2.2 Materials synthesis
Preparation of MMT nanosheets. Put 6.0 g MMT and 500 mL deionized water in a beaker and sonicate for 1 h. After that, a yellow turbidity dispersion was obtained. Separate the precipitation with a centrifuge (9000 rpm, 5 min) and collect the transparent solution MMT nanosheet colloid. Finally, the colloid was concentrated by a rotary evaporator at a concentration of 3.2 wt%.
Preparation of PAAS solution. First, the PAA solution was obtained by condensation polymerization of BPDA and DABA (molar ratio of 100:99.5) in DMAc (10 wt% solid content) at 5 oC for 12 h. KH550 was then added and stirred for 3 h (KH550: BPDA was 0.01:1). Last, the PAAS solution was prepared by adding TEA (2.0 mol equivalent to BPDA) to the mixture at room temperature and stirring for 4 h.
Surface treatment of PI substrate. The method was to cover one side of the DABPPI with 25 wt% NaOH solution for 25 min and then wash it thoroughly and dry it.
Preparation of the bioinspired polyimide composite film. A certain amount of MMT colloid was put into a three-neck flask and diluted to 2 wt% with deionized water. Subsequently, PAAS solution was added slowly with gentle agitation (the mass ratio of MMT to PAAS was 1:1). After continuous stirring for 4 h, uniform glue was obtained. The surface-treated PI was sandwiched on the flange ring, and the composite glue (20 mL) was poured onto the PI. The flange ring was placed in an oven and set the heating program to 50 ℃/4 h, 100 ℃/1 h, 150 ℃/1 h, and 220 ℃/1 h. Finally, the bioinspired polyimide composite film was gained and named MMT-PI.
Preparation of the bioinspired MMT film, MMT-PVA, and MMT-CMC.The specific preparation steps can be seen in Supporting Information .
Preparation of the coated PU foam. The PU foam was cut into 10 cm×10 cm×1 cm and then dipped in the MMT-PAAS solution for 10 min. The coated PU foam was placed in an oven and set the heating program to 50 ℃/4 h, 80 ℃/1 h. The coated PU foam was named MMT/PAAS-PU.