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Published on: June 28, 2017
Experimental evidence of a liquid-liquid critical point in supercooled water
Seonju You1, Marjorie Ladd-Parada2,3, Kyeongmin Nam1
1Department of Chemistry, POSTECH, Pohang, Republic of Korea.
Abstract:
The search for the liquid-liquid critical point in supercooled water is challenging owing to rapid crystallization. We studied supercooled water at timescales before ice formation by heating high- and low-density amorphous ices using infrared ultrafast laser pulses, followed by x-ray scattering. By varying the pump laser fluence, we accessed liquid states straddling the predicted critical point. We observed a crossover from a discontinuous to a continuous transition at which broad and slow structural variations occurred, consistent with critical fluctuations and slowing down. We also observed a rapid increase in the heat capacity indicating a critical divergence at 210 ± 8 K coincident with enhanced density fluctuations. These results suggest that our experiments have directly probed the vicinity of a critical point in supercooled water.
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