Dynamical simulation of dipolar Janus colloids: Dynamical properties

Abstract

The dynamical properties of dipolar Janus particles are studied through simulation using our previously-developed detailed pointwise (PW) model and an isotropically coarse-grained (CG) model [M. C. Hagy and R. Hernandez, J. Chem. Phys. 137, 044505 (2012)]. The CG model is found to have accelerated dynamics relative to the PW model over a range of conditions for which both models have near identical static equilibrium properties. Physically, this suggests dipolar Janus particles have slower transport properties (such as diffusion) in comparison to isotropically attractive particles. Time rescaling and damping with Langevin friction are explored to map the dynamics of the CG model to that of the PW model. Both methods map the diffusion constant successfully and improve the velocity autocorrelation function and the mean squared displacement of the CG model. Neither method improves the distribution of reversible bond durations f(tb) observed in the CG model, which is found to lack the longer duration reversible bonds observed in the PW model. We attribute these differences in f(tb) to changes in the energetics of multiple rearrangement mechanisms. This suggests a need for new methods that map the coarse-grained dynamics of such systems to the true time scale.

Dynamical simulation of electrostatic striped colloidal particles

“…These values were chosen from our previous study of dipolar Janus dynamics. 16 Additionally, the diffusion coefficient D is computed from these time correlation functions using the relationships…”

“…18 Both methods were found to improve time correlation functions and transport coefficients, but did not reproduce the bond dynamics of the PW model in the CG model. 16 These results suggest that current dynamical mapping methods do not address all of the remaining time and length scales upon coarse-graining, but we do not consider a solution to this problem here.…”

“…We have adapted this model for the simulation of systems of dipolar Janus particles in previous work. 15,16 Our PW model uses Coulomb-like interactions between points so that the overall potential is continuous and can be simulated by conventional molecular dynamics. The Coulomb interactions in the PW model are truncated at 25% of the particle radius (30 nm) so that they are still short-range.…”

“…In previous work, 15,16 we have studied the static and dynamic properties of dipolar Janus (DJ) colloids using molecular dynamics simulations. A pointwise (PW) model of DJ particles was developed to capture the short-range geometrydependent interactions.…”

“…15 In contrast, we found that the CG model had accelerated dynamics (e.g., larger transport coefficients) than the PW model. 16 Physically, this suggest DJ colloids will have slower dynamics than comparable isotropic colloids (e.g., depletion attracting colloids). It would be useful if the accelerated dynamics of the CG model could be related back to the original PW time-scale.…”