Modeling Homo- and Heterogeneous Crystal Nucleation from Charged Colloids

In this work, we performed molecular dynamics studies on the self-assembly of oppositely charged colloids in implicit water medium. Micrometer sized colloids interacting by a screened coulomb interaction, would aggregate irreversibly. A recent experimental work [Nature, 2020, 580, 487-492] showed that the neutral polymer brushes attached to the surfaces of the colloids can provide a repulsive interaction at close distances that prevents aggregation, and allows for the generation of ionic colloidal crystals, whose structures can be tuned via the particle size ratio and the solution salt concentration We previously employed a pairwise interaction potential that takes into account both the polymer brush and DLVO interaction potential to generate crystals consistent with those seen in experiment. Here, we study in more detail the effect of volume fraction and the salt concentration on the self-assembled structures. For a particular size ratio of the oppositely charged colloids, we observe a transition between the simple CsCl structure and various polymorphs that were not expected. Depending on the conditions, we find that nucleation can proceed via classical or non-classical pathways, which we are investigating in more detail. Finally, in our previous study, we employed a model of a charged wall to generate structures that were heterogeneously nucleated. Here we will investigate competition between homogeneous and heterogeneous nucleation pathways, which expand the range of polymorphs that can be observed within our simulations.