Investigation of the Alcohols and Water Hydrogen Bonding Structure via Monomer Fraction Studies

The hydrogen bonding structure of alcohols and water is studied in this work using two association equations of state (cubic-plus-association (CPA); perturbed-chain statistical associating fluid theory (PC-SAFT)) and a theory connecting the relative static permittivity (RSP) with hydrogen bonding (RSP theory). The results from the two models are compared to experimental and molecular simulation data for free-site, monomer, and k-times bonded fractions, as well as for tetrahedrally bonded fractions for water. The agreement is satisfactory for alcohols but less so for water, especially when the most recent structural data for water are considered. This indicates that the four-site or roughly tetrahedral assumption incorporated for water in both approaches may be erroneous. It has been attempted to fit the RSP theory parameters to recently obtained data; such data show a rather small number of tetrahedral water molecules. These data are obtained from studies related to the water two-state theory. The results provide some insight into whether water can be assumed to be a homogeneous liquid or a two-state liquid, at least in the context of the theories (CPA, PC-SAFT, and RSP theory). The results are also discussed in the context of other theories and recent developments

Investigation of the Alcohols and Water Hydrogen Bonding Structure via Monomer Fraction Studies

The hydrogen bonding structure of alcohols and water is studied in this work using two association equations of state (cubic-plus-association (CPA); perturbed-chain statistical associating fluid theory (PC-SAFT)) and a theory connecting the relative static permittivity (RSP) with hydrogen bonding (RSP theory). The results from the two models are compared to experimental and molecular simulation data for free-site, monomer, and k-times bonded fractions, as well as for tetrahedrally bonded fractions for water. The agreement is satisfactory for alcohols but less so for water, especially when the most recent structural data for water are considered. This indicates that the four-site or roughly tetrahedral assumption incorporated for water in both approaches may be erroneous. It has been attempted to fit the RSP theory parameters to recently obtained data; such data show a rather small number of tetrahedral water molecules. These data are obtained from studies related to the water two-state theory. The results provide some insight into whether water can be assumed to be a homogeneous liquid or a two-state liquid, at least in the context of the theories (CPA, PC-SAFT, and RSP theory). The results are also discussed in the context of other theories and recent developments.</p

Multiple Insights Call for Revision of Modern Thermodynamic Models to Account for Structural Fluctuations in Water

Modern thermodynamic models incorporate the concept of association (hydrogen bonding) and they can describe very satisfactorily many properties of water containing mixtures. They have not been successful in representing water's anomalous properties and this work provides a possible explanation. We have analyzed and interpreted recent experimental data, molecular simulation results, and two‐state theory approaches and compared against the predictions from thermodynamic models. We show that the dominance of the tetrahedral structure implemented in modern thermodynamic models may be the reason for their failure for describing water systems. While this study does not prove the two‐state theories for water, it indicates that a high level of tetrahedral structure of water is not in agreement with water's anomalous properties when used in thermodynamic models