Self-assembly of colloidal open crystals: programmed to yield

Programmed self-assembly of colloidal particles into certain colloidal open crystals has drawn much attention as a potential low-cost scalable fabrication route to photonic crystals with a complete photonic band gap in the visible spectrum. However, the self-assembly of these colloidal crystals comprising low-coordinated particles has proved a challenge from the perspectives of both thermodynamics and kinetics. Here we present a case study investigating the self-assembly of tetrastack crystals from designer triblock patchy particles with equal-size patches on the poles. We demonstrate how two distinct choices for the interactions between the patches alter the underlying energy landscapes to promote crystallisation. We show that if the equal-size patches on the poles are distinguished, either by a hierarchy of interactions or specificity of interactions to rule out the interactions between distinct patches, crystallisation is favoured by the suppression of the formation of five- and seven-member rings, which otherwise result in amorphous structures. Such mechanistic understanding is envisaged to have wider implications for the programmed self-assembly of colloidal open crystals.