Preparation of hemispherical particles by cleavage of micrometer-sized, spherical polystyrene/poly(methyl methacrylate) composite particles with Janus structures: effect of polystyrene-b-poly(methyl methacrylate)

Abstract

We recently reported that two micrometer-sized, hemispherical polymer particles were prepared as a result of the cleavage of spherical Janus polystyrene (PS)/poly(methyl methacrylate) (PMMA) composite particles after treatment with acetone. The original composite particles were prepared by slow evaporation of toluene from homogeneous PS/PMMA/toluene droplets dispersed in an aqueous solution of sodium dodecyl sulfate. This article aims to validate a proposed cleavage mechanism which is based on the induction of internal stress at the interface because of a great difference in the swelling ratio between the PS and PMMA phases. The effect of PS-b-PMMA, which should exist at the interface between both phases and decrease the internal stress, on the cleavage phenomenon was examined. PS/PS-b-PMMA/PMMA composite particles were prepared in the same way as the previous study. At 0.31 wt% or greater of PS-b-PMMA (number-average molecular weight: 10.6 × 104–b-9.9 × 104), the composite particles did not have a Janus structure but an ex-centered core-shell structure, resulting in no cleavage. At 0.18 wt% or less, they had a Janus structure, and the cleavage phenomenon was observed. The required time to cleave increased with increasing PS-b-PMMA content to below 0.18 wt%. Specifically, the existence of PS-b-PMMA delayed the cleavage of the composite particles into PS and PMMA hemispherical particles. This result supports the proposed cleavage mechanism and provides a tool to easily address the cleavage process for the production of hemispherical particles. Relationships between the interfacial area between PS and PMMA in a PS/PMMA (1/1, w/w) composite particles including various amounts (white circles 0; filled circles 0.05; white triangles 0.11; filled triangles 0.18 (wt % relative to the total amount of PS and PMMA)) of PS-b-PMMA (B11:Mn 10.6 × 104–b-9.9 × 104) and the required time to cleave into two parts (cleavage time, Tc) by addition of the acetone/water (9:1, v/v) solution to the dried particles