Model systems of charged spherical macroions with either monovalent, divalent, or trivalent counterions interacting solely through hard-core and Coulomb forces have been investigated by Monte Carlo simulations. Although the direct macroion-macroion interaction is purely repulsive, we find for sufficiently strong electrostatic coupling an effective attraction that separates the solution into two fluid phases. The attraction is short ranged and arises from correlations among counterions localized near different macroions. This mechanism for attraction differs from that attraction inferred to operate in solutions of charged latex particles presently challenging the classical DLVO theory.

Asymmetric electrolytes consisting of highly charged spherical macroions and small ions representing an aqueous solution of ionic surfactant micelles have been studied at different macroion concentrations by means of Monte Carlo simulations. The model system comprises macroions with 60 elementary charges and either monovalent, divalent, or trivalent counterions interacting solely through hard-core and Coulomb forces. Thermodynamic and structural properties are examined, and the effects of the counterion valency are discussed. For the lowest electrostatic macroion–counterion coupling (monovalent counterions), the macroions are well separated and an effective repulsive potential is acting between them. At stronger electrostatic coupling (divalent counterions), the double-layer repulsion between the macroions is strongly reduced and at short separations the attractive force becomes comparable to the double-layer repulsion. At even stronger coupling (trivalent counterions), the attractive correlation force between the macroions dominates and causes the solution to separate into two fluid phases of highly different density of the electrolyte. Our results differ quantitatively from the mean-field Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, one of the cornerstones of colloid science, which predicts a purely repulsive electrostatic force among like-charged colloidal particles under all conditions. At the same time, our results are consistent with similar finding of an attraction of electrostatic origin between two similarly charged planar surfaces at sufficiently large electrostatic coupling. A detailed analysis of the counterion distribution in the neighborhood of two macroions close to each other has also been performed for divalent counterions. Finally, the effect of salt addition has also been examined.

We study the electrophoretic mobility of spherical charged colloids in a low-salt suspension as a function of the colloidal concentration. Using an effective particle charge and a reduced screening parameter, we map the data for systems with different particle charges and sizes, including numerical simulation data with full electrostatics and hydrodynamics and experimental data for latex dispersions, on a single master curve. We observe two different volume fraction-dependent regimes for the electrophoretic mobility that can be explained in terms of the static properties of the ionic double layer.

We show that an electro-osmotic flow near the slippery hydrophobic surface depends strongly on the mobility of surface charges, which are balanced by counterions of the electrostatic diffuse layer. For a hydrophobic surface with immobile charges, the fluid transport is considerably amplified by the existence of a hydrodynamic slippage. In contrast, near the hydrophobic surface with mobile adsorbed charges, it is also controlled by an additional electric force, which increases the shear stress at the slipping interface. To account for this, we formulate electrohydrodynamic boundary conditions at the slipping interface, which should be applied to quantify electro-osmotic flows instead of hydrodynamic boundary conditions. Our theoretical predictions are fully supported by dissipative particle dynamics simulations with explicit charges. These results lead to a new interpretation of zeta potential of hydrophobic surfaces.

We present a new hybrid lattice-Boltzmann and Langevin molecular dynamics scheme for simulating the dynamics of suspensions of spherical colloidal particles. The solvent is modeled on the level of the lattice-Boltzmann method while the molecular dynamics is done for the solute. The coupling between the two is implemented through a frictional force acting both on the solvent and on the solute, which depends on the relative velocity. A spherical colloidal particle is represented by interaction sites at its surface. We demonstrate that this scheme quantitatively reproduces the translational and rotational diffusion of a neutral spherical particle in a liquid and show preliminary results for a charged spherical particle. We argue that this method is especially advantageous in the case of charged colloids.

Nanotechnology has enabled the discovery of a multitude of novel materials exhibiting unique physicochemical (PChem) properties compared to their bulk analogues. These properties have led to a rapidly increasing range of commercial applications; this, however, may come at a cost, if an association to long-term health and environmental risks is discovered or even just perceived. Many nanomaterials (NMs) have not yet had their potential adverse biological effects fully assessed, due to costs and time constraints associated with the experimental assessment, frequently involving animals. Here, the available NM libraries are analyzed for their suitability for integration with novel nanoinformatics approaches and for the development of NM specific Integrated Approaches to Testing and Assessment (IATA) for human and environmental risk assessment, all within the NanoSolveIT cloud-platform. These established and well-characterized NM libraries (e.g. NanoMILE, NanoSolutions, NANoREG, NanoFASE, caLIBRAte, NanoTEST and the Nanomaterial Registry (>2000 NMs)) contain physicochemical characterization data as well as data for several relevant biological endpoints, assessed in part using harmonized Organisation for Economic Co-operation and Development (OECD) methods and test guidelines. Integration of such extensive NM information sources with the latest nanoinformatics methods will allow NanoSolveIT to model the relationships between NM structure (morphology), properties and their adverse effects and to predict the effects of other NMs for which less data is available. The project specifically addresses the needs of regulatory agencies and industry to effectively and rapidly evaluate the exposure, NM hazard and risk from nanomaterials and nano-enabled products, enabling implementation of computational 'safe-by-design' approaches to facilitate NM commercialization.