Colloidal crystallization of spindle-shaped hematite particles coated with polymer brush in deionized aqueous suspension

摘要

Colloidal crystallization of highly monodisperse spindle-shaped hematite particles coated with poly(poly(ethylene oxide) methyl ether methacrylate) brush (SHB) was studied by reflection spectroscopy and optical microscopy. SHB suspensions were deionized exhaustively with the mixtures of cation- and anion-exchange resins more than 6 months. The liquid thin film along the vertical cell wall above the horizontal air-liquid interface showed the strong color bands. Furthermore, the reflection spectra composed of many sharp peaks shifted continuously toward shorter wavelengths with time. These observations support the presence of thin film of SHB suspension, where the width is thickened downward by the gravity and the layered liquid further flow downward with time. The rigidities of SHB crystals in the bulk phase estimated from the optical microscopy in the sedimentation equihbrium were 0.007 to 0.7 Pa as SHB concentration increased from 0.006 to 0.35 wt.%. The fluctuation parameter, b-factors of the anisotropic crystals, was from 0.025 to 0.035 and decreased slightly as particle concentration increased. Rigidities and the fluctuation parameters of SHB suspensions support that the elastic properties of the anisotropic-shaped colloidal crystals are close to those of typical crystals of colloidal spheres. Compression of the SHB crystals by the gravity is also suggested in the sedimentation equilibrium state.