J. S. Ho

Microscopic model for microemulsions. I. Ground state properties

The ground state of several variants of a new microemulsion model is examined in detail. We find oil–microemulsion–water and oil–surfactant–water equilibria, and coexistence between microemulsions of different geometrical structures (lamellar, tubular, and ‘‘brick’’). We find vanishing or low surface tension between bulk oil and water at the three‐phase coexistence in different versions of the model. Our results suggest that the model is capable of reproducing many of the striking features of real microemulsions and deserves a detailed study at nonzero temperatures.

Microscopic model for microemulsions. II. Behavior at low temperatures and critical point

Low temperature properties and critical behavior for the more simple versions of the microemulsion model introduced in Ref. 1 are investigated. For the lattice case with nearest‐neighbor interactions an analytic asymptotic expression for the surface tension at the oil–microemulsions–water coexistence is found for low T. For both lattice and continuum cases the critical point is determined, and we show how an oscillating phase (microemulsion) may be formed below the critical temperature.

Mean spherical approximation (MSA) for a simple model of electrolytes. I. Theoretical foundations and thermodynamics

A simple electrolyte in a polar solvent is modeled by a mixture of polar hard spheres and equal diameter charged hard spheres. The solution of the mean spherical approximation for this model is rederived to its full extent. Explicit expressions for thermodynamic quantities in terms of the MSA solution are established. A nice property of this MSA approach is the possibility to express quantities of physical interest in terms of a set of three parameters, which represent nothing but the excess internal energies due to charge–charge, charge–dipole, and dipole–dipole interactions, respectively.

Bicontinuous phase in a lattice model for surfactant mixtures

A lattice counterpart of a bicontinuous phase is found in a three‐dimensional lattice model of ternary surfactant mixtures. The structure of this phase is determined and discussed. The region of stability of the new phase in the parameter space is found at zero temperature. Also determined are the boundary of stability of the disordered phase, the water–water structure factor in this phase, and the disorder line.

Mean spherical approximation for a simple model of electrolytes. II. Correlation functions and thermodynamics: Numerical results

We investigate various properties of Blum’s solution of the MSA for a mixture of dipolar hard spheres and equal‐diameter charged hard spheres, fully rederived in a former publication. Numerical results for thermodynamic quantities, phase equilibria, and osmotic pressure are presented together with results for the ion–ion and ion–dipole correlation functions obtained via a simple integral‐equation procedure. A generalization of the MSA results to a system of polarizable dipolar hard spheres and charged hard spheres is also given.

Refractive index of polarizable fluids: Numerical results from the mean spherical approximation solution

The numerical solution of the MSA (mean spherical approximation) for a fluid of polarizable particles interacting via the electromagnetic dipole radiation field is presented. The effects of this interaction are studied for molecules with polarizabilities both independent and dependent on frequency. Imaginary and real parts of the refractive index are evaluated, and their behaviors in connection with the absorption bands are determined. Finally, time‐correlation and response functions have been evaluated.

The numerical solution of the linearized and exponential hypervertex approximations for electrolytes

In this paper we present numerical solution of the linearized and exponential hypervertex approximations for the restricted primitive model for electrolytes. The method of solution is based on a Newton–Raphson scheme previously applied to simple fluids. Thermodynamic results computed from both approximations agree remarkably well with previously published Monte Carlo data even to a greater extent than well‐known approximations such as the hypernetted‐chain equation.

Frequency spectra for fluids beyond the mean spherical approximation

In this paper, we investigate the frequency spectra of fluids (or fluid‐like disordered materials) composed of particles with embedded harmonic oscillators. The general treatment is particularized at the low density limit, and a working scheme to add corrections to the mean spherical approximation for arbitrary density is introduced. A detailed comparison with an exactly solvable model in one dimension is also presented.

Charge–cavity and charge–dipole effects in ionic fluids

The contribution of charge–dipole interactions to the thermodynamics and structure of ionic solutions is considered from the standpoint of two models—a quasicontinuum cavity model of charged spheres of dielectric constant e0 in a continuum of dielectric constant e as well as a molecular model consisting of charged‐sphere solute particles and dipolar‐sphere solvent particles. With suitable scaling of the interaction potentials one expects to obtain the cavity‐model description from the molecular model in the limit σd/σi→0, where σd and σi are the ion and dipolar‐particle diameters, respectively. We recover for the first time the full r−4 ‘‘cavity‐term’’ of the ion–ion cavity‐model pair potential in such a limit as well as a corresponding screened r−4 term in the solvent‐averaged direct correlation function, which is screened by the factor e−2λr and multiplied by the prefactor (1+λr)2, where λ is the ion–ion inverse screening length. Here, r is the distance between a pair of ions. We also show that if one m...

Frequency spectra of two‐band fluids and fluid mixtures: Mean spherical approximation and beyond

In the framework of a recently proposed approximation, we investigate here the frequency spectra of two‐band fluids (fluids composed of particles with two independent Drude oscillators embedded) as well as fluid mixtures of particles with one Drude oscillator. Both cases are analyzed in the low density regime where departures from the linear theories are more evident. Our theory, which goes beyond the mean spherical approximation (MSA), reproduces the correct low density spectra while retaining the proper qualitative behavior of the MSA at fluid densities.