Simulation of the passive separation of miscible fluid mixtures in two-dimensional micro-channels with uneven wetting conditions

Passive separation of miscible fluid mixtures at the microscale offers a promising route to energy-efficient and sustainable separation technologies. In this study, we investigate the feasibility of separating a water–ethanol-like binary mixture solely through wettability-driven interfacial forces using the multi-range, multi-component Shan–Chen Lattice Boltzmann Method (LBM). The model is validated analytically against the Navier–Stokes solution for single-phase flow and qualitatively through comparison with published molecular dynamics (MD) data for near-wall structuring. Systematic parametric studies reveal that tuning the cross-interaction coefficient ( $$G_{12}$$ ), solid–fluid interaction coefficients ( $$G_{1s}$$ , $$G_{2s}$$ ), relaxation times ( $$\tau $$ ), and channel geometry can significantly modulate local species distributions. Uneven wetting conditions and the introduction of patterned solid posts extend the effective range of surface forces, enhancing separation efficiency under static and flow conditions. Scaled species density profiles provide a direct measure of local separation efficiency, showing that passive structuring can lead to significant concentration gradients without external fields or chemical additives. These findings demonstrate the potential of wettability contrast and microchannel design to achieve passive separation of miscible mixtures, contributing to the development of next-generation microfluidic separation devices.