Fabrication of polyimide spheres using a pulsed laser at 355 nm

A new approach for manufacturing hollow polyimide (PI) microspheres is presented. The method is based on cavitation bubbles and small CO 2 gas bubble which can generate uniform microspheres. When liquid PI was irradiated by a 355- nm nanosecond pulsed laser in a gas pressure chamber, microspheres ranging from 25 to 35 μm and smaller spheres attached to the microspheres ranging from 5 μm to submicron dimensions were generated in the liquid. Microspheres ranging from 25 to 35 μm were fabricated by laser-induced formation. The spheres’ morphology was influenced by the pressure in the chamber. When the pressure is high in the chamber, non-uniform microspheres are produced due to flow caused by the laser-induced shockwave and change of the carbon dioxide concentration in the liquid. Smaller spheres with 5 μm to submicron dimensions attached onto the microspheres were fabricated by a gas bubble template method and laser-induced formation. The resulting shell of hollow PI microspheres was about 4 μm, and the sphere inside has a porous structure. Our results indicate that the proposed laser-induced formation technology in a gas pressure chamber can be used to prepare polymer spheres by controlling the gas pressure.