Decoupling Geometry and Surface Chemistry in 3D-Printed ALD-Functionalized Porous Ceramic Channels

Capillary-driven transport is traditionally attributed to the static pore geometry and wettability. However, the time-dependent surface energy of metal oxides, amplified by the high surface area of porous media, remains a key yet underexplored aspect. This study introduces a novel manufacturing route capable of decoupling macroscopic geometry from surface chemistry by integrating additive manufacturing combined with colloidal assembly (AMCA) and functionalization by atomic layer deposition (ALD). This approach enables the fabrication of highly porous aluminum-(III) oxide (Al₂O₃) and titanium dioxide (TiO₂) ceramic channels after thermal burn-out. Within these structures, the structural and chemical properties are tuned and investigated. Spontaneous imbibition experiments at 0, 6, and 24 h after burn-out reveal a transition from a classical Lucas-Washburn rise to a resistance-limited regime dominated by evaporation and viscous drag. Time-resolved contact-angle measurements revealed that both oxides become superhydrophilic after burn-out and undergo subsequent hydrophobic recovery. Despite TiO₂ being intrinsically more hydrophilic, Al₂O₃ channels consistently exhibited faster imbibition rates and a higher liquid rise. This behavior is attributed to the rapid surface relaxation of Al₂O₃, which reduces contact-line friction and minimizes pinning at high-energy adsorption sites, thereby enhancing fluid uptake. Macroscopic geometrical variations in printed channels did not affect the imbibition height but scaled linearly with imbibed volume, confirming the successful decoupling of geometric and chemical transport factors. The excellent structural reproducibility of the AMCA-ALD method establishes it as a robust manufacturing platform for programmable capillary transport. This approach provides a general pathway to design porous ceramics with independently engineered geometries and surface chemistries for applications in microfluidics, diagnostics, and catalysis.