High-frequency asymptote for the velocity auto-correlation function spectrum of argon-like systems.

The work is devoted to the analysis of high-frequency behavior of the velocity auto-correlation function spectrum ϕ(V)(ω) for argon-like systems. The theoretical predictions are compared with results of computer simulations of ϕ(V)(ω). It is shown that (1) ϕ(V)(ω) takes the exponential behavior ϕ(V)(ω)⇒ω(q(n)) (ω→∞)exp(-(ωτ(a)(n))(p(n))), where p(n), q(n), and τ(a)(n) are the definite functions of the steepness exponent n for the power repulsive part of interparticle potential; (2) there is full agreement between theoretical predictions and the values of p(n), q(n), and τ(a)(n) obtained in computer simulations. Weighty arguments about the universal character of the exponential frequency decay exp(-(ωτ(a)(n))(p(n))) for spectra of different correlation functions are given. The experimental spectrum of the depolarized light scattering in argon for high frequencies is analyzed. It is shown that the steepness exponent n for the power repulsive potential takes the value: n ≈ 24 that is essentially different from n = 12 characteristic for the Lennard-Jones potential.

Macro- and microdefinitions of fragility of hydrogen-bonded glass-forming liquids.

In the present paper, the nature of the fragility of liquids with a developed H-bond network is investigated. It is shown that the effective activation energy of the shear viscosity eta and the fragility parameter defined as m=d log eta/d(Tg/T)|t=t+g are immediately connected with the average number nH(T) of the H-bond per molecule. The consistency of the macroscopic (m) and the microscopic [M=d(u(2)(0)/2)>loc)/d(Tg/T)|T=T+8, where 2>loc=2>anharm - 2>harm] definitions of the fragility is established.

Nature of double critical points in binary solutions.

The nature of the reentrant demixing transition in binary solutions with H bonds is studied in the framework of an Ising-like Hamiltonian with effective spin-spin interaction constant. It is taken into account that the internal variables describing the H-bond network are characterized by the spatial time scales essentially shorter than those for the spin variables. Due to this the contribution of H bonds to the effective spin-spin interaction constant is described by thermodynamic methods. With the help of the catastrophe theory the classification of possible types of phase diagrams leading to the double critical point is given. The influence of small quantities of third component (electrolytes, water, and molecules similar to CCl4) is discussed.

Dipole fluid as a basic model for the equation of state of ionic liquids in the vicinity of their critical point.

A model of dipole fluid for ionic liquids similar to molten NaCl is proposed. The estimates for the critical parameters are obtained with the help of the van der Waals equation of state. The influence of the rotation on the characteristics of a dipole pair and the location of the critical point is discussed. The dissociation of such a fluid near the critical point is considered.

Critical behavior of ionic liquids.

The renormalization of the Landau-Ginzburg Hamiltonian for a system with Coulombic interactions caused by spatially inhomogeneous polarizational effects is discussed. It is shown that for ionic liquids with a strong dependence of the degree of dissociation on density, the nonclassical fluctuation region is significantly narrowed. The essential role of the association of ions is noted.

Influence of charge fluctuations on the critical behavior of electrolyte solutions.

The effective Hamiltonian of electrolyte solution near its critical point is constructed. The vapor-liquid critical point is investigated in detail. The strong dependence of the Landau-Ginsburg number on the concentration of electrolyte is demonstrated. It is shown that the charge fluctuations in electrolytes essentially suppress the fluctuation of the order parameter and broaden the region of classical behavior.