| This work focused on tailoring of pore structures and properties of syndiotactic polystyrene (sPS) aerogels, using proper selection of materials and preparation techniques, and further elucidating the structure-property relationships of aerogels.;An inorganic-organic hybrid mesoporous aerogel structure was synthesized by growing silica gel inside the networks of thermo-reversible sPS gel, and vice versa. The hybrid gel was converted into aerogel by exchanging the solvent with liquid carbon dioxide followed by supercritical drying. The aerogel presented a co-continuous network of pearl-necklace silica particles and strands of crystalline sPS and exhibited the 'petal effect' due to superhydrophobic sPS and hygroscopic silica. The compressive modulus and strain showed large enhancements over those of sPS and silica aerogels, indicating synergy. The hybrid aerogel showed a fast absorption rate and high absorption capacity for a representative hydrocarbon liquid. These results are presented in Chapter III.;In Chapter IV, a method for rendering sPS aerogels hydrophilic using polyethylene oxide (PEO) of different molecular weights was evaluated. The gels were prepared by thermo-reversible gelation in tetrahydrofuran (THF) in the presence of PEO. The gels were dried under supercritical condition to obtain aerogels. The data revealed that the pore structures and the surface energy could be controlled by varying the concentration and molecular weight of PEO and using different cooling rates during thermo-reversible gelation. In the first case, sPS aerogels, aerogels containing PEO of low molecular weight or low concentration showed superhydrophobic surfaces presenting the 'lotus effect'. In the second case, PEO at higher concentration or with higher molecular weight forms phase separated domains yielding new hydrophilic macropores (> mum) in the aerogel structures. These macropores contributed to superhydrophobic surface with the 'petal effect'. The cooling rate during gelation showed a strong influence on these two cases.;In Chapter V, a 'bottom up' approach to introduce sulfonic acid groups into the sPS gel/aerogel was applied. The sPS chains were modified by sulfonic acid groups, and the resultant ssPS was allowed to self-assemble into a gel network in THF. The crystalline domains of sPS acted as physical cross-linkers and the sulfonic acid domains served as functional entities. The high surface area networks of ssPS gels were utilized as templates to adsorb and protonate aniline. Polymerization of aniline was then initiated within these fixed domains by diffusion of an oxidant. The morphology and the pore structure of polyaniline coated aerogel showed dependences on the sulfonation level and solid polymer concentration. A uniform coating and narrow pore size distribution was achieved in the gel prepared from 0.15 g/mL of 10% sulfonated sPS.;In Chapter VI, the effects of multi-walled carbon nanotubes (MWCNTs) on density, surface area, compressive strength, and electrical conductivity of sPS aerogels were investigated. The non-covalently modified MWCNTs were dispersed in sPS solution before thermo-reversible gelation of the polymer. It was found that the sPS phase formed strands of approximately 50 nm in diameter and that MWCNTs formed an interpenetrating network within the sPS aerogel. The presence of MWCNTs caused little change in the morphology and crystalline structure of sPS, and the surface areas of the aerogels, but significantly increased the compressive modulus and electrical conductivity. |
