The anomalous properties of liquid water explained by a mixture model

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Title: The anomalous properties of liquid water explained by a mixture model
Author: Vedamuthu, Mary S.
Abstract: A semiempirical theory , which is a modernization of the 'mixture model ,' attempting quantitatively to correlate thermodynamic and dynamic effects of bulk and interfacial liquid water with various properties of ice polymorphs is proposed here . The basic concept rests on the disappearance , on the average , with increasing temperature or pressure , of open intermolecular tetrahedral bonding (Type -I ) having a density similar to that of ordinary ice , in favor of compacdy bonded regions (Type -II ) with a density near that of the dense ice polymorphs particularly , ice II , III , and V . The mixture model is employed to explain quantitatively the origins of the 'anomalous' properties of liquid water - density maximum , isotope effects , thermal minimum in the isothermal compressibility curve . Strong support for this model can be found from an analysis of the accurate experimental density data of liquid H2O and D2O from the supercooled regime to about +70 °C . Published density data can be fit to this model with six - to seven -decimal -point accuracy , in the case of liquid H2O and to the reported fivedecimal -point precision , in the case of liquid DjO . The output parameters from the fits indicate the presence of capacious intermolecular bonding with a density extremely close to that of ordinary ice -Ih , intermixed with compactly bonded regions having a density near that of the common dense forms of ice . A quantitative assessment of the temperature dependence of the isothermal compressibility of liquid water at atmospheric pressure was carried out . The 'anomalous' minimum in this quantity near 50 °C is shown to emerge naturally . Independent support for this model has been provided by the differential x -ray scattering experiments of Bosio et al . Their resuhs clearly indicate that a dynamic , temperature dependent mixture of ice -I - , -II - , -III - , and -V -type bonding is present in the liquid in the manner expected for the model described in this work . Based on eariier x -ray scattering studies , Kamb reached a similar conclusion about these mixed bonding forms in liquid water . Recently , computational studies conducted by Cho , Singh and Robinson in our laboratory have indicated that the density anomaly of liquid water can be explained by utilizing this mixture model concept . Ultrafast laser methods were used to analyze the properties of liquid water confined in small volumes . This study shows that interfacial water appears to be more structured and orientationally stiffer than bulk water .
URI: http : / /hdl .handle .net /2346 /11200
Date: 1996-05

Citation

Vedamuthu, Mary S. The anomalous properties of liquid water explained by a mixture model. Doctoral dissertation, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /11200 .

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