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This thesis is concerned with using diffusing molecules as a probe to understanding changes in both two- and three-dimensional polymer systems. Fluorescence correlation spectroscopy (FCS) is used to measure the diffusion coefficient of a fluorescently labelled molecule within poly (methacrylic acid) (PMAA hydrogels and adsorbed onto poly(alkyl mcthacrylate) thin films. Responsive hydrogels such as PMAA arc of great importance in controlled release systems such as drug delivery. The hydrogcls studied were found to respond to temperature, pH. and salt concentrations in ways that can be utilised for producing systems that change in predetermined ways under controlled conditions. Thin polymer films. both homopolymer and polymer blends are found to exhibit a transition process between glass and liquid states. Existing theories present the transition as a sharp. almost instantaneous process but FCS and ellipsometric measurements find this to be an insufficient model. Not only is the glass transition found to occur over a temperature range but the diffusion of adsorbed molecule and the measured friction coefficient. Are found to increase dralllatically at the transition temperature range after which they are similar to the values below the transition. Furthermore polymer blends (Ire found to exhibit two distinct transitions. each with an increase in adsorbed diffusion that are unexpected in the existing theoretical understanding of polymer blends.

The structural and magnetic properties of nickel manganite (NiMn(_2)O(_4)) have been investigated, for bulk, and thin film samples. NiMn(_2)O(_4) has partially inverted spinel structure, Mn(_v)Ni(_1-v)[Ni(_v)Mn(_2-v]O(_4), where v is the inversion parameter. Bulk samples were produced from co-precipitated metal hydroxides at various firing times and temperatures. Particular attention was given to determining the optimum preparation route. Nickel oxide was the major impurity encountered due to sub-optimal preparation conditions, but was difficult to detect using diffraction, due to considerable Bragg reflection overlap with those NiMn(_2)O(_4). Nickel oxide is believed to have been present in most samples studied by other researchers in the field. Pure material formed in air after firing for 48 hours in the region 780 C to 820 C; a much smaller range than previously reported. By controlling the cooling rate after firing, 0.7483(19) ≤ v ≤ 0.8830(22) was obtained; as determined by neutron diffraction measurements. Ferrimagnetic Curie temperatures (T(_c)) between 100 K and 147 K were obtained for the range of v studied; somewhat lower than previously reported. The magnetization below T(_c) exhibits P-type behaviour, which has hitherto not been observed in this compound. Evidence compatible with a local canted state at temperatures below -10 K was observed using muon spectrometry. The magnetic properties of electron-beam evaporated thin films of NiMn(_2)O(_4) were investigated with a custom built Alternating Gradient Field Magnetometer. The AGFM was initially constructed for a study of Dilute Magnetic Semiconductor (DMS) materials, and was capable of temperatures down to 77 K, and resolution of 14 pJT(^1). This instrument used a mechanically resonant quartz fibre sample holder, and piezoelectric detection. The response of the instrument to temperature drift, applied magnetic field, and differing sample properties is reported. The T(_c) of a typical thin film sample was measured, and v= 0.788(8) inferred from the relationship with T(_c), as determined for bulk material.

Absorbance spectra and colour for a coloured soda-lime-silica glass can be predicted from colorant concentrations and melting conditions; and conversely: the concentrations for each colorant ion, valence and site (octahedral, tetrahedral) can be "measured" from an absorbance spectrum. The necessary accurate mathematical descriptions for the absorbance spectra of the two most common colorants and contaminants, Cu and Fe, have been developed over the wavenumber range extending from UV to Near IR (200 - 3300 nm) in a soda-lime-silica (NCS) glass, singly or doubly doped with Cu and Fe. The effect of melting conditions on the absorbance spectra are studied over a concentration range from contamination level 0,01 to 2 mol % of added colorant. The obtained fitted spectra have been used to analyse the mutual redox ratios and concentrations of the Fe and Cu ions and sites for a number of contaminated, singly and doubly doped glasses at varied concentration levels, melted in reducing and oxidising conditions. The obtained absorbance spectra are in accordance with the known ligand field theory and each fitted absorbance peak has been identified, and the site configurations for each ion identified. Accurate fitting parameters of the absorbance spectra of Cu and Fe ions have been obtained for summed Gaussian peaks for each valence (Cu"', Cu2`, Fe2+ and Fe 3) and site (Fe2+ octahedral and tetrahedral, Fe 3+ octahedral and tetrahedral) in NCS glasses melted in oxidising and reducing conditions. The fitting parameters (peak heights, i. e. absorbance coefficients in (cm*mol %)-' units, peak positions and peak widths) have been defined and calibrated with known data for all five peaks of Fe2+ ions, nine peaks of Fe 3+ ions, four peaks of Cu2+ ions and one peak for Cu'+ ions, including the UV peaks of all these ions that define the UV-edge of the absorbance spectra and in most cases extend far into the visible range. Equally accurate fitting parameters and functions are developed also for background loss corrections of absorbance caused by surface reflections, OH-bands and IR-edge. For the first time the fitted spectra are shown to scale with Fe and Cu concentrations so well that the developed fitting method can be meaningfully used to analyse doubly and singly doped glasses melted under various conditions. Small, of the order of 0,002 mol % changes in site concentrations, e. g. for Fe 2+ ions in tetrahedral sites, can be repeatedly measured. The melting conditions have a complex effect on the spectrum of Fe 3+ ions in tetrahedral and octahedral sites, changing the proportion of the concentrations. Fe 2+ ions cause significant absorbance over the entire wavelength range studied. Several other novel results are also reported.

This thesis describes investigations of several complex fluid effects., including hydrodynamic spinodal decomposition, viscous instability. and self-assembly of a cubic surfactant phase, by simulating them with a lattice Boltzmann computational model. The introduction describes what is meant by the term "complex fluid", and why such fluids are both important and difficult to understand. A key feature of complex fluids is that their behaviour spans length and time scales. The lattice Boltzmann method is presented as a modelling technique which sits at a "mesoscale" level intermediate between coarse-grained and fine-grained detail, and which is therefore ideal for modelling certain classes of complex fluids. The following chapters describe simulations which have been performed using this technique, in two and three dimensions. Chapter 2 presents an investigation into the separation of a mixture of two fluids. This process is found to involve several physical mechanisms at different stages. The simulated behaviour is found to be in good agreement with existing theory, and a curious effect, due to multiple competing mechanisms, is observed, in agreement with experiments and other simulations. Chapter 3 describes an improvement to lattice Boltzmann models of Hele-Shaw flow, along with simulations which quantitatively demonstrate improvements in both accuracy and numerical stability. The Saffman-Taylor hydrodynamic instability is demonstrated using this model. Chapter 4 contains the details and results of the TeraGyroid experiment, which involved extremely large-scale simulations to investigate the dynamical behaviour of a self-assembling structure. The first finite- size-effect- free dynamical simulations of such a system are presented. It is found that several different mechanisms are responsible for the assembly; the existence of chiral domains is demonstrated, along with an examination of domain growth during self-assembly. Appendix A describes some aspects of the implementation of the lattice Boltzmann codes used in this thesis; appendix B describes some of the Grid computing techniques which were necessary for the simulations of chapter 4. Chapter 5 summarises the work, and makes suggestions for further research and improvement.

Στην παρούσα εργασία μελετήθηκαν μια σειρά ύαλοι στο ψευδοδυαδικό υαλοποιήσιμο σύστημα MgSiO3 – Mg2SiO4 συνδυάζοντας την φασματοσκοπία Raman με τις τεχνικές αιώρησης χωρίς επαφή και χρήση CO2 laser για την θέρμανση και την τήξη των υλικών. Μετρήθηκαν τα πολωμένα και αποπολωμένα φάσματα Raman σε συνθήκες περιβάλλοντος για όλες τις συστάσεις. Τα αποτελέσματα έδειξαν ομαλές και συστηματικές αλλαγές στις εντάσεις των κορυφών. Η ανάλυση των κορυφών Raman που παρατηρούνται στα φάσματα έγινε με όρους δονήσεων που οφέιλονται στα διάφορα γεφυρωτικά άτομα οξυγόνου των τετραέδρων SiO4 (ανάλυση ειδών Qn) και διαπιστώνεται η ύπαρξη τους στα άμορφα υλικά ακόμα και στο όριο της σύστασης της ένωσης Mg2SiO4. Στα φάσματα Raman χαμηλών συχνοτήτων παρουσιάζεται η συχνότητα της κορυφής Boson να είναι σταθερή, όπως συμβαίνει και στους τρόπους δόνησης των ειδών Qn, υποδηλώνοντας με αυτό τον τρόπο ότι δεν συμβαίνει καμία απότομη δομική αλλαγή μεταβάλλοντας την σύσταση. Προτείνεται ότι στη σύσταση της ένωσης Mg2SiO4 δημιουργείται ένα ιοντικό γυαλί, το οποίο προέρχεται από ένα πολύ «εύθραυστο» υγρό. / Container-less levitation techniques and CO2 laser heating were used to melt SiO2-MgO mixtures and prepare a series of glasses with compositions from enstatite MgSiO3 to forsterite Mg2SiO4 in intervals of ~0.02 mol% SiO2. Polarized and depolarized Raman spectra measured at ambient conditions for all these glasses show systematic and smooth band intensity changes with composition. Analysis of the Raman band contours in terms of vibrations due to different oxygen bridged SiO4 tetrahedral (Qi, species analysis), undoubtedly shows that bridging oxygens are present in all glass studied even in the limit of the forsterite composition (Mg2SiO4). The Boson peak frequency is invariant and the vibrational modes of the Qi species do not reflect any abrupt structural changes with composition. It is suggested that the forsterite (Mg2SiO4) forms an ionic-like glass arising from a very fragile liquid.

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Afin d'établir un lien entre les solutions servant de modèles dans la préparation de matériaux mésoporeux, on étudie les propriétés physiques à l'équilibre et hors équilibre de solutions micellaires aqueuses à base de deux tensioactifs fluorés : C8F17C2H4(OC2H4)9OH, [RF8(EO)9] and C7F15C2H4(OC2H4)8OH, [RF7(EO)8]. Cette étude devrait nous aider à comprendre pourquoi on obtient des matériaux mésoporeux bien ordonnés à partir de solutions micellaires du tensioactif RF8(EO)9 et des structures désordonnées lorsque l'on utilise RF7(EO)8. Les expériences sont menées sur quatre systèmes de deux surfactants: RF7(EO)8/H2O, RF7(EO)8/NaI/H2O, RF8(EO)9/H2O et RF8(EO)9/NaCl/H2O. Plusieurs techniques expérimentales sont utilisées: rhéologie, biréfringence d'écoulement et diffusion de neutrons aux petits angles dans le but de décrire ces quatre systèmes. Les diagrammes de phase des deux tensioactifs montrent qu'une phase micellaire L1 existe dans une large gamme de température et concentration. Mais dans tous les cas, la distance à la courbe de miscibilité a une influence sur les caractéristiques rhéologiques bien que toutes les solutions soient une phase L1. La biréfringence d'écoulement des deux systèmes apporte des informations complémentaires quant à la taille et la forme des micelles. Pour les deux systèmes, avec et sans sel, les résultats suggèrent l'existence de petites micelles allongées liées en chaines par des forces faibles excepté pour le système RF8(EO)9 qui ne présente pas de biréfringence notable; les micelles sont probablement petites avec une forme voisine de la sphère. Pour les quatre systèmes, on observe une perte du caractère Maxwellien lorsque les conditions de concentration et de température se rapprochent de la courbe de miscibilité. Ces résultats confortent l'idée selon laquelle : les conditions thermodynamiques choisies pour l'addition de la silice ne doivent pas être trop proches de la courbe de miscibilité, afin d'obtenir des matériaux mésoporeux ordonnés. Dans ces conditions, les solutions sont Maxwelliennes et les matériaux mésoporeux synthétisés sont ordonnés / To provide a link between the micellar templates and the mesoporous material characteristics in the final product, the physical properties of aqueous systems prepared with two kinds of fluorinated surfactants are described and analyzed under equilibrium and out-of-equilibrium conditions: the surfactants are C8F17C2H4(OC2H4)9OH, [RF8(EO)9] and C7F15C2H4(OC2H4)8OH, [RF7(EO)8]. This study may help us to understand why the ordered mesoporous materials are recovered only when RF8(EO)9 micellar solutions are used as building blocks while RF7(EO)8 solutions give rise to wormhole like structure. The distance to the lower consolute boundary (LCB) and a shift in position by salt additions are also taken into account. The experiments concern four systems of two surfactants; 1) pure RF7(EO)8 in water, 2) RF7(EO)8 in the presence of the NaI salt, 3) pure RF8(EO)9 in water, and 4) RF8(EO)9 in the presence of the NaCl salt. Several experimental techniques have been used (rheology, flow birefringence, neutron scattering) to shed light on the physical difference between the four systems. The phase diagrams of both surfactants show that a direct micellar phase (L1) exists in a wide range of concentrations and temperatures. In any cases, the distance to the LCB is a parameter which influences rheological behaviour although the micellar phase still is a L1 phase. The flow birefringence experiments performed on both systems bring complementary information of the size and shape of the micelles. For both systems, with and without salt, the results suggest the existence of small elongated micelles linked by weak forces except for the RF8(EO)9 system which shows no birefringence; the micelles in solution are probably small with a shape close to a sphere. From all four systems, the loss of the Maxwellian character is generally observed when the conditions approach the miscibility curve. These results consolidate the assumption that in order to prepare ordered mesoporous materials, the thermodynamical conditions at which the silica precursor is added to the micellar solution should not be too close to the miscibility curve. Therefore, this study suggests that the Maxwellian character seems to be a pre-requisite condition of the micellar solution for obtaining ordered mesoporous materials