Fig. 1. Preparation, structure characterization and composition of PSi aerogels. (a) Schematic illustration of the structure design of PSi aerogels. (b) Optical photograph of PSi-6 aerogel with a volume of 8.6 cm3 standing on the stamens of a flower without bending them. SEM images of (c) PSi-0 and (d) PSi-6 aerogels demonstrating the multi-scale architecture. (e) TEM image of PSi-6 aerogel demonstrating the homogeneous distribution of the silica constituents. (f) SEM-EDS images of PSi-6 aerogel. (g) FT-IR spectra of PSi aerogels. (h) TGA curves of PSi aerogels demonstrating the respective content of silica.

Fig. 2. Mechanical performance of PSi aerogels in the axial and radial directions. (a) Schematic illustration of compression tests performed on the PSi aerogels in the two different directions. (b) Compressive stress-strain curves of the PSi-0 and PSi-6 aerogels in the two directions. (c) Young's modulus of PSi aerogels in the two directions. (d) Compressive stress-strain curves of PSi-6 aerogel during loading-unloading cycles in the radial direction and experimental snapshots of a cycle (inset in d). (e) 500 cyclic compression stress-strain curves of PSi-6 aerogel in the radial direction with a compressive strain of 50%. (f) Variation of Young's modulus, maximum stress and energy loss coefficient versus compressive cycles. (g) Schematic mechanism for the structural robustness and high elasticity of PSi aerogels with cyclic compression in the radial direction. (h) Photographs of PSi-6 aerogel bended and recovered to its original shape, coiled around a plastic rod, knotted and shaped with desired geometry (scale bars are 2 cm).

Fig. 3. Thermal insulation properties of PSi aerogels. (a) The thermal conductivities of the PSi aerogels in the axial and radial directions. (b) Schematic illustration indicating the mechanism to achieve excellent thermal insulation. (c) Thermographic images of the PSi aerogels on a hot stage with surface temperatures of 100 °C and 200 °C. (d) Temperature difference (ΔT) between the PSi aerogels surface and the hot stage with temperatures ranging from 50 to 200 °C. (e) The thermal conductivity of the PSi-6 aerogel at different temperatures with constant absolute relative humidity (RH = 34 %). (f) The thermal conductivities of the PSi-6 aerogel at different temperatures and RH. (g) The thermal conductivity of PSi aerogels compared with other insulation materials at different temperatures and relative humidity.

Fig. 4. Flame resistance of PSi aerogels. Photography of (a) EPS foam, (b) PSi-0 and (c) PSi-6 aerogels burning by an alcohol lamp at different times. (d) Heat release rate (HRR) and (e) total heat release (THR) plots of PSi-0 and PSi-6 aerogels during microscale combustion calorimeter testing.

Fig. 5. Fire-retardant and thermal insulation properties of the PSi-6 aerogel in the axial direction under the heating at 1200 °C. (a) Schematic of the combustion test performed by butane blowlamp. (b) Thermographic image of the front side exposed to the butane blowlamp flame. (c) Thermographic images of the PSi-6 aerogel back side at different heating times. The average temperature of the circular region is marked. (d) Thermographic images of the back side of the 1.5 cm thick glass wool during heating process. (e) The time-dependent temperature profiles of the back side of the PSi-6 aerogel and glass wool. (f) Photography of the back side of the PSi-6 aerogel after the combustion test. Inset: the front side of the PSi-6 aerogel (scale bars are 5 cm). (g) SEM image of the front side of the PSi-6 aerogel after burning demonstrating the remaining SiO2 network.