This thesis is dedicated to the exploration of fluid phases confined in nanoporous materials using Nuclear Magnetic Resonance (NMR) techniques, with an aim to benefit catalysis research. Included in this report are studies of pure fluids and their mixtures, confined in titania and silica catalyst supports. These investigations are conducted at industrially-relevant, high-temperature (≥ 180 °C) and high-pressure conditions (up to 13 bar), made possible by a pilot-scale chemical reactor unit, designed to operate inside the strong magnetic fields of an NMR spectrometer. NMR spectroscopy, relaxation and pulsed field gradient (PFG) diffusion experiments were performed on each of the systems discussed in this report. Cyclohexane was initially studied inside a porous titania catalyst support at 188 °C and various pressures up to 13 bar. The adsorption and desorption processes of the cyclohexane were observed, revealing a number of previously unobserved phenomena. In addition to an overall, averaged diffusion coefficient, a slow diffusion coefficient was observed within the PFG NMR data attributable to surface diffusive processes occurring within the material. Additionally, T1 relaxation studies were found to provide experimental evidence for the differing configurations of adsorbed layers on the adsorption and desorption branch of the isotherm. Cyclohexane was subsequently studied alongside fluorobenzene in a series of silica catalyst supports of 6 nm, 10 nm and 20 nm pore size. In doing this, it was hoped that the multiple phenomena observed in the titania experiments might be deconvoluted, allowing a greater level of insight. The diffusivities of the fluids were found to differ significantly between the materials, and greater evidence was found of the slow-diffusing surface phase in each of the materials. Additionally, concentrations of cyclohexane and fluorobenzene in the gas and adsorbed layers inside the pore space were calculated via the results of the PFG NMR experiments, providing a map of confined phase behaviour. Competitive adsorption effects were found to become more significant, the smaller the pore size of the material. The results of the cyclohexane and fluorobenzene in silica studies were modelled, using approaches available in the literature, which were found to give varying levels of prediction. The data set acquired in this thesis was found to provide a useful standard, against which current and future models of confined phase behaviour might be verified.

L’objectif principal de la thèse a été d’étudier les propriétés de résistance des matériaux nanoporeux par des approches théoriques et numériques. Dans le contexte des méthodes d’homogénéisation, des critères de résistance macroscopiques ont été établis par des approches analytiques à l’homogénéisation non-linéaire et à l’analyse limite. Les critères de résistance ainsi obtenus permettent de tenir en compte les effets de taille, tout en améliorant les formulations déjà existantes.
 En outre, dans le but de servir de référence pour la calibration et/ou la validation des modèles analytiques, des simulations numériques basées sur la dynamique moléculaire ont été conduites, en se référant à des monocristaux d’aluminium contenant des nanopores sphériques, sous des conditions multiaxiales de vitesse de déformation. Par rapport aux simulations actuellement disponibles dans la littérature, les résultats obtenus ont clairement établi que les surfaces de résistance sont significativement influencées par les trois invariants isotropes de contrainte.
 Finalement, dans le but de mettre à profit les indications fournies par les simulations numériques, le cas d’un matériau nanoporeux constitué d’une matrice ductile sensible aux trois invariants isotropes a été étudié par une approche par l’analyse limite, en prenant en compte une formulation modifiée du critère de résistance de bigoni. La solution exacte du problème a été établie dans le cas d’un chargement isotrope. A partir des résultats ainsi obtenus, une approche d’analyse limite cinématique a été mise en place, et permet de fournir des estimations des propriétés de résistance macroscopiques sous chargements axisymétriques. / The main objectif of the thesis consisted in investigating strength properties of nanoporous materials by means of theoretical and numerical approaches. In the framework of homogenization methods, novel macroscopic strength criteria have been established via a non-linear homogenization procedure and a kinematic limit-analysis approach. Resulting yield functions allowed to take into account void-size effects on nanoporous materials strength properties, thereby resulting in a strong enhancement of available estimates. Furthermore, aiming to funish effective benchmarking evidence for the calibration and/or the assessment of theoretical models, molecular-dynamics based computations have been carried out on in-silico single crystals embedding spherical nanovoids, simulation domains undergoing multiaxial strain-rate boundary conditions. With respect to available numerical studies, proposed results clearly showed the influence of all the three isotropic stress invariants on computed material strength surfaces. Finally, with the aim to account for physical indications coming from numerical simulations, a ductile nanoporous material with a general isotropic plastic matrix has been investigated via a limit analysis approach, by referring to a modified version of the bigoni strength criterion. The limit state of a hollow-sphere model undergoing isotropic loadings has been exactly determined. Correspondigly, a novel strength criterion has been analytically established in the case of axysimmetric boundary conditions.

>Magister Scientiae - MSc / In the current study, we give a report when oxalic acid was used as an electrolyte to synthesize an AAO template with hexagonal pore array. Optimum parameters were observed as 0.4 M of oxalic acid, anodizing voltage of 45 V, temperature of approximately 8 °C and the period of 120 minutes. Atomic force microscope (AFM) and High resolution scanning electron microscope (HRSEM) showed that template has an average pore diameter of 103 nm. Co and MnOx (x = 1,2) nanostructures were selectively deposited in the pores of the template using a novel atomic layer deposition (ALD) technique. The diameter sizes and the array of the nanostructures and the template were corresponding. Energy dispersive xrays (EDX) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Co and MnOx (x =1,2) on the samples while x-ray diffraction (XRD) provided an indication of their orientations. Magnetic force microscopy as main characterization tool showed the existence of multi-domains on both Co and MnOx (x =1,2) nanostructures. / South Africa

Phase field models have played an important role in shaping our understanding of a variety of micro structural phenomena in materials. Their attractive features include (a) their ability to capture instabilities in microstructures, and (b) their ability to handle topological transitions { such as splitting or coalescence { gracefully. Therefore, we have chosen to use a phase field model in our study of instabilities in cylindrical pores in nanoporous membranes which eventually lead to their failure. Our study is motivated by recent studies on thermal stability of nanoporous membranes of alumina, titania and zirconia. The key feature in our model is its ability to incorporate surface discussion as the mechanism for mass transport. We first benchmark the model through a critical comparison of our results on early stages of surface evolution during Rayleigh instability and grain boundary grooving with those from linear theories of these phenomena. We have then used longer simulations (which go beyond early stages, and therefore, can incorporate non-lineare effects) to study instabilities in a hollow cylinder in three different systems: single crystal or amorphous solid (which fails through Rayleigh instability), a model sys-tem with parallel grain boundaries (which fails through grain boundary grooving), and a polycrystal (whose failure depends on a combination of grain growth and grooving). In all the cases, the surface energy is assumed to be isotropic, and the operative mechanism for mass transport is assumed to be surface discussion.

Le transport d’ions et de molécules à l’intérieur de canaux nanométriques diffère du transport à l’échelle micro- ou macroscopique du fait de rapports surface/volume bien plus élevés conduisant à de nouveaux phénomènes de transport. Les nanotubes de carbone avec leurs propriétés uniques apparaissent comme des canaux exceptionnellement intéressants pour mieux comprendre le transport ionique et fluidique à l’échelle nanométrique et pour d’éventuelles applications nanofluidiques. Ce travail est dédié à l’étude et la compréhension des mécanismes de transport des ions en phase aqueuse à l’intérieur de nanotubes de carbone, un sujet particulièrement important pour le développement d’applications dans le domaine du séquençage de l’ADN ou de l’analyse biochimique de petites molécules.Durant ce travail, un protocole a été développé pour la fabrication de dispositifs microfluidiques intégrant des nanotubes de carbone et permettant des mesures à la fois électriques et optiques. Les propriétés de transport à l’intérieur de nanotubes de carbone mono-feuillets ont été étudiées en combinant mesures de courant ionique sous application d’un champ électrique, spectroscopie Raman et modélisation théorique. Les résultats obtenus par cette étude démontrent la forte influence de l’environnement du nanotube sur la densité et la distribution des charges de surface et donc sur les propriétés de transport à l’intérieur de ces nano-canaux dont les parois sont d’épaisseur atomique. Les ordres de grandeur des courants ioniques mesurés expérimentalement sont en bon accord avec les modèles standards de transport ionique dans un nanocanal en considérant des densités de charge de surface et des longueurs de glissement physiquement raisonnables. De manière importante, ce travail a permis de mettre en évidence un transport ionique activé par champ électrique à l’intérieur de nanotubes de carbone, qui peut être expliqué en considérant un modèle de transport plus élaboré intégrant une ou plusieurs barrières d’énergie le long du nanotube. Les résultats de la caractérisation Raman suggèrent que ces barrières d’énergie résultent d’un dopage hétérogène le long du nanotube induit par la matrice polymère. / Ionic and molecular transport inside nanometer scale geometries is distinct from micro- and macroscale transport due to the large surface-to-volume ratios which lead to unique transport phenomena. Carbon nanotubes with their peerless properties appear as exceptional channels for understanding fluidic and ionic transport at the nanoscale and for developing nanofluidics-based applications. This work is devoted at studying and understanding the transport mechanisms of ions in aqueous phase through carbon nanotubes, which is especially important for various applications such as DNA sequencing or biochemical analysis of small molecules.During this work, a protocol was developed for the fabrication of carbon nanotubes-based microfluidic devices which are suitable for both electrical and optical measurements. The transport properties through single-walled carbon nanotubes were investigated by combining ion current measurements under an applied voltage, Raman spectroscopy and theoretical modelling. The results obtained from this study highlight the strong influence of the nanotube environment on their surface charge density and distribution and hence on the ionic transport properties through these nanochannels having walls of atomic thickness. The orders of magnitude of the ionic currents experimentally measured are in good agreement with the standard models of ion transport through nanochannels when considering physically reasonable values of surface charge densities and slip lengths. Importantly, this work allowed us to evidence a novel voltage-activated transport of ions through carbon nanotubes which can be accounted for by considering a more elaborate transport model including the presence of one or more energy barriers along the nanotube. Raman characterization results support that these energy barriers result from a heterogeneous doping along the nanotubes induced by the polymer matrix.

Single molecule studies using nanopores have gained attention due to the ability to sense single molecules in aqueous solution without the need to label them. In this study, short DNA molecules and proteins were detected with glass nanopores, whose sensitivity was enhanced by electron reshaping which decreased the nanopore diameter and created geometries with a reduced sensing length. Further, proteins having molecular weights (MW) ranging from 12 kDa to 480 kDa were detected, which showed that their corresponding current peak amplitude changes according to their MW. In the case of the 12 kDa ComEA protein, its DNA-binding properties to an 800 bp long DNA molecule was investigated. Moreover, the influence of the pH on the charge of the protein was demonstrated by showing a change in the translocation direction. This work emphasizes the wide spectrum of detectable molecules using nanopores from glass nanocapillaries, which stand out because of their inexpensive, lithography-free, and rapid manufacturing process

Identifying the protein content in a cell in a fast and reliable manner has become a relevant goal in the field of proteomics. This thesis computationally explores the potential for silicon nitride nanopores to sense and distinguish single miniproteins, which are small domains that promise to facilitate the systematic study of larger proteins. Sensing and identification of these biomolecules using nanopores happens by studying modulations in ionic current during translocation. The approach taken in this work was to study two miniproteins of similar geometry, using a cylindrical-shaped pore. I employed molecular mechanics to compare occupied pore currents computed based on the trajectory of ions. I further used density functional theory along with relative surface accessibility values to compute changes in interaction energies for single amino acids and obtain relative dwell times. While the protein remained inside the nanopore, I found no noticeable differences in the occupied pore currents of the two miniproteins for systems subject to 0.5 and 1.0 V bias voltages. Dwell times were estimated based on the translocation time of a protein that exhibits no interaction with the pore walls. I found that both miniproteins feel an attractive force to the pore wall and estimated their relative dwell times to differ by one order of magnitude. This means even in cases where two miniproteins are indistinguishable by magnitude changes in the ionic current, the dwell time might still be used to identify them. This work was an initial investigation that can be further developed to increase the accuracy of the results and be expanded to assess other miniproteins with the goal to aid future experimental work.

As former studies reveal, the nanoporous confinement could have influence on polymorphic drug crystallization. However, little attention has been paid to the question how crystallization of the commonly polymorphic drugs in nanoporous matrices influences the drug release. As a consequence, sufficient information about the crystallization conditions and their influence on phase behavior, crystal texture, and stability of polymorphs should be retrieved prior to drug delivery experiments. Drug release should be polymorph-selective and even crystal face-specific. Therefore, the topic of this PhD thesis is the systematic investigation of crystallization parameters (e.g., pore morphology, thermal history, presence or absence of a bulk surface reservoir) and their influence on the nucleation and crystal growth of the two selected model compounds in nanoporous matrices: acetaminophen (ACE) and n-tetracosane. Both are confined to two host-systems: AAO containing aligned cylindrical, isolated pores and CPG containing curved, interconnected pores. The guest materials inside the two model matrices have been investigated with X-ray diffraction (WAXS) and differential scanning calorimetry. In the first part it is shown that the nanopore morphology of the host systems determines into which polymorphic form ACE crystallizes. Moreover, the pore morphology influences the kinetics of solid/solid transitions. In AAO uniformly oriented form III crystals are converted into also uniformly oriented form II crystals by a solid/solid transition. Such a phase transition is kinetically suppressed in CPG membranes due to the curved pore morphology. In the second step, polymorph-specific release experiments with ACE from AAO membranes reveal that the drug dissolution is not exclusively diffusion-limited and can be described by the Korsmeyer-Peppas model. Dissolution of crystalline ACE having rough crystal faces exposed to the environment is nearly as fast as release of amorphous ACE. Encapsulating of ACE in AAO nanopores with a PLLA polymer retard the drug dissolution but does not modify the release kinetics. In the third part of this thesis crystallization of n-tetracosane, a saturated hydrocarbon, in nanoporous matrices was studied. n-Tetracosane shows inside AAO membranes the rotator phase sequence: triclinic−RV−RI−RII−liquid. Further, the long axes of the n-tetracosane molecules are oriented normal to the AAO pore axes. In general, n-tetracosane under confinement shows a more complex phase behavior than the polymeric analogue polyethylene. The presented work expands the available strategies for mesoscopic crystal engineering. The methods might be transferred into other areas of interest such as polymorphism screening or preparation of different types of nanowires with customized optoelectronic or ferroelectric properties.

Optofluidics is a relatively new and exciting field that includes the integration of optical waveguides into microfluidic platforms. The purpose of this field of study is to miniaturize previously developed optical systems used for biological and chemical analysis with the end goal of placing bench-top optics into microscopic packages. Mundane optical alignment and sample manipulation procedures would then be intrinsic to the platform and allow measurements to be completed quickly and with reduced human interaction. Biosensors based on AntiResonant Reflecting Optical Waveguides (ARROWs) consist of hollow-core waveguides used for fluid sample manipulation and analysis, as well as solid-core waveguides used in interfacing external components located at the chip edges. Hollow-core ARROWs are particularly useful for their ability to provide specifically tailored analyte volumes that are easily configurable depending upon the target experiment. Adaptations of standard planar microfabrication methods allow for complex integrated ARROW designs. Integrated spectral filtering with high rejection can be implemented on-chip, removing the need for additional off-chip components and increasing device sensitivity. Additional techniques to increase device sensitivity and utility, such as hybrid ARROW platforms and optical manipulation of samples, are also explored.

Broadband Dielectric Spectroscopy (BDS) in combination with a nanostructured electrode arrangement – which circumvents the conventional need to evaporate metal electrodes onto soft matter – is used to study the molecular dynamics of several glass forming materials confined in nanometric (> 5 nm) layers. Other complementary experimental tools employed in this work include spectroscopic vis-Ellipsometry (SE), AC-chip calorimetry (ACC), X-ray reflectrometry (XRR), Differential Scanning Calorimetry (DSC) and Atomic Force Microscopy (AFM). The latter is used to characterize the topography of the samples and to determine their thicknesses. Under the conditions of annealing samples (Tg + 50K) in high oil-free vacuum (10E-6 mbars) for at least 12 h and carrying out measurements in inert (dry nitrogen or argon) atmosphere, it is found for all studied thin layers that the structural relaxation, and hence the dynamic glass transition – in its mean relaxation times – remains within a margin ±3 K from the respective bulk behaviour. It is revealed, inter alia, that the one-dimensional confinement of thin films introduces restrictions on other (slower) molecular relaxation processes which manifest, depending on the specific system under investigation, as (i) an interruption of the end-to-end (normal mode) fluctuation of the chains, or (ii) a slowing down of the delta-relaxation when the system is cooled towards glass-formation. Furthermore, (iii) evidence is provided to show that the dimensionality of confinement plays a significant role in determining the resulting dynamics. A molecular understanding of these findings is given, and the discussion presented with respect to the on-going international debate about dynamics in confinement.:1. Introduction 2. The glass transition and chain dynamics 2.1 The phenomenology of the glass transition 2.2 Theories of the glass transition 2.2.1 Free volume theories 2.2.2 Cooperative concepts 2.2.3 Mode-coupling theory 2.3 Dynamics of polymer chains in melt 2.4 The dynamic glass transition in confinement 2.4.1 Experiments: state-of-the-art 2.4.2 Theoretical attempts at explaining dynamics in confinement 3. Sample preparation and experimental techniques 3.1 Thin-film preparation by spin-coating 3.1.1 Films on glass slides 3.1.2 Films on silicon wafers 3.1.3 Reproducibility of sample preparation 3.1.4 Stability of thin film samples 3.1.5 Film thickness determination 3.1.6 Sample annealing experiments 3.2 Use of nanostructured electrodes – a novel approach 3.3 Poly(cis-1,4-isoprene) (PI) in porous media 3.4 Experimental techniques 3.4.1 Broadband Dielectric Spectroscopy (BDS) 3.4.1.1 Polarization 3.4.1.2 Dielectric relaxation 3.4.1.3 Debye relaxation 3.4.1.4 Non-Debye relaxation 3.4.1.5 Dielectric data in the time domain 3.4.1.6 Conductivity contribution 3.4.1.7 The distribution of relaxation times 3.4.1.8 BDS – summary 3.4.2 Spectroscopic Ellipsometry (SE) 3.4.3 AC-chip calorimetry (ACC) 4. Results and Discussion 4.1 Effect of sample geometry on measured dynamics 4.1.1 Introduction 4.1.2 Experimental details 4.1.3 Results and discussion 4.1.4 Summary 4.2 Dynamics of polystyrene in a wide range of molecular weights 4.2.1 Introduction 4.2.2 Experimental details 4.2.3 Results and discussion 4.2.4 Summary 4.3 Molecular dynamics of itraconazole confined in thin supported layers 4.3.1 Introduction 4.3.2 Experimental details 4.3.3 Results and discussion 4.3.4 Summary 4.4 Segmental and chain dynamics in nanometric layers of poly(cis-1,4-isoprene) 4.4.1 Introduction 4.4.2 Experimental details and data analysis 4.4.2.1 Sample preparation 4.4.2.2 Data analysis 4.4.3 Results and discussion 4.4.3.1 1- versus 2-D confinement of poly(cis-1,4-isoprene) 4.4.4 Summary 5 Conclusions 5.1 Dynamics in confinement – a wider perspective