Molecular dynamics simulation was used to study a model colloidal suspension at a range of packing fractions from the dilute limit up to the freezing point. This study builds on previous work by the authors which modeled the colloidal particles with a hard core surrounded by a Weeks-Chandler-Anderson potential with modified interaction parameters, and included an explicit solvent. In this work, we study dynamical properties of the model by first calculating the velocity autocorrelation function, the self-diffusion coefficient, and the mutual diffusion coefficient. We also perform detailed calculations of the colloidal particle intermediate scattering function to study the change in dynamics leading up to the freezing point, and to determine whether the current model can be used to interpret light scattering experiments. We then perform a multiexponential analysis on the intermediate scattering function results and find that the data are fitted well by the sum of two exponentials, which is in line with previous analysis of experimental colloidal suspensions. The amplitudes and decay coefficients of the two modes are determined over a large range of wave vectors at packing fractions leading up to the freezing point. We found that the maximum wave vector at which macroscopic diffusive behavior was observed decreased as the packing fraction increased, and a simple extrapolation shows the maximum wave vector going to zero at the melting point. Lastly, the ratio of the two decay coefficients is compared to the scaling law proposed by Segrè and Pusey [Phys. Rev. Lett. 77, 771 (1996)PRLTAO0031-900710.1103/PhysRevLett.77.771]. It was found that the ratio was not constant, but instead was wave vector dependent.

Molecular dynamics simulation was used to study a model colloidal suspension with two species of slightly different sized colloidal particles in an explicit solvent. In this work we calculated the four interdiffusion coefficients for the ternary system, which were then used to calculate the decay coefficients D_{±} of the two independent diffusive modes. We found that the slower D_{-} decay mode, which is associated with the system's ability to undergo compositional changes, was responsible for the long-time decay in the intermediate scattering function. We also found that a decrease in D_{-} to negligible values at a packing fraction of Φ_{g}=0.592 resulted in an extreme slow-down in the long-time decay of the intermediate scattering function often associated with the glass transition. Above Φ_{g}, the system formed a long-lived metastable state that did not relax to its equilibrium crystal state within the simulation time window. We concluded that the inhibition of crystallization was caused by the inability of the quenched fluid to undergo the compositional changes needed for the formation of the equilibrium crystal.

Molecular dynamics simulation was used to study a colloidal suspension with explicit solvent to determine how inclusion of the solvent a↵ects the structure and dynamics of the system. The solute was modelled as a hard-core particle enclosed in a 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 e↵ects arose, leading to an e↵ective attraction and large deviations from hard-sphere structure for the colloidal component. It was found that these e↵ects 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 di↵erent 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 over a large range of packing fractions. We found that this model predicted the sign of the long time tail in the velocity autocorrelation function 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 di↵usion equation with a wavevector independent di↵usion coe cient, making this model an excellent analogue of experimentally studied hard sphere colloids.

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