Hierarchical Porous Microparticles via micro-Continuous Liquid Interface Production of Lyotropic Liquid Crystal Templates

Hierarchical porous materials with well-defined porosity spanning multiple length sales are highly desirable for separation and catalytic applications, where efficient mass transport and high surface-to-volume ratio are required. Conventional etching and self-templating approaches exist limited control over nanopore morphology and pore size. In addition, thin film fabrication through casting and molding techniques further inhibits engineering of three-dimensional transport pathways. Here we report an approach combining high-resolution continuous liquid interface production (CLIP) printing with lyotropic liquid crystal (LLC) guided soft-templating method to create open-cell microparticles containing hierarchical porosity ranging from nanometer to micrometer length scales. Prior to photopolymerization, LLC precursor mixtures are characterized with small-angle X-ray scattering (SAXS), and their self-assembled bicontinuous and lamellar mixed mesophases with characteristic d-spacing values of 52-60 Å are observed. Post photopolymerization, SAXS confirms the successful retention of sub-nanometer structure, and further inspection with SEM reveals the emergence of organized, concentration-dependent nano-porosity with pore diameters of 172-409 nm driven by polymerization induced microphase separation mechanism. The organized pores and their narrow pore size distribution are hypothesized to be guided by LLC amphiphilic molecular templating during photopolymerization. The approach combining high-resolution additive manufacturing and LLC soft-templating demonstrates the capability to create open-cell architected materials containing hierarchical porosity spanning sub-nanometer to micrometer length scales.