Tuning the order of colloidal monolayers: assembly of heterogeneously charged colloids close to a patterned substrate.

We study the behavior of negatively charged colloids with two positively charged polar caps close to a planar patterned surface. The competition between the different anisotropic components of the particle-particle interaction is able by itself to give rise to a rich assembly scenario: colloids with charged surface patterns already form different crystalline domains when adsorbed to a homogeneously charged substrate. Here we consider substrates composed of alternating (negative/neutral, positive/neutral and positive/negative) parallel stripes and, by means of Monte Carlo simulations, we investigate the ordering of the colloids on changing the number of the stripes. We show that the additional competition between the two different lengths scales characterizing the system (i.e., the particle interaction range and the size of the stripes) gives rise to a plethora of distinct particle arrangements, where some well-defined trends can be observed. By accurately tuning the substrate charged motif it is possible to, e.g., promote specific particle arrangements, disfavor crystalline domains or induce the formation of extended, open clusters.