Homogeneous solidification strategy for freeze-casting-assisted direct ink writing investigated by computational fluid dynamics modeling

Freeze-casting-assisted direct ink writing (DIW) enables the fabrication of three-dimensional (3D) aerogel architectures with improved geometric versatility. However, multilayer deposition often produces inter-layer microstructural nonuniformity because the pre-frozen underlying layers introduce additional thermal resistance. To address this challenge, we investigated a homogeneous solidification strategy using a computational fluid dynamics (CFD) model. The framework incorporates a moving substrate boundary condition, constant-temperature thermal boundary, and interface tracking, while the nanocomposite ink properties are explicitly modeled as functions of temperature and shear rate. Using the CFD results and a custom digital image-processing algorithm, the freezing time required for the extruded filaments to fully solidify on a cold substrate is quantified. Based on the extracted freezing-time data, we determined the substrate-temperature pairs that yield identical freezing times across sequential layers. The resulting process map provides practical guidelines for mitigating layer-to-layer thermal variations and enables the reliable printing of aerogels with uniform inter-layer microstructures.