Solvent Effects on Tuning Pore Structures in Polyimide Aerogels

This work evaluates the effects of solvents and a block copolymer surfactant on pore structures in polyimide aerogels synthesized via sol-gel reaction process. Specifically, cross-linked polyimide gel networks are synthesized in single or mixed solvents from a combination of dimethylformamide, N-methylpyrrolidone, and dimethylacetamide and supercritically dried to obtain aerogels. The bulk density, pore size, and mechanical properties of aerogels are determined. The results show that gel times are strongly dependent on the electron acceptance ability of the solvent system and concentration of the surfactant. At longer gel times, the polyimide strands coarsen and the pores in aerogel shift from predominantly mesoporous to macroporous state with corresponding reduction in compressive modulus. The block copolymer surfactant also slows down gelation and coarsens the polyimide strands but only weakly affects the compressive modulus of the aerogels.