In
recent years, anisotropic polymer particles have gained increased
interest owing to their special properties and broader applications,
such as drug delivery, optical traps, and e-paper display. Most strategies
to produce anisotropic polymer particles, however, require sophisticated
instruments or additional surfactants. Here, we develop a simple and
versatile method, the two-step solvent on-film annealing (2-SOFA)
technique, to make anisotropic polymer particles with different shapes.
Polystyrene (PS) microspheres spin-coated on poly(methyl methacrylate)
(PMMA) films are chosen as model materials. By sequentially annealing
the PS/PMMA composites in different solvent vapors, anisotropic polymer
particles with distinctive and diverse shapes can be produced, such
as half-eaten-peach-shaped, snowman-shaped, and bowler-hat-shaped
morphologies. An exquisite selective removal strategy is applied to
check the morphologies of the PS/PMMA composite films and to comprehend
the transformation mechanism at different annealing steps and times.
For particles merged from multiple microspheres, quantitative studies
are also performed to figure out the relationships between the sizes
of the merged particles and the numbers of the original microspheres.
These results have implications for colloidal self-assembly.