Anomalous Freezing of Nano‐Confined Water in Room‐Temperature Ionic Liquid 1‐Butyl‐3‐Methylimidazolium Nitrate

Non‐crystal formation of ice is investigated by simultaneous X‐ray diffraction and differential scanning calorimetry measurements upon cooling to −100 °C. At room temperature, size‐tunable water confinement (≈20 Å size) in a room‐temperature ionic liquid (RTIL, 1‐butyl‐3‐methylimidazolium nitrate, [C 4 mim][NO 3 ]) exists in a water‐rich region (70–90 mol % D 2 O). The confined water (water pocket) is characterized by almost monodispersive size distribution. In [C 4 mim][NO 3 ]‐ x  mol % D 2 O (70< x <94), the absence of sharp Bragg reflections and a distinct exothermal peak indicate that crystallization/cold crystallization both of [C 4 mim][NO 3 ] and D 2 O is suppressed, even upon slow cooling and heating.