Dense suspensions of small strongly interacting particles are complex systems that are rarely understood on the microscopic level. We investigate properties of dense suspensions and sediments of small spherical Al 2 O 3 particles in a shear cell by means of a combined molecular-dynamics and stochastic rotation dynamics simulation. We study structuring effects and the dependence of the suspension's viscosity on the shear rate and shear thinning for systems of varying salt concentration and pH value. To show the agreement of our results with experimental data, the relation between the bulk pH value and surface charge of spherical colloidal particles is modeled by Debye-Hückel theory in conjunction with a 2 pK charge regulation model.

It is theoretically shown that the excess liquid-liquid interfacial tension between two electrolyte solutions as a function of the ionic strength I behaves asymptotically as Oÿ I p for small I and as OI for large I. The former regime is dominated by the electrostatic potential due to an unequal partitioning of ions between the two liquids whereas the latter regime is related to a finite interfacial thickness. The crossover between the two asymptotic regimes depends sensitively on material parameters suggesting that the experimentally accessible range of ionic strengths can correspond to either the small or the large ionic strength regime. In the limiting case of a liquid-gas surface where ion partitioning is absent, the image charge interaction can dominate the surface tension for small ionic strength I such that an Onsager-Samaras limiting law O ÿ I lnI is expected. The temporal stability of liquid-liquid emulsions, which is of enormous importance for applications in, e.g., chemical, pharmaceutical, food, and cosmetic industries, largely hinges on the liquid-liquid interfacial tension [1] modified by surfactants, cosurfactants, and even colloidal particles [2]. In order to theoretically understand and predict the liquid-liquid interfacial tension as a function of additives, a first step is modeling a liquid-liquid interface in the presence of electrolytes but in the absence of surfactants. Remarkably, the dependence of the liquid-liquid interfacial tension on the electrolyte concentration is, in contrast to the liquid-gas surface tension [3], not well understood. This is quite astonishing because liquid-liquid interfaces have been investigated for a long time by means of electrocapillary measurements [4]. The few reported measurements of the liquid-liquid interfacial tension as a function of the ionic strength known to the authors, Refs. [5][6][7], seem to confirm the linear relation at large ionic strengths well known from liquid-gas surface tension measurements [8]. At low ionic strengths the liquid-gas surface tension exhibits the Jones-Ray effect, i.e., a minimum of the surface tension as a function of the ionic strength [9], whose analog for liquid-liquid interfacial tensions has been addressed in the experimental literature, to the authors' knowledge, only in Ref. [5]. Theoretical approaches to liquid-gas surfaces are very often based on the assumption that the gas phase is completely free of ions [3], which leads to a charge neutral liquid phase. Considering the image charge interaction as dominating the liquid-gas surface tension at low ionic strength the OnsagerSamaras limiting law can be derived [10]. However, assuming a nonvanishing ionic strength in the gas phase, Nichols and Pratt found indications that the liquid-gas surface tension in some instances can also scale with the square root of the ionic strength in the low salt limit [11]. By means of an elaborate Ginzburg-Landau-like model for liquid-liquid interfaces, taking ion densities and solvent composition explicitly into account, Onuki recentl...

The subtle interplay between critical phenomena and electrostatics is investigated by considering the effective force acting on two parallel walls confining a near-critical binary liquid mixture with added salt. The ion-solvent coupling can turn a non-critical repulsive electrostatic force into an attractive one upon approaching the critical point. However, the effective force is eventually dominated by the critical Casimir effect, the universal properties of which are not altered by the presence of salt. This observation allows a consistent interpretation of recent experimental data.

We study self-diffusion in complex fluids within dynamic density functional theory and explicitly account for the coupling to the fluctuating background. Applying the formalism to nematic and smectic liquid crystals, we find the temporary cages formed by neighboring particles to compete with permanent barriers in nonuniform systems, resulting in non-Gaussian diffusive motion that in different directions becomes correlated. Qualitative agreement with recent experiments demonstrates the importance of explicitly dealing with time-dependent self-consistent molecular fields.