Molecular dynamic simulations and global equation of state of square-well fluids with the well-widths fromλ = 1.1 to 2.1

Structures, cold pressure lines, and electronic properties of cubic Al2O and AlO: First-principles calculations

Aluminized explosive has attracted more and more attention in recent years because of its high explosive heat and high power. Al2O and AlO are indispensable aluminum oxides in the explosion process of aluminized explosives. The study of the physical properties of solid Al2O and AlO under pressure may play an important role in the understanding of the explosion mechanism of aluminized explosives. CONTEXT: The structures, cold-pressed lines and electronic properties of cubic Al2O and AlO are calculated and analyzed based on first-principles calculation in this paper. The optimized structures of Al2O and AlO are in good agreement with those previously studied. The cold pressure line shows that the specific volumes of Al2O and AlO decrease with increasing pressure. The peak values and peak positions of density of state of Al2O and AlO change greatly under pressure. METHODS: The CASTEP code was used to execute these calculations throughout the present work, where the plane-wave basis set and norm conserving pseudopotential were employed.

From Atoms to Colloids: Does the Frenkel Line Exist in Discontinuous Potentials?

The Frenkel line has been proposed as a crossover in the fluid region of phase diagrams between a "nonrigid" and a "rigid" fluid. It is generally described as a crossover in the dynamical properties of a material and as such has been described theoretically using a very different set of markers from those with which is it investigated experimentally. In this study, we have performed extensive calculations using two simple yet fundamentally different model systems: hard spheres and square-well potentials. The former has only hardcore repulsion, while the latter also includes a simple model of attraction. We computed and analyzed a series of physical properties used previously in simulations and experimental measurements and discuss critically their correlations and validity as to being able to uniquely and coherently locate the Frenkel line in discontinuous potentials.

A Simple Equation for the Free Energy of Liquids

A simple, three-parameter equation is proposed for the free energy of classical fluids composed of molecules which are not hydrogen bonded. Agreement with experiment is much the same as has been obtained from more complicated three-parameter equations. For spherical and nearly spherical molecules, semiquantitative relations between intermolecular pair potential parameters and the parameters of the proposed equation were found. For alkanes, relations between the parameters and carbon number were noted. These relationships contribute to the understanding of fluid state properties in terms of the properties of the molecules of which they are composed.

Effect of shape on liquid-vapor coexistence and surface properties of parallelepiped molecules

Liquid-vapor coexistence is calculated via molecular dynamics for a variety of parallelepiped shaped molecules. Models are constructed as an array of tangential hard spheres interacting with an attractive square-well potential. Each shape is formed by varying the number of spheres in their three sides. The initial density of the system is chosen close to the critical density of a SW fluid to obtain an equilibrated liquid-vapor coexistence curve by the process of spinodal decomposition. A pattern that relates the geometry of the molecular models and the existence or non-existence of a liquid-vapor orthobaric curve is shown.

Structure, thermodynamic properties, and phase diagrams of few colloids confined in a spherical pore

We study a system of few colloids confined in a small spherical cavity with event driven molecular dynamics simulations in the canonical ensemble. The colloidal particles interact through a short range square-well potential that takes into account the basic elements of attraction and excluded-volume repulsion of the interaction among colloids. We analyze the structural and thermodynamic properties of this few-body confined system in the framework of inhomogeneous fluids theory. Pair correlation function and density profile are used to determine the structure and the spatial characteristics of the system. Pressure on the walls, internal energy, and surface quantities such as surface tension and adsorption are also analyzed for a wide range of densities and temperatures. We have characterized systems from 2 to 6 confined particles, identifying distinctive qualitative behavior over the thermodynamic plane T - ρ, in a few-particle equivalent to phase diagrams of macroscopic systems. Applying the extended law of corresponding states, the square well interaction is mapped to the Asakura-Oosawa model for colloid-polymer mixtures. We link explicitly the temperature of the confined square-well fluid to the equivalent packing fraction of polymers in the Asakura-Oosawa model. Using this approach, we study the confined system of few colloids in a colloid-polymer mixture.

Driven on- and off-lattice gas

An on- and off-lattice analog of the driven lattice gas has been studied by molecular-dynamics simulation. In the model, particles move on a two-dimensional lattice potential under a constant driving force. They also interact with each other by an attractive square-well pair potential. A heat bath removes as heat the work done by the driving field. The case of zero field recovers equilibrium two-dimensional lattice and continuous-space results. With nonzero field and a strong lattice potential, the system is comparable to the driven lattice gas. As in the driven lattice gas, the anisotropic single-strip configuration persists to higher kinetic energy as the field strength increases. In the case of zero lattice strength, the model reduces to an off-lattice two-dimensional driven square-well fluid. Single-strip steady states are not observed off lattice.

Influence of nanoparticle addition on the properties of wormlike micellar solutions

The addition of positively charged, 30 nm diameter silica nanoparticles to cationic wormlike micellar solutions of cetyltrimethylammonium bromide and sodium nitrate is studied using a combination of rheology, small angle neutron scattering, dynamic light scattering, and cryo-transmission electron microscopy. The mixtures are single phase up to particle volume fractions of 1%. The addition of like-charged particles significantly increases the wormlike micelle (WLM) solution's zero shear rate viscosity, longest relaxation time, and storage modulus. The changes are hypothesized to originate from a close association of the particles with the micellar mesh. Small angle neutron scattering measurements with contrast matching demonstrate associations between particles mitigated by the WLMs. The effective interparticle interactions measured by SANS can explain the observed phase behavior. Dynamic light scattering measurements confirm the dynamic coupling of the particles to the micellar mesh.