ABSTRACT
Methanol as a basic liquid and the simplest alcohol is widely used in industry and scientific experiments. However, there are still no reliable data on the thermodynamic properties of methanol at high pressure. Here, we present an experimental and computational study of the thermodynamic properties of liquid methanol under high pressure up to 15 kbar, which significantly exceeds previously reported pressures. A temperature response to a small adiabatic change in pressure has been measured using a piston-cylinder apparatus. We have compared our experimental results with the literature data for lower pressures and NIST approximations. We find that all existing experimental data do not agree with each other and with our experiments. The NIST approximations are mainly based on low pressure data and appear to be unreliable in the high pressure region, giving even qualitatively wrong results. OPLS and COMPASS force field models have been used in the method of molecular dynamics. The agreement of molecular simulation with our experimental data is definitely unsatisfactory, which means that the most common computational models of methanol are not sufficiently good. We hope that these experimental data and approximations will help in developing better computational models.
ABSTRACT
Water is the most common liquid on the Earth. At the same time, it is the strangest liquid having numerous anomalous properties. For this reason, although water was investigated in numerous studies, many questions still remain unanswered. Even the thermodynamic properties of water at high pressures are unknown. In this paper, we present an experimental study of the thermodynamic properties of water up to a pressure of 12 kbar and a temperature of 473 K far above the range of pressures and temperatures in previous studies. We compare the experimental results to the results of computer simulations of two models of water (SPC/E and TIP4P) and show that the SPC/E model is not appropriate at high pressure, while the TIP4P model describes the equation of state of water, but fails to describe the heat capacity.
ABSTRACT
A differential scanning microcalorimeter for studying thermotropic conformational transitions of biopolymers at high pressure has been designed. The calorimeter allows taking measurements of partial heat capacity of biopolymer solutions vs. temperature at pressures up to 3000 atm. The principles of operation of the device, methods of its calibration, as well as possible applications are discussed.
