Temperature-driven capillary motion of liquid droplets in rough and chemically heterogeneous nanopores

This study investigates how surface roughness and chemical heterogeneity within nanopores can be harnessed to achieve temperature-induced capillary motion of confined liquid droplets. Such temperature-responsive capillary motion has promising applications in nanofluidics, energy storage, environmental engineering, and biomedicine, where precise, dynamic fluid control is essential. To explore this, we consider a model nanopore with two distinct regions: one with a smooth surface and another featuring roughness and chemical heterogeneity. We use a combination of thermodynamic modeling, Grand Canonical Transition Matrix Monte Carlo simulations, and molecular dynamics (MD) simulations. Our aim is to examine how variations in interfacial free energy, entropy, and interfacial fluctuations affect the droplet's motion. The thermodynamic model suggests that nanopores with regions of similar interfacial free energies but different interfacial fluctuations enable temperature-driven motion. Enhanced interfacial entropy in the rougher region, due to stronger solid-liquid interfacial fluctuations, leads to a greater reduction in interfacial free energy with temperature. MD simulations confirm that temperature changes influence droplet position, though interfacial frictional effects between regions pose free energy barriers that restrict full transition. Our findings suggest that, with tailored surface characteristics, it is possible to achieve temperature-driven capillary motion in nanopores, providing a basis for developing adaptable nanoscale fluidic systems. Future research could further explore these dynamics with varied surface designs and fluid types to advance temperature-responsive nanofluidic applications.