Thesis (PhD (Process Engineering))--University of Stellenbosch, 2000. / Stricter government regulations and higher energy costs have forced the chemical industry to focus more on environmentally friendly processes and to reduce energy consumption. The main goals of chemical companies are to obtain a high product yield and selectivity, and to reduce unwanted side products. Furthermore, if ractions can be performed at lower temperature, while maintaining the reaction conversion, it will result in large energy savings. Low termperature dehydrogenation reactions (below 300 degrees C) are very selective and do not produce many by-products, but conversion is limited by the reaction equilibrium. The conversion limitations have resulted in the development of alternative processes in recent years for producing alkenes from alkanes and aldehydes or ketones from alcohols....

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Inorganic membranes offer numerous advantages, such as stability at high temperatures and a long lifetime. Two Russian professors invented and patented a method for manufacturing a tubular ceramic membrane [Linkov & Belyakov, 1996]. Their membranes were used in the water purification industry and in gas separation research at the University of Stellenbosch [Keuier, 2000], but the performance of the membranes have been reported to be inconsistent. This project investigates the manufacturing process for these membranes in an attempt to improve their inconsistent performance. It also provides useful insight into relevant methods of evaluation. Thirty-two cerarruc membranes were successfully manufactured according to the patent by Linkov and Belyakov [1996], with slight modifications to the original manufacturing process. It was found for example that, to obtain membranes with a thickness of 1 mm, the casting suspension should contain 1.85 grams of water per gram of oxides, instead of the 1.15 grams of water per gram of oxides according to Linkov and Belyakov [1996]. The quality of the gypsum mould and the drying of the green body were found to be the most difficult steps in the manufacturing process. Gas permeabilities for the manufactured membranes were typically lxIO-5 mol/misl'a for argon and nitrogen and 4.SxIO-5 mol/rrr'sl'a for hydrogen. Water permeabilities for the manufactured membranes were typically 600 Vm2hbar. Gas permeability coefficients for the manufactured membranes were typically SxIO-15 m2 for nitrogen and argon and 8xIO-15 m2 for hydrogen. The water permeability coefficients were typically 1.7xl 0-15 m2 . The gas and water permeabilities for the manufactured membranes were typically 5 and 10 times higher than the permeability values for membranes manufactured by Linkov. Gas and liquid permeability coefficients for the manufactured membranes, taking into account the thickness of the membranes, were 7 and 14 times higher than those achieved with Linkov's membranes. Linkov's membranes were on average thinner than the manufactured membranes, while the permeability of the manufactured membranes was higher, explaining the high permeability coefficients. The nitrogen and argon permeabilities, as well as their permeability coefficients were found to increase linearly with increasing pressure difference. However, the hydrogen permeability and permeability coefficients as well as the water permeability coefficients, were pressure independent. The gas permeability results also indicated that the permeability of the manufactured membranes increased with increasing sintering time and temperature. Combining the gas permeability results with the selectivity results, manufactured membranes with higher gas permeability had the same selectivity as Linkov's membrane. Therefore the manufactured membranes had a higher capacity than Linkov's membranes, with the same selectivity. For the manufactured membranes, however, a lower mechanical strength was reported, typically 9 N/mm2 , compared to the mechanical strength of Linkov's membrane which was roughly 10 times higher. To further improve the membranes, a number of options can be investigated: • The influence of a higher zirconia content on the ceramic membranes (between 29W'1o and 36.6W'1o for best mechanical strength). • Increasing of the sintering time and temperature for a more sintered and mechanically stronger membrane. • Examining the relationship between the permeability and mechanical strength of the membranes. / AFRIKAANSE OPSOMMING: Anorganiese membrane besit 'n aantal voordele, soos stabiliteit by hoë temperatuur toepassings en 'n langer leeftyd. Twee Russiese professore het 'n vervaardigingsmethode vir buisvormige keramiekmembrane uitgevind en gepatenteer [Linkovand Belyakov, 1996]. Hulle membrane was gebruik in die watersuiwerings industrie sowel as in 'n gasskeidings ondersoek by die Universiteit van Stellenbosch [Keuier, 2000], maar die prestasie van die membrane was wisselvallig. Hierdie projek ondersoek die vervaardigings metode vir hierdie kerarniekmembrane in 'n poging die wisselvallige prestasie van die membrane te verbeter. Die projek gee ook bruikbare insig in relevante toetsmetodes vir die vervaardigde membrane. Twee en dertig keramiekmembrane was suksesvol vervaardig volgens die patent van Linkoven Belyakov [1996], met klein veranderings. Dit was byvoorbeeld gevind dat, om membrane te vervaardig met 'n dikte van 1 mm, die gietsuspensie 1.85 gram water per gram oxide moet bevat in plaas van een gram water per een gram oxides soos volgens Linkoven Belyakov [1996]. Die kwaliteit van die gips vorm en die droog van die groen liggaam was die moeilikste beheerbare stappe in die vervaardigingsproses. Die gasdeurlaatbaarheid van die vervaardigde membrane was tipies Ix 10-5 mollm2sPa vir argon en stikstof en 4.5xl0-s mol/m'sl'a vir waterstof Waterdeurlaatbaarheid van die vervaardigde membrane was 600 l/rrr'hbar. Gasdeurlaatbaarheidskoeffisiente vir die vervaardigde membrane was tipies 5xl 0-15 m2 vir argon en stikstof en 8xl 0-15 m2 vir waterstof Die waterdeurdringbaarheidskoeffisiente was tipies 1.7xl 0-15 m2 . Die gas- en waterdeurlaatbaarheid vir die vervaardigde membrane was tipies 5 en 10 maal hoër as die deurlaatbaarheid waardes vir membrane wat deur Linkov vervaardig is. Gas- en waterdeurlaatbaarheidskoeffisiente vir die vervaardigde membrane, wat deur die dikte van die membrane beinvloed word, was 7 en 14 maal hoër as die bereik met Linkov se membrane. Linkov se membrane was gemiddeld dunner as die vervaardigde membrane, terwyl die deurlaatbaarheid van die vervaardigde membrane hoër was, wat die hoë deurlaatbaarheidskoeffisiente verklaar. Daar was gevind dat die argon- en stikstofdeurlaatbaarhede sowel as hulle deurlaatbaarheidskoeffisiente lineêr toeneem met toenemende drukverskil. Die waterstofdeurlaatbaarheid en -deurlaatbaarheidskoeffisiente sowel as die waterdeurlaatbaarheidskoeffisiente egter, was onafhanklik van die drukverskil. Die gasdeurlaatbaarheid resultate het ook aangedui dat die deurlaatbaarheid van die vervaardigde membrane toeneem met toenemende sintertyd en -ternperatuur. Wanneer die gasdeurlaatbaarheid resultate gekombineer word met die selektiwiteit resultate blyk dit dat, terwyl dat die vervaardigde membrane 'n hoër gasdeurlaatbaarheid het as Linkov se membrane, hulle nog steeds dieselfde selektiwiteit het. Dit beteken dat die kapasiteit van die vervaardigde membrane hoër is, terwyl die selektiwiteit van die skeidingsproses behou word. Vir die vervaardigde membrane was 'n laer meganiese sterkte gevind, tipies 9 N/mm2 , terwyl die meganiese sterkte van Linkov se membrane omtrend 10keer hoër was. Verskeie opsies kan ondersoek word om die membrane te verbeter: • Die invloed van 'n hoër zirkonia inhoud op die keramiekmembrane (tussen 29m% en 36.6m% vir beste meganiese sterkte). • Verlenging van die sintertyd en -temperatuur om 'n meer gesinterde en meganies sterker keramiekmembraan te verkry. • Ondersoek na die verhouding tussen deurlaatbaarheid en die sterkte van die membraan.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2005. / An increased demand for hydrogen in recent years has led to a revival of interest in methods for hydrogen separation and purification. Palladium (Pd) and palladium composite membranes have therefore received growing attention largely due to their unique permselectivity for hydrogen and good mechanical and thermal stability. Previous research on Pd composite membranes by Keuler (2000) in the Department of Process Engineering at the University of Stellenbosch has shown that some assumptions which he made during characterisation procedures needed further investigation, such as the assumptions about the influence of support membranes on preparation of Pd composite membranes, method of precleaning before pretreatment, vacuum applied during electroless plating, and heat treatment after electroless plating. In this study, Pd composite membranes (with Pd film thickness of 1.7 μm ~ 4 μm) were prepared on the inside layer (claimed pore diameter of 200 nm) of α-alumina ceramic support membrane tubes, consisting of three layers with varying pore diameters from inside to the outside layer, via a modified electroless plating technique (with a gauge vacuum of 20 kPa applied on the shell side of the plating reactor). Bubble point tests and bubble point screening tests were performed on the support membranes before the electroless plating to investigate the influence of the substrates characteristics on the preparation of the Pd composite membranes. It was found that Pd composite membranes with a better permselectivity can be prepared on a support membrane that contains smaller pore sizes and a smoother surface. The surface pretreatment step was modified to provide a uniform Pd surface for Pd electroless plating. The membrane was first rinsed in PdCl2 solution for 15 min using a stirrer at a stirring speed of 1300 rpm, and was then dipped into distilled water 10 times (1-2 second each). Subsequently, the membrane was rinsed in SnCl2 solution for 15 min, and was then dipped into distilled water 10 times. These procedures were repeated 4 times. In addition, by using a new method of assessment for heat treatment (i.e. cutting the Pd composite membranes into two pieces and then exposing them to two different heating methods), the most effective heat treatment method could be identified without the influences of the substrates or the plating technique. The preferable procedures was to anneal the Pd composite membrane in N2 for 5 h from 20°C to 320°C, and then oxidize it in air for 2 h at 320°C, followed by annealing it in N2 for 130 min from 320°C to 450°C and then in H2 for 3 h at 450°C. Finally the membrane was cooled down in N2 to 350°C and held at this temperature for 30 min. Additional oxidation in air for more than 10 hours changes the structure of the Pd films. PdO then forms and decreases the H2 permeation through the Pd composite membrane. More detailed characterisations of the Pd composite membranes were performed by membrane permselectivity tests (from 350°C to 550 ◦C) using either H2 or N2 in single gas test, membrane morphology and structure analysis using scanning electron microscopy (SEM), energy dispersive detectors (EDS), atomic force microscopy (AFM), Brunauer-Emmett- Teller (BET) and X-ray diffraction (XRD) analysis. Hydrogen permeability between 4.5-12 μmol/(m2.Pa.s) and an average hydrogen/nitrogen permselectivity of ≥ 150 were achieved in this study. The permselectivities of the heat treated membranes were superior to Keuler’s membranes, which had an average permselectivity of ≥ 100. AFM and BET analysis showed that dense and smooth Pd films with smaller Pd crystals sizes and compact Pd layers were obtained.

Dissertation (Ph.D.)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: The deposition of platinum catalyst on cation-exchange membranes was achieved by a counter diffusion deposition method known as the Takenaka- Torikai method. The morphology of the platinum catalyst on the membranes were controlled by varying the conditions of the platinum deposition process, such as, temperature, type of reducing agent and concentration of the platinic acid solution. The effect of the sonication of platinic acid solution and the pre-treatment of membranes on the morphology of a platinum catalyst was also investigated. Platinum loading on cation-exchange membranes was determined by UV spectrophotometric and gravimetric analyses. Suitable conditions for the quantitative determination of the platinum loading on membranes by UV spectrophotometric analysis was established through the development of a protocol. Membranes were characterised using different techniques such as, Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Infrared spectrometry (IR), Dielectric analysis (DEA) and Brunauer Emmett Teller adsorption (BET). The roughness profile of a platinum catalyst embedded on a membrane was explored by various statistical methods. The statistical analysis of various data sets for a surface of a platinum-containing membrane was investigated using the Hurst exponent. The effect of surface modification of membranes on the deposition process, as well as the morphology of the platinum catalyst, was investigated. Membranes were modified with ethylene diamine (EDA) and cetyltrimethylammonium bromide surfactant. Modification of membranes with cetyltrimethylammonium bromide surfactant resulted in a unique textured platinum catalyst. The electrochemical "switching" phenomenon was investigated for EDAmodified membranes and EDA-modified membranes embedded with platinum catalyst. The "switching" phenomenon was observed in i-V cyclic curves, which were obtained by galvanodynamie measurements. The application of electro catalytic membrane systems in the anodic oxidation of water was investigated by electrochemical techniques such as galvanostatic and cyclic voltammetric measurements. / AFRIKAANSE OPSOMMING: Die deponering van 'n platinum katalis op katioon-uitruil membrane is suksesvol gedoen d.m.v. die Takenaka-Torikai metode. Die morfologie van die platinum katalis op die membrane is gekontrolleer deur variasie van die kondisies van die platinum deponeringsproses, bv. temperatuur, tipe reduseermiddel gebruik en konsentrasie van die platiensuuroplossing, asook die ultrasonifikasie van die platiensuuroplossing en voorafbehandeling van die membrane. UV spektrofotometriese asook gravimetriese analitiese metodes is gebruik om die platinumlading op katioon-uitruil membrane te bepaal. Geskikte kondisies vir die kwantitatiewe bepaling van die platinumlading op membrane d.m.v. UV spektrofotometriese analise is ontwikkel deur die skep van 'n protokol. Membrane is gekarakteriseer d.m.v. die volgende tegnieke: Atoomkrag Mikroskopie, Skanderingselektron Mikroskopie, Infrarooi Spektrometrie, di-elektriese analise en Brunauer Emmett Teller adsorpsie. Die skurtheidsprofiel van 'n platinum katalis op 'n membraan is ondersoek deur gebruik te maak van verskeie statistiese metodes. Statistiese analises van verskeie data stelsels van 'n platinum-bevattende membraan is ondersoek deur gebruik te maak van die Hurst eksponent. \ Die effek van oppervlakmodifikasie op membrane sowel as die deponeringsproses en morfologie van die platinum katalis is ondersoek deur die modifikasie van membrane met etileen diamien (EDA) en setieltrimetielammonium bromied as versepingsmiddel Die elektrochemiese omswaai van EDA-gemodifiseerde membrane sowel as gemodifiseerde platinum bevattende membrane is ondersoek d.m.v. galvanodinamiese metings. Die gebruik van elektro-katalitiese membraansisteme in die anodiese oksidasie van water is ondersoek deur gebruik te maak van elektrochemiese tegnieke, bv. galvanostatiese en sikliese voltammetriese metings.

Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: As there is inadequate control of the hydrothermal synthesis technique used to date in the synthesis of zeolite A membranes, the feasibility of a new synthesis approach was investigated, namely the static transverse synthesis method. The former technique involved (i) thorough mixing of the chemical components, (ii) gel-formation and ageing and (iii) heat treatment. The proposed new method for zeolite A synthesis concerns the use of two individual nutrient pools (AI and Si) on opposite sides of a porous medium (a-alumina tube). Diffusion of these two nutrients towards each other, due to concentration differences, results in their contact in the porous medium (crystallisation front), leading to gel formation and eventual zeolite crystal growth. By means of the new static transverse synthesis technique the application of very high nutrient concentrations (O.72g NaOH, 80.0g H20, 8.26g NaAI02 and 15.48g Na2Si03), contrary to what is used in conventional hydrothermal synthesis techniques (11.23g NaOH, 54.82g H20, 0.61g NaAI02 and 3.63g Na2Si03), is now possible. The advantage of using high nutrient concentrations lies in the fact that supersaturation exists immediately after gel formation occurs. Supersaturation is a prerequisite for grain growth, which, in tum, is the only way in which a very thin (4-6 urn), continuous (pinhole-free) zeolite crystal layers can be prepared. A variety of support materials have been used to provide the mechanical stability for zeolite membranes, because the chemical/physical interaction between a zeolite synthesis solution and the support also plays a role in the formation of a zeolite membrane. Hence, zeolite A crystal growth on four different types of supports was evaluated and the a-alumina tube proved to be the best support for zeolite A crystal growth. An exploratory study into the upgrading of the static transverse synthesis to a continuousflow synthesis was also undertaken. The nutrients were continuously passed over the opposite surfaces (internal and external) of the porous a-alumina tube. In this way the nutrients could be replenished throughout the synthesis. It was possible to make zeolite A membranes using this technique, although these membranes were not an improvement on the membranes produced with the STS method. The zeolite A crystal population in and on the surface of the porous supports was determined by scanning electron microscopy (SEM). The zeolite A crystallinity, symmetry and morphology were characterised using x-ray diffraction PCRD). The zeolite lattice vibrations, structure sensitive and structure insensitive vibrations were determined by infra red spectroscopy (IR). The wettability of the alumina support was determined by dynamic contact angle measurements. The zeolite A membranes prepared by the static transverse synthesis were tested for their helium permeance. They were also subjected to pervaporation experiments at 45°C, using a water/ethanol mixture (5 wt% water) and it was found that the fluxes varied between 0.2 -0.4 kg/m2h and the separation factors varied between 5000 and 16000. These results compare very favourably with results reported in the literature. In conclusion, the possibilities created by using a combination of membranes and catalysis, both on bench scale and in industry, are reviewed. / AFRIKAANSE OPSOMMING: Weens onvoldoende beheer oor die hitte behandeling sintese tegniek wat tans vir die sintese van zeoliet-A-membrane gebruik word, is die haalbaarheid van 'n nuwe sintese tegniek, nl. die statiese sydelingse sintese-metode, ondersoek. Eersgenoemde tegniek behels (i) deeglike vermenging van die chemiese komponente, (ii) jelvorming en -veroudering en (iii) hittebehandeling. Die voorgestelde nuwe sintese tegniek vir die bereiding van ondersteunde zeoliet-A-membrane behels die plasing van twee aparte voedingsbronne (Al en Si onderskeidelik), aan teenoorgestelde kante van 'n poreuse medium (a-aluminabuis). Diffusie van hierdie twee komponente na mekaar, agv konsentrasieverskille, veroorsaak dat die twee oplossings in die poreuse medium met mekaar in aanraking kom (kristallisasie front). Dit lei dan tot jelvorming en uiteindelik zeolietkristal groei. Met die nuwe sydelingse sintesetegniek is die aanwending van baie hoë konsentrasies van die voedingsbronne (O.72g NaOH, 80.0g H20, 8.26g NaAI02 en 15.48g Na2Si03) nou moontlik. Dit is in teenstelling met die konvensionele hitte behandelingstegnieke (11.23g NaOH, 54.82g H20, O.61g NaAl02 en 3.63g Na2Si03). Die voordeel van hoë voedingsbronkonsentrasies is dat oorversadiging onmiddelik na jelvorming bereik word. Absolute oorversadiging is 'n voorvereiste vir partikelgroei, wat op sy beurt die enigste manier is om baie dun (4-6 urn), aaneenlopende zeolietkristallae te verkry. 'n Verskeidenheid van draermateriale is al gebruik om meganiese stabiliteit aan zeolietmembrane te verleen, aangesien die chemiese/fisiese interaksie tussen die zeolietsintese-oplossing en die draermateriaal 'n rol speel in die vorming van die zeolietmembraan. Om hierdie rede is die groei van zeoliet-A-kristalle op vier verskillende tipes draermateriale ondersoek en die a-aluminabuis is as die beste draermateriaal vir zeoliet-A-kristalgroei bewys. 'n Aanvanklike studie na die moontlike opgradering van die statiese sydelingse sintese na aaneenlopende vloeisintese is ook onderneem. In hierdie studie is die voedingsbronne deurlopend oor die teenoorgestelde oppervlaktes (intern en ekstern) van die poreuse a-aluminabuis gepomp. Sodoende kon die voedingstowwe voortdurend tydens die sintese aangevul word. Dit was moontlik om zeoliet-A-membrane met behulp van hierdie tegniek te maak, alhoewel hierdie membrane nie 'n verbetering was op dié wat deur middel van die statiese sydelingse sintesetegniek gemaak is nie. Die teenwoordigheid van die zeoliet-A-kristalle op die verskillende oppervlaktes van die poreuse buis is met behulp van 'n skandeerelektronmikroskoop (SEM) bepaal. Die zeoliet-A-kristalliniteit, -simmetrie en -morfologie is met behulp van x-straaldiffraksie (XRD) gekarakteriseer. Die zeolietlatwerk-, struktuursensitiewe- en struktuuronsensitiewe vibrasies, is met behulp van infrarooispektroskopie (IR) en die benatbaarheid van die aluminabuis met dinamiese kontakhoekbepalings bepaal. Die zeoliet-A-membrane berei met die statiese sydelingse sintese-metode is vir helium-deurlaatbaarheid getoets en ook aan pervaporasie eksperimente by 45°C, deur gebruik te maak van 'n water/etanol mengsel (5 wt% water), onderwerp. Daar is gevind dat vloei tussen 0.2 - 0.4 kg/mh en dat skeidingsfaktore tussen 5000 en 16000 gevarieer het. Hierdie resultate vergelyk baie goed met die resultate in die literatuur. Samevattend word 'n oorsig gegee van die moontlikhede wat geskep word deur membraanskeidingstegnologie te kombineer met katalise op laboratorium- en industriële skaal.

Thesis (PhD)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: A new membrane based affinity separation system that is bio-specific, biocompatible, well characterised and capable of being regenerated or re-used is described. The amphiphilic non-ionic surfactant Pluronic® F108, was covalently derivatised to form two novel bioligands (Pluronic-Biotin and Pluronic-DMDDO) for the bio-specific immobilisation of avidin conjugated proteins and histidine tagged proteins respectively. Pluronic was also used to non-covalently functionalise nonporous membranes for ligand attachment and to simultaneously shield the surfaces from non-specific protein adsorption. Each component of this bioaffinity system (from the membrane matrix to the elution/desorption of the ligate/ligand system) was studied with the aim of producing a well characterised system and key quantitative data for the development of a robust, reliable, re-usable and scalable technology. Specifically, this study describes: 1. The fabrication and partial characterisation of nonporous planar and capillary membranes as model affinity matrices. 2. The development and evaluation of a robust protocol for solvent desorption and accurate colorimetric quantification of Pluronic® F108 and its derivatives. 3. Interfacial analysis of Pluronic adsorption onto nonporous affinity membranes, including the direct solid-state analysis of model, halogenated Pluronic derivatives using nuclear microprobe analysis. 4. Development of a surfactant based protocol for affinity membrane regeneration and re-use. 5. Specific bioaffinity immobilisation of avidin conjugated peroxidase onto biotinylated membranes in the presence of model protein foulants. 6. Cloning and expression of C-terminal hex-histidine tagged human cytochrome b5 into the bacterial expression system E. coli BL-21 DE3. 7. Development and characterisation of an immobilised metal affinity membrane system for metal chelation (Ni2+, Cu2+ and Zn2+) using a new chelator Pluronic- N,N-dicarboxymethyl-3,6-diazaoctanedioate and the bio-specific immobilisation of N-terminal hex-histidine tagged pantothenate kinase. / AFRIKAANSE OPSOMMING: 'n Nuwe membraan-gebaseerde affiniteitskeidingsisteem word beskryf wat biospesifiek, bioversoenbaar en goed gekarakteriseer is, en geregenereer of hergebruik kan word. Die amfifiliese nie-ioniese surfaktant Pluronic is kovalent gederivatiseer om twee nuwe bioligande (Pluronic-Biotien en Pluronic-DMDDO) te vorm vir biospesifieke immobilisering van proteïnligate. Pluronic is ook gebruik om nie-poreuse membrane niekovalent te funksionaliseer vir ligandaanhegting en om hulle oppervlaktes teen niespesifieke proteïen-adsorbsie af te skerm. Elke komponent van hierdie bioaffiniteitsisteem (van die membraanmatriks tot die uitwas/desorpsie van die ligaat/ligand sisteem) is ondersoek met die doel om 'n goed-gekarakteriseerde sisteem te produseer en om kwantitatiewe data te genereer vir die ontwikkeling van 'n robuuste, betroubare, herbruikbare en opskaleerbare tegnologie. Hierdie studie beskryf spesifiek: 1. Die fabrisering en gedeeltelike karakterisering van nie-poreuse planêre en kapillêre membrane as model affiniteitsmatrikse. 2. Die ontwikkeling en evaluering van 'n robuuste protokol vir oplosmiddel desorpsie en akkurate kolorimetriese kwantifikasie van Pluronic® F108 en afgeleides daarvan. 3. Intervlakanalises van Pluronic adsorpsie op nie-poreuse affiniteitsmembrane, insluitend die direkte vastetoestand analise van model ligand-gemodifiseerde Pluronic deur die gebruik van kern-mikrosonde analise. 4. Ontwikkeling van 'n surfaktant-gebaseerde protokol vir affiniteitsmembraan regenerering en hergebruik. 5. Spesifieke bioaffiniteitsimmobilisering van avidien-gekonjugeerde peroksidase op gebiotinileerde membrane in die teenwoordigheid van model bevuilende proteïne. 6. Klonering en uitdrukking van C-terminaal hex-histidien geëtiketeerde menslike sitochroom b5 in die bakteriële uitdrukkingsisteem E. coli BL-21 DE3. 7. Ontwikkeling en karakterisering van 'n geïmmobiliseerde metaalaffiniteitsmembraansisteem vir metaalchelering (Ni2+, Cu2+ en Zn2+) met behulp van die nuwe cheleerder Pluronic-N,N-dikarboksimetiel-3,6- diasaoktaandioaat en die bio-spesifieke immobilisering van N-terminaal hexhistidiengeëtiketerde pantotenaatkinase.

Silk fibroin has created a surge of interest for use as organic material due to its optical transparency, biocompatibility, biodegradability, and excellent physical properties. However, the implementation of silk films and structures into biomedical and sensing devices has been relatively low due to a lack of understanding of the mechanisms involved in such implementation. Increasing need for multifunctional high-performance organic materials has caused an emphasis on the ability of researchers to spatiotemporally pattern and control the structure and consequently functional properties of materials. Silk fibroin displays high potential for use as a controllable biomaterial that can be formed into a myriad of different structures for various applications. By implementation of an aqueous silk solution approach combining various fabrication techniques, several different pristine-silk and silk-composite membranes have been developed to investigate the importance of internal structuring. Different methods of investigation include: 1) incorporation of reinforcing nanoparticles within the silk matrix; 2) neutron reflectivity measurements of ultrathin silk films; 3) film patterning with nanoscale features followed by boundary organized surface mineralization of inorganic nanoparticles. The ultimate goal will be to provide fundamental data assisting in an increased knowledge of silk fibroin-based membranes and the effect of secondary structures on properties of interest.

Polymer based membranes play a key role in several industrially important gas separation technologies, e.g., removing CO2 from natural gas, with enormous economic and environmental impact. In this thesis, we develop a novel hybrid membrane construct comprised entirely of inorganic nanoparticles grafted with polymer chains. For all graft architectures studied, the permeability of several small gases and condensable solvents are higher in GNP membranes than the neat polymer analogs. More interestingly, the matrix-free GNPs displayed a non-monotonic peak in gas permeability as a function of grafted chain molecular weight, M_n, at a fixed grafting density, σ. Furthermore, in contrast to neat polymer membranes, which suffer from degraded performance over time due to chain densification and “aging”, the performance of GNP membranes is preserved for months to years. We show that these enhancements are not limited to a single polymer, thus we suggest that this grafting mechanism may be an option to improve permeability in polymer membranes in general. We conjecture the grafted polymer chains must stretch to fill the interstitial voids in the NP “lattice”, as such voids would be free-energetically unfavorable due to the relatively high surface tension of the polymer melt. Since this stretching leads to an unfavorable chain conformational entropy, we expect a decrease in the polymer density, which we verify experimentally as well as through molecular dynamics simulations. When a penetrant molecule is placed in these regions of highest distortion, the chains can assume more favored, undistorted conformations. This in turn creates a driving force for further penetrant uptake. Therefore, we systematically study the structure and dynamics of matrix-free GNP materials at various chain grafting densities and a wide range of graft molecular weight. Small angle scattering experiments reveal that the core nanoparticle spacing systematically increases with increasing molecular weight but the overall morphology remains amorphous and isotropic. Whereas previous studies1 have found the brush height in matrix-free GNPs scales as the degree of polymerization 〖~N〗^0.5, we find that the brush height in our systems scales 〖~N〗^0.7, indicating the chains are indeed highly stretched. Moreover, studies of the structural evolution upon swelling with solvent show that the brush is fully wetted and the solvent distribution is homogeneous within the film. Additionally, we systematically probe the dynamics of matrix-free GNP systems over broad length and time scales using linear and non-linear mechanical rheology, and broadband dielectric spectroscopy. The linear viscoelastic response shows that while the polymeric signal (e.g. glassy and Rouse dynamics) is equivalent for a range of graft chain lengths, the terminal flow of these materials is slowed by several decades compared to the neat melts of corresponding molecular weight. The low frequency (long time) response shows that below a critical molecular weight, these systems transition from polymeric to that of a colloidal system. To understand this behavior, a scaling theory is developed to describe the polymer brush conformation, which reveals that at this transition point the grafted particles behave as a system of packed “rigid” spheres. We note that the transition point coincides with the maximum observed in the transport behavior, and that the reduced system mobility may be responsible for the reduced aging effects. On the other hand, secondary relaxations for GNPs at this transition molecular weight are found to be faster than the neat polymer of corresponding molecular weight, which is attributed to a lower effective polymer density found in these samples. Therefore, the critical question underpinning this work is: how do the structure and dynamics influence and/or result from increased free volume in matrix-free grafted nanoparticle materials? We conclude that matrix-free grafted nanoparticle constructs allow for precise control of structure-property relationships over multiple length scales, and serve as a novel materials design platform with the potential to function as high performance gas separation technologies.

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Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 116-126).