Correlation between Hydrodynamic Slip and Contact Angle: Analysis on Atomistically Smooth and Nanopatterned Silica...

Understanding fluid behavior at the liquid-solid interface is essential for advancing micro/nanoscale technologies, yet current models struggle to capture the complexity introduced by surface heterogeneity. In this study, we investigate the interplay between nanoscale surface roughness, wettability, and hydrodynamic slip by using molecular dynamics simulations on nanopatterned silica surfaces. By systematically varying the droplet size and surface geometry, we characterize the influence of nanoscale pinning on contact angle hysteresis and determine the macroscopic equilibrium contact angles for six distinct rough surfaces. Parallel simulations of force-driven water flow through nanochannels reveal the local and average slip lengths associated with each surface. For smooth surfaces, slip length correlates well with contact angle, aligning with predictions from well-known theoretical models by Huang et al. and Sendner et al. However, on nanopatterned surfaces, significant deviations arise due to contact line pinning, which disrupts the expected correlation between wettability and slip. We observe a clear decoupling between hydrophobicity and interfacial mobility, which can be exemplified by rose petal-like behavior where high contact angles are accompanied by strong pinning and minimal slip. These findings underscore the limitations of existing theoretical models when applied to heterogeneous interfaces and emphasize the need for refined frameworks that account for pinning effects. This study offers such a framework, providing new insight into interfacial transport and guiding the design of functionally structured surfaces.