Actuating porous polyimide films.

We report a novel method for the fabrication of one-component self-folding polymer films. The approach is based on films with a vertical gradient of porosity and was demonstrated on an example of porous polyimide films. The inhomogeneous porosity of the films was achieved through the implementation of capillary forces and gravity during the drying of a dispersion of colloidal particles in a solution of polymer precursor. As a result, three-layered films were formed. A monolayer of particles comprises the top layer, the second layer is the pure polymer, and the third layer is formed by a mixture of particles and polymer. Etching out the particles leaves polyimide film with inhomogeneous distributed pores. These porous polymer films roll and form tubes in organic solvents as well as their vapors and reversibly unfold in air. The obtained films were used for design of actuators, which are able to capture and release different objects through the reversible folding.