Regulating Confined Phase Transition in Nanopores for Accelerating the Freeze-Drying Preparation of Mesoporous Silica Aerogels.

Freeze-drying has emerged as a viable drying technique for highly mesoporous aerogels due to its simplicity, safety, and sustainability, but it still struggles with prolonged processing cycles. Herein, we report a freeze-drying acceleration approach based on the regulation of a confined liquid-solid phase transition in nanopores by surface modification. Using silica gels as model systems, the interactions between pore walls and pore liquids were systematically modulated through the methylation of surface hydroxyl groups. Through surface methylation, the adsorption energy of water on pore walls was significantly reduced (from -109.5 to -68.7 kcal mol-1), while the phase transition enthalpy of the pore-confined solution was increased (from 221.71 to 242.63 J g-1). Multiscale characterization and simulations further revealed that this modification strategy effectively weakened interfacial interactions, thereby reducing the thickness of the adsorption-induced confined layer (from 0.365 to 0.269 nm). The effects of the confined liquid-solid phase transition on both the drying kinetics and the pore structure of aerogels were investigated. The optimized process achieves a 75% reduction in the freeze-drying time while preserving the mesoporous structure integrity. Furthermore, the surface methylation engineered the pore architecture by modifying confined liquids' eutectic dynamics. This novel approach offers new perspectives for the scalable and green production of functional porous materials.