Microscale mass transfer mechanisms and interfacial behaviors of Janus membranes in vacuum membrane distillation for solution regeneration: A molecular dynamics study

Membrane distillation-based absorption refrigeration (MDAR) utilizes low-grade heat for solution regeneration. However, processing highly concentrated (>50 wt%) LiBr solutions imposes a trade-off between liquid exclusion and water transport in conventional hydrophobic membranes. In this study, equilibrium molecular dynamics simulations were used to examine how surface hydroxyl density, LiBr concentration, and temperature regulate water mobility, hydration structure, ion association, and interfacial affinity in a Janus membrane comprising a feed-facing hydroxylated SiO 2 layer and an underlying hydrophobic PVDF substrate. Surface hydroxyl density produced a non-monotonic response, with the 80% configuration providing the most favorable overall balance among the investigated cases and maintaining a simulated interfacial water self-diffusion coefficient of 3.21 × 10 −5 cm 2 /s. Increasing the LiBr concentration to 60 wt% strengthened hydration competition and reduced the simulated water self-diffusion coefficient to 1.13 × 10 −5 cm 2 /s. The accompanying increase in Li + –Br − coordination and Br − affinity near PVDF indicated enhanced ion association and interfacial redistribution under high-concentration conditions. Increasing temperature enhanced local water mobility, but at 363 K the interfacial hydrogen-bond number decreased and Li + –Br − coordination increased, indicating weaker hydration organization and stronger ion association. Among the four investigated temperatures, 353 K appeared to provide the most favorable balance between molecular water mobility and interfacial structural stability. These results provide molecular-scale descriptors and mechanistic guidance for Janus membrane design and MDAR operating-condition selection.