PACS. 82.70.Kj Emulsions and suspensions, 47.20.Dr Surface-tension-driven instability, 83.10.Lk Multiphase flows,

A lattice-Boltzmann model for the study of the dynamics of oil-water-surfactant mixtures is constructed. The model, which is based on a Ginzburg-Landau theory of amphiphilic systems with a single, scalar order parameter, is then used to calculate the spectrum of undulation modes of an oil-water interface and the spontaneous emulsification of oil and water after a quench from two-phase coexistence into the lamellar phase. A comparison with some analytical results shows that the model provides an accurate description of the static and dynamic behavior of amphiphilic systems.Typeset using EURO-T E X

Amorphous alloys can be modelled as random networks of atoms or molecules of differing valencies. A statistical-mechanical theory of such networks is presented for the case of binary amorphous alloys. The existence of a continuous equilibrium phase transition, from the liquid state to the amorphous solid state driven by increasing the density of permanent random covalent bonds, is demonstrated. The structural and elastic properties of the amorphous solid state are calculated through the use of a variational Ansatz, and a discussion is given of the dependence of these properties on the relative concentration of the constituent atoms or molecules and their valencies. Implications of the present results in the context of gelation are addressed, especially with regard to the (primarily entropic) elastic properties of gels.

We investigate the dynamical behavior of lamellar phases in ternary amphiphilic systems of water, oil and amphiphile. The interaction between the amphiphilic monolayers is described by the steric interaction due to thermal fluctuations for uncharged, and by electrostatic interactions for charged systems. The dynamics of the system is determined by the hydrodynamics of the fluid layers. The basic parameters of our model are the viscosities of the two solvents, the average thicknesses of the oil and water layers, and the bending rigidity. The model allows to consider different monolayer interactions across the oil and water layers. Relaxation rates are calculated for arbitrary wave vectors parallel and perpendicular to the average monolayer plane. We find that there is a quite complex crossover behavior from a q 2 law for small parallel wave vectors to a q 3 law for large q . We discuss the relevance of our result for the interpretation of dynamic light-scattering and neutron-spin-echo experiments for these systems. PACS. 47.55.-t Nonhomogeneous flows -68.10.-m Fluid surfaces and fluid-fluid interfaces -82.70.-y Disperse systems