Inelastic x-ray scattering measurements of liquid waterglycerol mixtures

Kajihara, Y.; Shibata, Nanako; Inui, Masanori; Matsuda, Kazuhiro; Tsutsui, Satoshi

doi:10.1051/epjconf/201715106003

Cited by 2 publications

(1 citation statement)

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“…In the case of such samples, large signals are expected to be obtained because this method can detect the dynamical inhomogeneity. We have already started to elucidate the thermodynamic anomalies of water-alcohol mixtures [55,56]. We believe that this approach can be used for characterizing the melt of high entropy alloys [57,58] and glass transition liquids [59] with dynamical heterogeneity [60].…”

Section: Discussionmentioning

confidence: 99%

Experimental Observation of Mesoscopic Fluctuations to Identify Origin of Thermodynamic Anomalies of Ambient Liquid Water

Kajihara

Inui

Matsuda³

et al. 2021

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We report a new experimental approach for observing mesoscopic fluctuations underlying the thermodynamic anomalies of ambient liquid water. In this approach, two sound velocity measurements with different frequencies, namely inelastic X-ray scattering (IXS) in the terahertz band and ultrasonic (US) in the megahertz band, are required to investigate the relaxation phenomenon of sound waves with the characteristic frequency between the two aforementioned frequencies. We performed IXS measurements to obtain the IXS sound velocity of liquid water from the ambient conditions to the supercritical region of liquid-gas phase transition (LGT) and compared the results with the US sound velocity reported in the literature. We found that the ratio of the sound velocities, S f , which corresponds to the relaxation intensity, obtained using these two methods exhibits a simple but significant change. Two distinct rises were observed in the high-temperature and low-temperature regions, implying that two relaxation phenomena exist. In the high-temperature region, a peak was observed near the LGT critical ridge line, which was linked with changes in the magnitude of density fluctuation and isochoric and ishobaric specific heat capacities. This result indicates that the high-temperature relaxation originates from the LGT critical fluctuation, proving that this method is effective for observing such mesoscopic fluctuations. Meanwhile, in the low-temperature region, S f increased from 550 K toward the low-temperature region and reached a high value, attaining the "fast sound" state near ambient conditions. This result indicates that another mechanism of relaxation exists, which causes the sound velocity anomaly, including the "fast sound" phenomenon of liquid water near ambient conditions. The change in S f in the low-temperature region is linked with the change in the isochoric heat capacity, which implies that this relaxation causes the well-known heat capacity anomaly of liquid water. This low-temperature relaxation corresponds to the critical fluctuation of the liquid-liquid phase transition (LLT) that is speculated to exist in the supercooled region. In this study, both LGT and LLT critical fluctuations were observed, and the relationship between thermodynamics and the critical fluctuations was comprehensively discussed by analyzing the similarities and differences between the two phase transitions.

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