Preparation of Highly Crystalline Magnesium Oxide and Polystyrene/ Magnesium Hydroxide Composite Particles by Sol-Gel Processes in an Ionic Liquid

摘要

Highly crystalline magnesium hydroxide (Mg-(OH)2) was obtained by sol-gel process using magnesium nitrate (Mg(NO3)2) with ammonium hydroxide (NH4OH) in a hydro-philic ionic liquid, l-butyl-3-methylimidazolium chloride ([Bmim]-Cl) as a medium. Crystallite size of Mg(OH)2 obtained in [Bmim] CI was larger than that obtained in 2-propanol (used as a medium for comparison), which indicates that [Bmim] Cl worked as a template. The obtained Mg(OH)2 was transformed to magnesium oxide (MgO) by heat treatment under atmospheric pressure. After heat treatment, crystallite size of the MgO obtained in [Bmim]Cl was also larger than that obtained in 2-propanol, reflecting the crystallinity of Mg(OH)2 before heat treatment. Polystyrene (PS)/ Mg(OH)2 composite particles were successfully prepared by seeded dispersion sol-gel process in [Bmim] Cl in the presence of PS seed particles. The composite particles had smooth surfaces and core-shell morphology consisting of PS core and Mg(OH)2 shell having high crystallinity. The Mg(OH)2 content of the composite particles calculated from the weight loss measured by thermogravimetry (l7 wt %) agreed well with the theoretical value (19 wt %). Using 2-propanol as a medium, secondary nucleation of Mg(OH)2 was observed, and composite particles were not obtained. It was clarified that the core-shell structure was consistent with the predicted morphology from the viewpoint of the spreading coefficients calculated from the interfacial tensions.