Freeze‐cast honeycomb structures via gravity‐enhanced convection

The effect of gravity on directional solidification was investigated in solution‐based freeze casting. A preceramic siloxane‐based polymer was freeze‐cast with a cyclohexene solvent from two different directions: that against the direction of the gravitational force and that in concert with the gravitational force. Because the density of preceramic polymer is higher than the solvent, the segregated polymer creates a denser solution ahead of the freezing front than the underlying solution when the freezing direction is the same as the gravity direction. This results in convective flow in the liquid phase. This convective flow influences constitutional supercooling, which changes not only the pore size of freeze‐cast structure but also the pore morphology from dendritic to cellular pores. Conventional directional (upward) and convection‐enhanced (downward) freeze‐casting setups produce contrasting pore size and morphology in porous solids.