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Novel sulfonated poly(arylene ether sulfone)s multi-block copolymer membranes containing highly sulfonated hydrophilic blocks were synthesized. Different local concentration of sulfonic acid in their hydrophilic blocks affected chemical and physical properties of the SPAES. To investigate the effects of chemical composition on their membrane properties, different hydrophilic oligomers sharing same hydrophobic blocks gave us exact comparison of effect of hydrophilic blocks. The higher concentration of sulfonic acid groups resulted in higher proton conductivity under certain relative humidity conditions than that of the state-of-the-art perfluorinated sulfonic acid membrane and showed that the well-developed phase separation of SPAES.
A base monomer (1-vinyl imidazole, VIDz) was polymerized in the Nafion 112 membrane by UV irradiation in order to reduce methanol permeability. Small angle X-ray scattering analysis revealed that the size of hydrated ion cluster in the composite Nafion membranes was reduced and equilibrium water uptakes from liquid and vapor water were decreased with increasing VIDz content of the membrane. The transport properties such as ion conductivity, methanol permeability and electroosmotic drag were also affected by equilibrium water uptake and hydrated pore size. Even a little incorporation of base polymer showed a significant effect on proton conductivity and methanol permeability. Electro-osmotic drag of methanol was evaluated by using ex-situ methanol permeability test and in-situ limiting current density measurement. Although it was not easy to obtain the absolute number of methanol transported by electro-osmotic drag, it was possible to correlate the electro-osmotic drag of methanol with the state of water present in the composite membrane. The composite membrane with an optimum amount of VIDz was found to increase DMFC performance higher than that of Nafion membrane because of reduced methanol permeability and electro-osmotic drag effect.
Silicon nitride samples with aligned whisker seeds were prepared with different amounts of yttria and alumina as the sintering additives. Their sintering behaviors and the microstructural developments between 1850℃ and 2050℃ were examined. The sample with larger amount of the sintering additives showed faster densification and grain growth Even though addition of the aligned whisker seeds slightly retarded densification of silicon nitride, it improved the flexural strength and the fracture toughness. Both the flexural strength and the fracture toughness of silicon nitride with the aligned whisker seeds were increased as the amount of the sintering additives was increased.