Soft Matter

Patchy colloidal particles are promising candidates for building blocks in directed self-assembly. To be successful the surface patterns need to be simple enough to be synthesized, while feature-rich enough to cause the colloidal particles to self-assemble into desired structures. Achieving this is a challenge for traditional synthesis methods. Recently it has been suggested that the surface pattern themselves can be made to self-assemble. In this paper we present a design path for hierarchical targeted self-assembly of patchy colloidal particles based on self-assembling surface patterns. At the level of the surface structure, we use a predictive method utilizing the universality of stripes and spots, coupled with stoichiometric constraints, to cause highly specific and functional patterns to self-assemble on spherical surfaces. We use a minimalistic model of an alkanethiol on gold as a demonstration, showing that even with limited control over the interaction between surface constituents we can obtain patterns that cause the colloidal particles themselves to self-assemble into various complex geometric structures, such as strings, membranes, cubic aggregates and colloidosomes, as well as various crystalline patterns. D uring the last decade, patchy colloidal particles have emerged as candidate building blocks for colloidal selfassembly. By altering the position of attractive areas, patchy colloidal particles can for example be used to mimic the anisotropic interactions between folded proteins, drawing inspiration from how certain proteins self-assemble into capsid shells enclosing the viral genome [1]. With an ambition towards self-assembling meta materials and nano-sized functional structures, examples of colloidal self-assembly insilico or in-vivo have grown to encompass kagome lattice systems to colloidal strings [2, 3] using equally varied techniques. In this paper we explore the idea of self-organizing surface patterns on the patchy colloidal particles. We demonstrate in-silico hierarchical self-assembly of a range of geometrical structures: different crystals, membranes, strings, colloidosomes of different size and cubic aggregates, all in the context of a single model system. By modifying parameters that determine the interactions between the surface constituents, we are able to select which of the geometries that selfassemble. The parameter choices are based on a combination of more general design principles, also presented in this paper, and analytical predictions of the self-assembly processes on the surface [4]. Synthesization of large quantities of colloidal particles with attractive patches in specific directions and high specificity is difficult. The synthesis methods developed in the last decade [5] range from various coating techniques on thin films of colloidal particles on a substrate like dip-coating and glancing angle deposition [6], to techniques where colloidal particles are aligned using an external electric field combined with an evaporator [7], to multiphase colloidal particles where constituents are added or subtracted sequentially to produce highly anisotropic colloidal shapes [8]. A rather different method, suggested recently, is to let the surface coating itself self-assemble into desired patterns as a part of a hierarchical 1 Page 1 of 11 Soft Matter S of tM at te r A cc ep te d M an us cr ip t