Drying dissipative structures of spindle-shaped hematite particles coated with polymer brush

摘要

Macroscopic and microscopic drying patterns were observed on a cover glass, a watch glass, and a Petri glass dish during dryness of aqueous suspensions of spindle-shaped particles of hematite coated with polymer brush (SHB). Outer and inner broad rings formed and the spoke-lines appeared especially on a watch glass at the intermediate initial concentration of SHB. Cooperative drying processes of the convection, sedimentation, and solidification were supported also for the anisotropic particles. Most of the long axes of SHB particles distributed parallel to the substrate plane. There appeared the microscopic alignment of the several ten micrometers similar-sized aggregates composed of the SHB particles. The parallel-and/or flower-like (or spoke-like) arrangements of SHB particles were observed in the scanning electron microscopy. Effective shape of SHB particles including the electrical double layers during the convection flow processes are deduced to be near spherical. However, the effective shape came to be spindle-like during the sedimentary and solidification processes by the thinning of the double layers. The distorted paralleled and/or flower-like alignments of SHB particles were observed in the dried film.