Phase equilibria of associating fluids : spherical molecules with multiple bonding sites

The effect of molecular associations on the phase coexistence properties of fluids with one or two directional, attractive centres is investigated. The individual molecules are represented by hard-sphere repulsive cores with off-centre, square-well attractive sites. Such a system’s thermodynamic properties can be calculated by using expressions based on a theory recently proposed by Wertheim. Isothermal-isobaric Monte Carlo simulations of hard-sphere fluids with one or two attractive sites are shown to be in good agreement with the results of the theory. In order to study the system’s phase equilibria using the theory, a simple van der Waals mean-field term is added to account for the dispersion forces. The critical points and phase equilibria of the associating fluids are determined for various values of the strength and range of the attractive site. Furthermore, results are presented for the degree of association in the gas and liquid phases along the vapour pressure curve. The theory can treat fluids with strong hydrogen-bonding associations such as those found in the carboxylic acids, the aliphatic alcohols, hydrogen fluoride, water etc

The Young-Laplace equation for a solid-liquid interface

5 pags., 2 figs., 2 tabs.The application of the Young-Laplace equation to a solid-liquid interface is considered. Computer simulations show that the pressure inside a solid cluster of hard spheres is smaller than the external pressure of the liquid (both for small and large clusters). This would suggest a negative value for the interfacial free energy. We show that in a Gibbsian description of the thermodynamics of a curved solid-liquid interface in equilibrium, the choice of the thermodynamic (rather than mechanical) pressure is required, as suggested by Tolman for the liquid-gas scenario. With this definition, the interfacial free energy is positive, and the values obtained are in excellent agreement with previous results from nucleation studies. Although, for a curved fluid-fluid interface, there is no distinction between mechanical and thermal pressures (for a sufficiently large inner phase), in the solid-liquid interface, they do not coincide, as hypothesized by Gibbs.This work was funded by Grant Nos. FIS2016-78117-P and PID2019-105898GB-C21 and FIS2017-89361-C3-2-P of the MEC, by Project No. UCM-GR17-910570 from UCM, and by the USA National Science Foundation under Award No. CBET-1855465. P.M.d.H. acknowledges financial support from the FPI Grant No. BES-2017-080074

Surface-Driven High-Pressure Processing

10.1016/j.eng.2018.05.004Engineering43311-32