Polyimide (PI) aerogels have excellent mechanical properties (e.g. Young’s modulus over 100 MPa), high temperature stability (up to 600 °C), well aging resistant performance, good radiation resistance performance and outstanding flame retardant performance. However, the native PI aerogels are hydrophilic and therefore easy to absorb a large amount of water in the damp environment, which results in the destruction of the aerogel microstructure and the depravation of the aerogel performance. To improve the hydrophobicity of PI aerogels and their moisture resistance, great efforts including chemical (adding fluorine or PPG group) and physical (blending with hydrophobic components) strategies have been tried. However, these methods not only increase the cost but also decrease the thermal stability and mechanical properties. Leaves, petals, feathers, epidermis and antennae of many kinds of plants and animals in nature exhibit super-hydrophobicity, attributing to the intricate microstructure on its surface. For example, multi-level synaptic structure makes lotus leaf hydrophobic and self-cleanning (lotus effect), while rose petal exhibit super-hydrophobicity and high adhesion to droplets. These droplets could not roll off even with an 180° reversion of aerogel (petal effect).
Based on this, whether polyimide aerogels can achieve the hydrophobicity via microstructure design and modified, while its excellent performance could be not degraded? Recently the aerogel team of the Chinese Academy of Sciences has successfully prepared a series of polyimide aerogels with lotus and petal effect (as shown in Figure 1). The PI aerogels based on imidization of polyamide acid (PAA) from p-phenylene diamine (PPDA) and 4,4’-(4,4’-isopropylidenediphenoxy)-bis-(phthalic anhydride) (BPADA) blending of other PAA could be simply obtained by the segregation self-assembly process, which form a rough surface similar to that of the lotus leaf. The obtained aerogels exhibit superhydrophobic with CA up to 153° and the lotus effect that they could not be wetted by water droplets. Besides, DMBZ-BPDA aerogel and ODA-BPDA based PI aerogel with both petal effect could be easily obtained by the decrease the density. These aerogels show petal effect that water droplet could not easily roll off. The SEM shows that the reason for petal effect of low density aerogel is the increase of roughness (Figure 1).
The superhydrophobic polyimide aerogels prepared by the biomimetic methods exhibit excellent stability in mechanical and thermal properties. This method is also expected to be applied to other types of polymer systems. The research results have been published online on ACS Appl. Mater. Interfaces. (Full text link https://pubs.acs.org/doi/abs/10.1021/)
Xin Li and Professor Jin Wang are the co-first authors of the paper, and Professor Xuetong Zhang is the corresponding author of the paper. Collaborators include Zhao Yibo from the 703 Institute of the First Academy of Aerospace Engineering. The work is supported by the National Natural Science Foundation of China (51572285, 51773225), the National Key Research and Development Program (2016YFA0203301), the Newton Advanced Scholars Fund (NA170184), the Natural Science Foundation of Jiangsu Province (BK20151234, BK20170428) and the Suzhou Science and Technology Bureau Fund (SYG201630).
Figure 1 SEM images of the PI aerogels with lotus effect or petal effect and its contact angle.
