In order to describe the patch-patch interaction in detail we perform Molecular Dynamics (MD) simulations. Although limited to small system sizes and short timescales, this study will shed light on the role of specific colloidal interactions and will provide information for the development of the stochastic model developed at CFTC. Since MD takes into account the interaction potential between patches, the results may be used to determine mechanical properties and to evaluate the stability of the structures obtained within the stochastic model.
We describe patchy particles as a central particle with a radius of the size of the colloid and point surface particles representing the patches at a distance of the radius to the central one (with no relevant mass). We fix the relative position of the patches on the central particle, which is regarded as a molecule with fixed bonds. Forces are computed for each particle and the equations of motion are solved for the rigid molecule structure. We use Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) for efficient parallel simulations, and perform Langevin dynamics. We use a Yukawa potential for the colloid-colloid interaction (screened Coulomb interaction). The attractive patch-patch interaction is modeled by a Gaussian potential.
We found that in the limit of very strong bonds the relaxation is dominated by short- and long-time dynamics both near the substrate and in the bulk. We also found that the density of the film, in the bulk, does not change with the relaxation, although the density of connections does increase. By contrast, the restructuring on the substrate is more dramatic (to be published).
Non-equilibrium adsorption of 2AnB patchy colloids on substrates, C. S. Dias, N. A. M. Araújo and M. M. Telo da Gama, Soft Matter 9, 5616 (2013).
Nonequilibrium growth of patchy-colloid networks on substrates, C. S. Dias, N. A. M. Araújo and M. M. Telo da Gama, Physical Review E 87, 032308 (2013).