Formation of “Nano-Ice” and Density Maximum Anomaly of Water

Abstract

Abstract Water is still mysterious despite intensive and extensive studies over the years. Anomalous behavior of water as a liquid is yet to be fully comprehended. Here we show that the most generally known anomaly of water, the density maximum anomaly, is well accounted for by the formation of nanometer-size ice crystallite at low temperatures. We show spectroscopically that, in cold and super-cooled water, this nanometer-size ice crystallite is formed and coexists with the other two forms of water. Multivariate hyperspectral analysis of 140 temperature dependent Raman spectra in the range of −23∼45 °C determines the three distinct vibrational spectra of the three forms of water and their fractions at different temperatures. Simulation based on the determined fractions successfully reproduces the temperature dependence of density with a maximum at the right temperature. The mystery of the density maximum of water has thus been given an unequivocal solution. The nanometer-size ice crystallite might well be called “nano-ice”.