  Porous carbon ablators offer cost-effective thermal protection for aerospace
vehicles during re-entry into planetary atmospheres. However, the exploration
of more distant planets requires the development of ablators that are able to
withstand stronger thermal radiation conditions. Here, we report the
development of bio-inspired porous carbon insulators with pore sizes that are
deliberately tuned to enhance heat-shielding performance by increasing
scattering of high-temperature thermal radiation. Pore size intervals that
promote scattering are first estimated using an established model for the
radiative contribution to the thermal conductivity of porous insulators. On the
basis of this theoretical analysis, we identify a polymer additive that enables
the formation of pores in the desired size range through the
polymerization-induced phase separation of a mixture of phenolic resin and
ethylene glycol. Optical and electron microscopy, porosimetry and mechanical
tests are used to characterize the structure and properties of porous
insulators prepared with different resin formulations. Insulators with pore
sizes in the optimal scattering range reduce laser-induced damage of the porous
structures by up to 42%, thus offering a promising and simple route for the
fabrication of carbon ablators for enhanced thermal protection at high
temperatures.
