Fabrication of polyimide spheres using a pulsed laser at 355 nm

Abstract

A new approach for manufacturing hollow polyimide (PI) microspheres is presented. The method is based on cavitation bubbles and small CO2 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.