Hierarchical porous SiOC via freeze casting and self-assembly of block copolymers

Abstract

Surface area, permeability, and mechanical robustness are particularly crucial for porous ceramics utilized in filter and catalyst support applications. Unfortunately, these desirable properties are often inversely related to one another via porosity and pore size, creating a serious challenge in the optimization of these materials. To address this challenge, we propose a hierarchical porous composite, fabricated by freeze casting preceramic polymers and re-infiltrating with a self-assembling preceramic polymer/block copolymer blend. The resulting pyrolyzed SiOC hierarchical solid displayed a bimodal pore size distribution with macropores from the freeze-cast structure and mesopores in the self-assembled coating. Neither permeability, compressive strength, nor Young's modulus of the porous composite were compromised with the mesoporous conformal coatings. With the presented hierarchical structure, a better filtration material is expected with higher throughput and reaction rates. Furthermore, by adopting a two-step process, macropores and mesopores can be individually tuned to optimize structures for desired applications.

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