Microstructure and liquid mass transport control in nanocomposite materials

Doctoral thesis, 2015

Some of the biggest problems currently facing the world are closely tied to unsolved technological challenges in the material sciences. Many materials have a porous microstructure that controls their overall properties. In the case of porous materials their properties often relate to how liquids and dissolved substances move (liquid mass transport) through the pores of the material and how these substances interact with the pore walls. Challenges related to such processes can be found in applications related to energy storage, oil well engineering, food, chromatography, and drug release. It is not a trivial matter to design a material synthesis method that reproducibly produces a robust material with the correct pore-structure and surface properties and in the end, the intended function. An added difficulty is that the material should maintain its function over the intended usage period. These generic difficulties summarizes why some technological problems related to porous materials still remains unsolved. The research community is therefore trying to acquire a better understanding of the mechanisms that governs how the synthesis process affects the microstructure and the resultant liquid mass transport properties. The focus of this work has been to investigate the nanoparticle organization in dispersions and in aggregated microporous materials, and how this organization affects the liquid diffusion and permeability through the material. To study these processes several model material synthesis methods, characterization techniques, and theoretical models were developed. Specifically the work investigated how the particle concentration, shape and aggregation conditions affected the formed microstructure. The role of microstructure anisotropy was investigated by aligning plate-shaped particles in magnetic fields during the material synthesis. In addition, the effect of several different additives on the magnetic alignment process was explored. Furthermore, a responsive nanocomposite material was synthesized in which temperature could be used to reversibly adjust the pore size of the material. The findings showed that particle concentration, aggregation conditions, magnetic fields and temperature responsive microgels can be used to control the liquid mass transport through colloidal dispersions and gels. In some cases the experimental results together with simulations were used to derive microstructure and mass transport correlations for different particle aggregation conditions. These correlations are of general application when predicting the pore size and liquid mass transport in aggregated nanoparticle materials.