The nitrogen
isotherm is of type I, a characteristic of microporous materials.
The micropores are formed during the pyrolysis process as a result of
the evaporation of volatile species. Additionally, the fibers are intertwined
together as evidenced by the SEM micrographs, thus forming
macropores whose sizes cannot be determined reliably by nitrogen
sorption. In other words, the aerogels contain both micropores and
macropores.