Behavior of a wetting phase near a solid boundary: vapor near a weakly attractive surface

Density profiles of a LJ vapor near a weakly attractive surface with long-range fluid wall potential was studied along the pore coexistence curve. There are two localized density maxima near the pore wall: the first one is caused by localization of the molecules in the minimum of the fluid-wall potential, and the second one reflects adsorption of molecules at the first layer at higher densities. In addition, a third, weak density maximum is observed close to the critical temperature due to the competition between the long-range attractive tail of the fluid-wall potential and the effect of missing neighbors. This maximum separates the region of a gradual density depletion toward the surface due to the missing neighbor effect and the adsorption region further from the surface, where the density gradually increases toward the surface due to the attractive fluid-wall potential. When approaching the bulk critical temperature, this maximum moves away from the surface due to the divergence of the bulk correlation length. Applicability of various equations to describe the vapor density profiles is examined. Excess adsorption of vapor at low temperatures turns into excess depletion at higher temperatures. The crossover temperature increases with increasing pore size and strengthening fluid-wall interaction. The problems of the theory of the surface critical behavior of Ising models in a case of a non vanishing surface field and its mapping on a fluid is discussed.     

Critical properties of homopolymer fluids studied by a Lennard-Jones statistical associating fluid theory

A Lennard-Jones statistical associating fluid theory, the soft-SAFT equation of state, is used to study the dependence of the critical properties on chain length for pure polymers. The critical constants of chains up to 10⁶ monomer units are predicted. The main advantage of these calculations, versus others found in the literature, is the fact that the equation is able to accurately predict experimental data available only for short chain lengths and, at the same time, it is able to predict the critical properties in the infinite chain length scaling regime, without any further assumptions. The equation gives quantitative agreement with experimental and Monte Carlo simulation data for normal alkanes. For very long chains, the equation predicts mean-field scaling behaviour, as expected. Moreover, taking advantage of the linearity of the molecular volumes and dispersive energies with the chain molecular weight, a value of 1/5 is found for the critical compressibility factor of an infinitely long n-alkane chain. It is demonstrated that this is not contradictory to Wertheim's theory.     

Nonasymptotic critical thermodynamical behavior of fluids

The paper is concerned with some theoretical and empirical attempts to obtain a unified equation for the thermodynamic properties of fluids that incorporates the nonclassical scaling laws near the critical point and crosses over to a classical analytic equation far away from the critical point. Specifically we investigate to what extent the various proposed crossover models agree with the known theoretical predictions for the universal ratios among the asymptotic and correction-to-scaling amplitudes in the power-law expansions of the thermodynamic properties around the critical point.     

Two-scale-factor universality near the critical point of fluids

Experimental evidence is presented in support of the validity of the hypothesis of two-scale-factor universality for the correlation function of fluids near the gas-liquid critical point. For Xe, SF₆, and CO₂, the dimensionless quantity $\text{R = ξ}{}_0\text{(}\text{B}{}^2\text{P}{}_{\mathrm{c}}\text{Γk}{}_{\mathrm{B}}\text{T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ is universal within the experimental accuracy of 10% and agrees with the value predicted by theory.     

Growth rate of critical nuclei near the critical point of a fluid

The growth rate of critical nuclei for a fluid near its critical point is discussed on the basis of the stochastic equation for the probability distribution function of the local order parameter, which was derived previously by the author. The growth rate was found to depend on , the range of correlation of the order parameter fluctuation, andR, the radius of critical nuclei, as ⁰ R ^–3, in conformity with dynamical scaling. The rate of nucleation at the liquid-gas transition near the critical point is also discussed on the basis of this result.     

Nucleation in turbulent fluids near the critical point

Effects of turbulence on nucleation are investigated in classical fluids near the critical point. Turbulence can suppress the onset of nucleation, enhance the coagulation of droplets, and break up droplets. The final characteristic droplet size strongly depends on the temperature difference T_c − T and the Reynolds number Re.     

Simple approach to approximate predictions of the vapor–liquid equilibrium curve near the critical point and its application to Lennard-Jones fluids

We propose a simple analytical form of the vapor–liquid equilibrium curve near the critical point for Lennard-Jones fluids. Coexistence densities curves and vapor pressure have been determined using the Van der Waals and Dieterici equation of state. In described method the Bernoulli differential equations, critical exponent theory and some type of Maxwell?s criterion have been used. Presented approach has not yet been used to determine analytical form of phase curves as done in this Letter. Lennard-Jones fluids have been considered for analysis. Comparison with experimental data is done. The accuracy of the method is described.     

Spinodal decomposition in a Lennard-Jones fluid

A microscopic theory for the early stages of spinodal decomposition in a one-component fluid is presented. We show that in the unstable region of the phase diagram the amplitude of density fluctuations with wave vectors less than some critical value q_c , where q_c is the position of the pole in the static density response function of the uniform fluid, increases exponentially with time. The corresponding amplification factor is related to the Ornstein-Zernike direct correlation function of the uniform fluid. We have calculated the amplification factor for a Lennard-Jones fluid at several densities and temperatures. We find that these amplification factors are qualitatively different from those obtained from the analogue of Cahn's linearized theory of spinodal decomposition. Our calculated value of q_c at reduced density 0·35 and temperature 0·8 is in fairly good agreement with the result of a recent molecular dynamics simulation of a Lennard-Jones fluid quenched to this state.     

Molecular dynamics simulations of a fluid near its critical point

We present computer simulations for the static and dynamic behavior of a fluid near its consolute critical point. We study the Widom-Rowlinson mixture, which is a two component fluid where like species do not interact and unlike species interact via a hard core repulsion. At high enough densities this fluid exhibits a second order demixing transition that is in the Ising universality class. We find that the mutual diffusion coefficient DAB vanishes as DAB approximately xi(-1.26 +/- 0.08), where xi is the correlation length. This is different from renormalization-group and mode coupling theory predictions for model H, which are DAB approximately xi(-1.065) and DAB approximately xi(-1), respectively.     

Static dielectric behavior of charged fluids near freezing

The wavenumber-dependent, static dielectric function of classical charged fluids near freezing is obtained from structural data based on computer simulation or neutron diffraction, and its behavior is connected with the freezing process.     

Universal behavior of heavy-fermion metals near a quantum critical point

The behavior of the electronic system of heavy-fermion metals is considered. We show that there exist at least two main types of the behavior when the system is near quantum critical point, which can be identified as the fermion condensation quantum phase transition (FCQPT). We show that the first type is represented by the behavior of a highly correlated Fermi liquid, while the second type is depicted by the behavior of a strongly correlated Fermi liquid. If the system approaches FCQPT from the disordered phase, it can be viewed as a highly correlated Fermi liquid which at low temperatures exhibits the behavior of Landau Fermi liquid (LFL). At higher temperatures T, it demonstrates the non-Fermi liquid (NFL) behavior which can be converted into the LFL behavior by the application of magnetic fields B. If the system has undergone FCQPT, it can be considered as a strongly correlated Fermi liquid which demonstrates the NFL behavior even at low temperatures. It can be turned into LFL by applying magnetic fields B. We show that the effective mass M* diverges at the very point that the Neél temperature goes to zero. The B-T phase diagrams of both liquids are studied. We demonstrate that these B-T phase diagrams have a strong impact on the main properties of heavy-fermion metals, such as the magnetoresistance, resistivity, specific heat, magnetization, and volume thermal expansion.     

Simulation of critical fluid Rayleigh linewidth behavior by a normal fluid system

The dynamic droplet model of a critical fluid provides a simple physical model of a critical fluid. We use this to model an emulsion which mimics the Rayleigh linewidth behavior of a critical fluid in the nonhydrodynamic regime.     

Nuclear spin relaxation in molecular fluids near the critical point

The Watson version of the molecular vibration-rotation hamiltonian is expanded in terms of the scalar invariants of the inverse of the moment of inertia tensor using the generalized Lucas polynomials. The resultant expansion consists of the matrices Î, , ² with coefficients depending on the normal coordinates. This is in contrast to the usual expansion as a power series in the matrix .     

Freezing of a Lennard-Jones fluid: from nucleation to spinodal regime

Using molecular dynamics, we investigate the crystal nucleation in a Lennard-Jones fluid as a function of the degree of supercooling. At moderate supercooling, a nucleation picture applies, while for deeper quenches, the phenomenon progressively acquires a spinodal character. We show that in the nucleation regime, the freezing is a two-step process. The formation of the critical nucleus is indeed preceded by the abrupt formation of a precritical crystallite from a density fluctuation in the fluid. In contrast, as the degree of supercooling is increased, crystallization proceeds in a more continuous and collective fashion and becomes more spatially diffuse, indicating that the liquid is unstable and crystallizes by a spinodal mechanism.     

Viscosity of Lennard-Jones fluid: Integral equation method

One of the most useful models to study the real systems is the Lennard-Jones (LJ) potential which has an attractive and repulsive part. In this work we use this potential model and examine the viscosity of one-component LJ fluids and LJ binary fluid mixtures. For this purpose, we apply the integral equation method and solve numerically the Ornstein-Zernike (OZ) integral equation by using the mean spherical approximation (MSA). Thus, we obtain the pair correlation functions to calculate the viscosity of these fluids. Finally, we compare our results with computer simulation results and the available experimental data and illustrate the ability of the LJ model to predict the results.     

Transport properties of a Van der Waals fluid near the critical point

The behaviour of the transport coefficients of a Van der Waals fluid is studied in the one-phase region along the critical isochore of the liquid-vapour phase transition. When $\text{?=}\text{(T?T}{}_{\mathrm{c}}\text{)}\text{T}{}_{\mathrm{c}}\text{→0}$ the strongest singularity is found in the case of the bulk viscosity (??^?2). The divergence of the heat conductivity is shown to be weaker than $\text{?}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>3</mtext>}}$. The shear viscosity tends to a finite limit. The coefficients of the asymptotic laws are explicitly given. All the results are established in the region where the Ornstein-Zernike theory applies.     

Scaling of the viscoelasticity of weakly attractive particles

The rheological data of weakly attractive colloidal particles are shown to exhibit a surprising scaling behavior as the particle volume fraction, straight phi, or the strength of the attractive interparticle interaction, U, are varied. There is a critical onset of a solid network as either straight phi or U increase above critical values. For all solidlike samples, both the frequency-dependent linear viscoelastic moduli, and the strain-rate dependent stress can be scaled onto universal master curves. A model of a solid network interspersed in a background fluid qualitatively accounts for this behavior.