomerer till en dendritisk struktur. Traditionell anhydridkemi- och klickemireaktioner utfördes samtidigt och på så sätt kunde dendritiska strukturer erhållas med färre antal uppreningssteg. En ljusemitterande dendrimer syntetiserades genom att koppla azidfunktionella dendroner till en alkynfunktionell cyclenkärna. Europiumjoner inkorporerades i kärnan varpå dendrimerens fotofysiska egenskaper analyserades. Mätningarna visade att den bildade triazolen hade en sensibiliserande effekt på europiumjonen. Termiska studier på några av de syntetiserade dendrimerer utfördes för att se om några av dem kunde fungera som templat vid framställning av isoporösa filmer. / The need for new improved materials in cutting edge applications is constantly inspiring researchers to developing novel advanced macromolecular structures. A research area within advanced and complex macromolecular structures is dendrimers and their synthesis. Dendrimers consist of highly dense and branched structures that have promising properties suitable for biomedical and electrical applications and as templating materials. Dendrimers provide full control over the structure and property relationship since they are synthesized with unprecedented control over each reaction step. In this doctoral thesis, new methodologies for dendrimer synthesis are based on the concept of click chemistry in combination with traditional chemical reactions for dendrimer synthesis. This thesis discusses an accelerated growth approach, dendrimers with internal functionality, concurrent reactions and their applications. An accelerated growth approach for dendrimers was developed based on AB2- and CD2-monomers. These allow dendritic growth without the use of activation or deprotection of the peripheral end-groups. This was achieved by combining the chemoselective nature of click chemistry and traditional acid chloride reactions. Dendrimers with internal azide/alkyne functionality were prepared by adding AB2C monomers to a multifunctional core. Dendritic growth was obtained by employing carbodiimide mediated chemistry. The monomers carry a pendant C-functionality (alkyne or azide) that remains available in the dendritic interior resulting in dendrimers with internal and peripheral functionalities. The orthogonal nature of click chemistry was utilized for the simultaneous assembly of monomers into dendritic structures. Traditional anhydride chemistry and click chemistry were carried out concurrently to obtain dendritic structures. This procedure allows synthesis of dendritic structures using fewer purification steps. Thermal analyses on selected dendrimers were carried out to verify their use as templates for the formation of honeycomb membranes. Additionally, a light emitting dendrimer was prepared by coupling of azide functional dendrons to an alkyne functional cyclen core. A Europium ion was incorporated into the dendrimer core, and photophysical measurements on the metal containing dendrimer revealed that the formed triazole linkage possesses a sensitizing effect. / QC 20100629