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This document describes an experimental investigation into dense collections of hard spherical particles just large enough to be studied using a light microscope. These particles display colloidal properties, but also some similarities with granular materials. We improve the quantitative analysis of confocal micrographs of dense colloidal systems, which allows us to show that methods from simulations of granular materials are useful (but not sufficient) in analysing colloidal systems, in particular colloidal glasses and sediments. Collections of spheres are fascinating in their own right, but also make convincing models for real systems. Colloidal systems undergo an entropy-driven fluid-solid transition for hard spheres and a liquid-gas transition for suitable inter-particle attraction. Furthermore, experimental colloidal systems display a so far not well-understood glass transition at high densities, so that the equilibrium state is not achieved. This may be due to limited experimental timescales, but experiments under reduced gravity (both using the Space Shuttle and densitymatching solvents) suggest that it is not. Most colloidal studies have used scattering (i.e. non-microscopical) techniques, which provide no local information. Microscopy (particularly confocal) allows individual particles and their motion to be followed. However, quantitative microscopy of densely-packed, solidlyfluorescent particles, such as colloidal glasses, is challenging. We report, to our knowledge for the first time, a quantitative measure of confidence in individual particle locations and use this measure in an iterative best-fit procedure. This method was crucial for the investigation of the colloidal samples reported in this thesis. One of the disadvantages of microscopy is that it requires particles too large to be truly colloidal; gravity is no longer negligible. The particles used here rapidly sediment to form solid ”plugs”, which are supposedly ”random close packed” (RCP). At least in some cases, this is not the case, since some particles remain free to move. This observation, as well as some literature results, suggest that gravity has some influence on the structure of the sediment. In this document we consider some ideas from literature not normally considered in colloidal studies. Firstly, we discuss the RCP state, and the preferred Maximally Random Jammed state. Secondly, we borrow a technique designed to identify structures known as bridges in simulations of granular materials. Finding bridges, i.e. structures stable against gravity, in colloidal samples is the primary aim of this thesis. Gravity is important in colloidal sphere packings both in sediments and in glasses; its effect is not known but the best available candidate is bridging. The basic results of this analysis, the bridge size distributions, are close to those for granular systems, but differ little for samples of different volume fractions. We identify important stages of the analysis which require more investigation. Whilst questioning the usefulness of the bridge properties, we identify some related packing properties which show interesting trends. No theoretical predictions exist for these quantities. We investigated initially a non-density-matched system, but compare our results with a nearly density-matched system. The results from both systems are similar, despite the particles apparently acquiring a charge in the latter case. This thesis shows that reliable confocal microscopy of very dense systems of solidly-fluorescent particles is possible, and provides a range of unreported properties of dense sedimenting and sedimented nearly-Brownian sphere packings. It provides several suggestions for further analysis of these experimental systems, as well as some to be performed by those who simulate granular matter.

In this thesis we used atomic force microscopy (AFM) to investigate systematically the behaviour of both electrostatically stabilised silica and sterically stabilised polystyrene (PS) colloidal systems on freshly cleaved mica substrates. For the silica colloidal nanoparticles we explored the effect of colloidal suspension concentration, particle size, and different application techniques on both the adsorption behaviour and subsequent structuring of the particles. For the PS colloidal nanoparticles we explored concentration effects and experimented with both dip-coating and droplet application techniques. We showed that silica nanoparticles adsorbed onto mica via irreversible adsorption that possessed lateral mobility due to the weak attraction between the nanoparticles and the substrate, facilitating subsequent capillary structuring of the nanoparticles during drying. We associated the effects of volume fraction with Debye screening, and kinetics effects with particle size and volume fraction. We also successfully imaged a partially dried film and showed the role of convective/capillary forces in the structuring of the nanoparticles. Studies with variations in particle size generated a number of different topography structures; with dewetting phenomena observed for 10 nm nanoparticles and the formation of crystalline structures for 100 nm nanoparticles. Spin coating techniques were used to produce even larger crystalline structures of nanoparticles. Size dependent ordering occurred for low concentration samples due to the polydispersity of the colloidal suspension. We showed that acceleration can affect interparticle spacing. We also studied the role of rotational speed on the crystallinity of the particle configurations and showed how fine tuning of rotational speed can generate large scale monolayer crystalline formations of nanoparticles.

Orientador: Edvaldo Sabadini, Fred Yukio Fujiwara / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-19T09:00:39Z (GMT). No. of bitstreams: 1 Egidio_FernandadoCarmo_D.pdf: 2263055 bytes, checksum: 940b47bd50de20f4597683b091bd3faf (MD5) Previous issue date: 2011 / Resumo: O modelo de dois sítios, utilizado nos estudos de relaxação do solvente em soluções de carboidratos, pode ser transposto de forma satisfatória para soluções de polímeros hidrofílicos. Polímeros que possuem hidrogênios lábeis, isto é, que possuem hidrogênios disponíveis para troca química com os hidrogênios da água, causam aumento da taxa de relaxação spin-spin do solvente, R2, em relação ao valor obtido para a água pura O efeito torna-se mais intenso na medida em que a concentração dos polímeros aumenta. Polímeros que não possuem hidrogênios lábeis não alteram significativamente o R2 do solvente, pois o mecanismo de troca química não é estabelecido. A relaxação do solvente pode ser usada para estudar o processo de transição sol-gel em sistemas poliméricos. Conforme o gel e formado, as moléculas de água começam a ser confinadas e a taxa de relaxação do solvente aumenta significativamente. A estrutura de hidrogéis supramoleculares formados entre PEG e a-CD, a qual possui uma cavidade hidrofóbica em relação ao seu exterior hidrofílico, dependem das concentrações de seus constituintes e da massa molar do polímero. Quanto maior a massa molar do polímero, menor o numero de pontos de reticulação e mais frágil será o hidrogel. A partir da entrada de 2 moléculas de a-CD em uma cadeia de PEG linear 1.470 Da, a complexação torna-se mais intensa, levando ao recobrimento de toda a cadeia polimérica. A cinética de gelação entre a-CD e PEG, estudada por medidas do tempo de relaxação spin-spin (T2 = 1/R2) do solvente, fornece um perfil de curva que pode explicar o processo de complexação e formação do gel como um todo. A liberação e o confinamento de moléculas de água são refletidos no tempo de relaxação spin-spin destas. Ao liberar moléculas de água, observa-se uma diminuição nos valores de R2 da água até um ponto mínimo, a partir do qual os valores começam a aumentar devido ao confinamento destas moléculas / Abstract: The two sites model used in the studies of solvent relaxation in carbohydrate solutions was also applied for hydrophilic polymer solutions. Polymers with labile hydrogen atoms, meaning they have hydrogen available for chemical exchange with the hydrogen atoms of water, increase the solvent spin-spin relaxation rate, R2, relative to the pure water. The effect becomes more intense as the polymer concentration increases. Polymers without labile hydrogen do not affect significantly R2 of the solvent, because the chemical exchange mechanism is not established in this case. The solvent relaxation can be used to study the process of sol-gel transition in polymer systems. When the gel is formed, the water molecules become confined and the solvent relaxation rate increases significantly. The structure of supramolecular hydrogels formed from PEG and a-CD, which has a hydrophobic cavity and exterior hydrophilic, depends on the concentration of the constituents and the molar mass of the polymer. The higher is the molar mass of the polymer, the fewer is the crosslinking points and more the fragile is hydrogel. Since the inclusion of two a-CD molecules in a chain of linear PEG 1470 Da, the complexation becomes more intense, leading to the full inclusion complex. The kinetics of hydrogel formation between a-CD and PEG was studied by relaxation time measurements of the spin-spin (T2 = 1/R2) of the solvent, provides a curve, whose shape can used to explain the process of complexation and the gelation process at all. The release and confinement of water molecules of the gel are affect spin-spin relaxation the time of the water molecules. The releasing of the water molecules, results in the decreasing of R2 up to a minimum value, and beyond this point the values increases again, due to confinement of these molecules / Doutorado / Físico-Química / Doutor em Ciências

The synthesis of pyridinium cationic lipids, their counter-ion exchange, and the transfection of lipoplexes consisting of these lipids with firefly luciferase plasmid DNA (6.7 KDa), into lung, prostate and breast cancer cell lines was investigated. The transfection ability of these newly synthesized compounds was found to be twice as high as DOTAP/cholesterol and LipofectamineTM (two commercially available successful transfection agents). The compaction of the DNA onto silica (SiO2) nanoparticles was also investigated. For this purpose, it was necessary to study the stability and fusion studies of colloidal systems composed of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine), a zwitterionic lipid, and mixtures of DMPC with cationic DMTAP (1,2-dimyristoyl-3-trimethylammonium-propane). / Chemistry