Molecular dynamics simulation study of the static and dynamic properties of a model colloidal suspension with explicit solvent
SDW Hannam and PJ Daivis and G Bryant, MOLECULAR SIMULATION, 42, 511-521 (2016).
Molecular dynamics simulation was used to study a colloidal suspension with explicit solvent to determine how inclusion of the solvent affects the structure and dynamics of the system. The solute was modelled as a hard-core particle enclosed in a Weeks-Chandler-Andersen (WCA) potential shell, while the solvent was modelled as a simple WCA fluid. We found that when the solute-solvent interaction included a hard core equal to half of the solute hard-core diameter, large depletion effects arose, leading to an effective attraction and large deviations from hard-sphere structure for the colloidal component. It was found that these effects could be eliminated by reducing the hard-core distance parameter in the solute-solvent interaction, thus allowing the solvent to penetrate closer to the colloidal particles. Three different values for the solute-solvent hard-core parameter were systematically studied by comparing the static structure factor and radial distribution function to the predictions of the Percus-Yevick theory for hard spheres. When the optimal value of the solute-solvent hard-core interaction parameter was found, this model was then used to study the dynamical behaviour of the colloidal suspension. This was done by first measuring the velocity autocorrelation function (VACF) over a large range of packing fractions. We found that this model predicted the sign of the long-time tail in the VACF in agreement with experimental values, something that single component hard-sphere systems have failed to do. The intermediate scattering functions at low wavevector were briefly studied to determine their behaviour in a dilute system. It was found that they could be modelled using a simple diffusion equation with a wavevector independent diffusion coefficient, making this model an excellent analogue of experimentally studied hard-sphere colloids.
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