posted on 2018-05-08, 13:58authored byXin Li, Jin Wang, Yibo Zhao, Xuetong Zhang
Aerogels have been widely used in
the fields like thermal insulation, energy storage, environmental
remediation, catalysis, drug release, sensor, and cosmic dust collection,
etc. Hydrophobic functionalization not only determines the surface
energy and basic physical properties of the target aerogels but also
be critical for their long-term stability due to their highly open-porous
structures. However, there is still lack of facial and versatile methodologies
for the hydrophobic functionalization of aerogels, especially for
the nonsilica ones. Herein, two efficient fluorine-free strategies
were developed to synthesize various hydrophobic and even superhydrophobic
polyimide (PI) aerogels. First, superhydrophobic PI aerogels with
contact angle higher than 150° were fabricated by the segregation
self-assembly process between poly[4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic
anhydride)-co-p-phenylene diamine]
and poly[biphenyl-3,3′,3,4′-tetracarboxylic dianhydride-co-2,2′-dimethylbenzidine] (poly(BPDA-DMBZ)). These
PI aerogels exhibited a lotus effect that water droplets could not
wet the surface but could easily roll off. Second, various hydrophobic
PI aerogels, including the well-documented superhydrophilic PI aerogels
derived from DMBZ–BPDA and 4,4′-oxydianiline–BPDA,
were synthesized by the density-induced hydrophilicity–hydrophobicity
transition approach. These PI aerogels exhibited a petal effect that
water droplets on the aerogel surface appeared spherical in shape,
which could not roll off even when the aerogel was turned upside down.
These two reported strategies might open new and straightforward ways
to hydrophobic functionalization of other polymeric aerogel systems.