Force field for the atomistic simulation of the properties of hydrazine, organic hydrazine derivatives, and energetic hydrazinium ionic liquids

A force field (FF) is reported for hydrazine (N2H4) and organic hydrazine derivatives, including monomethylhydrazine, 1,1-dimethylhydrazine, monoethylhydrazine, and 2-hydroxyethylhydrazine. The FF successfully reproduces a range of equilibrium properties, including vapor–liquid coexistence densities, vapor pressures, enthalpies of vaporization, and critical properties. Several dynamic properties, including self-diffusion coefficients and rotational time constants, are reported and found to be qualitatively consistent with experimental viscosities. Using this as a basis, a FF is also developed for the protonated forms of these species, i.e., hydrazinium-based cations. Properties of 1:1 energetic salts formed by pairing these cations with the nitrate anion are computed and compared with a limited amount of experimental data. The simulations indicate that the ionic liquid (IL) 2-hydroxyethylhydrazinum nitrate (2-HEHN) has significantly slower dynamics than the other hydrazinium ILs.

Simulation of Fluid Phase Equilibria in Square-Well Fluids: From Three to Two Dimensions

We study the influence of geometric restrictions on vapour/liquid coexistence properties and critical data of square-well fluids. Starting with three-dimensional bulk systems, we model the confinement by slit-like pores with decreasing slit widths arriving finally at planar (two-dimensional) fluid layers. For both bulk and confined fluids, we use a uniform approach performing series of canonical ensemble Monte Carlo simulations with Widom-like (virtual) particle insertions to estimate chemical potential versus density isotherms. By estimating the corresponding vapour/liquid coexistence densities using a Maxwell-like equal area rule for the subcritical chemical potential isotherms, we are able to study the influence of the confinement not only on chemical potentials but also on the coexistence properties. Critical point data are calculated from the coexistence densities by means of scaling relations. In particular, we study the change of the critical temperature and critical density varying the slit width and including the two- and three-dimensional bulk fluids as limiting cases. While the difference between the bulk and the slit critical temperature is found to decay exponentially with an exponent reciprocal to a linear function in the slit width, no comparable simple relation describing the influence of the confinement on the critical density is found.

Vapour - Liquid Equilibrium Properties for Two- and Three-dimensional Lennard-Jones Fluids from Equations of State

Vapour–liquid equilibrium properties for both three- and two-dimensional Lennard-Jones fluids were obtained using simple cubic-in-density equations of state proposed by the authors. Results were compared with those obtained by other workers from computer simulations and also with results given by other more complex semi-theoretical or semi-empirical equations of state. In the three-dimensional case good agreement is found for all properties and all temperatures. In the two-dimensional case only the coexistence densities were compared, producing good agreement for low temperatures only. The present work is the first to give numerical data for the vapour–liquid equilibrium properties of Lennard-Jones fluids calculated from equations of state.

Monte Carlo Simulations of Growth Kinetics and Phase Transitions at Interfaces: Some Recent Results

ABSTRACTIn the first part Monte Carlo studies of the kinetics of multilayer adsorption (without screening) are described. The approach to the jamming coverage in each layer is asymptotically exponential. The jamming coverages approach the infinite-layer limit value according to a power law. In the second part, studies of phase transitions in two dimensional fluids are reviewed. With a combination of Monte Carlo and finite size scaling block analysis techniques, accurate values are obtained for the critical temperatures, coexistence densities and the compressibilities of an adsorbed fluid layer in an NVT ensemble.