Geometry Controls Confined Water Dynamics in Lipidic Mesophases

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.