Asymmetric In-Plane Dielectric Response of Interfacial Water to Biaxial Strain: Decoupling Orientational and Positional Order

Antiferroelectric (AFE) ordering in interfacial water strongly suppresses its in-plane dielectric constant, yet how to actively tune the dielectric response of AFE ordered water remains largely unexplored. Here, using molecular dynamics (MD) simulations on a model platinum surface, we investigate the influence of mechanical strain on the dielectric behavior of ordered interfacial water. The in-plane dielectric constant ε∥ exhibits an asymmetric V-shaped response to biaxial strain, where compression drives a sharp increase in ε∥ (∼2.52-fold), while tension induces a modest rise (∼1.62-fold). This asymmetry originates from the fact that the regular oxygen sublattice is preserved under tension, which continues to constrain dipole orientations. As a result, the AFE order parameter η decreases by only ∼11%. By contrast, the ordered structure is severely disrupted under compression, with η dropping by ∼49%. Tension thus selectively decouples orientational order from positional order in AFE interfacial water, which limits the release of dipolar fluctuations, leading to a moderate rise in the Kirkwood correlation factor GK and, consequently, a gentle enhancement of ε∥. Our findings identify mechanical strain as an effective physical tool for selectively decoupling orientational and positional order at interface.