Ultrasound-induced formation of polymer capsules by precipitation with compressed CO2

A novel route to synthesize polymer hollow capsules was proposed by combination of CO₂ antisolvent (poor solvent) and ultrasound techniques. In this method, a polymer in solution was precipitated by dissolving compressed CO₂ antisolvent into the polymer solution, during which the ultrasonic irradiation was introduced. The hollow nanospheres and nanotubes of polystyrene (PS) and poly(methyl methacrylate) (PMMA) have been successfully prepared. This method has some potential advantages for applications, such as simple, rapid, without the use of template, and the solution can be easily recycled.