Abstract
Water under nanoscale confinement is central to biological function, catalysis, and soft materials, yet how geometry dictates its structure and dynamics remains unresolved. Here, we establish a direct link between interfacial curvature and confined water behavior using an archaeal-inspired phytantriol-water lipidic mesophase platform. By systematically tuning curvature across lamellar, double-gyroid cubic, and reverse micellar phases, and integrating structural, thermodynamic, and ultrafast spectroscopies, we show that geometry controls the dimensionality and mobility of the hydrogen-bond network. Planar interfaces enforce 2D networks that slow down interfacial water through spatial constrain, whereas curved bicontinuous and micellar topologies promote 3D networks with accelerated reorientation. These findings reveal a geometric principle for governing water dynamics in soft nanoconfinement, providing molecular level design rules for confined transport and reactivity in membranes and functional materials.