Structure and dynamics of complex materials in the water-poor regime

Sammanfattning: In the solid state, molecules are normally ordered in a specific structure. With time, and as a result of influence from the surroundings, solid materials can change their molecular and/or crystal structure and, as a consequence, obtain completely different properties. Water is particularly important in this respect. Adsorption of minuscule amounts of water from the atmosphere may have huge effects on the properties and stability of solid materials. For instance, in pharmaceutics this can lead to harmful consequences if an active substance, with a specific solid-state structure, suddenly changes due to interaction with adsorbed moisture. In processing and during storage, it is therefore important to have a detailed molecular understanding of the material properties and how they depend on water content. The primary aim of this thesis is to investigate the effects of small amounts of adsorbed water on molecular structure and dynamics in complex materials. In this water-poor regime (loosely defined as <5% of water), solid substances are normally investigated by means of X-ray scattering, gravimetric techniques and calorimetry. In the thesis, these conventional techniques are supplemented by solid-state NMR. This opens new possibilities to understand not only the structure, but also the dynamics of the materials. The complex materials investigated in the thesis belong to the two large substance classes of surfactants and polymers. These types of substances are used widely in everyday products, such as pharmaceutics, paper, textiles, cosmetics and hygiene products. The results in the thesis show that solid-state NMR can be used to construct the equilibrium phase diagram of surfactant systems, in this case tetradecylmaltoside/H_2O in the water-poor regime, and also to determine the regions of metastability of the non-equilibrium solid phases. The combination of solid-state NMR and X-ray scattering is a powerful tool to elucidate the structure and molecular dynamics of crystalline carbohydrates, exemplified by cyclodextrins, upon hydration. Similarly, solid-state NMR was used to extract information about molecular structure and dynamics in different stages of cellulose dissolution. The solid and dissolved cellulose was investigated in aqueous dissolution media together with cosolutes sodium hydroxide or tetrabutylammonium hydroxide. Another area of application of polymers is within renewable power energy where they are used in polymer electrolyte membrane fuel cells. As a way of optimizing the functionality we used NMR-based diffusometry to investigate transport behaviour as a function of polymer membrane structure, temperature and water content. In the solid state, molecules are normally ordered in a specific structure. With time, and as a result of influence from the surroundings, solid materials can change their molecular and/or crystal structure and, as a consequence, obtain completely different properties. Water is particularly important in this respect. Adsorption of minuscule amounts of water from the atmosphere may have huge effects on the properties and stability of solid materials. For instance, in pharmaceutics this can lead to harmful consequences if an active substance, with a specific solid-state structure, suddenly changes due to interaction with adsorbed moisture. In processing and during storage, it is therefore important to have a detailed molecular understanding of the material properties and how they depend on water content. The primary aim of this thesis is to investigate the effects of small amounts of adsorbed water on molecular structure and dynamics in complex materials. In this water-poor regime (loosely defined as <5% of water), solid substances are normally investigated by means of X-ray scattering, gravimetric techniques and calorimetry. In the thesis, these conventional techniques are supplemented by solid-state NMR. This opens new possibilities to understand not only the structure, but also the dynamics of the materials. The complex materials investigated in the thesis belong to the two large substance classes of surfactants and polymers. These types of substances are used widely in everyday products, such as pharmaceutics, paper, textiles, cosmetics and hygiene products. The results in the thesis show that solid-state NMR can be used to construct the equilibrium phase diagram of surfactant systems, in this case tetradecylmaltoside/H_2O in the water-poor regime, and also to determine the regions of metastability of the non-equilibrium solid phases. The combination of solid-state NMR and X-ray scattering is a powerful tool to elucidate the structure and molecular dynamics of crystalline carbohydrates, exemplified by cyclodextrins, upon hydration. Similarly, solid-state NMR was used to extract information about molecular structure and dynamics in different stages of cellulose dissolution. The solid and dissolved cellulose was investigated in aqueous dissolution media together with cosolutes sodium hydroxide or tetrabutylammonium hydroxide. Another area of application of polymers is within renewable power energy where they are used in polymer electrolyte membrane fuel cells. As a way of optimizing the functionality we used NMR-based diffusometry to investigate transport behaviour as a function of polymer membrane structure, temperature and water content.