Liquid crystal soft interfaces reveal molecular-level influences on microscopic flow characteristics

Abstract Understanding boundary interactions at fluidic interfaces is critical for advancing synthetic and natural functional interfaces. However, classical hydrodynamic frameworks often fail to capture flow characteristics induced by localized molecular and ionic structuring at these boundaries. We present a microfluidic experimental oil–water co-flow platform, utilizing either a thermotropic liquid crystal (LC) or an isotropic oil, designed to systematically isolate the interfacial molecular and ionic mechanisms governing dynamic transport. Specifically, we provide experimental evidence of how water structuring, electroviscous drag, and molecular director alignment dictate interfacial flow, which remain poorly understood in conventional microfluidic systems. Our findings reveal that the precise spatial LC director configuration and ionic structuring at the interface fundamentally alter boundary layer slip conditions and drag. By bridging the long-standing gap between microscopic molecular events and macroscopic fluid mechanics near interfaces, this work introduces a design paradigm for engineering next-generation microfluidic and nanofluidic technologies, smart functional interfaces, and complex biological or technological systems.