Water-based freeze casting: Adjusting hydrophobic polymethylsiloxane for obtaining hierarchically ordered porous SiOC

The hydrophobic properties of methyl poly siloxane (MK) were pushed into the“hydrophilic”range by cross-linking it with (3-aminopropyl)triethoxysilane(APTES) and subsequent pyrolysis to enable water-based freeze casting. Fillerproperties are investigated by varying the ratios of MK to APTES (1:1, 1:2, 1:3,1:4, 1:5), and pyrolysis temperatures (400°C, 500°C, 600°C) for the purpose ofdetermining an optimal set of characteristics for freeze casting. Additionally, fillerselection for this purpose is facilitated by analysis of zeta potential values andvapor adsorption. It was found that water-based freeze casting with hybrid fillers,followed by a pyrolysis step (600°C-700°C), leads to a SiOC ceramic monolithwith a lamellar pore morphology and a hierarchically ordered micro/meso/macrop-ore structure. Samples pyrolyzed at 1000°C contain mesopores, having a SSA ashigh as 51.6 m2/g. The hierarchically porous structure is very promising for appli-cations involving gas or liquid transportation.