PREPARATION AND CHARACTERIZATION OF MONODISPERSE POLYMER MICROSPHEROIDS

An original scheme for producing monodisperse polymer microspheroids of precise size and shape was developed. Graft-copolymer-stabilized poly(methyl methacrylate) (PMMA) microspheres with diameters of 0.5 to 1.4 μm were prepared by dispersion polymerization. The microspheres were embedded in a matrix of poly(dimethylsiloxane) (PDMS) normally containing 1 to 10% PMMA particles. The matrix was subsequently crosslinked. The composite elastic material was deformed under uniaxial extension, at a temperature well above the glass transition temperature Tg of the particles, to produce prolate microspheroids with aspect ratios up to 8. The microspheroids were physically set by cooling below Tg and were then recovered after selective chemical degradation of the PDMS matrix. The particles were characterized by scanning electron microscopy and by a previously developed method of transmission electron microscopy with metallic double shadow casting (Keville et al., J. Microsc. 142, 327 (1986)). Deviations in the dimensions and aspect ratios were typically less than 5%. Uniaxial deformation of properly synthesized materials produced a smooth prolate shape when the particles were less stiff than the matrix, even when they were uncrosslinked. Stable dispersions of spheroids were prepared in alkanes and PDMS. These novel dispersions of model particles are well suited for elucidating the effects of shape and orientation on various properties of colloidal dispersions. © 1991.