A dynamic random impurity model is studied lor describing the evolution of an advancing interface through a multiphase random medium containing mobile impurities. A short range repulsion between the Iront and the impurities leads to an aggregation process along the front, and to the trapping of aggregates behind the front. The patterns of trapped impurities are found to be self-organized. Some theoretical treatment is performed through a transfer matrix technique in various geometries: trees with loops instead of branches, chains of squares and triangles joined by vertices. Arguments are given for applications of such concepts, techniques and models in various cases: chemistry, biology, trafic, sociology, economy,…

A simple model of confinement-induced freezing in thin liquid layers is presented. Under boundary conditions of vanishing displacement field at the walls, confinement suppresses the amplitude of fluctuations in a solid film below a critical value determined by the Lindemann criterion of melting. The resulting increase of the melting temperature compared to that of a bulk solid, is estimated and the connection with experiments is discussed.

We describe a theory for hole nucleation in volatile, wetting, thin liquid films. Hole nucleation in this system can occur due to two independent driving forces: evaporation (volatile hole nucleation) and by disjoining pressure effects (non-volatile hole nucleation). Although a concerted combination of these two can be in effect, the cases are treated separately here and will be treated jointly in the context of a simulation elsewhere. Growing holes – dry areas of the solid surface which are otherwise wet by solvent – are conjectured to be responsible for the formation of close-packed 2D annular ringlike arrays from dilute solutions of nearly monodisperse, large (3–5nm diameter), organically passivated metal particles [1]. When organic solutions of these nanoparticles are evaporated on a solid carbon substrate (a TEM grid), the resulting sub-monolayer structures are annular ringlike arrays due to the pinning of the rim of an opening hole by a sufficient collection of particles.

We study foam drainage using the large-Q Potts model extended to include gravity on a three dimensional lattice. Without adding liquid, homogeneously distributed liquid drains to the bottom of the foam until equilibrium between capillary effects and gravity is reached, while in an ordered dry foam, if a fixed amount of liquid is added from the top, a sharp fiat interface between the wet and dry foam develops. The wetting front profile forms a downward moving pulse, with a constant velocity. The pulse decays over time while its leading edge for a brief time behaves like a solitary wave. With continuous liquid addition from the top, the pulse does not decay and we observe a soliton front moving with a constant velocity. Continuously adding liquid to an initially wet foam keeps the liquid profile constant. Our simulations agree with both experimental data and simplified mean field analytical results for ordered foams but predict an unstable interface for disordered foams.

We use diffusing-wave spectroscopy (DWS) to study microscopic dynamics in the interior of 3-dimensional granular systems. We study two granular systems where particle motions are excited by different driving mechanisms – gravity-driven channel flow and a gas-fluidized bed. In both instances we obtain detailed information about short-time collisional dynamics such as rms velocity fluctuations, mean free paths, and collision frequencies. We also observe a slow crossover from short-time ballistic motions to long-time, grain-scale diffusive motions.

When an initially homogeneous binary mixture of granular media such as fine and coarse sand is poured near the closed edge of a “quasi-two-dimensional” Hele-Shaw cell consisting of two vertical transparent plates held a narrow distance apart, the mixture spontaneously forms alternating segregated layers. Using digital images taken with a CCD camera and Fourier transformed to obtain the structure function of the banding pattern, the wavelength selection mechanism and degree of segregation are studied as the plate separation of the Hele-Shaw cell is systematically increased. For a given flow rate, the degree of segregation, as reflected in the amplitude of the peak in the structure function, decreases as the plate separation increases. For wider plate spacings the peak in the structure function shifts to lower wavelengths. These results are compared to numerical simulations of the avalanche segregation using a stochastic sandpile model.

We study a simple model of a granular material or powder where the particles are excited by an external noise source and dissipate energy by inelastic collisions. Due to the inelastic collisions between particles there is an effective interaction between them. In one dimension this leads to long-range correlations between the particles in a gas phase despite the absence of long-range forces between the particles. In two dimensions the dissipative effects cause a very sharp liquid-gas phase transition at which the susceptibility has a pronounced peak.