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 degrees C. At room temperature, sizetunable water confinement (approximate to 20 angstrom size) in a room-temperature ionic liquid (RTIL, 1-butyl-3-methylimidazolium nitrate, [C(4)mim][NO3]) exists in a water-rich region (70-90 mol% D2O). The confined water (water pocket) is characterized by almost monodispersive size distribution. In [C(4)mim][NO3]-xmol% D2O (70< x< 94), the absence of sharp Bragg reflections and a distinct exothermal peak indicate that crystallization/cold crystallization both of [C(4)mim][NO3] and D2O is suppressed, even upon slow cooling and heating.