Tunable pore size and porosity of spherical polyimide aerogel by introducing swelling method based on spherulitic formation mechanism

• Published in: Microporous and mesoporous materials Vol. 288; p. 109546
• Main Authors: Lee, Daero, Kim, Jinyoung, Kim, Seohyun, Kim, Gunhwi, Roh, Jihun, Lee, Sangrae, Han, Haksoo
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.11.2019
• Subjects: Polyimide aerogel; Polymer spherulite; Pore enlargement; Pore size; Porous material; Polyimide aerogel; Pore size; Pore enlargement; Polymer spherulite; Porous material
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2019.06.008

In this study, the swelling method for controlling the pore size of the polyimide aerogel is demonstrated. The swelling method allows the pore size to be increased by changing the spherulitic formation. This newly developed method is simple and hardly affects original polymer chain and thus can be applied to a variety of precursor polymers without hindering the synthesis process. Unlike other methods, no foreign additives such as additional chemicals or crosslinkers are required to enlarge the pores of the aerogel, which contributes to higher homogeneity of the material. In order to test its effectiveness in pore size control and observe its behavior with different polyimides, various monomers—pyromellitic dianhydride, 3,3′,4,4′-benzophenonete-trac-arboxylic dianhydride, and 4,4′-oxydiphthalic anhydride—were tested to verify the potential of the proposed method. Depending on different polymer backbone, each aerogel showed a similar slope but different increase rate of the pore size. The retained thermal and structural properties of the synthesized aerogels were confirmed by thermogravimetric analysis, differential scanning calorimetry, and Fourier-transform infrared spectroscopy. This newly proposed simple method showed its effectiveness in increasing the pore sizes, enlarging the mesopore size from 4 nm to 20 nm and total pore volume from 1.29 cm3/g to 2.06 cm3/g for swollen aerogel when pyromellitic dianhydride was used. Also, the surface area increased from 54 m2/g to 88 m2/g, and the porosity increased from 58% to 73%. [Display omitted] •Polyimide aerogel formation is similar to the mechanism of polymer spherulites.•Formation of lamellar structures are fundamental factors for polyimide aerogel.•Porous characteristics are directly related to morphology of aerogel microparticles.•Swelling method affected morphology of lamellar structures and their assembly process.•Swelling is an easy way of controlling porous characteristics of polyimide aerogels.