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Charged colloidal suspensions: phase behaviour and aggregation kinetics


The colloidal suspensions with monovalent counter ions and salt ions will be studied by means of numerical simulations combining non-linear Poisson-Boltzmann equation (to treat the micro ionic degrees of freedom) with Brownian dynamics (for colloids). The colloidal interactions derived from the solution of the Poisson-Boltzmann equation include all electrostatic many-body interactions. With this simulation method the equation ofjstate of colloidal suspensions will be explored. The equation of state will be compared to the cell model predictions, which have not yet been validated in a broad parameter range. In case that phase coexistence will be observed, other methods, like Gibbs ensemble technique and thermodynamic free energy integration will be applied to study it in detail. Aggregation kinetics, which controls the colloidal stability, will also be studied combining the non-linear Poisson- Boltzmann equation with the population balance (Smoluchowski) equation describing the aggregation clusters population dynamics. The many-body electrostatic interactions calculated by this technique will be used to specify realistic input parameters for the aggregation kinetics, which will improve its predictive capabilities. Additionally, also a full Brownian dynamics simulation of the aggregation process (including electrostatic, dispersion and hydrodynamic interactions) will be performed. Clusters growth rate and fractal structure will be analyzed and their relation to the underlying interactions will be explored. The proposer will cooperate with experimental groups in Graz and Stuttgart in planning, performing and evaluating experiments on aggregation in 2D (by means of video microscopy arid laser tweezers) and in 3D (by means of light scattering). The combination of experiments, theory and simulations will provide the proposal with an ideal set of information useful to understand the fundamentally and technologically important aggregation process.

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