Colloidal dispersions have been much investigated recently, by experimental and simulation methods and are of great interest for companies like Schlumberger, Henkel, Bayer or BASF. They can be both prepared and characterised in a controlled way, and the effective interaction between the colloidal particles can be tailored. Exciting questions on the many-body effects induced by co-operation and self-organisation of many particles can be studied by experiments as well as by computer simulations. This has been demonstrated for the bulk freezing transition, the kinetic glass transition and for the crystal nucleation rates. At present many interesting questions concern the behaviour of colloids in external shear-, electric-, laser-optical-, and magnetic fields as well as in a confined geometry. We intend to contribute to the classification of the different self-organisation processes of these important soft matter systems as a function of particle complexity and the kind of external manipulation.
The behaviour of liquid crystals near solid and fluid interfaces, and the effective interactions between suspended micro and nanoparticles, is also of great interest. Deformation of the director field creates long-ranged effective forces between suspended colloidal particles, the nature of which is dependent on the surface anchoring conditions. The detailed investigation of forces between pairs of spherical particles, platelets, or long rods, is amenable to study by weighted sampling Monte Carlo methods; the same approaches find an application in the related problem of protein-protein interactions in membranes. The modelling of suspensions of many particles in the surrounding liquid crystalling solvent is too expensive for fully atomistic or particle-based simulations, and requires a mesoscale approach. The process of aggregation of such particles at the interfaces of a liquid which is going through the isotropic-nematic phase transition is itself a topical area of soft condensed matter physics, as it leads to new soft solid structures. The workshop will discuss possible modelling approaches for such highly heterogeneous systems.
Colloid-polymer mixtures are model materials for the phase behavior of ordinary condensed matter, since the polymer coils (which may overlap each other) create the well-known depletion attraction between the colloids (which may not overlap either each other or the polymers), and varying the range of attraction via the size ratio(gyration radius of the polymer / radius of the spherical colloid particles) one can "tune" the phase diagram. There are gas-like, liquid-like and crystalline phases of the colloids,but the gas-liquid critical point disappears, or becomes metastable, if the range of the depletion attraction becomes rather short. This behavior has been established, at least roughly, by experiment, theory, and simulation, but there is urgent need for more careful work to clarify the detailed behavior. Recent simulation advances have allowed to clarify the gas-liquid transition in the bulk as well as in confinement in slit pores and in random porous media. But there is need to explore in particular the solid-liquid and solid-"gas" transitions. This system is also very attractive to experiments (e.g. capillary waves have been directly visualized; dynamics of individual particles can be followed; etc.). Understanding the dynamics of these systems by simulations will require a multiscale approach, because of the hydrodynamic interactions mediated by the solvent.
(Johannes Gutenberg University Mainz)
(Physics Department, University of Konstanz)
(Universities of Warwick and Bristol)