Simple preparation of hemispherical polystyrene particles

We show the simple preparation of the hemispherical polymer particles. Submicron sized hemispherical polystyrene particles were prepared by adding a poor solvent (water) into a tetrahydrofran (THF) solution of polystyrene and following evaporation of THF. When the concentration of the polymer solution was higher than 0.4 g/L, spherical particles were formed. On the other hand, the hemispherical nano-particles were formed in the case of the dilute solution whose concentration was lower than 0.2 g/L. Turbidity change of the polymer solution due to THF evaporation starts from the surface of the solution. The light scattering experiment suggests that the hemispherical nano-particles were formed by precipitation at the air/solution interface.