The preparation of size-controllable hollow polyimide microspheres by surface imidization of electrosprayed droplets

Hollow polyimide (PI) microspheres are prepared through an electrospraying process, followed by surface imidization. The precipitation of droplets at the interface between two immiscible liquids provides a scaffold for the formation of a thin layer while an in situ imidization reaction prevents the irreversible deformation of the hollow shell. This strategy easily yields robust hollow structures of PI microspheres. The electrospray process permitts the sizes of the hollow PI microspheres to be controlled through adjustments to the flow rate and concentration of the poly(amic acid) (PAA) solution. The electrospraying approach described here may be the most facile means yet reported for obtaining size-controlled hollow PI particles without the need for additives or surfactants. Size-controllable hollow polyimide microspheres are prepared by surface imidization of electrosprayed droplets. A designed ES system is formulated based on certain solubility considerations, then a reactive system is applied using a thermal imidization reaction at the interfaces on droplet surfaces.