Vat photopolymerization of dual-scale porosity alumina honeycombs using phase-separable camphene porogen dissolved in binary photopolymer blends

Abstract

Dual-scale porosity ceramics comprised of macro-scale pore networks surrounded by porous frameworks manufactured by additive manufacturing (AM) can offer significantly enhanced functions compared to conventional porous ceramics. However, exploring new ways of more tightly controlling micro-scale porous structures for AM still remains challenging. Here, we propose a novel type of vat photopolymerization using camphene as a phase-separable porogen dissolved in binary photopolymer blends for manufacturing dual-scale porosity alumina honeycombs. More specifically, solid camphene with various contents (40 vol%, 50 vol%, and 60 vol%) could be completely dissolved in blends of triethylene glycol dimethacrylate (TEGDMA) and polyethylene glycol diacrylate (PEGDA) used as solvent and anti-solvent, respectively, at room temperature and then crystallize dendritically at ∼ 5 °C via phase separation. After which, thin layers of phase-separated alumina suspensions could be selectively photopolymerized by a digital light processing (DLP) engine to construct 3-dimensionally interconnected macro-scale pore channels. In addition, micro-scale pores could be created in alumina frameworks by removing camphene-rich crystals by freeze-drying. This new approach enabled manufacturing of well-defined macro-scale honeycomb structures with tailored micro-scale porosities. As the camphene content increased from 40 vol% to 60 vol%, micro-scale porosity increased from 39.1 ± 0.5 vol% to 57.5 ± 0.6 vol%, and thus the overall porosity increased from 58.5 ± 0.1 vol% to 68.8 ± 0.3 vol%, while the compressive strength decreased from 355.6 ± 67.1 MPa to 97.6 ± 10.2 MPa.